Robert Waymouth

All Publications

• Ligand Oxidation Activates a Ruthenium(II) Precatalyst for C-H Hydroxylation. Journal of the American Chemical Society Lauridsen, P. J., Kim, Y. J., Marron, D. P., Zhu, J. S., Waymouth, R. M., Du Bois, J. 2024

  Abstract

  A new class of Ru-sulfonamidate precatalysts for sp3 C-H hydroxylation is described along with a versatile process for assembling unique heteroleptic Ru(II) complexes. The latter has enabled structure-performance studies to identify an optimal precatalyst, 2h, bearing one 4,4'-di-tert-butylbipyridine (dtbpy) and one pyridylsulfonamidate ligand. Single-crystal X-ray analysis confirmed the structure and stereochemistry of this adduct. Catalytic hydroxylation reactions are conveniently performed in an aqueous, biphasic solvent mixture with 1 mol % 2h and ceric ammonium nitrate as the terminal oxidant and deliver oxidized products in yields ranging from 37 to 90%. A comparative mechanistic investigation of 2h against a related homoleptic precatalyst, [Ru(dtbpy)2(MeCN)2](OTf)2, convincingly establishes that the former generates one or more surprisingly long-lived active species under the reaction conditions, thus accounting for the high turnover numbers. Structure-performance, kinetics, mass spectrometric, and electrochemical analyses reveal that ligand oxidation is a prerequisite for catalyst activation. Our findings sharply contrast a large body of prior art showing that ligand oxidation is detrimental to catalyst function. We expect these results to stimulate future innovations in C-H oxidation research.

  View details for DOI 10.1021/jacs.4c04117

  View details for PubMedID 39134028

• Highly Selective O-Phenylene Bisurea Catalysts for ROP: Stabilization of Oxyanion Transition State by a Semiflexible Hydrogen Bond Pocket. Journal of the American Chemical Society Zhang, J., Lui, K. H., Zunino, R., Jia, Y., Morodo, R., Warlin, N., Hedrick, J. L., Talarico, G., Waymouth, R. M. 2024

  Abstract

  Organocatalyzed ring-opening polymerization (ROP) is a versatile technique for synthesizing biodegradable polymers, including polyesters and polycarbonates. We introduce o-phenylene bisurea (OPBU) (di)anions as a novel class of organocatalysts that are fast, easily tunable, mildly basic, and exceptionally selective. These catalysts surpass previous generations, such as thiourea, urea, and TBD, in selectivity (kp/ktr) by 8 to 120 times. OPBU catalysts facilitate the ROP of various monomers, achieving high conversions (>95%) in seconds to minutes, producing polymers with precise molecular weights and very low dispersities (Đ ≈ 1.01). This performance nearly matches the ideal distribution expected from living polymerization (Poisson distribution). Density functional theory (DFT) calculations reveal that the catalysts stabilize the oxyanion transition state via a hydrogen bond pocket similar to the "oxyanion hole" in enzymatic catalysis. Both experimental and theoretical analyses highlight the critical role of the semirigid o-phenylene linker in creating a hydrogen bond pocket that is tight yet flexible enough to accommodate the oxyanion transition state effectively. These new insights have provided a new class of organic catalysts whose accessibility, moderate basicity, excellent solubility, and unparalleled selectivity and tunability open up new opportunities for controlled polymer synthesis.

  View details for DOI 10.1021/jacs.4c04740

  View details for PubMedID 39102651

• Cobaltocene-Mediated Catalytic Hydride Transfer: Strategies for Electrocatalytic Hydrogenation. Journal of the American Chemical Society Marron, D. P., Galvin, C. M., Dressel, J. M., Waymouth, R. M. 2024

  Abstract

  The selective electrocatalytic hydrogenation of organics with transition metal hydrides is a promising strategy for electrosynthesis and energy storage. We report the electrocatalytic hydrogenation of acetone with a cyclopentadienone-iridium complex in a tandem electrocatalytic cycle with a cobaltocene mediator. The reductive protonation of cobaltocenium with mild acids generates (C5H5)CoI(C5H6) (CpCoI(CpH)), which functions as an electrocatalytic hydride mediator to deliver a hydride to cationic Ir(III) without generating hydrogen. Electrocatalytic hydride transfer by CpCoI(CpH) to a cationic Ir species leads to the efficient (Faradaic efficiency > 90%) electrohydrogenation of acetone, a valuable hydrogenation target as a liquid organic hydrogen carrier (LOHC). Hydride-transfer mediation presents a powerful strategy to generate metal hydrides that are inaccessible by stepwise electron/proton transfer.

  View details for DOI 10.1021/jacs.4c02177

  View details for PubMedID 38864712

• Isoprenoid CARTs: In Vitro and In Vivo mRNA Delivery by Charge-Altering Releasable Transporters Functionalized with Archaea-inspired Branched Lipids. Biomacromolecules Rahn, H. P., Sun, J., Li, Z., Waymouth, R. M., Levy, R., Wender, P. A. 2024

  Abstract

  The delivery of oligonucleotides across biological barriers is a challenge of unsurpassed significance at the interface of materials science and medicine, with emerging clinical utility in prophylactic and therapeutic vaccinations, immunotherapies, genome editing, and cell rejuvenation. Here, we address the role of readily available branched lipids in the design, synthesis, and evaluation of isoprenoid charge-altering releasable transporters (CARTs), a pH-responsive oligomeric nanoparticle delivery system for RNA. Systematic variation of the lipid block reveals an emergent relationship between the lipid block and the neutralization kinetics of the polycationic block. Unexpectedly, iA21A11, a CART with the smallest lipid side chain, isoamyl-, was identified as the lead isoprenoid CART for the in vitro transfection of immortalized lymphoblastic cell lines. When administered intramuscularly in a murine model, iA21A11-mRNA complexes induce higher protein expression levels than our previous lead CART, ONA. Isoprenoid CARTs represent a new delivery platform for RNA vaccines and other polyanion-based therapeutics.

  View details for DOI 10.1021/acs.biomac.4c00373

  View details for PubMedID 38814265

• Organ- and Cell-Selective Delivery of mRNA In Vivo Using Guanidinylated Serinol Charge-Altering Releasable Transporters. Journal of the American Chemical Society Li, Z., Amaya, L., Ee, A., Wang, S. K., Ranjan, A., Waymouth, R. M., Chang, H. Y., Wender, P. A. 2024

  Abstract

  Selective RNA delivery is required for the broad implementation of RNA clinical applications, including prophylactic and therapeutic vaccinations, immunotherapies for cancer, and genome editing. Current polyanion delivery relies heavily on cationic amines, while cationic guanidinium systems have received limited attention due in part to their strong polyanion association, which impedes intracellular polyanion release. Here, we disclose a general solution to this problem in which cationic guanidinium groups are used to form stable RNA complexes upon formulation but at physiological pH undergo a novel charge-neutralization process, resulting in RNA release. This new delivery system consists of guanidinylated serinol moieties incorporated into a charge-altering releasable transporter (GSer-CARTs). Significantly, systematic variations in structure and formulation resulted in GSer-CARTs that exhibit highly selective mRNA delivery to the lung (97%) and spleen (98%) without targeting ligands. Illustrative of their breadth and translational potential, GSer-CARTs deliver circRNA, providing the basis for a cancer vaccination strategy, which in a murine model resulted in antigen-specific immune responses and effective suppression of established tumors.

  View details for DOI 10.1021/jacs.4c02704

  View details for PubMedID 38743019

• Ethane-dependent synthesis of polyhydroxyalkanoates by the obligate methanotroph Methylocystis parvus OBBP CHEMICAL ENGINEERING JOURNAL Myung, J., Flanagan, J. A., Waymouth, R. M., Criddle, C. S. 2024; 483

  View details for DOI 10.1016/j.cej.2024.149210

  View details for Web of Science ID 001179373500001

• Insights into the Palladium(II)-Catalyzed Wacker-Type Oxidation of Styrene with Hydrogen Peroxide and tert-Butyl Hydroperoxide. ACS catalysis Mu, M., Walker, K. L., Sánchez-Sanz, G., Waymouth, R. M., Trujillo, C., Muldoon, M. J., García-Melchor, M. 2024; 14 (3): 1567-1574

  Abstract

  Wacker oxidations are ubiquitous in the direct synthesis of carbonyl compounds from alkenes. While the reaction mechanism has been widely studied under aerobic conditions, much less is known about such processes promoted with peroxides. Here, we report an exhaustive mechanistic investigation of the Wacker oxidation of styrene using hydrogen peroxide (H2O2) and tert-butyl hydroperoxide (TBHP) as oxidants by combining density functional theory and microkinetic modeling. Our results with H2O2 uncover a previously unreported reaction pathway that involves an intermolecular proton transfer assisted by the counterion [OTf]- present in the reaction media. Furthermore, we show that when TBHP is used as an oxidant instead of H2O2, the reaction mechanism switches to an intramolecular protonation sourced by the HOtBu moiety generated in situ. Importantly, these two mechanisms are predicted to outcompete the 1,2-hydride shift pathway previously proposed in the literature and account for the level of D incorporation in the product observed in labeling experiments with α-d-styrene and D2O2. We envision that these insights will pave the way for the rational design of more efficient catalysts for the industrial production of chemical feedstocks and fine chemicals.

  View details for DOI 10.1021/acscatal.3c05630

  View details for PubMedID 38327641

  View details for PubMedCentralID PMC10845106

• Ring-Opening Polymerization of Cyclic Esters and Carbonates with (Thio)urea/Cyclopropenimine Organocatalytic Systems. ACS macro letters Morodo, R., Dumas, D. M., Zhang, J., Lui, K. H., Hurst, P. J., Bosio, R., Campos, L. M., Park, N. H., Waymouth, R. M., Hedrick, J. L. 2024: 181-188

  Abstract

  Organocatalyzed ring-opening polymerization is a powerful tool for the synthesis of a variety of functional, readily degradable polyesters and polycarbonates. We report the use of (thio)ureas in combination with cyclopropenimine bases as a unique catalyst for the polymerization of cyclic esters and carbonates with a large span of reactivities. Methodologies of exceptionally effective and selective cocatalyst combinations were devised to produce polyesters and polycarbonates with narrow dispersities (D = 1.01-1.10). Correlations of the pKa of the various ureas and cyclopropenimine bases revealed the critical importance of matching the pKa of the two cocatalysts to achieve the most efficient polymerization conditions. It was found that promoting strong H-bonding interactions with a noncompetitive organic solvent, such as CH2Cl2, enabled greatly increased polymerization rates. The stereoselective polymerization of rac-lactide afforded stereoblock poly(lactides) that crystallize as stereocomplexes, as confirmed by wide-angle X-ray scattering.

  View details for DOI 10.1021/acsmacrolett.3c00716

  View details for PubMedID 38252690

• Coordination-Induced Bond Weakening and Electrocatalytic Proton-Coupled Electron Transfer of a Ruthenium Verdazyl Complex. Inorganic chemistry Galvin, C. M., Marron, D. P., Dressel, J. M., Waymouth, R. M. 2023

  Abstract

  Coordination of the leucoverdazyl ligand 2,4-diisopropyl-6-(pyridin-2-yl)-1,4-dihydro-1,2,4,5-tetrazin-3(2H)-one VdH to Ru significantly weakens the ligand's N-H bond. Electrochemical measurements show that the metalated leucoverdazyl Ru(VdH)(acetylacetonate)2 RuVdH has a lower pKa (-5 units), BDFE (-7 kcal/mol), and hydricity (-22 kcal/mol) than the free ligand. DFT calculations suggest that the increased acidity is in part attributable to stabilization of the conjugate base Vd-. When free, Vd- distorts to avoid an 8πe- antiaromatic state, but it remains planar when bound to Ru. Proton-coupled electron transfer (PCET) behavior is observed for both the free and metalated leucoverdazyls. PCET equilibrium between the Vd radical and TEMPOH affords a VdH BDFE that is in good agreement with that obtained from electrochemical methods. RuVd exhibits electrocatalytic PCET donor behavior. Under acidic conditions, it reduces the persistent trityl radical ·CAr3 (Ar = p-tert-butylphenyl) to the corresponding triarylmethane HCAr3 via net 1e-/1H+ transfer from RuVdH.

  View details for DOI 10.1021/acs.inorgchem.3c02775

  View details for PubMedID 38153690

• The STEMentors Program: Promoting the Academic Readiness and Community Building of Students within General Chemistry JOURNAL OF CHEMICAL EDUCATION Deweese, D., Nardo, J., Applebaum, I., Sundrani, S., Zur, A., Waymouth, R. M., Poehlmann, J., Salehi, S. 2023; 101 (1): 88-96

  View details for DOI 10.1021/acs.jchemed.3c01020

  View details for Web of Science ID 001139505400001

• Contrasting Roles of Counterions in Anionic Ring-Opening Polymerization Mediated by Heterocycle Organocatalysts ACS CATALYSIS Zhang, J., Lui, K., Jadrich, C. N., Jia, Y., Arrechea, P. L., Hedrick, J. L., Waymouth, R. M. 2023; 13 (24): 16097-16104

  View details for DOI 10.1021/acscatal.3c04772

  View details for Web of Science ID 001142879500001

• Charge-altering releasable transporters enhance mRNA delivery in vitro and exhibit in vivo tropism. Nature communications Li, Z., Amaya, L., Pi, R., Wang, S. K., Ranjan, A., Waymouth, R. M., Blish, C. A., Chang, H. Y., Wender, P. A. 2023; 14 (1): 6983

  Abstract

  The introduction of more effective and selective mRNA delivery systems is required for the advancement of many emerging biomedical technologies including the development of prophylactic and therapeutic vaccines, immunotherapies for cancer and strategies for genome editing. While polymers and oligomers have served as promising mRNA delivery systems, their efficacy in hard-to-transfect cells such as primary T lymphocytes is often limited as is their cell and organ tropism. To address these problems, considerable attention has been placed on structural screening of various lipid and cation components of mRNA delivery systems. Here, we disclose a class of charge-altering releasable transporters (CARTs) that differ from previous CARTs based on their beta-amido carbonate backbone (bAC) and side chain spacing. These bAC-CARTs exhibit enhanced mRNA transfection in primary T lymphocytes in vitro and enhanced protein expression in vivo with highly selective spleen tropism, supporting their broader therapeutic use as effective polyanionic delivery systems.

  View details for DOI 10.1038/s41467-023-42672-x

  View details for PubMedID 37914693

• Cyclopentadienone Iridium Bipyridyl Complexes: Acid-Stable Transfer Hydrogenation Catalysts ORGANOMETALLICS Marron, D. P., Galvin, C. M., Waymouth, R. M. 2023

  View details for DOI 10.1021/acs.organomet.3c00266

  View details for Web of Science ID 001038328300001

• Lysine-Derived Charge-Altering Releasable Transporters: Targeted Delivery of mRNA and siRNA to the Lungs. Bioconjugate chemistry Blake, T. R., Haabeth, O. A., Sallets, A., McClellan, R. L., Del Castillo, T. J., Vilches-Moure, J. G., Ho, W. C., Wender, P. A., Levy, R., Waymouth, R. M. 2023

  Abstract

  Targeted delivery of nucleic acid therapeutics to the lungs could transform treatment options for pulmonary disease. We have previously developed oligomeric charge-altering releasable transporters (CARTs) for in vivo mRNA transfection and demonstrated their efficacy for use in mRNA-based cancer vaccination and local immunomodulatory therapies against murine tumors. While our previously reported glycine-based CART-mRNA complexes (G-CARTs/mRNA) show selective protein expression in the spleen (mouse, >99%), here, we report a new lysine-derived CART-mRNA complex (K-CART/mRNA) that, without additives or targeting ligands, shows selective protein expression in the lungs (mouse, >90%) following systemic IV administration. We further show that by delivering siRNA using the K-CART, we can significantly decrease expression of a lung-localized reporter protein. Blood chemistry and organ pathology studies demonstrate that K-CARTs are safe and well-tolerated. We report on the new step economical, organocatalytic synthesis (two steps) of functionalized polyesters and oligo-carbonate-co-α-aminoester K-CARTs from simple amino acid and lipid-based monomers. The ability to direct protein expression selectively in the spleen or lungs by simple, modular changes to the CART structure opens fundamentally new opportunities in research and gene therapy.

  View details for DOI 10.1021/acs.bioconjchem.3c00019

  View details for PubMedID 36996808

• Mechanism-Guided Design of Robust Palladium Catalysts for Selective Aerobic Oxidation of Polyols. Journal of the American Chemical Society Ramsay-Burrough, S., Marron, D. P., Armstrong, K. C., Del Castillo, T. J., Zare, R. N., Waymouth, R. M. 2023

  Abstract

  The palladium complex [(L1)Pd(mu-OAc)]2[OTf]2 (L1 = neocuproine) is a selective catalyst for the aerobic oxidation of vicinal polyols to alpha-hydroxyketones, but competitive oxidation of the ligand methyl groups limits the turnover number and necessitates high Pd loadings. Replacement of the neocuproine ligand with 2,2'-biquinoline ligands was investigated as a strategy to improve catalyst performance and explore the relationship between ligand structure and reactivity. Evaluation of [(L2)Pd(mu-OAc)]2[OTf]2 (L2 = 2,2'-biquinoline) as a catalyst for aerobic alcohol oxidation revealed a threefold enhancement in turnover number relative to the neocuproine congener, but a much slower rate. Mechanistic studies indicated that the slow rates observed with L2 were a consequence of precipitation of an insoluble trinuclear palladium species─(L2Pd)3(mu-O)22+─formed during catalysis and characterized by high-resolution electrospray ionization mass spectrometry. Density functional theory was used to predict that a sterically modified biquinoline ligand, L3 = 7,7'-di-tert-butyl-2,2'-biquinoline, would disfavor the formation of the trinuclear (LPd)3(mu-O)22+ species. This design strategy was validated as catalytic aerobic oxidation with [(L3)Pd(mu-OAc)]2[OTf]2 is both robust and rapid, marrying the kinetics of the parent L1-supported system with the high aerobic turnover numbers of the L2-supported system. Changes in ligand structure were also found to modulate regioselectivity in the oxidation of complex glycoside substrates, providing new insights into structure-selectivity relationships with this class of catalysts.

  View details for DOI 10.1021/jacs.2c10667

  View details for PubMedID 36657018

• The legacy of Robert H. Grubbs: Scientific brilliance with humble empathy CHEM Suslick, B. A., Grubbs, R. B., Waymouth, R. M., Moore, J. S. 2022; 8 (10): 2562-2570

  View details for DOI 10.1016/j.chempr.2022.09.001

  View details for Web of Science ID 000889489000001

• Fingolimod-Conjugated Charge-Altering Releasable Transporters Efficiently and Specifically Deliver mRNA to Lymphocytes In Vivo and In Vitro. Biomacromolecules Testa, S., Haabeth, O. A., Blake, T. R., Del Castillo, T. J., Czerwinski, D. K., Rajapaksa, R., Wender, P. A., Waymouth, R. M., Levy, R. 2022

  Abstract

  Charge-altering releasable transporters (CARTs) are a class of oligonucleotide delivery vehicles shown to be effective for delivery of messenger RNA (mRNA) both in vitro and in vivo. Here, we exploited the chemical versatility of the CART synthesis to generate CARTs containing the small-molecule drug fingolimod (FTY720) as a strategy to increase mRNA delivery and expression in lymphocytes through a specific ligand-receptor interaction. Fingolimod is an FDA-approved small-molecule drug that, upon in vivo phosphorylation, binds to the sphingosine-1-phosphate receptor 1 (S1P1), which is highly expressed on lymphocytes. Compared to its non-fingolimod-conjugated analogue, the fingolimod-conjugated CART achieved superior transfection of activated human and murine T and B lymphocytes in vitro. The higher transfection of the fingolimod-conjugated CARTs was lost when cells were exposed to a free fingolimod before transfection. In vivo, the fingolimod-conjugated CART showed increased mRNA delivery to marginal zone B cells and NK cells in the spleen, relative to CARTs lacking fingolimod. Moreover, fingolimod-CART-mediated mRNA delivery induces peripheral blood T-cell depletion similar to free fingolimod. Thus, we show that functionalization of CARTs with a pharmacologically validated small molecule can increase transfection of a cellular population of interest while conferring some of the targeting properties of the conjugated small molecule to the CARTs.

  View details for DOI 10.1021/acs.biomac.2c00469

  View details for PubMedID 35748182

• A Cation-Dependent Dual Activation Motif for Anionic Ring-Opening Polymerization of Cyclic Esters. Journal of the American Chemical Society Jadrich, C. N., Pane, V. E., Lin, B., Jones, G. O., Hedrick, J. L., Park, N. H., Waymouth, R. M. 2022

  Abstract

  A new organocatalyst for the ring-opening polymerization of lactones has been identified. Under the tested conditions, the anions of 2,2'-bisindole promote fast, living polymerizations (as short as 10 ms) which are selective for chain elongation over transesterification (D ≤ 1.1). While structurally related to (thio)urea anion catalysts, anions of 2,2'-bisindole activate the monomer via the counterion rather than through hydrogen bonding. This new activation motif enables modulation of the polymerization rate by 2 orders of magnitude by changing the counterion.

  View details for DOI 10.1021/jacs.2c01436

  View details for PubMedID 35504294

• Potassium Trimethylsilanolate-Promoted, Anhydrous Suzuki-Miyaura Cross-Coupling Reaction Proceeds via the "Boronate Mechanism": Evidence for the Alternative Fork in the Trail. Journal of the American Chemical Society Delaney, C. P., Marron, D. P., Shved, A. S., Zare, R. N., Waymouth, R. M., Denmark, S. E. 2022

  Abstract

  Previous studies have shown that the critical transmetalation step in the Suzuki-Miyaura cross-coupling proceeds through a mechanism wherein an arylpalladium hydroxide complex reacts with an aryl boronic acid, termed the oxo-palladium pathway. Moreover, these same studies have established that the reaction between an aryl boronate and an arylpalladium halide complex (the boronate pathway) is prohibitively slow. Herein, studies on isolated intermediates, along with kinetic analysis, have demonstrated that the Suzuki-Miyaura reaction promoted by potassium trimethylsilanolate (TMSOK) proceeds through the boronate pathway, in contrast with other, established systems. Furthermore, an unprecedented, binuclear palladium(I) complex containing a mu-phenyl bridging ligand was characterized by NMR spectroscopy, mass spectrometry, and computational methods. Density functional theory (DFT) calculations suggest that the binuclear complex exhibits an open-shell ground electronic state, and reaction kinetics implicate the complex in the catalytic cycle. These results expand the breadth of potential mechanisms by which the Suzuki-Miyaura reaction can occur, and the novel binuclear palladium complex discovered has broad implications for palladium-mediated cross-coupling reactions of aryl halides.

  View details for DOI 10.1021/jacs.1c08283

  View details for PubMedID 35230833

• Photocleavable Regenerative Network Materials with Exceptional and Repeatable Viscoelastic Manipulability. Advanced science (Weinheim, Baden-Wurttemberg, Germany) Oka, M., Takagi, H., Miyazawa, T., Waymouth, R. M., Honda, S. 2021: e2101143

  Abstract

  The development of solventless system for modulating properties of network materials is imperative for the next generation sustainable technology. Utilization of photostimulation is important owing to its spatial and temporal locality, yet designing photoresponsive network materials exhibiting repeatable and dramatic change in their properties remains a challenge. Here, the authors report a photocleavable regenerative network (PRN) linked with photoresponsive hexaarylbiimidazoles (HABIs) synthesized from narrow dispersity star-shaped poly(dimethylsiloxane)s (PDMSs) having 2,4,5-triphenylimidazole end groups. The use of urea anion as a catalyst for ring opening polymerization (ROP) of cyclic siloxane initiated from silanols enables control of molecular weight and dispersity. The rheological measurements for the synthesized PRNs exhibit drastic changes in storage and loss moduli (G' and G) upon photoirradiation in the solid state (G' > G). This photocontrolled change in viscoelasticity with retaining solidity enables application of PRNs as a remotely-controlled photo-melt adhesive and photo-scissible string. The developed PRNs will enable a wide variety of applications such as industrially important next-generation sustainable adhesive, sealant, and reversibly-deformable 3D printing materials with their spatially and temporally local manipulability, solventless handleability, and excellent reversibility.

  View details for DOI 10.1002/advs.202101143

  View details for PubMedID 34338448

• An mRNA SARS-CoV-2 Vaccine Employing Charge-Altering Releasable Transporters with a TLR-9 Agonist Induces Neutralizing Antibodies and T Cell Memory. ACS central science Haabeth, O. A., Lohmeyer, J. J., Sallets, A., Blake, T. R., Sagiv-Barfi, I., Czerwinski, D. K., McCarthy, B., Powell, A. E., Wender, P. A., Waymouth, R. M., Levy, R. 2021; 7 (7): 1191-1204

  Abstract

  The SARS-CoV-2 pandemic has necessitated the rapid development of prophylactic vaccines. Two mRNA vaccines have been approved for emergency use by the FDA and have demonstrated extraordinary effectiveness. The success of these mRNA vaccines establishes the speed of development and therapeutic potential of mRNA. These authorized vaccines encode full-length versions of the SARS-CoV-2 spike protein. They are formulated with lipid nanoparticle (LNP) delivery vehicles that have inherent immunostimulatory properties. Different vaccination strategies and alternative mRNA delivery vehicles would be desirable to ensure flexibility of future generations of SARS-CoV-2 vaccines and the development of mRNA vaccines in general. Here, we report on the development of an alternative mRNA vaccine approach using a delivery vehicle called charge-altering releasable transporters (CARTs). Using these inherently nonimmunogenic vehicles, we can tailor the vaccine immunogenicity by inclusion of coformulated adjuvants such as oligodeoxynucleotides with CpG motifs (CpG-ODN). Mice vaccinated with the mRNA-CART vaccine developed therapeutically relevant levels of receptor binding domain (RBD)-specific neutralizing antibodies in both the circulation and in the lung bronchial fluids. In addition, vaccination elicited strong and long-lasting RBD-specific TH1 T cell responses including CD4+ and CD8+ T cell memory.

  View details for DOI 10.1021/acscentsci.1c00361

  View details for PubMedID 34341771

• Towards a Biomanufactory on Mars FRONTIERS IN ASTRONOMY AND SPACE SCIENCES Berliner, A. J., Hilzinger, J. M., Abel, A. J., McNulty, M. J., Makrygiorgos, G., Averesch, N. H., Sen Gupta, S., Benvenuti, A., Caddell, D. F., Cestellos-Blanco, S., Doloman, A., Friedline, S., Ho, D., Gu, W., Hill, A., Kusuma, P., Lipsky, I., Mirkovic, M., Meraz, J., Pane, V., Sander, K. B., Shi, F., Skerker, J. M., Styer, A., Valgardson, K., Wetmore, K., Woo, S., Xiong, Y., Yates, K., Zhang, C., Zhen, S., Bugbee, B., Clark, D. S., Coleman-Derr, D., Mesbah, A., Nandi, S., Waymouth, R. M., Yang, P., Criddle, C. S., McDonald, K. A., Seefeldt, L. C., Menezes, A. A., Arkin, A. P. 2021; 8

  View details for DOI 10.3389/fspas.2021.711550

  View details for Web of Science ID 000680691100001

• Electroreduction of Benzaldehyde with a Metal-Ligand Bifunctional Hydroxycyclopentadienyl Molybdenum(II) Hydride ORGANOMETALLICS Armstrong, K. C., Waymouth, R. M. 2020; 39 (24): 4415–19

  View details for DOI 10.1021/acs.organomet.0c00630

  View details for Web of Science ID 000607477400002

• Condensing water vapor to droplets generates hydrogen peroxide. Proceedings of the National Academy of Sciences of the United States of America Lee, J. K., Han, H. S., Chaikasetsin, S., Marron, D. P., Waymouth, R. M., Prinz, F. B., Zare, R. N. 2020

  Abstract

  It was previously shown [J. K. Lee et al., Proc. Natl. Acad. Sci. U.S.A, 116, 19294-19298 (2019)] that hydrogen peroxide (H2O2) is spontaneously produced in micrometer-sized water droplets (microdroplets), which are generated by atomizing bulk water using nebulization without the application of an external electric field. Here we report that H2O2 is spontaneously produced in water microdroplets formed by dropwise condensation of water vapor on low-temperature substrates. Because peroxide formation is induced by a strong electric field formed at the water-air interface of microdroplets, no catalysts or external electrical bias, as well as precursor chemicals, are necessary. Time-course observations of the H2O2 production in condensate microdroplets showed that H2O2 was generated from microdroplets with sizes typically less than 10 m. The spontaneous production of H2O2 was commonly observed on various different substrates, including silicon, plastic, glass, and metal. Studies with substrates with different surface conditions showed that the nucleation and the growth processes of condensate water microdroplets govern H2O2 generation. We also found that the H2O2 production yield strongly depends on environmental conditions, including relative humidity and substrate temperature. These results show that the production of H2O2 occurs in water microdroplets formed by not only atomizing bulk water but also condensing water vapor, suggesting that spontaneous water oxidation to form H2O2 from water microdroplets is a general phenomenon. These findings provide innovative opportunities for green chemistry at heterogeneous interfaces, self-cleaning of surfaces, and safe and effective disinfection. They also may have important implications for prebiotic chemistry.

  View details for DOI 10.1073/pnas.2020158117

  View details for PubMedID 33229543

• Electron-Rich Phenoxyl Mediators Improve Thermodynamic Performance of Electrocatalytic Alcohol Oxidation with an Iridium Pincer Complex. Journal of the American Chemical Society Galvin, C. M., Waymouth, R. M. 2020

  Abstract

  Electron-rich phenols, including alpha-rac-tocopherol Ar1OH, 2,4,6,-tri-tert-butylphenol Ar3OH, and butylated hydroxy-toluene Ar4OH, are effective electrochemical mediators for the electrocatalytic oxidation of alcohols by an iridium amido dihyride complex (PNP)Ir(H)2 (IrN 1, PNP = bis[2-diisopropylphosphino)ethyl]amide). Addition of phenol mediators leads to a decrease in the onset potential of catalysis from -0.65 V vs Fc+/0 under unmediated conditions to -1.07 V vs Fc+/0 in the presence of phenols. Mechanistic analysis suggests that oxidative turnover of the iridium amino trihydride (PNHP)Ir(H)3 (IrH 2, PNHP = bis[2-diisopropylphosphino)ethyl]amine) to IrN 1 proceeds through two successive hydrogen atom transfers (HAT) to 2 equiv of phenoxyl that are generated transiently at the anode. Isotope studies and comparison to known systems are consistent with initial homolysis of an Ir-H bond being rate-determining. Turnover frequencies up to 14.6 s-1 and an average Faradaic efficiency of 93% are observed. The mediated system shows excellent chemoselectivity in bulk oxidations of 2-propanol and 1,2-benzenedimethanol in THF and is also viable in neat 2-propanol.

  View details for DOI 10.1021/jacs.0c09605

  View details for PubMedID 33138365

• Ultrafast and Controlled Ring-Opening Polymerization with Sterically Hindered Strong Bases MACROMOLECULES Lin, B., Jadrich, C. N., Pane, V. E., Arrechea, P. L., Erdmann, T., Dausse, C., Hedrick, J. L., Park, N. H., Waymouth, R. M. 2020; 53 (20): 9000–9007

  View details for DOI 10.1021/acs.macromol.0c01571

  View details for Web of Science ID 000586789500028

• Electrochemically Regenerable Hydrogen Atom Acceptors: Mediators in Electrocatalytic Alcohol Oxidation Reactions ACS CATALYSIS McLoughlin, E. A., Armstrong, K. C., Waymouth, R. M. 2020; 10 (19): 11654–62

  View details for DOI 10.1021/acscatal.0c03240

  View details for Web of Science ID 000577156300067

• Mechanistic Study of Isotactic Poly(propylene oxide) Synthesis using a Tethered Bimetallic Chromium Salen Catalyst. ACS catalysis Lipinski, B. M., Walker, K. L., Clayman, N. E., Morris, L. S., Jugovic, T. M., Roessler, A. G., Getzler, Y. D., MacMillan, S. N., Zare, R. N., Zimmerman, P. M., Waymouth, R. M., Coates, G. W. 2020; 10 (15): 8960-8967

  Abstract

  Initial catalyst dormancy has been mitigated for the enantioselective polymerization of propylene oxide using a tethered bimetallic chromium(III) salen complex. A detailed mechanistic study provided insight into the species responsible for this induction period and guided efforts to remove them. High-resolution electrospray ionization-mass spectrometry and density functional theory computations revealed that a μ-hydroxide and a bridged 1,2-hydroxypropanolate complex are present during the induction period. Kinetic studies and additional computation indicated that the μ-hydroxide complex is a short-lived catalyst arrest state, where hydroxide dissociation from one metal allows for epoxide enchainment to form the 1,2-hydroxypropanolate arrest state. While investigating anion dependence on the induction period, it became apparent that catalyst activation was the main contributor for dormancy. Using a 1,2-diol or water as chain transfer agents (CTAs) led to longer induction periods as a result of increased 1,2-hydroxyalkanolate complex formation. With a minor catalyst modification, rigorous drying conditions, and avoiding 1,2-diols as CTAs, the induction period was essentially removed.

  View details for DOI 10.1021/acscatal.0c02135

  View details for PubMedID 34367720

  View details for PubMedCentralID PMC8345319

• Synthesis and mechanistic investigations of pH-responsive cationic poly(aminoester)s CHEMICAL SCIENCE Blake, T. R., Ho, W. C., Turlington, C. R., Zang, X., Huttner, M. A., Wender, P. A., Waymouth, R. M. 2020; 11 (11): 2951–66

  View details for DOI 10.1039/c9sc05267d

  View details for Web of Science ID 000521247400006

• Synthesis and mechanistic investigations of pH-responsive cationic poly(aminoester)s. Chemical science Blake, T. R., Ho, W. C., Turlington, C. R., Zang, X., Huttner, M. A., Wender, P. A., Waymouth, R. M. 2020; 11 (11): 2951-2966

  Abstract

  The synthesis and degradation mechanisms of a class of pH-sensitive, rapidly degrading cationic poly(α-aminoester)s are described. These reactive, cationic polymers are stable at low pH in water, but undergo a fast and selective degradation at higher pH to liberate neutral diketopiperazines. Related materials incorporating oligo(α-amino ester)s have been shown to be effective gene delivery agents, as the charge-altering degradative behavior facilitates the delivery and release of mRNA and other nucleic acids in vitro and in vivo. Herein, we report detailed studies of the structural and environmental factors that lead to these rapid and selective degradation processes in aqueous buffers. At neutral pH, poly(α-aminoester)s derived from N-hydroxyethylglycine degrade selectively by a mechanism involving sequential 1,5- and 1,6-O→N acyl shifts to generate bis(N-hydroxyethyl) diketopiperazine. A family of structurally related cationic poly(aminoester)s was generated to study the structural influences on the degradation mechanism, product distribution, and pH dependence of the rate of degradation. The kinetics and mechanism of the pH-induced degradations were investigated by 1H NMR, model reactions, and kinetic simulations. These results indicate that polyesters bearing α-ammonium groups and appropriately positioned N-hydroxyethyl substituents are readily cleaved (by intramolecular attack) or hydrolyzed, representing dynamic "dual function" materials that are initially polycationic and transform with changing environment to neutral products.

  View details for DOI 10.1039/c9sc05267d

  View details for PubMedID 34122796

  View details for PubMedCentralID PMC8157522

• Reversible RNA acylation for control of CRISPR-Cas9 gene editing CHEMICAL SCIENCE Habibian, M., McKinlay, C., Blake, T. R., Kietrys, A. M., Waymouth, R. M., Wender, P. A., Kool, E. T. 2020; 11 (4): 1011–16

  View details for DOI 10.1039/c9sc03639c

  View details for Web of Science ID 000510929600008

• Charge-altering releasable transporters enable phenotypic manipulation of natural killer cells for cancer immunotherapy. Blood advances Wilk, A. J., Weidenbacher, N. L., Vergara, R. n., Haabeth, O. A., Levy, R. n., Waymouth, R. M., Wender, P. A., Blish, C. A. 2020; 4 (17): 4244–55

  Abstract

  Chimeric antigen receptor (CAR) natural killer (NK) cells are an emerging cell therapy with promising results in oncology trials. However, primary human NK cells are difficult to transfect, hampering both mechanistic studies and clinical applications of NK cells. Currently, NK cell CAR modification relies on viral vectors or cell activation. The former raises cost and tolerability issues, while the latter alters NK cell biology. Here, we report that readily synthesized and inexpensive nonviral charge-altering releasable transporters (CARTs) efficiently transfect primary human NK cells with messenger RNA without relying on NK cell activation. Compared with electroporation, CARTs transfect NK cells more efficiently, better preserve cell viability, and cause minimal reconfiguration of NK cell phenotype and function. We use CARTs to generate cytotoxic primary anti-CD19 CAR NK cells, demonstrating this technology can drive clinical applications of NK cells. To our knowledge, CARTs represent the first efficacious transfection technique for resting primary human NK cells that preserves NK cell phenotype and can enable new biological discoveries and therapeutic applications of this understudied lymphocyte subset.

  View details for DOI 10.1182/bloodadvances.2020002355

  View details for PubMedID 32898247

• Electrocatalytic Alcohol Oxidation with Iron-Based Acceptorless Alcohol Dehydrogenation Catalyst. Inorganic chemistry McLoughlin, E. A., Matson, B. D., Sarangi, R., Waymouth, R. M. 2019

  Abstract

  Electrochemical and chemical studies reveal that the amido complex (PNHxP)Fe(CO)(H)(X) (FeN 1, x = 0, X = 0; Fe(H)(NH) 2, x = 1, X = H; PNHP = bis[2-(diisopropylphosphino)ethyl]amine) is active for the electrocatalytic oxidation of isopropanol. At room temperature, the amido FeN 1 dehydrogenates isopropanol to form acetone. The resulting amino hydride complex Fe(H)(NH) 2 is subsequently oxidized by one electron at a low potential (-0.74 V versus ferrocene/ferrocenium, Fc0/+) in tetrahydrofuran. In the presence of strong base (phosphazene base P2-Et, Et-N = P2(dma)5, P2), this oxidation process becomes a two-electron, two-proton process that regenerates FeN 1. FeN 1 is active for the electrooxidation of isopropanol in the presence of strong base (i.e., P2) with an onset potential near -1 V versus Fc0/+. By cyclic voltammetry, fast turnover frequencies of 1.7 s-1 for isopropanol oxidation are achieved with FeN 1. Controlled potential electrolysis studies confirm that the product of isopropanol electrooxidation is acetone, generated with high Faradaic efficiency (100%).

  View details for DOI 10.1021/acs.inorgchem.9b03230

  View details for PubMedID 31886655

• Reversible RNA acylation for control of CRISPR-Cas9 gene editing. Chemical science Habibian, M., McKinlay, C., Blake, T. R., Kietrys, A. M., Waymouth, R. M., Wender, P. A., Kool, E. T. 2019; 11 (4): 1011-1016

  Abstract

  We report the development of post-transcriptional chemical methods that enable control over CRISPR-Cas9 gene editing activity both in in vitro assays and in living cells. We show that an azide-substituted acyl imidazole reagent (NAI-N3) efficiently acylates CRISPR single guide RNAs (sgRNAs) in 20 minutes in buffer. Poly-acylated ("cloaked") sgRNA was completely inactive in DNA cleavage with Cas9 in vitro, and activity was quantitatively restored after phosphine treatment. Delivery of cloaked sgRNA and Cas9 mRNA into HeLa cells was enabled by the use of charge-altering releasable transporters (CARTs), which outperformed commercial transfection reagents in transfecting sgRNA co-complexed with Cas9 encoding functional mRNA. Genomic DNA cleavage in the cells by CRISPR-Cas9 was efficiently restored after treatment with phosphine to remove the blocking acyl groups. Our results highlight the utility of reversible RNA acylation as a novel method for temporal control of genome-editing function.

  View details for DOI 10.1039/c9sc03639c

  View details for PubMedID 34084356

  View details for PubMedCentralID PMC8145180

• Spontaneous generation of hydrogen peroxide from aqueous microdroplets. Proceedings of the National Academy of Sciences of the United States of America Lee, J. K., Walker, K. L., Han, H. S., Kang, J., Prinz, F. B., Waymouth, R. M., Nam, H. G., Zare, R. N. 2019

  Abstract

  We show H2O2 is spontaneously produced from pure water by atomizing bulk water into microdroplets (1 mum to 20 m in diameter). Production of H2O2, as assayed by H2O2-sensitve fluorescence dye peroxyfluor-1, increased with decreasing microdroplet size. Cleavage of 4-carboxyphenylboronic acid and conversion of phenylboronic acid to phenols in microdroplets further confirmed the generation of H2O2 The generated H2O2 concentration was 30 M (1 part per million) as determined by titration with potassium titanium oxalate. Changing the spray gas to O2 or bubbling O2 decreased the yield of H2O2 in microdroplets, indicating that pure water microdroplets directly generate H2O2 without help from O2 either in air surrounding the droplet or dissolved in water. We consider various possible mechanisms for H2O2 formation and report a number of different experiments exploring this issue. We suggest that hydroxyl radical (OH) recombination is the most likely source, in which OH is generated by loss of an electron from OH- at or near the surface of the water microdroplet. This catalyst-free and voltage-free H2O2 production method provides innovative opportunities for green production of hydrogen peroxide.

  View details for DOI 10.1073/pnas.1911883116

  View details for PubMedID 31451646

• Block copolymer composition drives function of self-assembled nanoparticles for delivery of small-molecule cargo. Journal of polymer science. Part A, Polymer chemistry Maikawa, C. L., Sevit, A., Lin, B., Wallstrom, R. J., Mann, J. L., Yu, A. C., Waymouth, R. M., Appel, E. A. 2019; 57 (12): 1322-1332

  Abstract

  Nanoparticles are useful for the delivery of small molecule therapeutics, increasing their solubility, in vivo residence time, and stability. Here, we used organocatalytic ring opening polymerization to produce amphiphilic block copolymers for the formation of nanoparticle drug carriers with enhanced stability, cargo encapsulation, and sustained delivery. These polymers comprised blocks of poly(ethylene glycol) (PEG), poly(valerolactone) (PVL), and poly(lactide) (PLA). Four particle chemistries were examined: (a) PEG-PLA, (b) PEG-PVL, (c) a physical mixture of PEG-PLA and PEG-PVL, and (d) PEG-PVL-PLA tri-block copolymers. Nanoparticle stability was assessed at room temperature (20 °C; pH = 7), physiological temperature (37 °C; pH = 7), in acidic media (37 °C; pH = 2), and with a digestive enzyme (lipase; 37 °C; pH = 7.4). PVL-based nanoparticles demonstrated the highest level of stability at room temperature, 37 °C and acidic conditions, but were rapidly degraded by lipase. Moreover, PVL-based nanoparticles demonstrated good cargo encapsulation, but rapid release. In contrast, PLA-based nanoparticles demonstrated poor stability and encapsulation, but sustained release. The PEG-PVL-PLA nanoparticles exhibited the best combination of stability, encapsulation, and release properties. Our results demonstrate the ability to tune nanoparticle properties by modifying the polymeric architecture and composition. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1322-1332.

  View details for DOI 10.1002/pola.29393

  View details for PubMedID 31244507

  View details for PubMedCentralID PMC6582505

• Oligo(serine ester) Charge-Altering Releasable Transporters: Organocatalytic Ring-Opening Polymerization and their Use for in Vitro and in Vivo mRNA Delivery JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Benner, N. L., McClellan, R. L., Turlington, C. R., Haabeth, O. W., Waymouth, R. M., Wender, P. A. 2019; 141 (21): 8416–21

  View details for DOI 10.1021/jacs.9b03154

  View details for Web of Science ID 000470034500006

• Dual catalysis for the copolymerisation of epoxides and lactones. Chemical communications (Cambridge, England) Clayman, N. E., Morris, L. S., LaPointe, A. M., Keresztes, I., Waymouth, R. M., Coates, G. W. 2019

  Abstract

  A dual catalysis system was developed to synthesize hydrolyzable polyether-polyester copolymers from propylene oxide and cyclic esters such as gamma-butyrolactone, delta-valerolactone, and epsilon-caprolactone. A bimetallic chromium catalyst active for the enantioselective polymerisation of propylene oxide and an organocatalyst active for the ring-opening polymerisation of lactones were used in conjunction with an alcohol chain shuttling agent to create new copolymers. The monomer and alcohol ratios were varied to yield a wide range of copolymers with varying monomer ratios, molecular weights, and crystallinities.

  View details for DOI 10.1039/c9cc00493a

  View details for PubMedID 31139794

• Programmable High-Throughput Platform for the Rapid and Scalable Synthesis of Polyester and Polycarbonate Libraries. Journal of the American Chemical Society Lin, B., Hedrick, J. L., Park, N. H., Waymouth, R. M. 2019

  Abstract

  The critical role of composition, architecture, molecular weight, and molecular weight distribution on the functional properties of macromolecular materials underscores the need for reproducible, robust, scalable, and programmable synthetic methods to generate macromolecules that span a systematic and wide range of structure-property space. Herein, we describe the marriage of tunable and highly active organic catalysts with programmed continuous-flow reactors to rapidly generate libraries of polyester and polycarbonate homopolymers and block copolymers with exquisite efficiency and control. Under continuous-flow conditions, highly controlled polymerizations occur with residence times as low as 6 ms (TOF = 24 000 000 h-1) and can be readily scaled-up to generate polymers at a rate of tens of grams per minute. We describe an in-flow catalyst switch strategy to enable the rapid generation of block copolymer libraries (100 distinct polymers in 9 min) from monomers with drastically different reactivity profiles.

  View details for DOI 10.1021/jacs.9b02450

  View details for PubMedID 31117549

• Effect of Redox Active Ligands on the Electrochemical Properties of Manganese Tricarbonyl Complexes. Inorganic chemistry Matson, B. D., McLoughlin, E. A., Armstrong, K. C., Waymouth, R. M., Sarangi, R. 2019

  Abstract

  The synthesis, structural characterization, and electrochemical behavior of the neutral Mn(azpy)(CO)3(Br) 4 (azpy = 2-phenylazopyridine) complex is reported and compared with its structural analogue Mn(bipy)(CO)3(Br) 1 (bipy = 2,2'-bipyridine). 4 exhibits reversible two-electron reduction at a mild potential (-0.93 V vs Fc+/0 in acetonitrile) in contrast to 1, which exhibits two sequential one-electron reductions at -1.68 V and -1.89 V vs Fc+/0 in acetonitrile. The key electronic structure differences between 1 and 4 that lead to disparate electrochemical properties are investigated using a combination of Mn-K-edge X-ray absorption spectroscopy (XAS), Mn-Kbeta X-ray emission spectroscopy (XES), and density functional theory (DFT) on 1, 4, their debrominated analogues, [Mn(L)(CO)3(CH3CN)][CF3SO3] (L = bipy 2, azpy 5), and two-electron reduced counterparts [Mn(bipy)(CO)3][K(18-crown-6)] 3 and [Mn(azpy)(CO)3][Cp2Co] 6. The results reveal differences in the distribution of electrons about the CO and bidentate ligands (bipy and azpy), particularly upon formation of the highly reduced, formally Mn(-1) species. The data show that the degree of ligand noninnocence and resulting redox-activity in Mn(L)(CO)3 type complexes impacts not only the reducing power of such systems, but the speciation of the reduced complexes via perturbation of the monomer-dimer equilibrium in the singly reduced Mn(0) state. This study highlights the role of redox-active ligands in tuning the reactivity of metal centers involved in electrocatalytic transformations.

  View details for DOI 10.1021/acs.inorgchem.9b00652

  View details for PubMedID 31117629

• Local Delivery of Ox40l, Cd80, and Cd86 mRNA Kindles Global Anticancer Immunity CANCER RESEARCH Haabeth, O., Blake, T. R., McKinlay, C. J., Tveita, A. A., Sallets, A., Waymouth, R. M., Wender, P. A., Levy, R. 2019; 79 (7): 1624–34

  View details for DOI 10.1158/0008-5472.CAN-18-2867

  View details for Web of Science ID 000463005700033

• X-ray Absorption Spectroscopy and Theoretical Investigation of the Reductive Protonation of Cyclopentadienyl Cobalt Compounds INORGANIC CHEMISTRY McLoughlin, E. A., Giles, L. J., Waymouth, R. M., Sarangi, R. 2019; 58 (2): 1167–76

  View details for DOI 10.1021/acs.inorgchem.8b02475

  View details for Web of Science ID 000456633400024

• Mechanistic Study of Ruthenium-Catalyzed C-H Hydroxylation Reveals an Unexpected Pathway for Catalyst Arrest JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Mack, J. C., Walker, K. L., Robinson, S. G., Zare, R. N., Sigman, M. S., Waymouth, R. M., Du Bois, J. 2019; 141 (2): 972–80

  View details for DOI 10.1021/jacs.8b10950

  View details for Web of Science ID 000456350300037

• X-ray Absorption Spectroscopy and Theoretical Investigation of the Reductive Protonation of Cyclopentadienyl Cobalt Compounds. Inorganic chemistry McLoughlin, E. A., Giles, L. J., Waymouth, R. M., Sarangi, R. 2019

  Abstract

  Cobalt(III) hydrides, formed via protonation of basic cobalt(I) centers, have long been recognized as key intermediates in the electrocatalytic reduction of protons to hydrogen. An understanding of the structural and electronic factors that govern their formation is key to developing more efficient and potent catalysts. A combination of Co K-edge X-ray absorption spectroscopy, extended X-ray absorption fine structure, density functional theory (DFT), and time-dependent DFT methods have been used to investigate several cyclopentadienyl (Cp) Co(III)L (L = ligand) species and their two-electron reduced Co(I) analogues. The results reveal that when L is strongly pi-accepting, the reduced species demonstrates strong backbonding between the electron-rich Co(I) center and the ligand L, resulting in a weakly basic Co center that does not protonate to form a Co(III)-H. In contrast, a weakly pi-accepting or sigma-donating ligand system results in an electron-rich Co(I) center, which is readily protonated to form a Co(III)-H. This study reveals the strength of a combined X-ray spectroscopy/theory method in understanding the role of ligands in tuning the electronic structure and subsequent reactivity of the metal center.

  View details for PubMedID 30623659

• Mechanistic Study of Ruthenium-Catalyzed C-H Hydroxylation Reveals an Unexpected Pathway for Catalyst Arrest. Journal of the American Chemical Society Mack, J. B., Walker, K. L., Robinson, S. G., Zare, R. N., Sigman, M. S., Waymouth, R. M., Du Bois, J. 2019

  Abstract

  We have recently disclosed [(dtbpy)2RuCl2] as an effective precatalyst for chemoselective C-H hydroxylation of C(sp3)-H bonds and have noted a marked disparity in reaction performance between 4,4'-di- tert-butyl-2,2'-bipyridine (dtbpy)- and 2,2'-bipyridine (bpy)-derived complexes. A desire to understand the origin of this difference and to further advance this catalytic method has motivated the comprehensive mechanistic investigation described herein. Details of this reaction have been unveiled through evaluation of ligand structure-activity relationships, electrochemical and kinetic studies, and pressurized sample infusion high-resolution mass spectrometry (PSI-MS). Salient findings from this investigation include the identification of more than one active oxidant and three disparate mechanisms for catalyst decomposition/arrest. Catalyst efficiency, as measured by turnover number, has a strong inverse correlation with the rate and extent of ligand dissociation, which is dependent on the identity of bipyridyl 4,4'-substituent groups. Dissociated bipyridyl ligand is oxidized to mono- and bis- N-oxide species under the reaction conditions, the former of which is found to act as a potent catalyst poison, yielding a catalytically inactive tris-ligated [Ru(dtbpy)2(dtbpy N-oxide)]2+ complex. Insights gained through this work highlight the power of PSI-MS for studies of complex reaction processes and are guiding ongoing efforts to develop high-performance, next-generation catalyst systems for C-H hydroxylation.

  View details for PubMedID 30601662

• Reactivity of NO2 with Porous and Conductive Copper Azobispyridine Metallopolymers. Inorganic chemistry Clayman, N. E., Manumpil, M. A., Matson, B. D., Wang, S. n., Slavney, A. H., Sarangi, R. n., Karunadasa, H. I., Waymouth, R. M. 2019

  Abstract

  We report the reactivity of copper azobispyridine (abpy) metallopolymers with nitrogen dioxide (NO2). The porous and conductive [Cu(abpy)] n mixed-valence metallopolymers undergo a redox reaction with NO2, resulting in the disproportionation of NO2 gas. Solid- and gas-phase vibrational spectroscopy and X-ray analysis of the reaction products of the NO2-dosed metallopolymer show evidence of nitrate ions and nitric oxide gas. Exposure to NO2 results in complete loss of porosity and a decrease in the room-temperature conductivity of the metallopolymer by four orders of magnitude with the loss of mixed-valence character. Notably, the porous and conductive [Cu(abpy)] n metallopolymers can be reformed by reducing the Cu-nitrate species.

  View details for DOI 10.1021/acs.inorgchem.9b01190

  View details for PubMedID 31364839

• Ubiquity of polystyrene digestion and biodegradation within yellow mealworms, larvae of Tenebrio molitor Linnaeus (Coleoptera: Tenebrionidae) CHEMOSPHERE Yang, S., Wu, W., Brandon, A. M., Fan, H., Receveur, J. P., Li, Y., Wang, Z., Fan, R., McClellan, R. L., Gao, S., Ning, D., Phillips, D. H., Peng, B., Wang, H., Cai, S., Li, P., Cai, W., Ding, L., Yang, J., Zheng, M., Ren, J., Zhang, Y., Gao, J., Xing, D., Ren, N., Waymouth, R. M., Zhou, J., Tao, H., Picard, C. J., Benbow, M., Criddle, C. S. 2018; 212: 262–71

  View details for DOI 10.1016/j.chemosphere.2018.08.078

  View details for Web of Science ID 000447478100030

• Carving Out Pores in Redox-Active One-Dimensional Coordination Polymers ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Clayman, N. E., Manumpil, M., Umeyama, D., Rudenko, A. E., Karunadasa, H. I., Waymouth, R. M. 2018; 57 (44): 14585–88

  View details for DOI 10.1002/anie.201807506

  View details for Web of Science ID 000448049800031

• Delivery of Inorganic Polyphosphate into Cells Using Amphipathic Oligocarbonate Transporters. ACS central science Fernandes-Cunha, G. M., McKinlay, C. J., Vargas, J. R., Jessen, H. J., Waymouth, R. M., Wender, P. A. 2018; 4 (10): 1394-1402

  Abstract

  Inorganic polyphosphate (polyP) is an often-overlooked biopolymer of phosphate residues present in living cells. PolyP is associated with many essential biological roles. Despite interest in polyP's function, most studies have been limited to extracellular or isolated protein experiments, as polyanionic polyP does not traverse the nonpolar membrane of cells. To address this problem, we developed a robust, readily employed method for polyP delivery using guanidinium-rich oligocarbonate transporters that electrostatically complex polyPs of multiple lengths, forming discrete nanoparticles that are resistant to phosphatase degradation and that readily enter multiple cell types. Fluorescently labeled polyPs have been monitored over time for subcellular localization and release from the transporter, with control over release rates achieved by modulating the transporter identity and the charge ratio of the electrostatic complexes. This general approach to polyP delivery enables the study of intracellular polyP signaling in a variety of applications.

  View details for DOI 10.1021/acscentsci.8b00470

  View details for PubMedID 30410977

  View details for PubMedCentralID PMC6202642

• Protonation of a Cobalt Phenylazopyridine Complex at the Ligand Yields a Proton, Hydride, and Hydrogen Atom Transfer Reagent JOURNAL OF THE AMERICAN CHEMICAL SOCIETY McLoughlin, E. A., Waldie, K. M., Ramakrishnan, S., Waymouth, R. M. 2018; 140 (41): 13233–41

  View details for DOI 10.1021/jacs.8b06156

  View details for Web of Science ID 000447953600020

• Synthesis, Characterization, and Reactivity of Hydroxycyclopentadienyl Cobalt Complexes ORGANOMETALLICS Wu, W., Solis-Ibarra, D., Walker, K. L., Waymouth, R. M. 2018; 37 (19): 3298–3302

  View details for DOI 10.1021/acs.organomet.8b00486

  View details for Web of Science ID 000447118700011

• Protonation of a Cobalt Phenylazopyridine Complex at the Ligand Yields a Proton, Hydride, and Hydrogen Atom Transfer Reagent. Journal of the American Chemical Society McLoughlin, E. A., Waldie, K. M., Ramakrishnan, S., Waymouth, R. M. 2018

  Abstract

  Protonation of the Co(I) phenylazopyridine (azpy) complex [CpCo(azpy)] 2 occurs at the azo nitrogen of the 2-phenylazopyridine ligand to generate the cationic Co(I) complex [CpCo(azpyH)]+ 3 with no change in oxidation state at Co. The N-H bond of 3 exhibits diverse hydrogen transfer reactivity, as studies with a variety of organic acceptors demonstrate that 3 can act as a proton, hydrogen atom, and hydride donor. The thermodynamics of all three cleavage modes for the N-H bond (i.e., proton, hydride, and hydrogen atom) were examined both experimentally and computationally. The N-H bond of 3 exhibits a p Ka of 12.1, a hydricity of Delta G°H- = 89 kcal/mol, and a bond dissociation free energy (BDFE) of Delta G°H = 68 kcal/mol in CD3CN. Hydride transfer from 3 to the trityl cation (Delta G°H- = 99 kcal/mol) is exergonic but takes several hours to reach completion, indicating that 3 is a relatively poor hydride donor, both kinetically and thermodynamically. Hydrogen atom transfer from 3 to 2,6-di- tert-butyl-4-(4'-nitrophenyl)phenoxyl radical (tBu2NPArO·, Delta G°H = 77.8 kca/mol) occurs rapidly, illustrating the competence of 3 as a hydrogen atom donor.

  View details for PubMedID 30285438

• mRNA vaccination with charge-altering releasable transporters elicits human T cell responses and cures established tumors in mice PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Haabeth, O. W., Blake, T. R., McKinlay, C. J., Waymouth, R. M., Wender, P. A., Levy, R. 2018; 115 (39): E9153–E9161

  View details for DOI 10.1073/pnas.1810002115

  View details for Web of Science ID 000445545200016

• Carving Out Pores in Redox-Active One-Dimensional Coordination Polymers. Angewandte Chemie (International ed. in English) Clayman, N. E., Manumpil, M. A., Umeyama, D., Rudenko, A. E., Karunadasa, H. I., Waymouth, R. M. 2018

  Abstract

  Reduction of the insulating one-dimensional coordination polymer [Cu(abpy)PF6 ]n , 1a(PF6 ), (abpy=2,2'-azobispyridine) yields the conductive, porous polymer [Cu(abpy)]n , 2a. Pressed pellets of neutral 2a exhibit a conductivity of 0.093 Scm-1 at room temperature and a Brunauer-Emmett-Teller (BET) surface area of 56 m2 g-1 . Fine powders of 2a have a BET surface area of 90 m2 g-1 . Cyclic voltammetry shows that the reduction of 1a(PF6 ) to 2a is quasi-reversible, indicative of facile charge transfer through the bulk material. The BET surface area of the reduced polymer 2 can be controlled by changing the size of the counteranion X in the cationic [Cu(abpy)X]n . Reduction of [Cu(abpy)X]n with X=Br (2b) or BArF (2c; BArF =tetrakis(3,5-bis(trifluoromethyl)phenyl)), affords [Cu(abpy)]n polymers with surface areas of 60 and 200 m2 g-1 , respectively.

  View details for PubMedID 30230677

• Ligand-Induced Reductive Elimination of Ethane from Azopyridine Palladium Dimethyl Complexes JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Rudenko, A. E., Clayman, N. E., Walker, K. L., Maclaren, J. K., Zimmerman, P. M., Waymouth, R. M. 2018; 140 (36): 11408–15

  View details for DOI 10.1021/jacs.8b06398

  View details for Web of Science ID 000444793400040

• mRNA vaccination with charge-altering releasable transporters elicits human T cell responses and cures established tumors in mice. Proceedings of the National Academy of Sciences of the United States of America Haabeth, O. A., Blake, T. R., McKinlay, C. J., Waymouth, R. M., Wender, P. A., Levy, R. 2018

  Abstract

  In vivo delivery of antigen-encoding mRNA is a promising approach to personalized cancer treatment. The therapeutic efficacy of mRNA vaccines is contingent on safe and efficient gene delivery, biological stability of the mRNA, and the immunological properties of the vaccine. Here we describe the development and evaluation of a versatile and highly efficient mRNA vaccine-delivery system that employs charge-altering releasable transporters (CARTs) to deliver antigen-coding mRNA to antigen-presenting cells (APCs). We demonstrate in human peripheral blood mononuclear cells that CART vaccines can activate a robust antigen-specific immune response against mRNA-encoded viral epitopes. In an established mouse model, we demonstrate that CARTs preferentially target professional APCs in secondary lymphoid organs upon i.v. injections and target local APCs upon s.c. injection. Finally, we show that CARTs coformulated with mRNA and a Toll-like receptor ligand simultaneously transfect and activate target cells to generate an immune response that can treat and cure mice with large, established tumors.

  View details for PubMedID 30201728

• Ligand-Induced Reductive Elimination of Ethane from Azopyridine Palladium Dimethyl Complexes. Journal of the American Chemical Society Rudenko, A. E., Clayman, N. E., Walker, K. L., Maclaren, J. K., Zimmerman, P. M., Waymouth, R. M. 2018

  Abstract

  Reductive elimination (RE) is a critical step in many catalytic processes. The reductive elimination of unsaturated groups (aryl, vinyl and ethynyl) from Pd(II) species is considerably faster than RE of saturated alkyl groups. Pd(II) dimethyl complexes ligated by chelating diimine ligands are stable toward RE unless subjected to a thermal or redox stimulus. Herein, we report the spontaneous RE of ethane from (azpy)PdMe2 complexes and the unique role of the redox-active azopyridine (azpy) ligands in facilitating this reaction. The (azpy)PdMe2 complexes are air- and moisture-stable in the solid form, but they readily produce ethane upon dissolution in polar solvents at temperatures from 10 °C to room temperature without the need for an external oxidant or elevated temperatures. Experimental and computational studies indicate that a bimolecular methyl transfer precedes the reductive elimination step, where both steps are facilitated by the redox-active azopyridine ligand.

  View details for PubMedID 30160962

• Functional DNA Delivery Enabled by Lipid-Modified Charge-Altering Releasable Transporters (CARTs) BIOMACROMOLECULES Benner, N. L., Near, K. E., Bachmann, M. H., Contag, C. H., Waymouth, R. M., Wender, P. A. 2018; 19 (7): 2812–24

  Abstract

  Safe and effective DNA delivery systems are required to enable or enhance clinical strategies and research involving gene therapy and DNA vaccinations. To address this delivery problem, a series of charge-altering releasable transporters (CARTs) with varied lipid content were prepared and evaluated for plasmid DNA (pDNA) delivery into cultured cells. These lipid-modified CART co-oligomers were synthesized in only two steps via sequential organocatalytic ring-opening polymerization of lipid-containing cyclic carbonate monomers and morpholinone monomers. Lipid variations of the CARTs substantially impacted the delivery efficiency of pDNA, with oleyl- and linoleyl-based CARTs showing enhanced performance relative to the commercial transfection agent Lipofectamine 2000 (L2000). The best-performing oleyl CART was carried forward to study stable luciferase transfection with a Sleeping Beauty ( SB) transposon system. The oleyl CART outperformed the L2000 positive control with respect to stable transfection efficiency. CART-pDNA complexes represent a new DNA delivery system for research and clinical applications.

  View details for DOI 10.1021/acs.biomac.8b00401

  View details for Web of Science ID 000438470800044

  View details for PubMedID 29727572

• Enhanced mRNA delivery into lymphocytes enabled by lipid-varied libraries of charge-altering releasable transporters. Proceedings of the National Academy of Sciences of the United States of America McKinlay, C. J., Benner, N. L., Haabeth, O. A., Waymouth, R. M., Wender, P. A. 2018; 115 (26): E5859–E5866

  Abstract

  We report a strategy for generating a combinatorial library of oligonucleotide transporters with varied lipid domains and their use in the efficient transfection of lymphocytes with mRNA in vitro and in vivo. This library is based on amphiphilic charge-altering releasable transporters (CARTs) that contain a lipophilic block functionalized with various side-chain lipids and a polycationic alpha-amino ester mRNA-binding block that undergoes rearrangement to neutral small molecules, resulting in mRNA release. We show that certain binary mixtures of these lipid-varied CARTs provide up to a ninefold enhancement in mRNA translation in lymphocytes in vitro relative to either a single-lipid CART component alone or the commercial reagent Lipofectamine 2000, corresponding to a striking increase in percent transfection from 9-12% to 80%. Informed by the results with binary mixtures, we further show that CARTs consisting of optimized ratios of the two lead lipids incorporated into a single hybrid-lipid transporter molecule maintain the same delivery efficacy as the noncovalent mixture of two CARTs. The lead lipid CART mixtures and hybrid-lipid CARTs show enhanced lymphocyte transfection in primary T cells and in vivo in mice. This combinatorial approach for rapidly screening mRNA delivery vectors has provided lipid-varied CART mixtures and hybrid-lipid CARTs that exhibit significant improvement in mRNA delivery to lymphocytes, a finding of potentially broad value in research and clinical applications.

  View details for PubMedID 29891683

• Enhanced mRNA delivery into lymphocytes enabled by lipid-varied libraries of charge-altering releasable transporters PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA McKinlay, C. J., Benner, N. L., Haabeth, O. A., Waymouth, R. M., Wender, P. A. 2018; 115 (26): E5859–E5866

  View details for DOI 10.1073/pnas.1805358115

  View details for Web of Science ID 000436245000007

• Transfer Hydrogenation of Aldehydes, Allylic Alcohols, Ketones, and Imines Using Molybdenum Cyclopentadienone Complexes ORGANOMETALLICS Wu, W., Seki, T., Walker, K. L., Waymouth, R. M. 2018; 37 (9): 1428–31

  View details for DOI 10.1021/acs.organomet.8b00086

  View details for Web of Science ID 000432477000012

• Catalysis as an Enabling Science for Sustainable Polymers. Chemical reviews Zhang, X., Fevre, M., Jones, G. O., Waymouth, R. M. 2018; 118 (2): 839–85

  Abstract

  The replacement of current petroleum-based plastics with sustainable alternatives is a crucial but formidable challenge for the modern society. Catalysis presents an enabling tool to facilitate the development of sustainable polymers. This review provides a system-level analysis of sustainable polymers and outlines key criteria with respect to the feedstocks the polymers are derived from, the manner in which the polymers are generated, and the end-of-use options. Specifically, we define sustainable polymers as a class of materials that are derived from renewable feedstocks and exhibit closed-loop life cycles. Among potential candidates, aliphatic polyesters and polycarbonates are promising materials due to their renewable resources and excellent biodegradability. The development of renewable monomers, the versatile synthetic routes to convert these monomers to polyesters and polycarbonate, and the different end-of-use options for these polymers are critically reviewed, with a focus on recent advances in catalytic transformations that lower the technological barriers for developing more sustainable replacements for petroleum-based plastics.

  View details for PubMedID 29048888

• Catalysis as an Enabling Science for Sustainable Polymers CHEMICAL REVIEWS Zhang, X., Fevre, M., Jones, G. O., Waymouth, R. M. 2018; 118 (2): 839–85

  View details for DOI 10.1021/acs.chemrev.7b00329

  View details for Web of Science ID 000423495900009

• Pd-Catalyzed Aerobic Oxidation Reactions: Strategies To Increase Catalyst Lifetimes JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Ho, W. C., Chung, K., Ingram, A. J., Waymouth, R. M. 2018; 140 (2): 748–57

  Abstract

  The palladium complex [(neocuproine)Pd(μ-OAc)]2[OTf]2 (1, neocuproine = 2,9-dimethyl-1,10-phenanthroline) is an effective catalyst precursor for the selective oxidation of primary and secondary alcohols, vicinal diols, polyols, and carbohydrates. Both air and benzoquinone can be used as terminal oxidants, but aerobic oxidations are accompanied by oxidative degradation of the neocuproine ligand, thus necessitating high Pd loadings. Several strategies to improve aerobic catalyst lifetimes were devised, guided by mechanistic studies of catalyst deactivation. These studies implicate a radical autoxidation mechanism initiated by H atom abstraction from the neocuproine ligand. Ligand modifications designed to retard H atom abstractions as well as the addition of sacrificial H atom donors increase catalyst lifetimes and lead to higher turnover numbers (TON) under aerobic conditions. Additional investigations revealed that the addition of benzylic hydroperoxides or styrene leads to significant increases in TON as well. Mechanistic studies suggest that benzylic hydroperoxides function as H atom donors and that styrene is effective at intercepting Pd hydrides. These strategies enabled the selective aerobic oxidation of polyols on preparative scales using as little as 0.25 mol % of Pd, a major improvement over previous work.

  View details for PubMedID 29244945

• Biodegradation of polystyrene wastes in yellow mealworms (larvae of Tenebrio molitor Linnaeus): Factors affecting biodegradation rates and the ability of polystyrene-fed larvae to complete their life cycle CHEMOSPHERE Yang, S., Brandon, A., Flanagan, J., Yang, J., Ning, D., Cai, S., Fan, H., Wang, Z., Ren, J., Benbow, E., Ren, N., Waymouth, R. M., Zhou, J., Criddle, C. S., Wu, W. 2018; 191: 979–89

  Abstract

  Commercial production of polystyrene (PS) -a persistent plastic that is not biodegradable at appreciable rates in most environments-has led to its accumulation as a major contaminant of land, rivers, lakes, and oceans. Recently, however, an environment was identified in which PS is susceptible to rapid biodegradation: the larval gut of Tenebrio molitor Linnaeus (yellow mealworms). In this study, we evaluate PS degradation capabilities of a previously untested strain of T. molitor and assess its survival and PS biodegradation rates for a range of conditions (two simulated food wastes, three temperatures, seven PS waste types). For larvae fed PS alone, the %PS removed in the short (12-15 h) residence time of the mealworm gut gradually increased for 2-3 weeks then stabilized at values up to 65%. Thirty two-day survival rates were >85% versus 54% for unfed larvae. For mealworms fed ∼10% w/w PS and ∼90% bran, an agricultural byproduct, rates of PS degradation at 25 °C nearly doubled compared to mealworms fed PS alone. Polymer residues in the frass showed evidence of partial depolymerization and oxidation. All of the tested PS wastes degraded, with the less dense foams degrading most rapidly. Mealworms fed bran and PS completed all life cycle stages (larvae, pupae, beetles, egg), and the second generation had favorable PS degradation, opening the door for selective breeding.

  View details for PubMedID 29145143

• Delivery of Inorganic Polyphosphate into Cells Using Amphipathic Oligocarbonate Transporters ACS Cent. Sci. Fernandes Cunha, G., McKinlay, C., Vargas, J., Jessen, H., Waymouth, R., Wender, P. 2018

  View details for DOI 10.1021/acscentsci.8b00470

• Formation of Polymeric Nanocubes by Self-Assembly and Crystallization of Dithiolane-Containing Triblock Copolymers ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Margulis, K., Zhang, X., Joubert, L., Bruening, K., Tassone, C. J., Zare, R. N., Waymouth, R. M. 2017; 56 (51): 16357–62

  View details for DOI 10.1002/anie.201709564

  View details for Web of Science ID 000419399800041

• Expanding the range of polyhydroxyalkanoates synthesized by methanotrophic bacteria through the utilization of omega-hydroxyalkanoate co-substrates. AMB Express Myung, J., Flanagan, J. C., Waymouth, R. M., Criddle, C. S. 2017; 7 (1): 118-?

  Abstract

  The first methanotrophic syntheses of polyhydroxyalkanoates (PHAs) that contain repeating units beyond 3-hydroxybutyrate and 3-hydroxyvalerate are reported. New PHAs synthesized by methanotrophs include poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P(3HB-co-4HB)), poly(3-hydroxybutyrate-co-5-hydroxyvalerate-co-3-hydroxyvalerate) (P(3HB-co-5HV-co-3HV)), and poly(3-hydroxybutyrate-co-6-hydroxyhexanoate-co-4-hydroxybutyrate) (P(3HB-co-6HHx-co-4HB)). This was achieved from a pure culture of Methylocystis parvus OBBP where the primary substrate is methane and the corresponding ω-hydroxyalkanoate monomers are added as a co-substrate after the cells are subjected to nitrogen-limited conditions.

  View details for DOI 10.1186/s13568-017-0417-y

  View details for PubMedID 28587442

• Formation of Polymeric Nanocubes by Self-Assembly and Crystallization of Dithiolane-Containing Triblock Copolymers. Angewandte Chemie (International ed. in English) Margulis, K., Zhang, X., Joubert, L., Bruening, K., Tassone, C. J., Zare, R. N., Waymouth, R. M. 2017

  Abstract

  Template-free fabrication of non-spherical polymeric nanoparticles is desirable for various applications, but has had limited success owing to thermodynamic favorability of sphere formation. Herein we present a simple way to prepare cubic nanoparticles of block copolymers by self-assembly from aqueous solutions at room temperature. Nanocubes with edges of 40-200 nm are formed spontaneously on different surfaces upon water evaporation from micellar solutions of triblock copolymers containing a central poly(ethylene oxide) block and terminal trimethylene carbonate/dithiolane blocks. These polymers self-assemble into 28±5 nm micelles in water. Upon drying, micelle aggregation and a kinetically controlled crystallization of central blocks evidently induce solid cubic particle formation. An approach for preserving the structures of these cubes in water by thiol- or photo-induced crosslinking was developed. The ability to solubilize a model hydrophobic drug, curcumin, was also explored.

  View details for PubMedID 29080292

• Recent Progress on the Synthesis of Cyclic Polymers via Ring-Expansion Strategies JOURNAL OF POLYMER SCIENCE PART A-POLYMER CHEMISTRY Chang, Y. A., Waymouth, R. M. 2017; 55 (18): 2892–2902

  View details for DOI 10.1002/pola.28635

  View details for Web of Science ID 000406937100004

• Mechanism of Catalytic Oxidation of Styrenes with Hydrogen Peroxide in the Presence of Cationic Palladium(II) Complexes JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Walker, K. L., Dornan, L. M., Zare, R. N., Waymouth, R. M., Mudoon, M. J. 2017; 139 (36): 12495–503

  Abstract

  Kinetic studies, isotope labeling, and in situ high-resolution mass spectrometry are used to elucidate the mechanism for the catalytic oxidation of styrenes using aqueous hydrogen peroxide (H2O2) and the cationic palladium(II) compound, [(PBO)Pd(NCMe)2][OTf]2 (PBO = 2-(pyridin-2-yl)benzoxazole). Previous studies have shown that this reaction yields acetophenones with high selectivity. We find that H2O2 binds to Pd(II) followed by styrene binding to generate a Pd-alkylperoxide that liberates acetophenone by at least two competitive processes, one of which involves a palladium enolate intermediate that has not been previously observed in olefin oxidation reactions. We suggest that acetophenone is formed from the palladium enolate intermediate by protonation from H2O2. We replaced hydrogen peroxide with t-butyl hydroperoxide and found that, although the palladium enolate intermediate was observed, it was not on the major product-generating pathway, indicating that the form of the oxidant plays a key role in the reaction mechanism.

  View details for PubMedID 28849921

• Cyclopentadienyl Cobalt Complexes as Precatalysts for Electrocatalytic Hydrogen Evolution EUROPEAN JOURNAL OF INORGANIC CHEMISTRY Waldie, K. M., Kim, S., Ingram, A. J., Waymouth, R. M. 2017: 2755–61

  View details for DOI 10.1002/ejic.201700188

  View details for Web of Science ID 000403683400015

• Multielectron Transfer at Cobalt: Influence of the Phenylazopyridine Ligand JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Waldie, K. M., Ramakrishnan, S., Kim, S., Maclaren, J. K., Chidsey, C. E., Waymouth, R. M. 2017; 139 (12): 4540-4550

  Abstract

  The dicationic complex [CpCo(azpy)(CH3CN)](ClO4)2 1 (azpy = phenylazopyridine) exhibits a reversible two-electron reduction at a very mild potential (-0.16 V versus Fc(0/+)) in acetonitrile. This behavior is not observed with the analogous bipyridine and pyrazolylpyridine complexes (3 and 4), which display an electrochemical signature typical of Co(III) systems: two sequential one-electron reductions to Co(II) at -0.4 V and Co(I) at -1.0 to -1.3 V versus Fc(0/+). The doubly reduced, neutral complex [CpCo(azpy)] 2 is isolated as an air-stable, diamagnetic solid via chemical reduction with cobaltocene. Crystallographic and spectroscopic characterization together with experimentally calibrated density functional theory calculations illuminate the key structural and electronic changes that occur upon reduction of 1 to 2. The electrochemical potential inversion observed with 1 is attributed to effective overlap between the metal d and the low-energy azo π* orbitals in the intermediary redox state and additional stabilization of 2 from structural reorganization, leading to a two-electron reduction. This result serves as a key milestone in the quest for two-electron transformations with mononuclear first-row transition metal complexes at mild potentials.

  View details for DOI 10.1021/jacs.7b01047

  View details for Web of Science ID 000398247100051

  View details for PubMedID 28263588

• 1,2-Dithiolane-Derived Dynamic, Covalent Materials: Cooperative Self-Assembly and Reversible Cross-Linking. Journal of the American Chemical Society Zhang, X., Waymouth, R. M. 2017

  Abstract

  The use of dithiolane-containing polymers to construct responsive and dynamic networks is an attractive strategy in material design. Here, we provide a detailed mechanistic study on the self-assembly and gelation behavior of a class of ABA triblock copolymers containing a central poly(ethylene oxide) block and terminal polycarbonate blocks with pendant 1,2-dithiolane functionalities. In aqueous solution, these amphiphilic block copolymers self-assemble into bridged flower micelles at high concentrations. The addition of a thiol initiates the reversible ring-opening polymerizations of dithiolanes in the micellar cores to induce the cross-linking and gelation of the micellar network. The properties of the resulting hydrogels depend sensitively on the structures of 1,2-dithiolanes. While the methyl asparagusic acid-derived hydrogels are highly dynamic, adaptable, and self-healing, those derived from lipoic acid are rigid, resilient, and brittle. The thermodynamics and kinetics of ring-opening polymerization of the two dithiolanes were investigated to provide important insights on the dramatically different properties of the hydrogels derived from the two different dithiolanes. The incorporation of both dithiolane monomers into the block copolymers provides a facile way to tailor the properties of these hydrogels.

  View details for DOI 10.1021/jacs.7b00039

  View details for PubMedID 28244754

• Urea Anions: Simple, Fast, and Selective Catalysts for Ring-Opening Polymerizations JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Lin, B., Waymouth, R. M. 2017; 139 (4): 1645-1652

  Abstract

  Aliphatic polyesters and polycarbonates are a class of biorenewable, biocompatible, and biodegradable materials. One of the most powerful methods for accessing these materials is the ring-opening polymerization (ROP) of cyclic monomers. Here we report that the deprotonation of ureas generates a class of versatile catalysts that are simultaneously fast and selective for the living ring-opening polymerization of several common monomers, including lactide, δ-valerolactone, ε-caprolactone, a cyclic carbonate, and a cyclic phosphoester. Spanning several orders of magnitude, the reactivities of several diaryl urea anions correlated to the electron-withdrawing substituents on the aryl rings. With the appropriate urea anions, the polymerizations reached high conversions (∼90%) at room temperature within seconds (1-12 s), yielding polymers with narrow molecular weight distributions (Đ = 1.06 to 1.14). These versatile catalysts are simple to prepare, easy to use, and exhibit a range of activities that can be tuned for the optimal performance of a broad range of monomers.

  View details for DOI 10.1021/jacs.6b11864

  View details for Web of Science ID 000393355600048

  View details for PubMedID 28105810

• Charge-altering releasable transporters (CARTs) for the delivery and release of mRNA in living animals PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA McKinlay, C. J., Vargas, J. R., Blake, T. R., Hardy, J. W., Kanada, M., Contag, C. H., Wender, P. A., Waymouth, R. M. 2017; 114 (4): E448-E456

  Abstract

  Functional delivery of mRNA to tissues in the body is key to implementing fundamentally new and potentially transformative strategies for vaccination, protein replacement therapy, and genome editing, collectively affecting approaches for the prevention, detection, and treatment of disease. Broadly applicable tools for the efficient delivery of mRNA into cultured cells would advance many areas of research, and effective and safe in vivo mRNA delivery could fundamentally transform clinical practice. Here we report the step-economical synthesis and evaluation of a tunable and effective class of synthetic biodegradable materials: charge-altering releasable transporters (CARTs) for mRNA delivery into cells. CARTs are structurally unique and operate through an unprecedented mechanism, serving initially as oligo(α-amino ester) cations that complex, protect, and deliver mRNA and then change physical properties through a degradative, charge-neutralizing intramolecular rearrangement, leading to intracellular release of functional mRNA and highly efficient protein translation. With demonstrated utility in both cultured cells and animals, this mRNA delivery technology should be broadly applicable to numerous research and therapeutic applications.

  View details for DOI 10.1073/pnas.1614193114

  View details for Web of Science ID 000392597000002

  View details for PubMedID 28069945

  View details for PubMedCentralID PMC5278438

• Electrocatalytic Alcohol Oxidation with Ruthenium Transfer Hydrogenation Catalysts JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Waldie, K. M., Flajslik, K. R., McLoughlin, E., Chidsey, C. E., Waymouth, R. M. 2017; 139 (2): 738-748

  Abstract

  Octahedral ruthenium complexes [RuX(CNN)(dppb)] (1, X = Cl; 2, X = H; CNN = 2-aminomethyl-6-tolylpyridine, dppb = 1,4-bis(diphenylphosphino)butane) are highly active for the transfer hydrogenation of ketones with isopropanol under ambient conditions. Turnover frequencies of 0.88 and 0.89 s(-1) are achieved at 25 °C using 0.1 mol % of 1 or 2, respectively, in the presence of 20 equiv of potassium t-butoxide relative to catalyst. Electrochemical studies reveal that the Ru-hydride 2 is oxidized at low potential (-0.80 V versus ferrocene/ferrocenium, Fc(0/+)) via a chemically irreversible process with concomitant formation of dihydrogen. Complexes 1 and 2 are active for the electrooxidation of isopropanol in the presence of strong base (potassium t-butoxide) with an onset potential near -1 V versus Fc(0/+). By cyclic voltammetry, fast turnover frequencies of 3.2 and 4.8 s(-1) for isopropanol oxidation are achieved with 1 and 2, respectively. Controlled potential electrolysis studies confirm that the product of isopropanol electrooxidation is acetone, generated with a Faradaic efficiency of 94 ± 5%.

  View details for DOI 10.1021/jacs.6b09705

  View details for Web of Science ID 000392459300032

  View details for PubMedID 27997178

• Fast and selective ring-opening polymerizations by alkoxides and thioureas. Nature chemistry Zhang, X., Jones, G. O., Hedrick, J. L., Waymouth, R. M. 2016; 8 (11): 1047-1053

  Abstract

  Ring-opening polymerization of lactones is a versatile approach to generate well-defined functional polyesters. Typical ring-opening catalysts are subject to a trade-off between rate and selectivity. Here we describe an effective catalytic system combining alkoxides with thioureas that catalyses rapid and selective ring-opening polymerizations. Deprotonation of thioureas by sodium, potassium or imidazolium alkoxides generates a hydrogen-bonded alcohol adduct of the thiourea anion (thioimidate). The ring-opening polymerization of L-lactide mediated by these alcohol-bonded thioimidates yields highly isotactic polylactide with fast kinetics and living polymerization behaviour, as evidenced by narrow molecular weight distributions (Mw/Mn < 1.1), chain extension experiments and minimal transesterifications. Computational studies indicate a bifunctional catalytic mechanism whereby the thioimidate activates the carbonyl of the monomer and the alcohol initiator/chain end to effect the selective ring-opening of lactones and carbonates. The high selectivity of the catalyst towards monomer propagation over transesterification is attributed to a selective activation of monomer over polymer chains.

  View details for DOI 10.1038/nchem.2574

  View details for PubMedID 27768102

• Zwitterionic Ring-Opening Polymerization of N-Substituted Eight-Membered Cyclic Carbonates to Generate Cyclic Poly(carbonate)s ACS MACRO LETTERS Chang, Y. A., Rudenko, A. E., Waymouth, R. M. 2016; 5 (10): 1162-1166

  View details for DOI 10.1021/acsmacrolett.6b00591

  View details for Web of Science ID 000385913800019

• Catalytic Carbonylative Spirolactonization of Hydroxycyclopropanols. Journal of the American Chemical Society Davis, D. C., Walker, K. L., Hu, C., Zare, R. N., Waymouth, R. M., Dai, M. 2016; 138 (33): 10693-10699

  Abstract

  A palladium-catalyzed cascade carbonylative spirolactonization of hydroxycyclopropanols has been developed to efficiently synthesize oxaspirolactones common to many complex natural products of important therapeutic value. The mild reaction conditions, high atom economy, broad substrate scope, and scalability of this new method were highlighted in expedient total syntheses of the Turkish tobacco natural products α-levantanolide and α-levantenolide in two and four steps, respectively. The hydroxycyclopropanol substrates are readily available in one step via a Kulinkovich reaction of the corresponding lactones. Mechanistic studies utilizing high-resolution electrospray ionization mass spectrometry (ESI-MS) identified several key intermediates in the catalytic cycle, as well as those related to catalyst decomposition and competitive pathways.

  View details for DOI 10.1021/jacs.6b06573

  View details for PubMedID 27459274

• Reversible Electropolymerization of Nickel Complexes Based on Redox-Mediated Ligand Exchange CHEMISTRYSELECT Rudenko, A. E., Clayman, N. E., Maclaren, J. K., Waymouth, R. M. 2016; 1 (13): 3491-3496

  View details for DOI 10.1002/slct.201600523

  View details for Web of Science ID 000392302300014

• Selective Catalytic Oxidation of Unprotected Carbohydrates ACS CATALYSIS Chung, K., Waymouth, R. M. 2016; 6 (7): 4653-4659

  View details for DOI 10.1021/acscatat.6b01501

  View details for Web of Science ID 000379457300072

• Poly(hydroxyalkanoate)s from Waste Biomass: A Combined Chemical-Biological Approach CHEMISTRYSELECT Flanagan, J. C., Myung, J., Criddle, C. S., Waymouth, R. M. 2016; 1 (10): 2327-2331

  View details for DOI 10.1002/slct.201600592

  View details for Web of Science ID 000395417800036

• Methane or methanol-oxidation dependent synthesis of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) by obligate type II methanotrophs PROCESS BIOCHEMISTRY Myung, J., Flanagan, J. C., Waymouth, R. M., Criddle, C. S. 2016; 51 (5): 561-567

  View details for DOI 10.1016/j.procbio.2016.02.005

  View details for Web of Science ID 000375338400002

• Cell-Penetrating, Guanidinium-Rich Oligophosphoesters: Effective and Versatile Molecular Transporters for Drug and Probe Delivery JOURNAL OF THE AMERICAN CHEMICAL SOCIETY McKinlay, C. J., Waymouth, R. M., Wender, P. A. 2016; 138 (10): 3510-3517

  Abstract

  The design, synthesis, and biological evaluation of a new family of highly effective cell-penetrating molecular transporters, guanidinium-rich oligophosphoesters, are described. These unique transporters are synthesized in two steps, irrespective of oligomer length, by the organocatalytic ring-opening polymerization (OROP) of 5-membered cyclic phospholane monomers followed by oligomer deprotection. Varying the initiating alcohol results in a wide variety of cargo attachment strategies for releasable or nonreleasable transporter applications. Initiation of oligomerization with a fluorescent probe produces, upon deprotection, a transporter-probe conjugate that is shown to readily enter multiple cell lines in a dose-dependent manner. These new transporters are superior in cell uptake to previously studied guanidinium-rich oligocarbonates and oligoarginines, showing over 2-fold higher uptake than the former and 6-fold higher uptake than the latter. Initiation with a protected thiol gives, upon deprotection, thiol-terminated transporters which can be thiol-click conjugated to a variety of probes, drugs and other cargos as exemplified by the conjugation and delivery of the model probe fluorescein-maleimide and the medicinal agent paclitaxel (PTX) into cells. Of particular significance given that drug resistance is a major cause of chemotherapy failure, the PTX-transporter conjugate, designed to evade Pgp export and release free PTX after cell entry, shows efficacy against PTX-resistant ovarian cancer cells. Collectively this study introduces a new and highly effective class of guanidinium-rich cell-penetrating transporters and methodology for their single-step conjugation to drugs and probes, and demonstrates that the resulting drug/probe-conjugates readily enter cells, outperforming previously reported guanidinium-rich oligocarbonates and peptide transporters.

  View details for DOI 10.1021/jacs.5b13452

  View details for Web of Science ID 000372477700036

• Experimental and Theoretical Study of CO2 Insertion into Ruthenium Hydride Complexes. Inorganic chemistry Ramakrishnan, S., Waldie, K. M., Warnke, I., De Crisci, A. G., Batista, V. S., Waymouth, R. M., Chidsey, C. E. 2016; 55 (4): 1623-1632

  Abstract

  The ruthenium hydride [RuH(CNN)(dppb)] (1; CNN = 2-aminomethyl-6-tolylpyridine, dppb = 1,4-bis(diphenylphosphino)butane) reacts rapidly and irreversibly with CO2 under ambient conditions to yield the corresponding Ru formate complex 2. In contrast, the Ru hydride 1 reacts with acetone reversibly to generate the Ru isopropoxide, with the reaction free energy ΔG°298 K = -3.1 kcal/mol measured by (1)H NMR in tetrahydrofuran-d8. Density functional theory (DFT), calibrated to the experimentally measured free energies of ketone insertion, was used to evaluate and compare the mechanism and energetics of insertion of acetone and CO2 into the Ru-hydride bond of 1. The calculated reaction coordinate for acetone insertion involves a stepwise outer-sphere dihydrogen transfer to acetone via hydride transfer from the metal and proton transfer from the N-H group on the CNN ligand. In contrast, the lowest energy pathway calculated for CO2 insertion proceeds by an initial Ru-H hydride transfer to CO2 followed by rotation of the resulting N-H-stabilized formate to a Ru-O-bound formate. DFT calculations were used to evaluate the influence of the ancillary ligands on the thermodynamics of CO2 insertion, revealing that increasing the π acidity of the ligand cis to the hydride ligand and increasing the σ basicity of the ligand trans to it decreases the free energy of CO2 insertion, providing a strategy for the design of metal hydride systems capable of reversible, ergoneutral interconversion of CO2 and formate.

  View details for DOI 10.1021/acs.inorgchem.5b02556

  View details for PubMedID 26835983

• Bioorthogonal Catalysis: A General Method To Evaluate Metal Catalyzed Reactions in Real Time in Living Systems Using a Cellular Luciferase Reporter System BIOCONJUGATE CHEMISTRY Hsu, H., Trantow, B. M., Waymouth, R. M., Wender, P. A. 2016; 27 (2): 376-382

  Abstract

  The development of abiological catalysts that can function in biological systems is an emerging subject of importance with significant ramifications in synthetic chemistry and the life sciences. Herein we report a biocompatible ruthenium complex [Cp(MQA)Ru(C3H5)](+)PF6(-) 2 (Cp = cyclopentadienyl, MQA = 4-methoxyquinoline-2-carboxylate) and a general analytical method for evaluating its performance in real time based on a luciferase reporter system amenable to high throughput screening in cells and by extension to evaluation in luciferase transgenic animals. Precatalyst 2 activates alloc-protected aminoluciferin 4b, a bioluminescence pro-probe, and releases the active luminophore, aminoluciferin (4a), in the presence of luciferase-transfected cells. The formation and enzymatic turnover of 4a, an overall process selected because it emulates pro-drug activation and drug turnover by an intracellular target, is evaluated in real time by photon counting as 4a is converted by intracellular luciferase to oxyaminoluciferin and light. Interestingly, while the catalytic conversion (activation) of 4b to 4a in water produces multiple products, the presence of biological nucleophiles such as thiols prevents byproduct formation and provides almost exclusively luminophore 4a. Our studies show that precatalyst 2 activates 4b extracellularly, exhibits low toxicity at concentrations relevant to catalysis, and is comparably effective in two different cell lines. This proof of concept study shows that precatalyst 2 is a promising lead for bioorthogonal catalytic activation of pro-probes and, by analogy, similarly activatable pro-drugs. More generally, this study provides an analytical method to measure abiological catalytic activation of pro-probes and, by analogy with our earlier studies on pro-Taxol, similarly activatable pro-drugs in real time using a coupled biological catalyst that mediates a bioluminescent readout, providing tools for the study of imaging signal amplification and of targeted therapy.

  View details for DOI 10.1021/acs.bioconjchem.5b00469

  View details for Web of Science ID 000370582600012

  View details for PubMedID 26367192

  View details for PubMedCentralID PMC4772775

• Electrooxidation of Alcohols with Electrode-Supported Transfer Hydrogenation Catalysts ACS CATALYSIS Buonaiuto, M., De Crisci, A. G., Jaramillo, T. F., Waymouth, R. M. 2015; 5 (12): 7343-7349

  View details for DOI 10.1021/acscatal.5b01830

  View details for Web of Science ID 000366153300034

• A Simple and Facile Approach to Aliphatic N-Substituted Functional Eight-Membered Cyclic Carbonates and Their Organocatalytic Polymerization JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Venkataraman, S., Ng, V. W., Coady, D. J., Horn, H. W., Jones, G. O., Fung, T. S., Sardon, H., Waymouth, R. M., Hedrick, J. L., Yang, Y. Y. 2015; 137 (43): 13851-13860

  Abstract

  Aliphatic N-substituted functional eight-membered cyclic carbonates were synthesized from N-substituted diethanolamines by intramolecular cyclization. On the basis of the N-substituent, three major subclasses of carbonate monomers were synthesized (N-aryl, N-alkyl and N-carbamate). Organocatalytic ring opening polymerization (ROP) of eight-membered cyclic carbonates was explored as a route to access narrowly dispersed polymers of predictable molecular weights. Polymerization kinetics was highly dependent on the substituent on the nitrogen atom and the catalyst used for the reaction. The use of triazabicyclodecene (TBD), instead of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), as the catalyst for the N-alkyl substituted monomers significantly enhanced the rate of polymerizations. Computational studies were performed to rationalize the observed trends for TBD catalyzed polymerizations. With the optimal organocatalyst all monomers could be polymerized generating well-defined polymers within a timespan of ≤2 h with relatively high monomer conversion (≥80%) and low molar-mass dispersity (Đ(M) ≤ 1.3). Both the glass transition temperatures (T(g)) and onset of degradation temperatures (T(onset)) of these polymers were found to be N-substituent dependent and were in the range of about -45 to 35 °C and 230 to 333 °C, respectively. The copolymerization of the eight membered monomers with 6-membered cyclic comonomers including commercially available l-lactide and trimethylene carbonate produced novel copolymers. The combination of inexpensive starting materials, ease of ring-closure and subsequent polymerization makes this an attractive route to functional polycarbontes.

  View details for DOI 10.1021/Jacs.5b06355

  View details for Web of Science ID 000364355900027

  View details for PubMedID 26456146

• Catalytic Role of Multinuclear Palladium-Oxygen Intermediates in Aerobic Oxidation Followed by Hydrogen Peroxide Disproportionation JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Ingram, A. J., Walker, K. L., Zare, R. N., Waymouth, R. M. 2015; 137 (42): 13632-13646

  Abstract

  Aerobic oxidation of alcohols are catalyzed by the Pd-acetate compound [LPd(OAc)]2(OTf)2 (L = neocuproine = 2,9-dimethyl-1,10-phenanthroline) to form ketones and the release of hydrogen peroxide, but the latter rapidly undergoes disproportionation. We employ a series of kinetic and isotope labeling studies made largely possible by electrospray ionization mass spectrometry to determine the role of intermediates in causing this complex chemical transformation. The data suggested that multiple catalytic paths for H2O2 disproportionation occur, which involve formation and consumption of multinuclear Pd species. We find that the trinuclear compound [(LPd)3(μ(3)-O)2](2+), which we have identified in a previous study, is a product of dioxygen activation that is formed during aerobic oxidations of alcohols catalyzed by [LPd(OAc)]2(OTf)2. It is also a product of hydrogen peroxide activation during disproportionation reactions catalyzed by [LPd(OAc)]2(OTf)2. The results suggest that this trinuclear Pd compound is involved in one of the simultaneous mechanisms for the reduction of oxygen and/or the disproportionation of hydrogen peroxide during oxidation catalysis. Electrospray ionization mass spectrometry of hydrogen peroxide disproportionation reactions suggested the presence of other multinuclear Pd-O2 species in solution. Theoretical calculations of these compounds yield some insight into their structure and potential chemistry.

  View details for DOI 10.1021/jacs.5b08719

  View details for Web of Science ID 000363916600031

  View details for PubMedID 26444100

• Catalytic Dimerization of Crotonates ACS CATALYSIS Flanagan, J. C., Kang, E. J., Strong, N. I., Waymouth, R. M. 2015; 5 (9): 5328-5332

  View details for DOI 10.1021/acscatal.5b00930

  View details for Web of Science ID 000361089700040

• Cyclopropenimine Superbases: Competitive Initiation Processes in Lactide Polymerization. ACS macro letters Stukenbroeker, T. S., Bandar, J. S., Zhang, X., Lambert, T. H., Waymouth, R. M. 2015; 4 (8): 853-856

  Abstract

  Cyclopropenimine superbases were employed to catalyze the ring-opening polymerization of lactide. Polymerization occurred readily in the presence and absence of alcohol initiators. Polymerizations in the absence of alcohol initiators revealed a competitive initiation mechanism involving deprotonation of lactide by the cyclopropenimine to generate an enolate. NMR and MALDI-TOF analysis of the poly(lactides) generated from cyclopropenimines in the absence of alcohol initiators showed acylated lactide and hydroxyl endgroups. Model studies and comparative experiments with guanidine and phosphazene catalysts revealed the subtle influence of the nature of the superbase on competitive initiation processes.

  View details for DOI 10.1021/acsmacrolett.5b00421

  View details for PubMedID 26913218

  View details for PubMedCentralID PMC4762272

• Cyclopropenimine Superbases: Competitive Initiation Processes in Lactide Polymerization ACS MACRO LETTERS Stukenbroeker, T. S., Bandar, J. S., Zhang, X., Lambert, T. H., Waymouth, R. M. 2015; 4 (8): 853-856

  Abstract

  Cyclopropenimine superbases were employed to catalyze the ring-opening polymerization of lactide. Polymerization occurred readily in the presence and absence of alcohol initiators. Polymerizations in the absence of alcohol initiators revealed a competitive initiation mechanism involving deprotonation of lactide by the cyclopropenimine to generate an enolate. NMR and MALDI-TOF analysis of the poly(lactides) generated from cyclopropenimines in the absence of alcohol initiators showed acylated lactide and hydroxyl endgroups. Model studies and comparative experiments with guanidine and phosphazene catalysts revealed the subtle influence of the nature of the superbase on competitive initiation processes.

  View details for DOI 10.1021/acsmacrolett.5b00421

  View details for Web of Science ID 000359891200010

  View details for PubMedCentralID PMC4762272

• Structurally Dynamic Hydrogels Derived from 1,2-Dithiolanes JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Barcan, G. A., Zhang, X., Waymouth, R. M. 2015; 137 (17): 5650-5653

  Abstract

  The design and generation of adaptable materials derived from structurally dynamic polymers provides a strategy for generating smart materials that can respond to environmental stimuli or exhibit self-healing behavior. Herein we report an expedient organocatalytic ring-opening polymerization of cyclic carbonates containing pendant dithiolanes (trimethylene carbonate/dithiolane, TMCDT) from poly(ethylene oxide) diols to generate water-soluble triblock (ABA) copolymers containing a central poly(ethylene oxide) block and terminal dithiolane blocks. Hydrogels generated from the triblock copolymers and a cross-linking dithiol exhibited dynamic behavior as a result of the reversible ring opening of the pendant 1,2-dithiolanes. These materials exhibit self-healing behavior, can be injected through a syringe, and rapidly recover their mechanical properties after a severe strain deformation. The dynamic properties of these gels can be modulated with the number of dithiolane units, pH, and temperature.

  View details for DOI 10.1021/jacs.5b02161

  View details for Web of Science ID 000354338500004

  View details for PubMedID 25917449

• N-Heterocyclic Carbene-Catalyzed Ring Opening Polymerization of e-Caprolactone with and without Alcohol Initiators: Insights from Theory and Experiment. journal of physical chemistry. B Jones, G. O., Chang, Y. A., Horn, H. W., Acharya, A. K., Rice, J. E., Hedrick, J. L., Waymouth, R. M. 2015; 119 (17): 5728-5737

  Abstract

  Computational investigations with density functional theory (DFT) have been performed on the N-heterocyclic carbene (NHC) catalyzed ring-opening polymerization of ε-caprolactone in the presence and in the absence of a methanol initiator. Much like the zwitterionic ring opening (ZROP) of δ-valerolactone which was previously reported, calculations predict that the mechanism of the ZROP of caprolactone that occurs without an alcohol present involves a high-barrier step involving ring opening of the zwitterionic tetrahedral intermediate formed after the initial nucleophilic attack of NHC on caprolactone. However, the operative mechanism by which caprolactone is polymerized in the presence of an alcohol initiator does not involve the analogous mechanism involving initial nucleophilic attack by the organocatalytic NHC. Instead, the NHC activates the alcohol through hydrogen bonding and promotes nucleophilic attack and the subsequent ring-opening steps that occur during polymerization. The largest free energy barrier for the hydrogen-bonding mechanism in alcohol involves nucleophilic attack, while that for both ZROP processes involves ring opening of the initially formed zwitterionic tetrahedral intermediate. The DFT calculations predict that the rate of polymerization in the presence of alcohol is faster than the reaction performed without an alcohol initiator; this prediction has been validated by experimental kinetic studies.

  View details for DOI 10.1021/acs.jpcb.5b01595

  View details for PubMedID 25848823

• Organocatalytic Ring-Opening Polymerization of Trimethylene Carbonate To Yield a Biodegradable Polycarbonate JOURNAL OF CHEMICAL EDUCATION Chan, J. M., Zhang, X., Brennan, M. K., Sardon, H., Engler, A. C., Fox, C. H., Frank, C. W., Waymouth, R. M., Hedrick, J. L. 2015; 92 (4): 708-713

  View details for DOI 10.1021/ed500595k

  View details for Web of Science ID 000353368000023

• Ion pairing effects in the zwitterionic ring opening polymerization of delta-valerolactone POLYMER CHEMISTRY Chang, Y. A., Waymouth, R. M. 2015; 6 (29): 5212-5218

  View details for DOI 10.1039/c5py00662g

  View details for Web of Science ID 000358024800005

• Synthesis and Topological Trapping of Cyclic Poly(alkylene phosphates) MACROMOLECULES Stukenbroeker, T. S., Solis-Ibarra, D., Waymouth, R. M. 2014; 47 (23): 8224-8230

  View details for DOI 10.1021/ma501764c

  View details for Web of Science ID 000346325300012

• Disassembly and reassembly of polyhydroxyalkanoates: Recycling through abiotic depolymerization and biotic repolymerization BIORESOURCE TECHNOLOGY Myung, J., Strong, N. I., Galega, W. M., Sundstrom, E. R., Flanagan, J. C., Woo, S., Waymouth, R. M., Criddle, C. S. 2014; 170: 167-174

  Abstract

  An abiotic-biotic strategy for recycling of polyhydroxyalkanoates (PHAs) is evaluated. Base-catalyzed PHA depolymerization yields hydroxyacids, such as 3-hydroxybutyrate (3HB), and alkenoates, such as crotonate; catalytic thermal depolymerization yields alkenoates. Cyclic pulse addition of 3HB to triplicate bioreactors selected for an enrichment of Comamonas, Brachymonas and Acinetobacter. After each pulse, poly(3-hydroxybutyrate) (P3HB) transiently appeared: accumulation of P3HB correlated with hydrolysis of polyphosphate; consumption of P3HB correlated with polyphosphate synthesis. Cells removed from the cyclic regime and incubated with 3HB under nitrogen-limited conditions produced P3HB (molecular weight>1,000,000Da) at 50% of the cell dry weight (<8h). P3HB also resulted from incubation with acetate, crotonate, or a mixture of hydrolytic depolymerization products. Poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid) (PHBV) resulted from incubation with valerate or 2-pentenoate. A recycling strategy where abiotic depolymerization of waste PHAs yields feedstock for customized PHA re-synthesis appears feasible, without the need for energy-intensive feedstock purification.

  View details for DOI 10.1016/j.biortech.2014.07.105

  View details for Web of Science ID 000341357600022

• Zwitterionic Ring Opening Polymerization with Isothioureas ACS MACRO LETTERS Zhang, X., Waymouth, R. M. 2014; 3 (10): 1024-1028

  View details for DOI 10.1021/mz500525n

  View details for Web of Science ID 000343673200014

• Organocatalytic Ring-Opening Polymerization of Morpholinones: New Strategies to Functionalized Polyesters JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Blake, T. R., Waymouth, R. M. 2014; 136 (26): 9252-9255

  Abstract

  The oxidative lactonization of N-substituted diethanolamines with the Pd catalyst [LPd(OAc)]2(2+)[OTf(-)]2 generates N-substituted morpholin-2-ones. The organocatalytic ring-opening polymerization of N-acyl morpholin-2-ones occurs readily to generate functionalized poly(aminoesters) with N-acylated amines in the polyester backbone. The thermodynamics of the ring-opening polymerization depends sensitively on the hybridization of the nitrogen of the heterocyclic lactone. N-Acyl morpholin-2-ones polymerize readily to generate polymorpholinones, but the N-aryl or N-alkyl substituted morpholin-2-ones do not polymerize. Experimental and theoretical studies reveal that the thermodynamics of ring opening correlates to the degree of pyramidalization of the endocyclic N-atom. Deprotection of the poly(N-Boc-morpholin-2-one) yields a water-soluble, cationic polymorpholinone.

  View details for DOI 10.1021/ja503830c

  View details for Web of Science ID 000338692700005

  View details for PubMedID 24946200

• Experimental and Computational Studies on the Mechanism of Zwitterionic Ring-Opening Polymerization of delta-Valerolactone with N-Heterocyclic Carbenes JOURNAL OF PHYSICAL CHEMISTRY B Acharya, A. K., Chang, Y. A., Jones, G. O., Rice, J. E., Hedrick, J. L., Horn, H. W., Waymouth, R. M. 2014; 118 (24): 6553-6560

  Abstract

  Experimental and computational investigations of the zwitterionic ring-opening polymerization (ZROP) of δ-valerolactone (VL) catalyzed by the N-heterocyclic carbenes (NHC) 1,3-diisopropyl-4,5-dimethyl-imidazol-2-ylidene (1) and 1,3,4,5-tetramethyl-imidazol-2-ylidene (2) were carried out. The ZROP of δ-valerolactone generates cyclic poly(valerolactone)s whose molecular weights are higher than predicted from [VL]0/[NHC]0. Kinetic studies reveal the rate of polymerization is first order in [VL] and first order in [NHC]. Density functional theory (DFT) calculations were carried out to elucidate the key steps involved in the ring-opening of δ-valerolactone and its subsequent oligomerization. These studies have established that the initial steps of the mechanism involve nucleophilic attack of the NHC on δ-valerolactone to form a zwitterionic tetrahedral intermediate. DFT calculations indicate that the highest activation barrier of the entire mechanism is associated with the ring-opening of the tetrahedral intermediate formed from the NHC and δ-valerolactone, a result consistent with inefficient initiation to generate reactive zwitterions. The large barrier in this step is due to the fact that ring-opening requires a partial positive charge to develop next to the directly attached NHC moiety which already bears a delocalized positive charge.

  View details for DOI 10.1021/jp500200b

  View details for Web of Science ID 000337784100023

• Trinuclear pd3 o2 intermediate in aerobic oxidation catalysis. Angewandte Chemie (International ed. in English) Ingram, A. J., Solis-Ibarra, D., Zare, R. N., Waymouth, R. M. 2014; 53 (22): 5648-5652

  Abstract

  The activation of O2 is a key step in selective catalytic aerobic oxidation reactions mediated by transition metals. The bridging trinuclear palladium species, [(LPd(II))3(μ(3)-O)2](2+) (L=2,9-dimethylphenanthroline), was identified during the [LPd(OAc)]2(OTf)2-catalyzed aerobic oxidation of 1,2-propanediol. Independent synthesis, structural characterization, and catalytic studies of the trinuclear compound show that it is a product of oxygen activation by reduced palladium species and is a competent intermediate in the catalytic aerobic oxidation of alcohols. The formation and catalytic activity of the trinuclear Pd3O2 species illuminates a multinuclear pathway for aerobic oxidation reactions catalyzed by Pd complexes.

  View details for DOI 10.1002/anie.201400134

  View details for PubMedID 24711099

• Zwitterionic Ring-Opening Polymerization: Models for Kinetics of Cyclic Poly(caprolactone) Synthesis MACROMOLECULES Brown, H. A., Xiong, S., Medvedev, G. A., Chang, Y. A., Abu-Omar, M. M., Caruthers, J. M., Waymouth, R. M. 2014; 47 (9): 2955-2963

  View details for DOI 10.1021/ma500395j

  View details for Web of Science ID 000336020900023

• Titanium Bis(amidinates) Bearing Electron Donating Pendant Arms as Catalysts for Stereospecific Polymerization of Propylene ORGANOMETALLICS Elkin, T., Botoshansky, M., Waymouth, R. M., Eisen, M. S. 2014; 33 (4): 840-843

  View details for DOI 10.1021/om401165g

  View details for Web of Science ID 000331991800003

• Zwitterionic Polymerization to Generate High Molecular Weight Cyclic Poly(Carbosiloxane)s JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Brown, H. A., Chang, Y. A., Waymouth, R. M. 2013; 135 (50): 18738-18741

  Abstract

  The zwitterionic ring-opening of 2,2,5,5-tetramethyl-2,5-disila-1-oxacyclopentane (TMOSC) with N-heterocyclic carbenes generates high molecular weight cyclic p(TMOSC). The NHC-mediated polymerization of TMOSC with 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes, 1) generates the poly(carbosiloxane) p(TMOSC) with molecular weights from 27,000 < Mn < 80,000 Da (1.4 < Mw/Mn < 2.2) within 30 min at room temp. With the more nucleophilic carbene 1,3,4,5-tetramethyl-imidazol-2-ylidene (4), the ring-opening polymerization occurs within minutes at room temperature to generate cyclic p(TMOSC) with molecular weights up to Mn = 940,000 Da (Mw/Mn = 3.2). The resulting p(TMOSC)s are predominantly cyclic as evidenced by dilute solution viscosity studies and MALDI-TOF MS. DFT calculations provide support for both zwitterionic and neutral, cyclic intermediates.

  View details for DOI 10.1021/ja409843v

  View details for Web of Science ID 000328865100009

  View details for PubMedID 24308512

• Zwitterionic Ring-Opening Polymerization for the Synthesis of High Molecular Weight Cyclic Polymers ACCOUNTS OF CHEMICAL RESEARCH Brown, H. A., Waymouth, R. M. 2013; 46 (11): 2585-2596

  Abstract

  Cyclic polymers are an intriguing class of macromolecules. Because of the constraints of the cyclic topology and the absence of chain ends, the properties of these molecules differ from those of linear polymers in ways that remain poorly understood. Cyclic polymers present formidable synthetic challenges because the entropic penalty of coupling the chain ends grows exponentially with increasing molecular weight. In this Account, we describe recent progress in the application of zwitterionic ring-opening polymerization (ZROP) as a strategy for the synthesis of high molecular weight, cyclic polymers. Zwitterionic ring-opening polymerization involves the addition of neutral organic nucleophiles to strained heterocyclic monomers; under appropriate conditions, cyclization of the resultant macrozwitterions generates cyclic macromolecules. We discuss the mechanistic and kinetic features of these zwitterionic ring-opening reactions and the conditions that influence the efficiency of the initiation, propagation, and cyclization to generate high molecular weight cyclic polymers. N-Heterocyclic carbenes (NHC) are potent nucleophiles and relatively poor leaving groups, two features that are important for the generation of high molecular weight polymers. Investigations of the nature of the monomer and nucleophile have helped researchers understand the factors that govern the reactivity of these systems and their impact on the molecular weight and molecular weight distributions of the resulting cyclic polymers. We focus primarily on ZROP mediated by N-heterocyclic carbene nucleophiles but also discuss zwitterionic polymerizations with amidine, pyridine, and imidazole nucleophiles. The ZROP of N-carboxyanhydrides with N-hetereocyclic carbenes generates a family of functionalized cyclic polypeptoids. We can synthesize gradient lactone copolymers by exploiting differences in relative reactivity present in ZROP that differ from those of traditional metal-mediated polymerizations. These new synthetic methods have allowed us to investigate the influence of topology on the crystallization behavior, stereocomplexation, and solution properties of cyclic macromolecules.

  View details for DOI 10.1021/ar400072z

  View details for Web of Science ID 000327360800023

  View details for PubMedID 23789724

• A Renewable Lignin-Lactide Copolymer and Application in Biobased Composites ACS SUSTAINABLE CHEMISTRY & ENGINEERING Chung, Y., Olsson, J. V., Li, R. J., Frank, C. W., Waymouth, R. M., Billington, S. L., Sattely, E. S. 2013; 1 (10): 1231-1238

  View details for DOI 10.1021/sc4000835

  View details for Web of Science ID 000325512000004

• Electrooxidation of alcohols catalyzed by amino alcohol ligated ruthenium complexes. Journal of the American Chemical Society Brownell, K. R., McCrory, C. C., Chidsey, C. E., Perry, R. H., Zare, R. N., Waymouth, R. M. 2013; 135 (38): 14299-14305

  Abstract

  Ruthenium transfer hydrogenation catalysts physisorbed onto edge-plane graphite electrodes are active electrocatalysts for the oxidation of alcohols. Electrooxidation of CH3OH (1.23 M) in a buffered aqueous solution at pH 11.5 with [(η(6)-p-cymene)(η(2)-N,O-(1R,2S)-cis-1-amino-2-indanol)]Ru(II)Cl (2) on edge-plane graphite exhibits an onset current at 560 mV vs NHE. Koutecky-Levich analysis at 750 mV reveals a four-electron oxidation of methanol with a rate of 1.35 M(-1) s(-1). Mechanistic investigations by (1)H NMR, cyclic voltammetry, and desorption electrospray ionization mass spectrometry indicate that the electroxidation of methanol to generate formate is mediated by surface-supported Ru-oxo complexes.

  View details for DOI 10.1021/ja4055564

  View details for PubMedID 24044700

• Chemoselective pd-catalyzed oxidation of polyols: synthetic scope and mechanistic studies. Journal of the American Chemical Society Chung, K., Banik, S. M., De Crisci, A. G., Pearson, D. M., Blake, T. R., Olsson, J. V., Ingram, A. J., Zare, R. N., Waymouth, R. M. 2013; 135 (20): 7593-7602

  Abstract

  The regio- and chemoselective oxidation of unprotected vicinal polyols with [(neocuproine)Pd(OAc)]2(OTf)2 (1) (neocuproine = 2,9-dimethyl-1,10-phenanthroline) occurs readily under mild reaction conditions to generate α-hydroxy ketones. The oxidation of vicinal diols is both faster and more selective than the oxidation of primary and secondary alcohols; vicinal 1,2-diols are oxidized selectively to hydroxy ketones, whereas primary alcohols are oxidized in preference to secondary alcohols. Oxidative lactonization of 1,5-diols yields cyclic lactones. Catalyst loadings as low as 0.12 mol % in oxidation reactions on a 10 g scale can be used. The exquisite selectivity of this catalyst system is evident in the chemoselective and stereospecific oxidation of the polyol (S,S)-1,2,3,4-tetrahydroxybutane [(S,S)-threitol] to (S)-erythrulose. Mechanistic, kinetic, and theoretical studies revealed that the rate laws for the oxidation of primary and secondary alcohols differ from those of diols. Density functional theory calculations support the conclusion that β-hydride elimination to give hydroxy ketones is product-determining for the oxidation of vicinal diols, whereas for primary and secondary alcohols, pre-equilibria favoring primary alkoxides are product-determining. In situ desorption electrospray ionization mass spectrometry (DESI-MS) revealed several key intermediates in the proposed catalytic cycle.

  View details for DOI 10.1021/ja4008694

  View details for PubMedID 23659308

• Octahedral Group IV Bis(phenolate) Catalysts for 1-Hexene Homopolymerization and Ethylene/1-Hexene Copolymerization MACROMOLECULES Kiesewetter, E. T., Waymouth, R. M. 2013; 46 (7): 2569-2575

  View details for DOI 10.1021/ma400116w

  View details for Web of Science ID 000317438300006

• Chemoselective Oxidation of Polyols with Chiral Palladium Catalysts ORGANOMETALLICS De Crisci, A. G., Chung, K., Oliver, A. G., Solis-Ibarra, D., Waymouth, R. M. 2013; 32 (7): 2257-2266

  View details for DOI 10.1021/om4001549

  View details for Web of Science ID 000317370000028

• Polymerizing Base Sensitive Cyclic Carbonates Using Acid Catalysis ACS MACRO LETTERS Coady, D. J., Horn, H. W., Jones, G. O., Sardon, H., Engler, A. C., Waymouth, R. M., Rice, J. E., Yang, Y. Y., Hedrick, J. L. 2013; 2 (4): 306-312

  View details for DOI 10.1021/mz3006523

  View details for Web of Science ID 000317813200006

• Semicrystalline Dihydroxyacetone Copolymers Derived from Glycerol MACROMOLECULES Simon, J., Olsson, J. V., Kim, H., Tenney, I. F., Waymouth, R. M. 2012; 45 (23): 9275-9281

  View details for DOI 10.1021/ma302311h

  View details for Web of Science ID 000312122600006

• Amidine-Mediated Zwitterionic Polymerization of Lactide ACS MACRO LETTERS Brown, H. A., De Crisci, A. G., Hedrick, J. L., Waymouth, R. M. 2012; 1 (9): 1113-1115

  View details for DOI 10.1021/mz300276u

  View details for Web of Science ID 000308855900005

• Designed guanidinium-rich amphipathic oligocarbonate molecular transporters complex, deliver and release siRNA in cells PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Geihe, E. I., Cooley, C. B., Simon, J. R., Kiesewetter, M. K., Edward, J. A., Hickerson, R. P., Kaspar, R. L., Hedrick, J. L., Waymouth, R. M., Wender, P. A. 2012; 109 (33): 13171-13176

  Abstract

  The polyanionic nature of oligonucleotides and their enzymatic degradation present challenges for the use of siRNA in research and therapy; among the most notable of these is clinically relevant delivery into cells. To address this problem, we designed and synthesized the first members of a new class of guanidinium-rich amphipathic oligocarbonates that noncovalently complex, deliver, and release siRNA in cells, resulting in robust knockdown of target protein synthesis in vitro as determined using a dual-reporter system. The organocatalytic oligomerization used to synthesize these co-oligomers is step-economical and broadly tunable, affording an exceptionally quick strategy to explore chemical space for optimal siRNA delivery in varied applications. The speed and versatility of this approach and the biodegradability of the designed agents make this an attractive strategy for biological tool development, imaging, diagnostics, and therapeutic applications.

  View details for DOI 10.1073/pnas.1211361109

  View details for Web of Science ID 000307807000017

  View details for PubMedID 22847412

  View details for PubMedCentralID PMC3421195

• Organocatalytic Synthesis of Quinine-Functionalized Poly(carbonate)s BIOMACROMOLECULES Edward, J. A., Kiesewetter, M. K., Kim, H., Flanagan, J. C., Hedrick, J. L., Waymouth, R. M. 2012; 13 (8): 2483-2489

  Abstract

  The ring-opening polymerization of substituted cyclic carbonates with 1-(3,5-bis-trifluoromethyl-phenyl)-3-cyclohexyl-thiourea (TU)/1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) organocatalysts afford highly functionalized oligocarbonates. The fluorescent alkaloid quinine can be readily incorporated into the oligocarbonates either by initiation from quinine or by ring-opening polymerization of a quinine-functionalized cyclic carbonate (MTC-Q). Copolymerization of MTC-Q with a boc-protected guanidinium cyclic carbonate affords, after deprotection, highly water-soluble cationic copolymers functionalized with both quinine and pendant guanidinium groups. When multiple quinine groups are attached to the oligomers, they exhibit minimal fluorescence due to self-quenching. Upon hydrolysis, the fluorescence intensity increases, providing a potential strategy for monitoring the hydrolysis rates in real time.

  View details for DOI 10.1021/bm300718b

  View details for Web of Science ID 000307422300031

  View details for PubMedID 22849552

• Facile Synthesis of Functionalized Lactones and Organocatalytic Ring-Opening Polymerization ACS MACRO LETTERS Kim, H., Olsson, J. V., Hedrick, J. L., Waymouth, R. M. 2012; 1 (7): 845-847

  View details for DOI 10.1021/mz3001397

  View details for Web of Science ID 000306503400013

• Stereoselective and Regioselective Propylene Polymerization with Group 4 Bisphenolate Ether Complexes JOURNAL OF POLYMER SCIENCE PART A-POLYMER CHEMISTRY Randoll, S., Kiesewetter, E. T., Waymouth, R. M. 2012; 50 (13): 2604-2611

  View details for DOI 10.1002/pola.26028

  View details for Web of Science ID 000304447800011

• Transient Ru-methyl formate intermediates generated with bifunctional transfer hydrogenation catalysts PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Perry, R. H., Brownell, K. R., Chingin, K., Cahill, T. J., Waymouth, R. M., Zare, R. N. 2012; 109 (7): 2246-2250

  Abstract

  Desorption electrospray ionization (DESI) coupled to high-resolution Orbitrap mass spectrometry (MS) was used to study the reactivity of a (β-amino alcohol)(arene)RuCl transfer hydrogenation catalytic precursor in methanol (CH(3)OH). By placing [(p-cymene)RuCl(2)](2) on a surface and spraying a solution of β-amino alcohol in methanol, two unique transient intermediates having lifetimes in the submillisecond to millisecond range were detected. These intermediates were identified as Ru (II) and Ru (IV) complexes incorporating methyl formate (HCOOCH(3)). The Ru (IV) intermediate is not observed when the DESI spray solution is sparged with Ar gas, indicating that O(2) dissolved in the solvent is necessary for oxidizing Ru (II) to Ru (IV). These proposed intermediates are supported by high-resolution and high mass accuracy measurements and by comparing experimental to calculated isotope profiles. Additionally, analyzing the bulk reaction mixture using gas chromatography-MS and nuclear magnetic resonance spectroscopy confirms the formation of HCOOCH(3). These results represent an example that species generated from the (β-amino alcohol)(arene)RuCl (II) catalytic precursor can selectively oxidize CH(3)OH to HCOOCH(3). This observation leads us to propose a pathway that can compete with the hydrogen transfer catalytic cycle. Although bifunctional hydrogen transfer with Ru catalysts has been well-studied, the ability of DESI to intercept intermediates formed in the first few milliseconds of a chemical reaction allowed identification of previously unrecognized intermediates and reaction pathways in this catalytic system.

  View details for DOI 10.1073/pnas.1118934109

  View details for Web of Science ID 000300489200024

  View details for PubMedID 22315417

  View details for PubMedCentralID PMC3289342

• Stereocomplexation in Cyclic and Linear Polylactide Blends MACROMOLECULES Shin, E. J., Jones, A. E., Waymouth, R. M. 2012; 45 (1): 595-598

  View details for DOI 10.1021/ma202184j

  View details for Web of Science ID 000298905000063

• Palladium-Catalyzed Carbonylation of Diols to Cyclic Carbonates ADVANCED SYNTHESIS & CATALYSIS Pearson, D. M., Conley, N. R., Waymouth, R. M. 2011; 353 (16): 3007-3013

  View details for DOI 10.1002/adsc.201100240

  View details for Web of Science ID 000297099100023

• Polycondensation of Butenediol: Synthesis of Telechelic 2-Butene-1,4-diol Oligomers JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Kiesewetter, M. K., Edward, J. A., Kim, H., Waymouth, R. M. 2011; 133 (41): 16390-16393

  Abstract

  The catalytic condensation of cis-2-butene-1,4-diol with CpRu(MQA)(C(3)H(5)) (Cp = cyclopentadienyl, MQA = 4-methoxyquinoline-2-carboxylate) generates poly(2-butenediol), an unsaturated telechelic polyether diol with molecular weights between 400 and 4600 g/mol. This Ru(IV) allyl catalyst enchains 2-butene-1,4-diol primarily as the linear trans-2-butenyl ether (92%) along with vinyl branches (8%). These telechelic oligomers are useful chain extenders and macromonomers, as demonstrated by their use in the synthesis of poly(lactide)-b-poly(butenediol)-b-poly(lactide) triblock copolymers. Model studies support a proposed mechanism involving the formation of Ru(IV) allyl intermediates from allylic alcohols and chain growth by selective nucleophilic displacement at the terminus of the Ru(IV) allyl to generate trans-2-butenyl ether linkages.

  View details for DOI 10.1021/ja207465h

  View details for Web of Science ID 000295997500019

  View details for PubMedID 21939269

• Synthesis and Structural Diversity of Mono-, Di- and Trinuclear Complexes with N,N '-Bis[(2-diphenylphosphanyl)phenyl]formamidine EUROPEAN JOURNAL OF INORGANIC CHEMISTRY Son, K., Pearson, D. M., Jeon, S., Waymouth, R. M. 2011: 4256-4261

  View details for DOI 10.1002/ejic.201100492

  View details for Web of Science ID 000296143500017

• Thermoresponsive nanostructured polycarbonate block copolymers as biodegradable therapeutic delivery carriers BIOMATERIALS Kim, S. H., Tan, J. P., Fukushima, K., Nederberg, F., Yang, Y. Y., Waymouth, R. M., Hedrick, J. L. 2011; 32 (23): 5505-5514

  Abstract

  Water-soluble, thermoresponsive block copolymers based on a biodegradable platform were synthesized by the ring opening polymerization of cyclic carbonate monomers functionalized with hydrophilic and hydrophobic groups for application as nanocarriers in medicine. The approach based on cyclic carbonate monomers derived from 2,2-bis(methylol)propionic acid (bis-MPA) allowed a simple and versatile route to functional monomers capable of undergoing ring opening polymerization (ROP). The resulting polymers possessed the predicted molecular weights based on the molar ratio between monomers to initiators and the narrow molecular weight distributions. Transmittance measurement for aqueous polymer solutions provided an evidence for temperature-responsiveness with lower critical solution temperature (LCST) in the range of 36 °C-60 °C, depending on the molecular weight of hydrophilic poly(ethylene glycol) (PEG) chains, compositions of copolymers, molar ratios of hydrophilic to hydrophobic monomers in the corona, and the hydrophobic core. This study showed synthetic advancement toward the design and preparation of biodegradable thermoresponsive polymers with extremely low CMC values for injectable drug delivery systems. TRC350-10,30,60, which possessed an LCST of 36 °C in PBS, was identified as a useful model polymer. Paclitaxel, an anti-cancer drug, was loaded into the micelles efficiently, giving rise to nano-sized particles with a narrow size distribution. Paclitaxel release from the micelles was faster, and cellular uptake of the micelles was higher at the body temperature (i.e. 37 °C) as compared to a temperature below the LCST. While the polymer was not cytotoxic, paclitaxel-loaded micelles killed HepG2 human liver carcinoma cells more efficiently at the body temperature as compared to free paclitaxel and paclitaxel-loaded micelles at the temperature below the LCST. These micelles are ideally suited to deliver anti-cancer drugs to tumor tissues through local injection.

  View details for DOI 10.1016/j.biomaterials.2011.04.017

  View details for Web of Science ID 000291900900020

  View details for PubMedID 21529935

• Crystallization of Cyclic Polymers: Synthesis and Crystallization Behavior of High Molecular Weight Cyclic Poly(epsilon-caprolactone)s MACROMOLECULES Shin, E. J., Jeong, W., Brown, H. A., Koo, B. J., Hedrick, J. L., Waymouth, R. M. 2011; 44 (8): 2773-2779

  View details for DOI 10.1021/ma102970m

  View details for Web of Science ID 000289593200047

• Oxidatively Resistant Ligands for Palladium-Catalyzed Aerobic Alcohol Oxidation ORGANOMETALLICS Pearson, D. M., Conley, N. R., Waymouth, R. M. 2011; 30 (6): 1445-1453

  View details for DOI 10.1021/om101037k

  View details for Web of Science ID 000288470900028

• Stereospecific polymerization and selective oligomerization with coordination catalysts 241st National Meeting and Exposition of the American-Chemical-Society (ACS) Waymouth, R. M., Kiesewetter, E. T., Son, K. AMER CHEMICAL SOC. 2011

  View details for Web of Science ID 000291982807265

• Organocatalytic Depolymerization of Poly(ethylene terephthalate) JOURNAL OF POLYMER SCIENCE PART A-POLYMER CHEMISTRY Fukushima, K., Coulembier, O., Lecuyer, J. M., Almegren, H. A., Alabdulrahman, A. M., Alsewailem, F. D., Mcneil, M. A., Dubois, P., Waymouth, R. M., Horn, H. W., Rice, J. E., Hedrick, J. L. 2011; 49 (5): 1273-1281

  View details for DOI 10.1002/pola.24551

  View details for Web of Science ID 000288465400027

• Zwitterionic Copolymerization: Synthesis of Cyclic Gradient Copolymers ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Shin, E. J., Brown, H. A., Gonzalez, S., Jeong, W., Hedrick, J. L., Waymouth, R. M. 2011; 50 (28): 6388-6391

  View details for DOI 10.1002/anie.201101853

  View details for Web of Science ID 000292642600035

  View details for PubMedID 21618374

• Kinetics of an Air- and Water-Stable Ruthenium(IV) Catalyst for the Deprotection of Allyl Alcohol in Water ORGANOMETALLICS Kiesewetter, M. K., Waymouth, R. M. 2010; 29 (22): 6051-6056

  View details for DOI 10.1021/om100892v

  View details for Web of Science ID 000284290600047

• Chemoselectivity Diversity in the Reaction of LiNC6F5SiMe3 with Nitriles and the Synthesis, Structure, and Reactivity of Zirconium Mono- and Tris[2-(2-pyridyl)tetrafluorobenzimidazolate] Complexes INORGANIC CHEMISTRY Aharonovich, S., Botoshansky, M., Waymouth, R. M., Eisen, M. S. 2010; 49 (20): 9217-9229

  Abstract

  Unlike the reaction of LiNTMS(2)·TMEDA (TMS = SiMe(3); TMEDA = tetramethylethylenediamine) with 2-cyanopyridine, which results in the nearly exclusive formation of the amidinate, (Me(3)SiNC(6)F(5))Li·TMEDA (1) reacts with 2-cyanopyridine in toluene to yield quantitatively the lithium pyridyltetrafluorobenzimidazolate complex [C(6)F(4)N(2)C(2-C(5)H(4)N)]Li·TMEDA (3). In this work, the reactivity of complex 1 toward aromatic nitriles Ar-CN (Ar = Ph, o-OMeC(6)H(4), C(6)F(5), 2-pyridyl) was examined. Whereas complex 1 fails to react with o-methoxybenzonitrile, its reaction with benzonitrile or pentafluorobenzonitrile gives triphenyl-1,3,5-triazine (4) or the hexacoordinate lithium polymer [LiN(4-NCC(6)F(4))(C(6)F(5))·THF·TMEDA](n) (7), respectively. When 1 is reacted with 2-cyanopyridine in tetrahydrofuran (THF), the benzimidazolate coordination polymer {[C(6)F(4)N(2)C(2-C(5)H(4)N)]Li·THF}(n) (5) is obtained. Herein we discuss how this diverse chemoselectivity in the reaction of the examined lithium N-silylated amides LiNRTMS·TMEDA (R = TMS, C(6)F(5)) with nitriles is influenced by the electronic properties of the nitrile or amide substituents and by the ability of these substituents to interact with the lithium or silicon atoms. Further, we present the syntheses and structures of zirconium tris(pyridyltetrafluorobenzimidazolate) chloride (10) and zirconium bis(dimethylamido)(pyridyltetrafluorobenzimidazolate) chloride·THF (11) complexes. These complexes, the first prepared zirconium mono- and tris(benzimidazolate)s, were crystallographically characterized and examined in the polymerization of propylene with methyl aluminoxane (1:1000 Zr/Al molar ratio).

  View details for DOI 10.1021/ic100696r

  View details for Web of Science ID 000282783400020

  View details for PubMedID 20857913

• Selective Ethylene Oligomerization in the Presence of ZnR2: Synthesis of Terminally-Functionalized Ethylene Oligomers ORGANOMETALLICS Son, K., Waymouth, R. M. 2010; 29 (16): 3515-3520

  View details for DOI 10.1021/om100503v

  View details for Web of Science ID 000280794400008

• The Depolymerization of Poly(ethylene terephthalate) (PET) Using N-Heterocyclic Carbenes from Ionic Liquids JOURNAL OF CHEMICAL EDUCATION Kamber, N. E., Tsujii, Y., Keets, K., Waymouth, R. M., Pratt, R. C., Nyce, G. W., Hedrick, J. L. 2010; 87 (5): 519-521

  View details for DOI 10.1021/ed800152c

  View details for Web of Science ID 000276639900021

• Stereospecific Octahedral Group 4 Bis(phenolate) Ether Complexes for Olefin Polymerization JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Kiesewetter, E. T., Randoll, S., Radlauer, M., Waymouth, R. M. 2010; 132 (16): 5566-?

  Abstract

  Octahedral group 4 bisphenolate ether complexes, activated by methylaluminoxane, are highly active and stereospecific alpha-olefin polymerization catalysts. X-ray crystallographic analysis reveals the Zr and Hf complexes to be closely isostructural; the bond lengths of the Hf complex are slightly shorter, but the maximum deviation is only 0.062 A. Despite the structural similarity of the Hf and Zr complexes, the Hf complexes generate more highly stereoselective catalysts. In addition to the influence of the transition metal, the structure of the ligand has a large influence on the stereospecificity. Bis-tert-butyl phenyl substituted complexes of Hf and Zr, when activated by MAO at 50-80 degrees C, generate high molecular weight polypropylene (M(n) = 130,000-360,000 g/mol) with isotacticities [mmmm] > 97% and melting points as high as 165 degrees C.

  View details for DOI 10.1021/ja100627x

  View details for Web of Science ID 000276991700016

  View details for PubMedID 20359183

• Stereospecific Styrene Polymerization and Ethylene-Styrene Copolymerization with Titanocenes Containing a Pendant Amine Donor JOURNAL OF POLYMER SCIENCE PART A-POLYMER CHEMISTRY Son, K., Waymouth, R. M. 2010; 48 (7): 1579-1585

  View details for DOI 10.1002/pola.23912

  View details for Web of Science ID 000275848000013

• Organocatalysis: Opportunities and Challenges for Polymer Synthesis MACROMOLECULES Kiesewetter, M. K., Shin, E. J., Hedrick, J. L., Waymouth, R. M. 2010; 43 (5): 2093-2107

  View details for DOI 10.1021/ma9025948

  View details for Web of Science ID 000274928400001

• Acyclic Guanidines as Organic Catalysts for Living Polymerization of Lactide MACROMOLECULES Zhang, L., Pratt, R. C., Nederberg, F., Horn, H. W., Rice, J. E., Waymouth, R. M., Wade, C. G., Hedrick, J. L. 2010; 43 (3): 1660-1664

  View details for DOI 10.1021/ma901776x

  View details for Web of Science ID 000274268400067

• Lithium Furyl and Pyridyl Amidinates as Building Blocks in Coordination Polymers, Ladder and Cage Structures INORGANIC CHEMISTRY Aharonovich, S., Botoshanski, M., Rabinovich, Z., Waymouth, R. M., Eisen, M. S. 2010; 49 (3): 1220-1229

  Abstract

  Lithium N,N'-bis(trimethylsilyl)heterocyclic amidinate complexes with 3- and 4-pyridyl and 3-furyl carbon substituents were prepared by addition of the corresponding nitriles to LiN(SiMe(3))(2) (LiNTMS(2)) solution. In the presence of N,N,N',N' tetramethylethylene diamine (TMEDA), both pyridyl amidinates crystallize as coordination polymers with an amidinate-Li-pyridyl backbone. The 4-pyridyl derivative (7) creates a linear polymer with amidinate-Li-TMEDA units as side chains, whereas the 3-pyridyl polymer (6) has a two-dimensional (2D) network structure in which TMEDA serves as a cross-linker. Solvation of the reaction mixture of 3-furonitrile and LiNTMS(2) with TMEDA affords the monomeric 3-furyl amidinate Li TMEDA complex (3). Crystals of the Li(2)O complex {[3-furyl-C-(NTMS)(2)Li](4).Li(2)O}.C(7)H(8) (4) are obtained from toluene by partial hydrolysis of the unsolvated 3-furyl amidinate (2). Degradation of the polymer (7) to monomeric units can be achieved by solvation in toluene or by reaction with TMS(2)NLi.TMEDA that affords crystals of the complex {NTMS(2)Li.[4-C(5)H(4)N-C(NTMS)(2)Li.TMEDA]}(2).(NTMS(2)Li.TMEDA) (8). The formation of these aggregates can be rationalized by directed substitution of TMEDA with pyridyl moieties and by the laddering principle.

  View details for DOI 10.1021/ic902183c

  View details for Web of Science ID 000273785500054

  View details for PubMedID 20039691

• Mono- and bis-amidinate 2,6-xylylimido vanadium chlorides: synthesis, structure, and reactivity DALTON TRANSACTIONS Aharonovich, S., Botoshansky, M., Tumanskii, B., Nomura, K., Waymouth, R. M., Eisen, M. S. 2010; 39 (24): 5643-5649

  Abstract

  Salt metathesis of (2,6-xylylimido) vanadium trichloride (1) with the unsolvated or the TMEDA lithium p-Et benzamidinate complexes (2 and 3, respectively, in 1 : 2 V : Li molar ratio) yields bis[N,N'-bis(trimethylsilyl) p-Et benzamidinate](2,6-xylylimido)VCl (4) as dark brown, diamond-shaped crystals. When equimolar amounts of complexes 1 and 2 are reacted, a mixture of the bis (4) and mono (5) imidovanadium amidinates results. A similar mixture is also obtained by a ligand metathesis reaction of the bis amidinate complex 4 and complex 1. When the synthesis of the mono amidinate 5 is attempted with the TMEDA lithium amidinate complexes 3 or the 3-pyridyl derivative (7) (in 1 : 1 V : Li molar ratio) a redox reaction takes place to produce (kappa(2)-TMEDA)(2,6-xylylimido)V(IV)Cl(2) (6) as crystalline, mustard-yellow plates. The activity of complex 4 in ethylene polymerization was negligible with MAO or MAO\(CPh(3))(+)[B(C(6)F(5))(4)](-) as co-catalysts.

  View details for DOI 10.1039/b925974k

  View details for Web of Science ID 000278588000011

  View details for PubMedID 20480084

• Selective Catalytic Oxidation of Glycerol to Dihydroxyacetone ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Painter, R. M., Pearson, D. M., Waymouth, R. M. 2010; 49 (49): 9456-9459

  View details for DOI 10.1002/anie.201004063

  View details for Web of Science ID 000285210300028

  View details for PubMedID 21031380

• Cyclic Guanidine Organic Catalysts: What Is Magic About Triazabicyclodecene? JOURNAL OF ORGANIC CHEMISTRY Kiesewetter, M. K., Scholten, M. D., Kirn, N., Weber, R. L., Hedrick, J. L., Waymouth, R. M. 2009; 74 (24): 9490-9496

  Abstract

  The bicyclic guanidine 1,5,7- triazabicyclo[4.4.0]dec-5-ene (TBD) is an effective organocatalyst for the formation of amides from esters and primary amines. Mechanistic and kinetic investigations support a nucleophilic mechanism where TBD reacts reversibly with esters to generate an acyl-TBD intermediate that acylates amines to generate the amides. Comparative investigations of the analogous bicyclic guanidine 1,4,6-triazabicyclo[3.3.0]oct-4-ene (TBO) reveal it to be a much less active acylation catalyst than TBD. Theoretical and mechanistic studies imply that the higher reactivity of TBD is a consequence of both its higher basicity and nucleophilicity than TBO as well as the high reactivity of the acyl-TBD intermediate, which is sterically prevented from adopting a planar amide structure.

  View details for DOI 10.1021/jo902369g

  View details for Web of Science ID 000272462100033

  View details for PubMedID 19928812

• Oligocarbonate Molecular Transporters: Oligomerization-Based Syntheses and Cell-Penetrating Studies JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Cooley, C. B., Trantow, B. M., Nederberg, F., Kiesewetter, M. K., Hedrick, J. L., Waymouth, R. M., Wender, P. A. 2009; 131 (45): 16401-?

  Abstract

  A new family of guanidinium-rich molecular transporters featuring a novel oligocarbonate backbone with 1,7-side chain spacing is described. Conjugates can be rapidly assembled irrespective of length in a one-step oligomerization strategy that can proceed with concomitant introduction of probes (or by analogy drugs). The new transporters exhibit excellent cellular entry as determined by flow cytometry and fluorescence microscopy, and the functionality of their drug delivery capabilities was confirmed by the delivery of the bioluminescent small molecule probe luciferin and turnover by its intracellular target enzyme.

  View details for DOI 10.1021/ja907363k

  View details for Web of Science ID 000271723000030

  View details for PubMedID 19860416

  View details for PubMedCentralID PMC2789006

• Mechanistic Studies of the Oxidative Dehydrogenation of Methanol Using a Cationic Palladium Complex ORGANOMETALLICS Pearson, D. M., Waymouth, R. M. 2009; 28 (13): 3896-3900

  View details for DOI 10.1021/om900217s

  View details for Web of Science ID 000267694100047

• Hierarchical Supermolecular Structures for Sustained Drug Release SMALL Tan, J. P., Kim, S. H., Nederberg, F., Appel, E. A., Waymouth, R. M., Zhang, Y., Hedrick, J. L., Yang, Y. Y. 2009; 5 (13): 1504-1507

  View details for DOI 10.1002/smll.200801756

  View details for Web of Science ID 000267903200003

  View details for PubMedID 19326354

• Simple Approach to Stabilized Micelles Employing Miktoarm Terpolymers and Stereocomplexes with Application in Paclitaxel Delivery BIOMACROMOLECULES Nederberg, F., Appel, E., Tan, J. P., Kim, S. H., Fukushima, K., Sly, J., Miller, R. D., Waymouth, R. M., Yang, Y. Y., Hedrick, J. L. 2009; 10 (6): 1460-1468

  Abstract

  A simple and versatile approach to miktoarm co- and terpolymers from carbonate functional oligomers is described. The key building block employed is a carboxylic acid functional cyclic carbonate, derived from 2,2-bis(methylol)propionic acid, that was readily coupled to a hydroxyl functional monomethylether poly(ethylene glycol) oligomer. Ring-opening of the cyclic carbonate using functional amines generates a carbamate linkage bearing a functional group capable of initiating either controlled radical or ring-opening polymerization, together with a primary hydroxyl group for ring-opening polymerization. Two tandem polymerization steps were possible which add the second two arms, thus generating the targeted ABC miktoarm terpolymer. The resulting amphiphilic miktoarm terpolymers containing poly(D- and L-lactide) formed polylactide stereocomplexes in the bulk. In aqueous solution, the stereocomplex mixture of Y-shaped miktoarm copolymers, poly(ethylene glycol)-poly(D-lactide)-poly(D-lactide) and poly(ethylene glycol)-poly(L-lactide)-poly(L-lactide), or the stereoblock miktoarm poly(ethylene glycol)-poly(D-lactide)-poly(L-lactide) form stabilized micelles with a significantly lower critical micelle concentration than those derived from conventional stereo regular linear or Y-shaped amphiphiles. This simple and versatile approach provides a useful synthetic route to complex macromolecular architectures that can assemble into stable micelles. These micelles provide high capacity for loading of the anticancer drug paclitaxel and possess narrow size distribution as well as unique structure, leading to sustained and near zero-ordered release of drug without significant initial burst.

  View details for DOI 10.1021/bm900056g

  View details for Web of Science ID 000266860700018

  View details for PubMedID 19385659

• Zwitterionic Polymerization: A Kinetic Strategy for the Controlled Synthesis of Cyclic Polylactide JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Jeong, W., Shin, E. J., Culkin, D. A., Hedrick, J. L., Waymouth, R. M. 2009; 131 (13): 4884-4891

  Abstract

  The zwitterionic ring-opening polymerization of lactide initiated by N-heterocyclic carbenes generates cyclic polylactides with well-defined molecular weights between M(n) = 5000 and 30,000 g/mol with narrow polydispersities (M(w)/M(n) < or = 1.31). These zwitterionic polymerizations are extremely rapid (k(p) = 48.7 M(-1) s(-1)), but also exhibit exceptional control of molecular weight and molecular weight distribution. The unusual kinetic features of these zwitterionic polymerizations are illuminated with kinetic and mechanistic investigations, which implicate a mechanism that involves a slow initiation step (second order in [M]), a propagation step (first order in [M]) that is much faster than initiation (k(i) = 0.274 M(-2) s(-1)), cyclization (k(c) = 0.0575 s(-1)), and depropagation (k(d) = 0.208 s(-1)). Numerical and stochastic simulations of the kinetic data provide a kinetic rationale for the evolution of molecular weight with monomer conversion: the molecular weights increase with increasing monomer conversion, exhibit a nonzero intercept near 0% monomer conversion, and are relatively insensitive to the initial monomer-to-initiator ratio. The observed narrow molecular weight distributions are due to a high rate of propagation relative to cyclization and chain transfer. Kinetic simulations define the kinetic criteria under which the active zwitterions remain in solution; these simulations were substantiated by chain-extension experiments, which provide experimental evidence for chain extension of the zwitterions and reinitiation by the N-heterocyclic carbenes liberated upon macrocyclization. The kinetic model rationalizes some of the unique features of zwitterionic ring-opening polymerization and provides a useful mechanistic framework to optimize these polymerizations as a strategy to generate well-defined cyclic polyesters.

  View details for DOI 10.1021/ja809617v

  View details for Web of Science ID 000264806300064

  View details for PubMedID 19334780

• N-Heterocyclic Carbenes for the Organocatalytic Ring-Opening Polymerization of epsilon-Caprolactone MACROMOLECULES Kamber, N. E., Jeong, W., Gonzalez, S., Hedrick, J. L., Waymouth, R. M. 2009; 42 (5): 1634-1639

  View details for DOI 10.1021/ma802618h

  View details for Web of Science ID 000263883000035

• Mixed Micelle Formation through Stereocomplexation between Enantiomeric Poly(lactide) Block Copolymers MACROMOLECULES Kim, S. H., Tan, J. P., Nederberg, F., Fukushima, K., Yang, Y. Y., Waymouth, R. M., Hedrick, J. L. 2009; 42 (1): 25-29

  View details for DOI 10.1021/ma801739x

  View details for Web of Science ID 000262263200006

• Copolymerization of Styrene and Ethylene at High Temperature with Titanocenes Containing a Pendant Amine Donor MACROMOLECULES Son, K., Joege, F., Waymouth, R. M. 2008; 41 (24): 9663-9668

  View details for DOI 10.1021/ma801853f

  View details for Web of Science ID 000261767400024

• Application of Block-Copolymer Supramolecular Assembly for the Fabrication of Complex TiO2 Nanostructures SMALL Kim, S. H., Park, O., Nederberg, F., Topuria, T., Krupp, L. E., Kim, H., Waymouth, R. M., Hedrick, J. L. 2008; 4 (12): 2162-2165

  View details for DOI 10.1002/smll.200801115

  View details for Web of Science ID 000261905100015

  View details for PubMedID 18975297

• Organocatalytic Approach to Amphiphilic Comb-Block Copolymers Capable of Stereocomplexation and Self-Assembly BIOMACROMOLECULES Fukushima, K., Pratt, R. C., Nederberg, F., Tan, J. P., Yang, Y. Y., Waymouth, R. M., Hedrick, J. L. 2008; 9 (11): 3051-3056

  Abstract

  Biocompatible amphiphilic block copolymers comprised of poly(ethylene glycol) (PEG) as the hydrophilic component and a poly(methylcarboxytrimethylene carbonate) (PMTC) as a hydrophobic backbone having either poly(L-lactide) (L-PLA) or poly(D-lactide) (D-PLA) branches were prepared by organocatalytic ring-opening polymerization (ROP). The polycarbonate backbone was prepared by copolymerization of two different MTC-type monomers (MTCs) including a tetrahydropyranyloxy protected hydroxyl group, a masked initiator for a subsequent ROP step. Interestingly, the organic catalyst used in the ROP of MTCs was also effective for acetylation of the hydroxyl end-groups by the addition of acetic anhydride added after polymerization. Acidic deprotection of the tetrahydropyranyloxy (THP) protecting group on the carbonate chain generated hydroxyl functional groups that served as initiators for the ROP of either D- or L-lactide. Comb-shaped block copolymers of predictable molecular weights and narrow polydispersities (approximately 1.3) were prepared with up to 8-PLA branches. Mixtures of the D- and L-lactide based copolymers were studied to understand the effect of noncovalent interactions or stereocomplexation on the properties.

  View details for DOI 10.1021/bm800526k

  View details for Web of Science ID 000260856900012

  View details for PubMedID 18844407

• Group Transfer Polymerization of Acrylates Catalyzed by N-Heterocyclic Carbenes MACROMOLECULES Scholten, M. D., Hedrick, J. L., Waymouth, R. M. 2008; 41 (20): 7399-7404

  View details for DOI 10.1021/ma801281q

  View details for Web of Science ID 000260255800023

• Copolymerization behavior of titanium imidazolin-2-iminato complexes JOURNAL OF POLYMER SCIENCE PART A-POLYMER CHEMISTRY Stelzig, S. H., Tamm, M., Waymouth, R. M. 2008; 46 (18): 6064-6070

  View details for DOI 10.1002/pola.22918

  View details for Web of Science ID 000259325100010

• Structure-reactivity relationships of amido-pyridine-supported rare-earth-metal alkyl complexes ORGANOMETALLICS Zimmermann, M., Tornroos, K. W., Waymouth, R. M., Anwander, R. 2008; 27 (17): 4310-4317

  View details for DOI 10.1021/om701195x

  View details for Web of Science ID 000258898300008

• The reaction mechanism for the organocatalytic ring-opening polymerization of L-lactide using a guanidine-based catalyst: Hydrogen-bonded or covalently bound? JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Chuma, A., Horn, H. W., Swope, W. C., Pratt, R. C., Zhang, L., Lohmeijer, B. G., Wade, C. G., Waymouth, R. M., Hedrick, J. L., Rice, J. E. 2008; 130 (21): 6749-6754

  Abstract

  We have investigated two alternative mechanisms for the ring-opening polymerization of l-lactide using a guanidine-based catalyst, the first involving acetyl transfer to the catalyst, and the second involving only hydrogen bonding to the catalyst. Using computational chemistry methods, we show that the hydrogen bonding pathway is considerably preferred over the acetyl transfer pathway and that this is consistent with experimental information.

  View details for DOI 10.1021/ja0764411

  View details for Web of Science ID 000256158200042

  View details for PubMedID 18454532

• POLY 125-Stereocomplex interactions in cyclic and linear polylactides 235th American-Chemical-Society National Meeting Jones, A. E., Shin, E. J., Waymouth, R. M. AMER CHEMICAL SOC. 2008

  View details for Web of Science ID 000271802800281

• POLY 277-Organocatalytic ring-opening polymerization approach to fully degradable amphiphilic copolymers 235th American-Chemical-Society National Meeting Fukushima, K., Pratt, R. C., Nederberg, F., Waymouth, R. M., Hedrick, J. L. AMER CHEMICAL SOC. 2008

  View details for Web of Science ID 000271802800446

• POLY 129-Living ring-opening polymerization of cyclic esters with phosphazene organocatalysts 235th American-Chemical-Society National Meeting Kester, B. S., Logan, J. W., Nederberg, F., Pratt, R. C., Wade, C. G., Waymouth, R. M., Hedrick, J. L. AMER CHEMICAL SOC. 2008

  View details for Web of Science ID 000271802800488

• New bimetallic complexes of late transition metals involving pyrazole-bridged bis N-heterocyclic carbene ligands DALTON TRANSACTIONS Jeon, S., Waymouth, R. M. 2008: 437-439

  Abstract

  Bimetallic Ni, Rh, and Ir complexes of pyrazolate biscarbene containing bulky substituents have been synthesized and characterized by X-ray crystallography; the Ni complex dimerizes to a highly congested L(2)Ni(2) structure, whereas the corresponding Rh and Ir complexes form bimetallic LM(2) structures.

  View details for DOI 10.1039/b715212d

  View details for Web of Science ID 000252254300003

  View details for PubMedID 18185857

• Tagging alcohols with cyclic carbonate: a versatile equivalent of (meth)acrylate for ring-opening polymerization CHEMICAL COMMUNICATIONS Pratt, R. C., Nederberg, F., Waymouth, R. M., Hedrick, J. L. 2008: 114-116

  Abstract

  Cyclic carbonate monomers based on a single biocompatible scaffold allow for incorporation of a wide range of functional groups into macromolecules via ring-opening polymerization.

  View details for DOI 10.1039/b713925j

  View details for Web of Science ID 000251633000026

  View details for PubMedID 18399418

• Hierarchical assembly of nanostructured organosilicate networks via stereocomplexation of block copolymers NANO LETTERS Kim, S. H., Nederberg, F., Zhang, L., Wade, C. G., Waymouth, R. M., Hedrick, J. L. 2008; 8 (1): 294-301

  Abstract

  The effect of the stereochemistry of polylactide (PLA)-based block copolymers on templated inorganic nanostructures has been investigated from the self-assembly of a stereoisomer pair/organosilicate mixture followed by organosilicate vitrification and copolymer thermolysis. Isomeric PLA homopolymers, block copolymers, and a stereoblock copolymer were prepared by ring-opening polymerization of D-, L-, or rac-lactide using an organocatalytic catalyst. Both differential scanning calorimetry and atomic force microscopy showed the formation of a stereocomplex between enantiomeric stereoisomers, that is, block copolymer/block copolymer and block copolymer/homopolymer mixtures as well as a stereoblock copolymer. The unique noncovalent interactions driven by stereocomplexation of D- and L-lactide provided supramolecular structures with a hierarchical order as characterized by distinctive vertical and horizontal growth of toroidal nanostructured inorganic features. This study demonstrates the potential of hierarchically assembling suprastructures that bridge the nano- to mesoscale feature sizes in the design of tunable functional nanomaterials suitable for future applications of microelectronics, material science, and bioengineering.

  View details for DOI 10.1021/nl0726813

  View details for Web of Science ID 000252257700052

  View details for PubMedID 18095737

• Organocatalytic ring-opening polymerization CHEMICAL REVIEWS Kamber, N. E., Jeong, W., Waymouth, R. M., Pratt, R. C., Lohmeijer, B. G., Hedrick, J. L. 2007; 107 (12): 5813-5840

  View details for DOI 10.1021/cr068415b

  View details for Web of Science ID 000251583300012

  View details for PubMedID 17988157

• Synthesis of biomimetic poly(hydroxybutyrate): Alkoxy- and carboxytriazolines as latent ionic initiator MACROMOLECULES Coulembier, O., Delva, X., Hedrick, J. L., Waymouth, R. M., Dubois, P. 2007; 40 (24): 8560-8567

  View details for DOI 10.1021/ma071575k

  View details for Web of Science ID 000251094500013

• Aerobic alcohol oxidation with cationic palladium complexes: insights into catalyst design and decomposition ORGANOMETALLICS Conley, N. R., Labios, L. A., Pearson, D. M., McCrory, C. C., Waymouth, R. M. 2007; 26 (23): 5447-5453

  View details for DOI 10.1021/om700492n

  View details for Web of Science ID 000250556900001

• New ground for organic catalysis: A ring-opening polymerization approach to hydrogels BIOMACROMOLECULES Nederberg, F., Trang, V., Pratt, R. C., Mason, A. F., Frank, C. W., Waymouth, R. M., Hedrick, J. L. 2007; 8 (11): 3294-3297

  Abstract

  Herein, we describe an organocatalytic living polymerization approach to network and subsequent hydrogel formation. Cyclic carbonate-functionalized macromolecules were ring-opened using an alcoholic initiator in the presence of an organic catalyst, amidine 1,8-diazabicyclo[5.4.0]undec-7-ene. A model reaction for the cross-linking identified monomer concentration-dependent reaction regimes, and enhanced kinetic control was demonstrated by introducing a co-monomer, trimethylene carbonate. The addition of the co-monomer facilitated near-quantitative conversion of monomer to polymer (>96%). Resulting poly(ethylene glycol) networks swell significantly in water, and an open co-continuous (water-gel) porous structure was observed by scanning electron microscopy. The organocatalytic ring-opening polymerization of cyclic carbonate functional macromonomers using alcoholic initiators provides a simple, efficient, and versatile approach to hydrogel networks.

  View details for DOI 10.1021/bm700895d

  View details for Web of Science ID 000250960300002

  View details for PubMedID 17994785

• N-Alkoxyimidazolylidene transition-metal complexes: Application to [5+2] and [4+2] cycloaddition reactions ORGANOMETALLICS Gomez, F. J., Kamber, N. E., Deschamps, N. M., Cole, A. P., Wender, P. A., Waymouth, R. M. 2007; 26 (18): 4541-4545

  View details for DOI 10.1021/om700493y

  View details for Web of Science ID 000248865600026

• POLY 556-Group transfer polymerization of acrylates and methacrylates using N-heterocyclic carbene catalysts Scholten, M. D., Hedrick, J. L., Waymouth, R. M. AMER CHEMICAL SOC. 2007

  View details for Web of Science ID 000207593908625

• POLY 260-Polyesters from renewable resources: Organocatalytic strategies for controlled polymerization reactions Waymouth, R. M., Hedrick, J. L., Pratt, R. C., Nederberg, F., Lohmeijer, B. G., Culkin, D. A., Coulembier, O., Kamber, N. E., Jeong, W., Kiesewetter, M. K., Shin, E. J. AMER CHEMICAL SOC. 2007

  View details for Web of Science ID 000207593908491

• POLY 538-An organocatalytic route to functional and biodegradable hydrogels Nederberg, F., Pratt, R. C., Mason, A. F., Waymouth, R. M., Hedrick, J. L. AMER CHEMICAL SOC. 2007

  View details for Web of Science ID 000207593908578

• N-Heterocyclic carbene-mediated zwitterionic polymerization: An expedient organocatalytic route to cyclic polyesters Jeong, W., Shin, E. J., Culkin, D. A., Hedrick, J. L., Waymouth, R. M. AMER CHEMICAL SOC. 2007

  View details for Web of Science ID 000207593905678

• POLY 484-Phosphazene bases for the organocatalytic living ring-opening polymerization of cyclic esters Zhang, L., Nederberg, F., Pratt, R., Waymouth, R., Hedrick, J. L., Wade, C. G. AMER CHEMICAL SOC. 2007

  View details for Web of Science ID 000207593908263

• POLY 508-Functionalizing polyesters and polycarbonates: Covalent tagging of alcohols for ring-opening polymerization Pratt, R. C., Nederberg, F., Waymouth, R. M., Hedrick, J. L. AMER CHEMICAL SOC. 2007

  View details for Web of Science ID 000207593908580

• Synthesis and reactivity of allyl nickel(II) N-heterocyclic carbene enolate complexes JOURNAL OF POLYMER SCIENCE PART A-POLYMER CHEMISTRY Benson, S., Payne, B., Waymouth, R. M. 2007; 45 (16): 3637-3647

  View details for DOI 10.1002/pola.22113

  View details for Web of Science ID 000248354900016

• Organic spirocyclic initiators for the ring-expansion polymerization of beta-lactones JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Jeong, W., Hedrick, J. L., Waymouth, R. M. 2007; 129 (27): 8414-?

  View details for DOI 10.1021/ja072037q

  View details for Web of Science ID 000247759400008

  View details for PubMedID 17579414

• Phosphazene bases: A new category of organocatalysts for the living ring-opening polymerization of cyclic esters MACROMOLECULES Zhang, L., Nederberg, F., Pratt, R. C., Waymouth, R. M., Hedrick, J. L., Wade, C. G. 2007; 40 (12): 4154-4158

  View details for DOI 10.1021/ma070316s

  View details for Web of Science ID 000247138500013

• Zwitterionic polymerization of lactide to cyclic poly(lactide) by using N-heterocyclic carbene organocatalysts ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Culkin, D. A., Jeong, W., Csihony, S., Gomez, E. D., Balsara, N. R., Hedrick, J. L., Waymouth, R. M. 2007; 46 (15): 2627-2630

  View details for DOI 10.1002/anie.200604740

  View details for Web of Science ID 000245614600017

  View details for PubMedID 17330912

• Organocatalytic ring opening polymerization of trimethylene carbonate BIOMACROMOLECULES Nederberg, F., Lohmeijer, B. G., Leibfarth, F., Pratt, R. C., Choi, J., Dove, A. P., Waymouth, R. M., Hedrick, J. L. 2007; 8 (1): 153-160

  Abstract

  A variety of organocatalysts has been surveyed in the ring opening polymerization of trimethylene carbonate. Excellent control was found for several of these catalysts yielding well-defined polycarbonates with molecular weights up to 50,000 g mol(-1), polydispersities below 1.08, and high end-group fidelity. Melt or bulk polymerization was accomplished without loss of control of molecular weight or polydispersity, and random ester-carbonate bulk polymerizations were also demonstrated. Furthermore, by combining disparate polymerization techniques using bifunctional initiators, the mild polymerization conditions allow for the preparation of new block copolymers. Hydrogen-bond activation of monomer and initiator/propagating species is proposed as the underlying mechanism, which can be tuned to mitigate adverse side reactions.

  View details for DOI 10.1021/bm060795n

  View details for Web of Science ID 000243337600021

  View details for PubMedID 17206801

• A distinctive organocatalytic approach to complex macromolecular architectures ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Coulembier, O., Kiesewetter, M. K., Mason, A., Dubois, P., Hedrick, J. L., Waymouth, R. M. 2007; 46 (25): 4719-4721

  View details for DOI 10.1002/anie.200700522

  View details for Web of Science ID 000247558200017

  View details for PubMedID 17506056

• Guanidine and amidine organocatalysts for ring-opening polymerization of cyclic esters MACROMOLECULES Lohmeijer, B. G., Pratt, R. C., Leibfarth, F., Logan, J. W., Long, D. A., Dove, A. P., Nederberg, F., Choi, J., Wade, C., Waymouth, R. M., Hedrick, J. L. 2006; 39 (25): 8574-8583

  View details for DOI 10.1021/ma0619381

  View details for Web of Science ID 000242515800007

• Well-controlled living polymerization of perylene-labeled polyisoprenes and their use in single-molecule Imaging MACROMOLECULES Gavranovic, G. T., Csihony, S., Bowden, N. B., Hawker, C. J., Waymouth, R. M., Moerner, W. E., Fuller, G. G. 2006; 39 (23): 8121-8127

  View details for DOI 10.1021/ma0612475

  View details for Web of Science ID 000241813200046

• Exploration, optimization, and application of supramolecular thiourea-amine catalysts for the synthesis of lactide (co)polymers MACROMOLECULES Pratt, R. C., Lohmeijer, B. G., Long, D. A., Lundberg, P. N., Dove, A. P., Li, H., Wade, C. G., Waymouth, R. M., Hedrick, J. L. 2006; 39 (23): 7863-7871

  View details for DOI 10.1021/ma061607o

  View details for Web of Science ID 000241813200016

• Effects of temperature and chemical modification on polymer Langmuir films JOURNAL OF PHYSICAL CHEMISTRY B Gavranovic, G. T., Smith, M. M., Jeong, W., Wong, A. Y., Waymouth, R. M., Fuller, G. G. 2006; 110 (44): 22285-22290

  Abstract

  We previously reported on a rheological study of Langmuir films of poly(tert-butyl methacrylate) (PtBMA), and this work describes further studies on this system. Here, surface pressure-area (Pi-A) isotherms and interfacial shear rheology experiments are performed to better understand the effects of two modifications: varying the temperature between 5 and 40 degrees C and introducing small amounts of carboxylic acid groups by partially hydrolyzing the polymer. Increased temperature produced isotherms with lower plateau surface pressures, Pip, and Pi values shifted to lower areas above Pip. Film properties transition from being primarily viscous to being dominated by elasticity as Pip is crossed for all temperatures studied, even as the value of Pip changes. Increasing the hydrolysis fraction leads to isotherms shifted to lower areas throughout the curve and higher Pip values. Both temperature variation and chemical modification are believed to affect the relative importance of polymer-polymer and polymer-subphase interactions.

  View details for DOI 10.1021/jp063396v

  View details for Web of Science ID 000241729300034

  View details for PubMedID 17078671

• Organocatalytic living ring-opening polymerization of cyclic carbosiloxanes ORGANIC LETTERS Lohmeijer, B. G., Dubois, G., Leibfarth, F., Pratt, R. C., Nederberg, F., Nelson, A., Waymouth, R. M., Wade, C., Hedrick, J. L. 2006; 8 (21): 4683-4686

  Abstract

  [reaction: see text] An organocatalytic route to narrowly dispersed poly(carbosiloxanes) of predictable molecular weight and end group fidelity is described. N-Heterocyclic carbenes (NHC) and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) catalyze the ring opening of cyclic carbosiloxanes. The pK(b) of the catalyst is important in preventing adverse transetherification reactions and obtaining well-defined polymers. Mechanistic studies indicate that hydrogen bonding to TBD or the NHC activates alcohols or silanols for ring-opening reactions.

  View details for DOI 10.1021/ol0614166

  View details for Web of Science ID 000241030900004

  View details for PubMedID 17020277

• POLY 612-Organocatalytic polymerization of ethylene oxide and the controlled synthesis of PEO-based hydrogel networks Mason, A. F., Lohmeijer, B. G., Li, H., Pratt, R. C., Liao, Q., Frank, C. W., Kingsbury, K., Waymouth, R. M., Hedrick, J. L. AMER CHEMICAL SOC. 2006

  View details for Web of Science ID 000207781701272

• POLY 264-Organocatalytic ring opening polymerization: Activation through hydrogen bonding Lohmeijer, B. G., Pratt, R. C., Li, H., Dove, A. P., Nederberg, F., Mason, A. F., Eade, G. F., Choi, J., Waymouth, R. M., Wade, C., HEDRICK, J. L. AMER CHEMICAL SOC. 2006

  View details for Web of Science ID 000207781701299

• POLY 407-Organocatalysis: A powerful strategy for controlled polymerization reactions Waymouth, R. M., Hedrick, J. L., Culkin, D. A., Pratt, R. C., Jeong, W., Kamber, N. E., Lohmeijer, B. G., Coulembier, O. AMER CHEMICAL SOC. 2006

  View details for Web of Science ID 000207781701155

• PMSE 337-Covalently tailoring the surface properties of a self-assembling protein scaffold for materials applications Jeong, W., Culkin, D. A., Coulembier, O., Hedrick, J. L., Waymouth, R. M. AMER CHEMICAL SOC. 2006: 315–315

  View details for Web of Science ID 000207781700307

• PMSE 617-Effect of counterions on the liquid properties of aqueous polyurethane dispersions prepared through the acetone process Nederberg, F., Lohmeijer, B. G., Pratt, R. C., Mason, A. F., Eade, G., Choi, J., Balsara, N. P., Waymouth, R. M., HEDRICK, J. L. AMER CHEMICAL SOC. 2006: 247–247

  View details for Web of Science ID 000207781700240

• POLY 261-N-heterocyclic carbenes as organocatalysts for the ring-opening polymerization of e-caprolactone Kamber, N. E., Kiesewetter, M. K., Hedrick, J. L., Waymouth, R. M. AMER CHEMICAL SOC. 2006

  View details for Web of Science ID 000207781701367

• POLY 646-Organocatalytic ring-opening polymerizations of morpholine-2,6-diones: A route to functionalized poly(lactide)s and pseudopeptides Pratt, R. C., Lohmeijer, B. G., Mason, A. F., Waymouth, R. M., Hedrick, J. L. AMER CHEMICAL SOC. 2006

  View details for Web of Science ID 000207781701159

• Alcohol adducts of N-heterocyclic carbenes: Latent catalysts for the thermally-controlled living polymerization of cyclic esters MACROMOLECULES Coulembier, O., Lohmeijer, B. G., Dove, A. P., Pratt, R. C., Mespouille, L., Culkin, D. A., Benight, S. J., Dubois, P., Waymouth, R. M., Hedrick, J. L. 2006; 39 (17): 5617-5628

  View details for DOI 10.1021/ma0611366

  View details for Web of Science ID 000239758400009

• Monolayered organosilicate toroids and related structures: A phase diagram for templating from block copolymers NANO LETTERS Choi, J., Hermans, T. M., Lohmeijer, B. G., Pratt, R. C., Dubois, G., Frommer, J., Waymouth, R. M., Hedrick, J. L. 2006; 6 (8): 1761-1764

  Abstract

  Here we report the controlled generation of micelle-templated organosilicate nanostructures resulting from self-assembly of a block copolymer/organosilicate mixture followed by organosilicate vitrification and copolymer thermolysis. Variation of solution condition and the copolymer/organosilicate mixture composition generates widely different film morphologies ranging from toroids to linear features to contiguous nanoporous monolayers. The use of reactive organosilicates for block copolymer templation generates functional inorganic nanostructures with thermal and mechanical stability.

  View details for DOI 10.1021/nl0612906

  View details for Web of Science ID 000239623900033

  View details for PubMedID 16895370

• Density functional theory calculations of Ti-TEMPO complexes: Influence of ancillary Ligation on the strength of the Ti-O bond ORGANOMETALLICS Huang, K., Han, J. H., Musgrave, C. B., Waymouth, R. M. 2006; 25 (14): 3317-3323

  View details for DOI 10.1021/om060148c

  View details for Web of Science ID 000238534400008

• Metal-free catalyzed ring-opening polymerization of, beta-lactones: Synthesis of amphiphilic triblock copolymers based on poly(dimethylmalic acid) MACROMOLECULES Coulembier, O., Mespouille, L., Hedrick, J. L., Waymouth, R. M., Dubois, P. 2006; 39 (12): 4001-4008

  View details for DOI 10.1021/ma060552n

  View details for Web of Science ID 000238051600008

• Metal and ligand K-edge XAS of titanium-TEMPO complexes: Determination of oxidation states and insights into Ti-O bond homolysis INORGANIC CHEMISTRY George, S. D., Huang, K., Waymouth, R. M., Solomon, E. I. 2006; 45 (11): 4468-4477

  Abstract

  Ti-TEMPO (TEMPO = 2,2,6,6-tetramethylpiperidine-N-oxyl) provides a means for generating Ti(III) complexes by homolysis of the Ti-O bond. It has been determined that bis-Cp-Ti-TEMPO complexes readily undergo homolytic cleavage while the mono-Cp-Ti-TEMPO complexes do not. Here Ti K- and Cl K-edge XAS are applied to directly determine the oxidation state of TiCl3TEMPO, TiCpCl2TEMPO, and TiCp2ClTEMPO, with reference to Ti(III) and Ti(IV) complexes of known oxidation state. The Ti K-edge data show that Ti(III) complexes exhibit a pre-edge feature approximately 1 eV lower than any of the Ti(IV) complexes; while the Cl K-edges show that Ti(III) complexes have a Cl K- pre-edge feature to approximately 1 eV higher energy than any of the Ti(IV) complexes. Taken together, the Ti and Cl K-edge data indicate that the Ti-TEMPO complexes are best described as Ti(IV)-TEMPO anions (rather than Ti(III)-nitroxyl radicals). In addition, the Cl K-edges indicate that replacement of Cl by Cp weakens the bonding with the remaining ligands, with the Cl 3p covalency decreasing from 25% to 21% to 17% on going from TiCl3TEMPO to TiCpCl2TEMPO to TiCp2ClTEMPO. DFT calculations also show that the electronic structures of the Ti-TEMPO complexes are modulated by the replacement of chloride by Cp. The effect of the Cp on the ancillary ligation is one factor that contributes to facile Ti-O bond homolysis in TiCp2ClTEMPO. However, the results indicate the primary contribution to the energetics of Ti-O bond homolysis in TiCp2ClTEMPO is stabilization of the three-coordinate product by Cp.

  View details for DOI 10.1021/ic060402t

  View details for Web of Science ID 000237690700029

  View details for PubMedID 16711697

• N-Heterocyclic carbenes: Effective organic catalysts for living polymerization POLYMER Dove, A. P., Pratt, R. C., Lohmeijer, B. G., Culkin, D. A., Hagberg, E. C., Nyce, G. W., Waymouth, R. M., Hedrick, J. L. 2006; 47 (11): 4018-4025

  View details for DOI 10.1016/j.polymer.2006.02.037

  View details for Web of Science ID 000238366200041

• Triazabicyclodecene: A simple bifunctional organocatalyst for acyl transfer and ring-opening polymerization of cyclic esters JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Pratt, R. C., Lohmeijer, B. G., Long, D. A., Waymouth, R. M., Hedrick, J. L. 2006; 128 (14): 4556-4557

  Abstract

  1,5,7-Triazabicyclo[4.4.0]dec-5-ene (TBD) is an effective organocatalyst for acyl transfer as well as the ring-opening polymerization of cyclic esters. Its high activity is attributed to its ability to simultaneously activate both esters and alcohols, as demonstrated in a model reaction. This unique mechanism makes TBD a remarkably simple example of a bifunctional catalyst. The simplicity of the reaction conditions, the ready commercial availability of the catalyst, and its high activity provide an accessible methodology to allow future studies of tailor-made polyesters.

  View details for DOI 10.1021/ja060662+

  View details for Web of Science ID 000236770300030

  View details for PubMedID 16594676

• Synthesis, structure, and polymerization activity of a titanium complex with a chelating [(hydroxy-kappa O)amino-kappa N]phenolato(2-)-kappa O ligand HELVETICA CHIMICA ACTA Kraft, B. M., Huang, K., Cole, A. P., Waymouth, R. M. 2006; 89 (8): 1589-1595

  View details for Web of Science ID 000240370500009

• Stereoselective polymerization of rac- and meso-lactide catalyzed by sterically encumbered N-heterocyclic carbenes CHEMICAL COMMUNICATIONS Dove, A. P., Li, H., Pratt, R. C., Lohmeijer, B. G., Culkin, D. A., Waymouth, R. M., Hedrick, J. L. 2006: 2881-2883

  Abstract

  New sterically encumbered N-heterocyclic carbene catalysts were synthesized and used to polymerize rac-lactide to give highly isotactic polylactide or meso-lactide to give heterotactic polylactide.

  View details for DOI 10.1039/b601393g

  View details for Web of Science ID 000239251200014

  View details for PubMedID 17007404

• Application of solvent-directed assembly of block copolymers to the synthesis of nanostructured materials with low dielectric constants ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Hermans, T. M., Choi, J., Lohmeijer, B. G., Dubois, G., Pratt, R. C., Kim, H., Waymouth, R. M., Hedrick, J. L. 2006; 45 (40): 6648-6652

  View details for DOI 10.1002/anie.200601888

  View details for Web of Science ID 000241474500009

  View details for PubMedID 16906604

• Dynamic NMR studies of cationic bis(2-phenylindenyl) zirconium pyridyl complexes: Evidence for syn conformers in solution ORGANOMETALLICS Lincoln, A. L., Wilmes, G. M., Waymouth, R. M. 2005; 24 (24): 5828-5835

  View details for DOI 10.1021/om050473k

  View details for Web of Science ID 000233378900010

• Thiourea-based bifunctional organocatalysis: Supramolecular recognition for living polymerization JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Dove, A. P., Pratt, R. C., Lohmeijer, B. G., Waymouth, R. M., Hedrick, J. L. 2005; 127 (40): 13798-13799

  Abstract

  A versatile, metal-free, organocatalytic approach to the living ring-opening polymerization of lactide using a bifunctional thiourea-tertiary amine catalyst is described. Mild and highly selective polymerization conditions produced poly(lactides) with predictable molecular weights and extremely narrow polydispersities ( approximately 1.05), characteristic of a living polymerization. The extraordinary selectivity of this catalyst system for polymerization relative to transesterification is remarkably unusual. The low polydispersities and exceptional control observed are a consequence of selective transesterification of lactide relative to the open chain esters. Presumably, the ring strain of lactide provides both a driving force for the polymerization and a kinetic preference for polymerization relative to transesterification with catalyst. We postulate that the initiating/propagating alcohol is activated by acid-base interaction with the tertiary amine moiety and the carbonyl of the lactide monomer is simultaneously activated by hydrogen bonding to the thiourea moiety of the catalyst.

  View details for DOI 10.1021/ja0543346

  View details for Web of Science ID 000232413300028

  View details for PubMedID 16201794

• [H(OEt2)(2)](+) and [Ph3C](+) salts of the borate anions [B(CF3)(4)](-), [(CF3)(3)BCN](-), and [B(CN)(4)](-) ORGANOMETALLICS Finze, M., Bernhardt, E., Berkei, M., Willner, H., Hung, J., Waymouth, R. M. 2005; 24 (21): 5103-5109

  View details for DOI 10.1021/om050463j

  View details for Web of Science ID 000232387800034

• Unconstrained geometry complexes: Ethylene/alpha-olefin copolymerizations with a tetramethyldisilyl-bridged Cp-amido titanium complex JOURNAL OF POLYMER SCIENCE PART A-POLYMER CHEMISTRY Hung, J., Waymouth, R. M. 2005; 43 (17): 3840-3851

  View details for DOI 10.1002/pola.20862

  View details for Web of Science ID 000231369700014

• Single-component catalyst/initiators for the organocatalytic ring-opening polymerization of lactide JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Csihony, S., Culkin, D. A., Sentman, A. C., Dove, A. P., Waymouth, R. M., Hedrick, J. L. 2005; 127 (25): 9079-9084

  Abstract

  The synthesis and characterization of a series of primary and secondary alcohol adducts of 1,3-dimesitylimidazolin-2-ylidene is described. These adducts are stable as solids at room temperature, but readily release alcohol and the free carbene in solution. These alcohol adducts function as excellent single-component catalyst/initiators for the ring-opening polymerization of lactide under mild conditions, providing polymers with controlled molecular weights and narrow polydispersities. Multifunctional adducts were used to prepare poly(lactide)s of more complex architectures.

  View details for Web of Science ID 000230010600049

  View details for PubMedID 15969586

• Amine bis(phenolate) zirconium complexes: Influence of ligand structure and cocatalyst on copolymerization behavior MACROMOLECULES Reybuck, S. E., Lincoln, A. L., Ma, S. D., Waymouth, R. M. 2005; 38 (7): 2552-2558

  View details for DOI 10.1021/ma0476386

  View details for Web of Science ID 000228067600005

• Homolysis of weak Ti-O bonds: Experimental and theoretical studies of titanium oxygen bonds derived from stable nitroxyl radicals JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Huang, K. W., Han, J. H., Cole, A. P., Musgrave, C. B., Waymouth, R. M. 2005; 127 (11): 3807-3816

  Abstract

  Titanium-oxygen bonds derived from stable nitroxyl radicals are remarkably weak and can be homolyzed at 60 degrees C. The strength of these bonds depends sensitively on the ancillary ligation at titanium. Direct measurements of the rate of Ti-O bond homolysis in Ti-TEMPO complexes Cp2TiCl(TEMPO) (3) and Cp2TiCl(4-MeO-TEMPO) (4) (TEMPO = 2,2,6,6-tetramethylpiperidine-N-oxyl, 4-MeO-TEMPO = 2,2,6,6-tetramethyl-4-methoxypiperidine-N-oxyl) were conducted by nitroxyl radical exchange experiments. Eyring plots gave the activation parameters, deltaH++ = 27(+/- 1) kcal/mol, deltaS++ = 6.9(+/- 2.3) eu for 3 and deltaH++ = 28(+/- 1) kcal/mol, deltaS++ = 9.0(+/- 3.0) eu for 4, consistent with a process involving the homolysis of a weak Ti-O bond to generate the transient Cp2Ti(III)Cl and the nitroxyl radical. Thermolysis of the titanocene TEMPO complexes in the presence of epoxides leads to the Cp2Ti(III)Cl-mediated ring-opening of the epoxide followed by trapping by the nitroxyl radical. The X-ray crystal structure of the Ti-TEMPO derivative, Cp2TiCl(4-MeO-TEMPO) (4), is reported. DFT (B3LYP/6-31G*) calculations and experimental studies reveal that the strength of the Ti-O bond decreases dramatically with the number of cyclopentadienyl groups on titanium. The calculated Ti-O bond strength of the monocyclopentadienyl complex 2 is 43 kcal/mol, whereas that of the biscyclopentadienyl complex 3 is 17 kcal/mol, a difference of 26 kcal/mol. These studies reveal that the strength of these Ti-O bonds can be tuned over an interesting and experimentally accessible temperature range by appropriate ligation on titanium.

  View details for DOI 10.1021/ja044512f

  View details for Web of Science ID 000227738700047

  View details for PubMedID 15771515

• Silver(I)-carbene complexes/ionic liquids: Novel N-heterocyclic carbene delivery agents for organocatalytic transformations JOURNAL OF ORGANIC CHEMISTRY Sentman, A. C., Csihony, S., Waymouth, R. M., Hedrick, J. L. 2005; 70 (6): 2391-2393

  Abstract

  [reaction: see text] N-Heterocyclic carbene (NHC) complexes with silver were investigated as sources of unsaturated NHC carbene catalysts via thermal decomposition. The NHC complex (1-ethyl-3-methylimidazol-2-ylidene)silver(I) chloride is an ionic liquid, and was found to catalyze the ring-opening polymerization of lactide at elevated temperatures to give narrowly dispersed polylactide of predictable molecular weight. Silver-carbene complexes can also be used for the catalysis of small molecule transesterification reactions. Thermolysis of the silver complexes in the presence of CS(2) yielded the zwitterionic CS(2) adducts of the carbene, implicating the intermediacy of the free carbene in these reactions.

  View details for DOI 10.1021/jo048555q

  View details for Web of Science ID 000227566400067

  View details for PubMedID 15760240

• Latent, thermally activated organic catalysts for the on-demand living polymerization of lactide ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Coulembier, O., Dove, A. P., Pratt, R. C., Sentman, A. C., Culkin, D. A., Mespouille, L., Dubois, P., Waymouth, R. M., HEDRICK, J. L. 2005; 44 (31): 4964-4968

  View details for DOI 10.1002/anie.200500723

  View details for Web of Science ID 000231185400029

  View details for PubMedID 16007717

• Synthesis, structure, and olefin polymerization with nickel(II) N-heterocyclic carbene enolates CHEMICAL COMMUNICATIONS Ketz, B. E., Ottenwaelder, X. G., Waymouth, R. M. 2005: 5693-5695

  Abstract

  Two novel N-heterocylic carbene enolate nickel complexes have been prepared and shown to be active for ethylene and propylene polymerization to yield linear polymers.

  View details for DOI 10.1039/b511202h

  View details for Web of Science ID 000233458800029

  View details for PubMedID 16292393

• Cyclopentadienyl titanium hydroxylaminato complexes as highly active catalysts for the polymerization of propylene CHEMICAL COMMUNICATIONS Dove, A. P., Xie, X. J., Waymouth, R. M. 2005: 2152-2154

  Abstract

  Half sandwich complexes of titanium bearing eta1 or eta2 bound nitroxide ligands are highly active catalysts for the polymerisation of propylene to high molecular weight atactic poly(propylene).

  View details for DOI 10.1039/b418778d

  View details for Web of Science ID 000228559200026

  View details for PubMedID 15846430

• A neutron scattering study of the structure and water partitioning of selectively deuterated copolymer micelles LANGMUIR Stancik, C. M., Lavoie, A. R., Achurra, P. A., Waymouth, R. M., Gast, A. P. 2004; 20 (21): 8975-8987

  Abstract

  We present a scattering study of a selectively deuterated micelle-forming diblock copolymer. The copolymer comprises a partially deuterated polystyrene (d,h-PS) block and an imidazolium-functionalized PS (IL) block. In toluene solutions, the copolymers assemble into elongated micelles where the IL block forms the micelle core. Through dynamic light scattering (DLS) measurements, we obtain the overall size of the micelles. In our small-angle neutron scattering (SANS) studies, we use contrast matching to characterize the IL core and the PS shell of the micelles independently. The PS block forming the micelle shell exhibits either a starlike or brushlike conformation depending upon the size of the core to which it is tethered. We find the IL block to be in an extended conformation, driving the formation of slightly elongated and relatively stiff micelle cores. The elongated micelle core cross-sectional radius and length depend linearly on the length of the IL block. We find that the micelles can sequester a few water molecules for each IL repeat unit; the addition of water slightly increases the cross section of the elongated micelles.

  View details for DOI 10.1021/la0364183

  View details for Web of Science ID 000224391600008

  View details for PubMedID 15461476

• A general and versatile approach to thermally generated N-heterocyclic carbenes CHEMISTRY-A EUROPEAN JOURNAL Nyce, G. W., Csihony, S., Waymouth, R. M., HEDRICK, J. L. 2004; 10 (16): 4073-4079

  Abstract

  The synthesis of N-heterocyclic carbene (NHC) adducts by condensation of diamines with appropriately substituted benzaldehydes is described. This simplified approach provides the NHC adduct without first having to generate the carbene followed by its protection. These adducts undergo thermal deprotection to generate N-heterocyclic carbene in situ. Adduct decomposition temperatures were investigated as a function of catalyst structure by using thermal analysis and spectroscopic techniques. Importantly, unlike adducts derived from chloroform, the new pentafluorobenzene-based adducts are more readily prepared and are stable at room temperature. The utility of these adducts as organic catalyst precursors for living ring-opening polymerization (ROP) of lactide, transesterification reactions, and the synthesis of N-heterocyclic carbene ligated organometallic complexes is also described.

  View details for DOI 10.1002/chem.200400196

  View details for Web of Science ID 000223593400023

  View details for PubMedID 15317058

• Catalytic syntheses of alternating, stereoregular ethylene/cycloolefin copolymers TETRAHEDRON Lavoie, A. R., Waymouth, R. M. 2004; 60 (34): 7147-7155

  View details for DOI 10.1016/j.tet.2004.06.020

  View details for Web of Science ID 000223090800005

• Bredereck's reagent revisited: Latent anionic ring-opening polymerization and transesterification reactions ADVANCED SYNTHESIS & CATALYSIS Csihony, S., Beaudette, T. T., Sentman, A. C., Nyce, G. W., Waymouth, R. M., Hedrick, J. L. 2004; 346 (9-10): 1081-1086

  View details for DOI 10.1002/adsc.200404097

  View details for Web of Science ID 000224217700008

• Ethylene/1-hexene copolymerization with tetramethyldisiloxane-bridged bis(indenyl) metallocenes JOURNAL OF POLYMER SCIENCE PART A-POLYMER CHEMISTRY Reybuck, S. E., Waymouth, R. M. 2004; 42 (13): 3323-3331

  View details for DOI 10.1002/pola.20170

  View details for Web of Science ID 000222124600021

• Structure and reactivity of an allylpalladium N-heterocyclic carbene enolate complex ORGANOMETALLICS Ketz, B. E., Cole, A. P., Waymouth, R. M. 2004; 23 (12): 2835-2837

  View details for DOI 10.1021/om049838b

  View details for Web of Science ID 000221773600003

• Effects of ligand substitutions on the rotation rate of indenyl ligands in bis(2-arylindenyl)zirconocenes by NMR line-shape analysis and relaxation in the rotating frame ORGANOMETALLICS Wilmes, G. M., France, M. B., Lynch, S. R., Waymouth, R. M. 2004; 23 (10): 2405-2411

  View details for DOI 10.1021/om034166v

  View details for Web of Science ID 000221231100027

• Investigation of bridge and 2-phenyl substituent effects on ethylene/alpha-olefin copolymerization behavior with 1,2 '-Bridged bis(indenyl)zirconium dichlorides MACROMOLECULES Reybuck, S. E., Waymouth, R. M. 2004; 37 (7): 2342-2347

  View details for DOI 10.1021/ma035365t

  View details for Web of Science ID 000220581700004

• Silver(I)-carbene complexes ionic liquids: Novel N-heterocyclic carbene delivery agents for living polymerization 227th National Meeting of the American-Chemical Society Sentman, A., Csihony, S., Nyce, G. W., Waymouth, R. M., HEDRICK, J. L. AMER CHEMICAL SOC. 2004: U456–U456

  View details for Web of Science ID 000223655702396

• Synthesis, structure, and reactivity of hydroxylaminato alkyltitanium complexes ORGANOMETALLICS Mahanthappa, M. K., Cole, A. P., Waymouth, R. M. 2004; 23 (6): 1405-1410

  View details for DOI 10.1021/om0305521

  View details for Web of Science ID 000220093200035

• Synthesis, structure, and ethylene/alpha-olefin polymerization behavior of (cyclopentadienyl),(nitroxide)titanium complexes ORGANOMETALLICS Mahanthappa, M. K., Cole, A. P., Waymouth, R. M. 2004; 23 (4): 836-845

  View details for DOI 10.1021/om034096s

  View details for Web of Science ID 000188872700026

• Heterogeneous composition and microstructure of elastomeric polypropylene from a sterically hindered 2-arylindenylhafnium catalyst MACROMOLECULES Wiyatno, W., Chen, Z. R., Liu, Y. X., Waymouth, R. M., Krukonis, V., Brennan, K. 2004; 37 (3): 701-708

  View details for DOI 10.1021/ma020332j

  View details for Web of Science ID 000188803000006

• Micelles of imidazolium-functionalized polystyrene diblock copolymers investigated with neutron and light scattering LANGMUIR Stancik, C. M., Lavoie, A. R., Schutz, J., Achurra, P. A., Lindner, P., Gast, A. P., Waymouth, R. M. 2004; 20 (3): 596-605

  Abstract

  We synthesize a series of block copolymers comprising a polystyrene (PS) block and an imidazolium-functionalized PS (IL) block and characterize their assembly properties. We use small-angle neutron scattering and dynamic light scattering to determine the micelle size and shape in dilute solutions and to assess the micelle interactions in concentrated solutions. By studying a series of copolymers with fixed PS block length, we find that the length of the IL block governs the micelle dimensions. Our data suggest that these copolymers form elongated micelle structures where the IL block is extended in the micelle core. We find that these micelles can sequester water and that interactions between the micelles lead to structure factor peaks at elevated concentrations.

  View details for DOI 10.1021/la0353632

  View details for Web of Science ID 000188660600013

  View details for PubMedID 15773081

• Hydrolysis of CpTiCl2(TEMPO) and its application on one-pot syntheses of CpTiCl(OR)(2) complexes DALTON TRANSACTIONS Huang, K. W., Waymouth, R. M. 2004: 354-356

  Abstract

  The eta1-hydroxylamido half-titanocene complex, CpTiCl2(TEMPO) 1, hydrolyzes extremely efficiently to generate (CpTiClO)4 and the protonated hydroxylamine. The efficient hydrolysis chemistry provides selective syntheses of CpTi dialkoxide and diaryloxide complexes.

  View details for DOI 10.1039/b314027j

  View details for Web of Science ID 000188433900002

  View details for PubMedID 15252536

• Propylene polymerization with 1,2 '-bridged bis(indenyl)zirconium dichlorides MACROMOLECULES Finze, M., Reybuck, S. E., Waymouth, R. M. 2003; 36 (25): 9325-9334

  View details for DOI 10.1021/ma0303972

  View details for Web of Science ID 000187178000012

• The dual-site alternating cyclocopolymerization of 1,3-butadiene with ethylene JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Choo, T. N., Waymouth, R. M. 2003; 125 (30): 8970-8971

  Abstract

  The copolymerization of ethylene with 1,3-butadiene was studied with the series of ansa-metallocenes Me2Si(Cp)(9-Flu)ZrCl2 (1), Me2Si(1-Ind)(9-Flu)ZrCl2 (2), and Me2Si(9-Flu)2ZrCl2 (3) with methylaluminoxane (MAO) as cocatalyst. The catalyst 2/MAO yields a cyclocopolymer composed of two ethylene monomer units for every one butadiene in a novel periodic architecture of 1,2-enchained cyclopentane units separated by three methylenes. The high butadiene content in the copolymer and the high selectivity for alternating cyclocopolymerization to form methylene-1,2-cyclopentane units implicate a dual-site mechanism where butadiene and ethylene are enchained at different coordination sites.

  View details for DOI 10.1021/ja034903x

  View details for Web of Science ID 000184364500002

  View details for PubMedID 15369326

• Synthesis and characterization of [TiF2(NMe2)(2)](4) and its use for olefin polymerizations INORGANICA CHIMICA ACTA Straus, D. A., Kamigaito, M., Cole, A. P., Waymouth, R. M. 2003; 349: 65-68

  View details for DOI 10.1016/S0020-1693(02)01515-3

  View details for Web of Science ID 000183673100009

• High comonomer selectivity in ethylene/hexene copolymerization by unbridged indenyl metallocenes MACROMOLECULES Dankova, M., Waymouth, R. M. 2003; 36 (11): 3815-3820

  View details for DOI 10.1021/ma021075l

  View details for Web of Science ID 000183247700012

• Sequence and stereoselectivity of the C-1-symmetric metallocene Me2Si(1-(4,7-Me(2)Ind))(9-Flu)ZrCl2 MACROMOLECULES Fan, W., Waymouth, R. M. 2003; 36 (9): 3010-3014

  View details for DOI 10.1021/ma020037z

  View details for Web of Science ID 000182646600006

• In vitro epithelialization of a synthetic polymer for generation of corneal onlay/keratoprosthesis Annual Meeting of the Association-for-Research-in-Vision-and-Ophthalmology Pilyugina, S. A., Lavoie, A., Huie, P., Derr, K., SMITH, A. J., Noolandi, J., Waymouth, R. M., Ta, C. ASSOC RESEARCH VISION OPHTHALMOLOGY INC. 2003: U321–U321

  View details for Web of Science ID 000184606801294

• Nucleation and crystallization of low-crystallinity polypropylene followed in situ by hot stage atomic force microscopy MACROMOLECULES Schonherr, H., Waymouth, R. M., Frank, C. W. 2003; 36 (7): 2412-2418

  View details for DOI 10.1021/ma0208335

  View details for Web of Science ID 000182045800031

• Control of sequence distribution of ethylene copolymers: Influence of comonomer sequence on the melting behavior of ethylene copolymers MACROMOLECULES Hung, J., Cole, A. P., Waymouth, R. A. 2003; 36 (7): 2454-2463

  View details for DOI 10.1021/ma021779v

  View details for Web of Science ID 000182045800036

• In situ generation of carbenes: A general and versatile platform for organocatalytic living polymerization JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Nyce, G. W., Glauser, T., CONNOR, E. F., Mock, A., Waymouth, R. M., Hedrick, J. L. 2003; 125 (10): 3046-3056

  Abstract

  A metal-free, organocatalytic approach to living polymerization using N-heterocyclic carbenes as nucleophilic catalysts generated and used in situ in a single-pot process is detailed. The N-heterocyclic carbene catalyst platform is extremely versatile, as the nature of the substituents has a pronounced effect of catalyst stability and activity toward different substrates. The generation of imidazolium- and thiazaolium-based carbenes was accomplished from the reaction of the corresponding salts with the appropriate bases. This allowed the rapid screening of libraries of catalysts that provided a basic understanding of catalyst structure (sterics, electronics, etc.) with the polymerization rate, control, substrate, and range of molecular weights. The imidazole-based catalysts were significantly more active toward ROP than the thiazolium-based analogues. No appreciable differences between imidazol-2-ylidene and imidazolin-2-ylidene catalysts were observed. Less sterically demanding carbenes were found to be more active toward ring-opening polymerization (ROP) than their sterically encumbered analogues for lactone polymerization. These data prompted the investigation of ionic liquid as a precatalyst reservoir in a phase-transfer polymerization with an immiscible THF solution of monomer and initiator. In situ activation of the ionic liquid generates carbene that migrates to the organic phase effecting living ROP. Precatalyst (ionic liquid) regeneration terminates polymerization. This simple reaction/recycle protocol readily allows repetitive ROPs from the ionic liquid using commercially available materials.

  View details for DOI 10.1021/ja021084+

  View details for Web of Science ID 000181409500051

  View details for PubMedID 12617671

• Component stress-strain behavior and small-angle neutron scattering investigation of stereoblock elastomeric polypropylene MACROMOLECULES Wiyatno, W., Fuller, G. G., Pople, J. A., Gast, A. P., Chen, Z. R., Waymouth, R. M., Myers, C. L. 2003; 36 (4): 1178-1187

  View details for DOI 10.1021/na020477q

  View details for Web of Science ID 000181117200032

• Ring opening metathesis polymerization on non-covalently functionalized single-walled carbon nanotubes CHEMICAL COMMUNICATIONS Gomez, F. J., Chen, R. J., Wang, D. W., Waymouth, R. M., Dai, H. J. 2003: 190-191

  Abstract

  Norbornene polymerization has been initiated selectively on the surface of single-walled carbon nanotubes (SWNTs) via a specifically adsorbed pyrene-linked ROMP initiator, resulting in a homogeneous non-covalent poly(norbornene) coating.

  View details for DOI 10.1039/b211194b

  View details for PubMedID 12585385

• Alternating stereospecific copolymerization of cyclopentene and ethylene with constrained geometry catalysts CHEMICAL COMMUNICATIONS Lavoie, A. R., Ho, M. H., Waymouth, R. M. 2003: 864-865

  Abstract

  The stereoselective copolymerization of cyclopentene (cP) and ethylene (E) to generate highly alternating polymers with isotactic cis 1,2-cyclopentene enchainment is reported.

  View details for DOI 10.1039/b300841j

  View details for Web of Science ID 000181774700025

  View details for PubMedID 12739650

• Synthesis of polyethylene graft block copolymers from styrene, butyl acrylate, and butadiene MACROMOLECULES Bowden, N. B., Dankova, M., Wiyatno, W., Hawker, C. J., Waymouth, R. M. 2002; 35 (25): 9246-9248

  View details for DOI 10.1021/ma020544g

  View details for Web of Science ID 000179623200002

• Dynamic response of stereoblock elastomeric polypropylene studied by rheooptics and X-ray scattering. 1. Influence of isotacticity MACROMOLECULES Wiyatno, W., Pople, J. A., Gast, A. P., Waymouth, R. M., Fuller, G. G. 2002; 35 (22): 8488-8497

  View details for DOI 10.1021/ma020261o

  View details for Web of Science ID 000178738000033

• Dynamic response of stereoblock elastomeric polypropylene studied by rheooptics and X-ray scattering. 2. Orthogonally oriented crystalline chains MACROMOLECULES Wiyatno, W., Pople, J. A., Gast, A. P., Waymouth, R. M., Fuller, G. G. 2002; 35 (22): 8498-8508

  View details for DOI 10.1021/ma020262g

  View details for Web of Science ID 000178738000034

• Expanding the catalytic activity of nucleophilic N-heterocyclic carbenes for transesterification reactions ORGANIC LETTERS Nyce, G. W., Lamboy, J. A., CONNOR, E. F., Waymouth, R. M., Hedrick, J. L. 2002; 4 (21): 3587-3590

  Abstract

  [reaction: see text] Currently, there is a renewed interest in reactions that are catalyzed by organic compounds. Typical organic catalysts for acylation or transesterification reactions are based on either nucleophilic tertiary amines or phosphines. This communication discusses the use of nucleophilic N-heterocyclic carbenes as efficient transesterification catalysts. These relatively unexplored and highly versatile organic catalysts were found to be mild, selective, and more active than traditional organic nucleophiles.

  View details for DOI 10.1021/ol0267228

  View details for Web of Science ID 000178522700010

  View details for PubMedID 12375894

• Synthesis of fluorescently labeled polymers and their use in single-molecule imaging MACROMOLECULES Bowden, N. B., Willets, K. A., Moerner, W. E., Waymouth, R. M. 2002; 35 (21): 8122-8125

  View details for DOI 10.1021/ma020780r

  View details for Web of Science ID 000178444400037

• 2-arylindene metallocenes: Conformationally dynamic catalysts to control the structure and properties of polypropylenes ACCOUNTS OF CHEMICAL RESEARCH Lin, S., Waymouth, R. M. 2002; 35 (9): 765-773

  Abstract

  Polymerization of propylene with catalysts derived from unbridged 2-arylindene metallocenes leads to elastomeric, low-tacticity polypropylenes. The polymerization behavior of these conformationally dynamic catalyst systems is interpreted in terms of a multistate mechanism where the catalyst enchains the monomer from both stereoselective and nonstereoselective conformations during the lifetime of a single polymer chain. The structure and properties of the polypropylenes depend sensitively on the metallocene and the polymerization conditions (temperature, pressure, monomer concentration); samples of low to intermediate isotacticity ([mmmm] = 20-40%) are elastomeric, with low densities and broad melting ranges that extend to 150 degrees C. Samples of higher tacticity ([mmmm] = 40-70%) behave as softened thermoplastics.

  View details for DOI 10.1021/ar010081j

  View details for Web of Science ID 000178085700010

  View details for PubMedID 12234206

• Influence of cocatalyst on the stereoselectivity of unbridged 2-phenylindenyl metallocene catalysts MACROMOLECULES Wilmes, G. M., Polse, J. L., Waymouth, R. M. 2002; 35 (18): 6766-6772

  View details for DOI 10.1021/ma020512t

  View details for Web of Science ID 000177688800008

• Synthesis of polyethylene graft block copolymers from butyl acrylate, styrene, and butadiene. Bowden, N. B., Waymouth, R. M., Dankova, M., Wiyatno, W. AMER CHEMICAL SOC. 2002: U153–U153

  View details for Web of Science ID 000177422300762

• Rotation rates of bis(2-arylindenyl)zirconocenes: Effects of ligands and implications for formation of stereoblock polypropylene. Wilmes, G. M., France, M. B., Lynch, S. R., Waymouth, R. M. AMER CHEMICAL SOC. 2002: U685–U686

  View details for Web of Science ID 000177422203519

• Coordination chemistry of stable radicals: Homolysis of a titanium-oxygen bond JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Huang, K. W., Waymouth, R. M. 2002; 124 (28): 8200-8201

  Abstract

  Thermolysis of Cp2TiCl(TEMPO) (TEMPO = 2,2,6,6-tetramethylpiperidine-1-oxyl) at 60 degrees C in a benzene/CCl4 mixture generates Cp2TiCl2. Kinetic studies implicate a mechanism involving the reversible cleavage of a Ti-O bond to generate the TEMPO radical and Cp2TiCl, which is trapped by CCl4 to give Cp2TiCl2. The rate of this reaction is strongly inhibited by added TEMPO and increases with increasing CCl4 concentration, indicating that the coupling of TEMPO to Cp2TiCl is faster than chloride atom abstraction from CCl4.

  View details for DOI 10.1021/ja0264854

  View details for Web of Science ID 000176843200009

  View details for PubMedID 12105895

• Propylene polymerization with sterically hindered unbridged 2-arylindene metallocenes MACROMOLECULES Wilmes, G. M., Lin, S., Waymouth, R. M. 2002; 35 (14): 5382-5387

  View details for DOI 10.1021/ma012241c

  View details for Web of Science ID 000176535600012

• Effect of tacticity on coil dimensions and thermodynamic properties of polypropylene MACROMOLECULES Jones, T. D., Chaffin, K. A., Bates, F. S., Annis, B. K., HAGAMAN, E. W., Kim, M. H., Wignall, G. D., Fan, W., Waymouth, R. 2002; 35 (13): 5061-5068

  View details for DOI 10.1021/ma011547g

  View details for Web of Science ID 000176215500031

• Cyclocopolymerization: A mechanistic probe for dual-site alternating copolymerization of ethylene and alpha-olefins JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Choo, T. N., Waymouth, R. M. 2002; 124 (16): 4188-4189

  Abstract

  The copolymerization of ethylene with 1,5-hexadiene or 1-hexene was studied with the series of ansa-metallocenes Me2Si(Cp)(9-Flu)ZrCl2 (1), Me2Si(1-Ind)(9-Flu)ZrCl2 (3), and Me2Si(9-Flu)2ZrCl2 (4). 1,5-Hexadiene, a monomer which requires two insertion events to be cyclopolymerized, when copolymerized with ethylene using 3/MAO, gave a copolymer with a novel architecture. When compared with the copolymerization of 1-hexene with ethylene, the observed striking differences between the two copolymers provided compelling evidence for a dual-site alternating copolymerization mechanism in both cases. The copolymerization results from 1/MAO and 4/MAO further support this.

  View details for DOI 10.1021/ja0177071

  View details for Web of Science ID 000175088600010

  View details for PubMedID 11960429

• Syndiospecific propylene polymerization using C-1-symmetric ansa-metallocene catalysts: Substituent and bridge effects MACROMOLECULES Gomez, F. J., Waymouth, R. M. 2002; 35 (9): 3358-3368

  View details for DOI 10.1021/ma011910j

  View details for Web of Science ID 000175112100010

• Crystallization of the alpha and gamma forms of isotactic polypropylene as a tool to test the degree of segregation of defects in the polymer chains MACROMOLECULES De Rosa, C., Auriemma, F., Circelli, T., Waymouth, R. M. 2002; 35 (9): 3622-3629

  View details for DOI 10.1021/ma0116248

  View details for Web of Science ID 000175112100045

• Models for conformationally dynamic metallocenes. Copolymerization behavior of the unbridged metallocene (1-methyl-2-phenylindenyl)(2-phenylindenyl)zirconium dichloride MACROMOLECULES Dankova, M., Kravchenko, R. L., Cole, A. P., Waymouth, R. M. 2002; 35 (8): 2882-2891

  View details for DOI 10.1021/ma011486m

  View details for Web of Science ID 000174818600007

• Morphology of thermoplastic elastomers: Elastomeric polypropylene MACROMOLECULES Schonherr, H., Wiyatno, W., Pople, J., Frank, C. W., Fuller, G. G., Gast, A. P., Waymouth, R. M. 2002; 35 (7): 2654-2666

  View details for DOI 10.1021/ma010959m

  View details for Web of Science ID 000174559600037

• Copolymerization behavior of unbridged indenyl metallocenes: Substituent effects on the degree of comonomer incorporation MACROMOLECULES Reybuck, S. E., Meyer, A., Waymouth, R. M. 2002; 35 (3): 637-643

  View details for DOI 10.1021/ma011517d

  View details for Web of Science ID 000173478200011

• Polymer synthesis - Catalysts rise to the challenge SCIENCE Gomez, F. J., Waymouth, R. M. 2002; 295 (5555): 635-636

  View details for Web of Science ID 000173560900028

  View details for PubMedID 11809956

• Synthesis and molecular structure of titanium complexes containing a reduced TEMPO radical CHEMICAL COMMUNICATIONS Mahanthappa, M. K., Huang, K. W., Cole, A. P., Waymouth, R. M. 2002: 502-503

  Abstract

  Two titanium compounds containing monoanionic ligands derived from TEMPO were synthesized and structurally characterized, demonstrating the flexibility of the coordination modes adopted by the ligand.

  View details for Web of Science ID 000174220200052

  View details for PubMedID 12120561

• Polystyrene-supported 2-arylindenyl zirconocene catalysts for propylene polymerization ISRAEL JOURNAL OF CHEMISTRY Diehl, S. C., Waymouth, R. M. 2002; 42 (4): 393-401

  View details for Web of Science ID 000184667600013

• Titanium-mediated syndiospecific styrene polymerizations: Role of oxidation state JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Mahanthappa, M. K., Waymouth, R. M. 2001; 123 (48): 12093-12094

  View details for DOI 10.1021/ja016521j

  View details for Web of Science ID 000172591000034

  View details for PubMedID 11724621

• Alternating copolymerization of ethylene and propylene: Evidence for selective chain transfer to ethylene MACROMOLECULES Fan, W., Waymouth, R. M. 2001; 34 (25): 8619-8625

  View details for Web of Science ID 000172414100008

• Alternating stereospecific copolymerization of ethylene and propylene with metallocene catalysts JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Fan, W., Leclerc, M. K., Waymouth, R. M. 2001; 123 (39): 9555-9563

  Abstract

  The copolymerization of ethylene and propylene with bridged metallocenes Me(2)E(3-RCp)(Flu)X(2)/MAO (E = C, X = Me; E = Si, X = Cl; R = H or alkyl) was investigated. Ethylene/propylene copolymerization with metallocenes having heterotopic active sites (R =Me, i-Pr) yield alternating, isotactic ethylene/propylene copolymers with percentages of alternating EPE+PEP triads in the range of 61-76% at 50% ethylene incorporation. Both the nature of the substituent R and the bridge E influence the copolymerization behavior including the copolymerization activity, copolymer sequence distribution, molecular weight, and stereochemistry. Silicon-bridged metallocenes produce copolymers with higher activity and molecular weight but lower propylene incorporation at similar feeds than the carbon-bridged analogues. Isotactic PEPEP sequences were observed for all metallocenes, while the tacticities of the EPPE sequences varied with the bridge and the substituent on the metallocene ligand. Isotactic PEPEP sequences and atactic EPPE sequence errors in the alternating copolymers are consistent with a mechanism where the comonomers are enchained alternately at the heterotopic coordination sites of the metallocenes. Isotactic EPPE sequences are indicative of occasional multiple insertions at the stereospecific site, caused by an isomerization of the chain prior to monomer insertion (backskip).

  View details for DOI 10.1021/ja0100773

  View details for Web of Science ID 000171407800007

  View details for PubMedID 11572675

• Rheo-optics and X-ray Scattering study of elastomeric polypropylene. Wiyatno, W., Pople, J. A., Gast, A. P., Waymouth, R., Fuller, G. G. AMER CHEMICAL SOC. 2001: U365–U365

  View details for Web of Science ID 000170690102037

• Chain end functionalization in nitroxide-mediated "Living" free radical polymerizations MACROMOLECULES Harth, E., Hawker, C. J., Fan, W., Waymouth, R. M. 2001; 34 (12): 3856-3862

  View details for DOI 10.1021/ma0019297

  View details for Web of Science ID 000169049000011

• Syndiospecific propylene polymerization with C-1 symmetric group 4 ansa-metallocene catalysts MACROMOLECULES LEINO, R., Gomez, F. J., Cole, A. P., Waymouth, R. M. 2001; 34 (7): 2072-2082

  View details for Web of Science ID 000167615600008

• Kinetics of propylene polymerization using bis(2-phenylindenyl)zirconium dichloride/methylaluminoxane JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Lin, S., Tagge, C. D., Waymouth, R. M., Nele, M., Collins, S., PINTO, J. C. 2000; 122 (46): 11275-11285

  View details for DOI 10.1021/ja002003h

  View details for Web of Science ID 000165600300001

• Two-state models for olefin polymerization using metallocene catalysts. 1. Application to fluxional metallocene catalyst systems MACROMOLECULES Nele, M., Collins, S., Dias, M. L., PINTO, J. C., Lin, S., Waymouth, R. M. 2000; 33 (20): 7249-7260

  View details for DOI 10.1021/ma000401z

  View details for Web of Science ID 000089735800009

• Ethylene and hydrogen effects in propylene polymerization with 2-arylindenyl zirconocenes International Zamaraev Conference on Physical Methods for Catalytic Research at the Molecular Level Lin, S., Kravchenko, R., Waymouth, R. M. ELSEVIER SCIENCE BV. 2000: 423–27

  View details for Web of Science ID 000089201200060

• Ring-opening reactions of oxabicyclic alkene compounds: enantioselective hydride and ethyl additions catalyzed by group 4 metals The Journal of organic chemistry Millward, D. B., Sammis, G., Waymouth, R. M. 2000; 65 (13): 3902-9

  Abstract

  Titanium and zirconium catalysts selectively catalyze either the ethyl or hydride addition to [2.2.1] 4, 5-bis(methoxymethyl)-7-oxabicycloheptene (6); the ring-opened products formed depend on catalyst, temperature, alkylaluminum reagent, and the concentration of alkylaluminum. Bis(neoisomenthylindenyl)zirconium dichloride catalyzes the ethyl addition ring-opening of 6 to produce (1R,2S,3S,6R)-2, 3-bis(methoxymethyl)-6-ethylcyclohex-4-enol (7) in 96% ee. Zirconium catalysts catalyze the ring-opening of [3.2.1] 2, 4-dimethyl-3-(benzyloxy)-8-oxabicyclo-6-octene (7) when ethylmagnesium bromide is used as a reagent. Both hydride and ethyl addition products are obtained at all conditions studied. Bis(neoisomenthylindenyl)zirconium dichloride catalyzes the ethyl addition ring-opening of 7 to produce (1S,2R,3S,4S,7S)-2, 4-dimethyl-3-(benzyloxy)-7-ethyl-5-cyclohexen-1-ol (8) in 48% ee.

  View details for PubMedID 10866606

• Ring-opening reactions of oxabicyclic alkene compounds: enantioselective hydride and ethyl additions catalyzed by group 4 metals JOURNAL OF ORGANIC CHEMISTRY Millward, D. B., Sammis, G., Waymouth, R. M. 2000; 65 (13): 3902-3909

  View details for DOI 10.1021/jo991429f

  View details for Web of Science ID 000087925800003

• Catalytic carboalumination of olefins with cyclopentadienylamidotitanium dichloride complexes ORGANOMETALLICS Millward, D. B., Cole, A. P., Waymouth, R. M. 2000; 19 (10): 1870-1878

  View details for Web of Science ID 000087021000013

• Accurate structural control and block formation in the living polymerization of 1,3-dienes by nitroxide-mediated procedures MACROMOLECULES Benoit, D., Harth, E., Fox, P., Waymouth, R. M., Hawker, C. J. 2000; 33 (2): 363-370

  View details for Web of Science ID 000085021800030

• Olefin polymerization with Me4Cp-amido complexes with electron-withdrawing groups US-Japan Seminar on Polymer Synthesis Kamigaito, M., Lal, T. K., Waymouth, R. M. WILEY-BLACKWELL. 2000: 4649–4660

  View details for Web of Science ID 000165713600005

• Regioirregular propene insertion in polypropenes synthesized with unbridged bis(2-aryl)indenyl zirconium dichloride catalysts: Implications on activity MACROMOLECULES Lin, S., Waymouth, R. M. 1999; 32 (25): 8283-8290

  View details for Web of Science ID 000084329300007

• Component relaxation processes within elastomeric polypropylene MACROMOLECULES Carlson, E. D., Fuller, G. G., Waymouth, R. M. 1999; 32 (24): 8100-8106

  View details for Web of Science ID 000084020000021

• Influence of trialkylaluminum reagents on the propylene polymerization behavior of bridged and unbridged 2-arylindene metallocene polymerization catalysts MACROMOLECULES Petoff, J. L., Myers, C. L., Waymouth, R. M. 1999; 32 (24): 7984-7989

  View details for Web of Science ID 000084020000004

• Transient birefringence of elastomeric polypropylene subjected to step shear strain MACROMOLECULES Carlson, E. D., Fuller, G. G., Waymouth, R. M. 1999; 32 (24): 8094-8099

  View details for Web of Science ID 000084020000020

• Synthesis of unbridged bis(2-R-indenyl)zirconocenes containing functional groups and investigations in propylene polymerization ORGANOMETALLICS Witte, P., Lal, T. K., Waymouth, R. M. 1999; 18 (20): 4147-4155

  View details for Web of Science ID 000083033500031

• Elastomeric polypropylenes from unbridged 2-phenylindene zirconocene catalysts: Temperature dependence of crystallinity and relaxation properties MACROMOLECULES Hu, Y. R., Carlson, E. D., Fuller, G. G., Waymouth, R. M. 1999; 32 (10): 3334-3340

  View details for Web of Science ID 000080441900021

• Ethylene norbornene copolymerizations with titanium CpA catalysts MACROMOLECULES McKnight, A. L., Waymouth, R. M. 1999; 32 (9): 2816-2825

  View details for Web of Science ID 000080179200002

• Mixed ligand metallocenes as catalysts for elastomeric polypropylene ORGANOMETALLICS Tagge, C. D., Kravchenko, R. L., Lal, T. K., Waymouth, R. M. 1999; 18 (3): 380-388

  View details for Web of Science ID 000078873600014

• Metallocene/borate-catalyzed copolymerization of 5-N,N-diisopropylamino-1-pentene with 1-hexene or 4-methyl-1-pentene MACROMOLECULES Stehling, U. M., Stein, K. M., Fischer, D., Waymouth, R. M. 1999; 32 (1): 14-20

  View details for Web of Science ID 000078475700003

• Steric and electronic effects of R in (2-(4-R-C6H4)indenyl)(2)ZrCl2 catalysts on the synthesis of elastomeric polypropylene JOURNAL OF MOLECULAR CATALYSIS A-CHEMICAL Lin, S., Hauptman, E., Lal, T. K., Waymouth, R. M., Quan, R. W., Ernst, A. B. 1998; 136 (1): 23-33

  View details for Web of Science ID 000076817300003

• Elastomeric polypropylene from unbridged 2-arylindenyl zirconocenes: Modeling polymerization behavior using ansa-metallocene analogues JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Petoff, J. L., Agoston, T., Lal, T. K., Waymouth, R. M. 1998; 120 (44): 11316-11322

  View details for Web of Science ID 000076987100013

• Group 4 ansa-Cyclopentadienyl-Amido Catalysts for Olefin Polymerization. Chemical reviews McKnight, A. L., Waymouth, R. M. 1998; 98 (7): 2587-2598

  View details for PubMedID 11848972

• Group 4 ansa-cyclopentadienyl-amido catalysts for olefin polymerization CHEMICAL REVIEWS McKnight, A. L., Waymouth, R. M. 1998; 98 (7): 2587-2598

  View details for Web of Science ID 000076981900006

• Elastomeric polypropylenes from unbridged (2-phenylindene)zirconocene catalysts: Thermal characterization and mechanical properties MACROMOLECULES Hu, Y. R., Krejchi, M. T., Shah, C. D., Myers, C. L., Waymouth, R. M. 1998; 31 (20): 6908-6916

  View details for Web of Science ID 000076389300024

• Rheological and thermal properties of elastomeric polypropylene MACROMOLECULES Carlson, E. D., Krejchi, M. T., Shah, C. D., Terakawa, T., Waymouth, R. M., Fuller, G. G. 1998; 31 (16): 5343-5351

  View details for Web of Science ID 000075347600020

• Synthesis of poly(olefin) graft copolymers by a combination of metallocene and "living" free radical polymerization techniques MACROMOLECULES Stehling, U. M., Malmstrom, E. E., Waymouth, R. M., Hawker, C. J. 1998; 31 (13): 4396-4398

  View details for Web of Science ID 000074627400050

• Statistical analysis and simulation of pentad distributions of stereoblock polypropylenes MACROMOLECULES BRUCE, M. D., Waymouth, R. M. 1998; 31 (9): 2707-2715

  View details for Web of Science ID 000073516300001

• Alternating ethene/propene copolymerization with a metallocene catalyst ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Leclerc, M. K., Waymouth, R. M. 1998; 37 (7): 922-925

  Abstract

  A small variation in the substituent R' on the metallocene catalyst employed in the copolymerization of ethene and propene leads to a highly alternating (81-83%) structure (1) rather than a statistical copolymer. Such copolymers were until recently only accessible by hydrogenation of polyisoprene or 1,4-poly(pentadiene).

  View details for Web of Science ID 000073339000010

• Metallocene/borate-catalyzed polymerization of amino-functionalized alpha-olefins MACROMOLECULES Stehling, U. M., Stein, K. M., Kesti, M. R., Waymouth, R. M. 1998; 31 (7): 2019-2027

  View details for Web of Science ID 000073079100001

• Strategies for synthesis of elastomeric polypropylene: Fluxional metallocenes with C-1-symmetry JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Kravchenko, R., Masood, A., Waymouth, R. M., Myers, C. L. 1998; 120 (9): 2039-2046

  View details for Web of Science ID 000072499100010

• Ethylene-propylene copolymerization with 2-arylindene zirconocenes MACROMOLECULES Kravchenko, R., Waymouth, R. M. 1998; 31 (1): 1-6

  View details for Web of Science ID 000071556500001

• Propylene polymerization with unbridged metallocenes: Ligand effects on the selectivity for elastomeric polypropylene ORGANOMETALLICS Petoff, J. L., BRUCE, M. D., Waymouth, R. M., Masood, A., Lal, T. K., Quan, R. W., Behrend, S. J. 1997; 16 (26): 5909-5916

  View details for Web of Science ID 000071423300049

• Effect of metal on the stereospecificity of 2-arylindene catalysts for elastomeric polypropylene JOURNAL OF THE AMERICAN CHEMICAL SOCIETY BRUCE, M. D., COATES, G. W., Hauptman, E., Waymouth, R. M., Ziller, J. W. 1997; 119 (46): 11174-11182

  View details for Web of Science ID A1997YG90100005

• Propylene polymerization with chiral and achiral unbridged 2-arylindene metallocenes ORGANOMETALLICS Kravchenko, R., Masood, A., Waymouth, R. M. 1997; 16 (16): 3635-3639

  View details for Web of Science ID A1997XP42600015

• Selectivity in propylene polymerization with group 4 Cp-amido catalysts ORGANOMETALLICS McKnight, A. L., Masood, M. A., Waymouth, R. M., Straus, D. A. 1997; 16 (13): 2879-2885

  View details for Web of Science ID A1997XG56200019

• The effect of ligand structure on the polymerization behavior of unbridged metallocenes Petoff, J. L., BRUCE, M. D., Waymouth, R. M., Masood, A. AMER CHEMICAL SOC. 1997: 156-INOR

  View details for Web of Science ID A1997WP18700322

• Zirconocene-mediated cyclization of 2-bromo alpha,omega-dienes ORGANOMETALLICS Millward, D. B., Waymouth, R. M. 1997; 16 (6): 1153-1158

  View details for Web of Science ID A1997WN91700012

• Homo-, co- and terpolymerization of 1,5-hexadiene using a methylalumoxane activated mono-Cp-amido-complex POLYMER BULLETIN Sernetz, F. G., Mulhaupt, R., Waymouth, R. M. 1997; 38 (2): 141-148

  View details for Web of Science ID A1997WF93800004

• Pd2+-catalyzed cyclocopolymerization of 1,5-hexadiene and CO: Regioselectivity of olefin insertion MACROMOLECULES BORKOWSKY, S. L., Waymouth, R. M. 1996; 29 (20): 6377-6382

  View details for Web of Science ID A1996VJ53100003

• Effect of metal in the production of elastomeric polypropylene BRUCE, M. D., COATES, G. W., Waymouth, R. M. AMER CHEMICAL SOC. 1996: 88-INOR

  View details for Web of Science ID A1996VA91502209

• Temporal chirality: Dynamic stereocontrol in the polymerization of propylene Coates, G., Hauptman, E., Bruce, M., Waymouth, R. AMER CHEMICAL SOC. 1996: 234-POLY

  View details for Web of Science ID A1996VB00901087

• Influence of polymerization conditions on the copolymerization of styrene with ethylene using Me(2)Si(Me(4)Cp)(N-tert-butyl)TiCl2 methylaluminoxane Ziegler-Natta catalysts MACROMOLECULAR CHEMISTRY AND PHYSICS Sernetz, F. G., Mulhaupt, R., Waymouth, R. M. 1996; 197 (3): 1071-1083

  View details for Web of Science ID A1996UC64600025

• Polymer synthesis and stereochemistry with transition metal catalysts NATO Advanced Study Institute on Chemical Synthesis - Gnosis to Prognosis Waymouth, R., COATES, G. W., Ciardelli, F., Carlini, C., Altomare, A. KLUWER ACADEMIC PUBL. 1996: 453–473

  View details for Web of Science ID A1996BG02W00020

• METALLOCENE CATALYSTS FOR STEREOSELECTIVE POLYMERIZATION Coates, G., MOGSTAD, A. L., Hauptman, E., Bruce, M., KREJCHE, M., Kravchenko, R., Waymouth, R. AMER CHEMICAL SOC. 1995: 167-ORGN

  View details for Web of Science ID A1995RP25900515

• STEREOSPECIFIC OLEFIN POLYMERIZATION WITH CHIRAL METALLOCENE CATALYSTS ANGEWANDTE CHEMIE-INTERNATIONAL EDITION IN ENGLISH Brintzinger, H. H., Fischer, D., Mulhaupt, R., Rieger, B., Waymouth, R. M. 1995; 34 (11): 1143-1170

  View details for Web of Science ID A1995RF70200001

• OSCILLATING CATALYSTS FOR PROPYLENE POLYMERIZATION Coates, G., MOGSTAD, A. L., Hauptman, E., Bruce, M., Waymouth, R. AMER CHEMICAL SOC. 1995: 191-POLY

  View details for Web of Science ID A1995QP23301327

• ENVIRONMENTALLY BENIGN POLYMER SYNTHESIS - POLYSILANE PHOTORESISTS Hsiao, Y. L., Waymouth, R. M., Beach, J. V., Loy, D. A. AMER CHEMICAL SOC. 1995: 127-ORGN

  View details for Web of Science ID A1995QP23300246

• ENVIRONMENTALLY FRIENDLY POLYSILANES - AN ALTERNATIVE ROUTE TO POLYSILANE PHOTORESISTS Beach, J. V., Loy, D. A., Hsiao, Y. L., Waymouth, R. M. AMER CHEMICAL SOC. 1995: 121-PMSE

  View details for Web of Science ID A1995QP23301647

• CONSTRUCTING CYCLICS FROM SIMPLE OLEFINS CHEMTECH WAYMOUTH, R. H., Knight, K. S. 1995; 25 (4): 15-21

  View details for Web of Science ID A1995QU89200008

• THERMAL AND STRUCTURAL CHARACTERIZATION OF POLY(METHYLENE-1,3-CYCLOPENTANE) SAMPLES OF DIFFERENT MICROSTRUCTURES MACROMOLECULES DEBALLESTEROS, O. R., Venditto, V., Auriemma, F., Guerra, G., RESCONI, L., Waymouth, R., MOGSTAD, A. L. 1995; 28 (7): 2383-2388

  View details for Web of Science ID A1995QQ03800036

• OSCILLATING STEREOCONTROL - A STRATEGY FOR THE SYNTHESIS OF THERMOPLASTIC ELASTOMERIC POLYPROPYLENE SCIENCE COATES, G. W., Waymouth, R. M. 1995; 267 (5195): 217-219

  Abstract

  A strategy has been developed for the synthesis of thermoplastic elastomeric polypropylene based on the catalytic activity of the unbridged metallocene bis(2-phenylindenyl)zirconium dichloride [(2-PhInd)(2)ZrCl(2)]. This catalyst was designed to isomerize between achiral and chiral coordination geometries during the polymerization reaction to produce atactic-isotactic stereoblock polymers. The metallocene precursor (2-PhInd)(2)ZrCl(2) in the presence of methylaluminoxane polymerizes propylene to yield rubbery polypropylene. The isotacticity of the polymer, described by the isotactic pentad content, increases with increasing propylene pressure and decreasing polymerization temperature to produce polypropylenes with an isotactic pentad content ranging from 6.3 to 28.1 percent.

  View details for Web of Science ID A1995QB15300028

  View details for PubMedID 17791342

• Environmentally friendly polysilane photoresists Symposium on Microelectronics Technology - Polymers for Advanced Imaging and Packaging, at the 209th National Meeting of the American-Chemical-Society Beach, J. V., Loy, D. A., Hsiao, Y. L., Waymouth, R. M. AMER CHEMICAL SOC. 1995: 355–366

  View details for Web of Science ID A1995BE45Z00023

• FREE-RADICAL HYDROSILYLATION OF POLY(PHENYLSILANE) - SYNTHESIS OF FUNCTIONAL POLYSILANES JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Hsiao, Y. L., Waymouth, R. M. 1994; 116 (21): 9779-9780

  View details for Web of Science ID A1994PN45200065

• A NEW ROUTE TO FUNCTIONALIZED POLY(PHENYLSILANES) Hsiao, Y. L., Waymouth, R. M. AMER CHEMICAL SOC. 1994: 52-INOR

  View details for Web of Science ID A1994MY95402813

• SYNTHESIS OF CONTROLLED POLYMER STRUCTURES USING TRANSITION-METAL CATALYSTS Coates, G., MOGSTAD, A. L., Bruce, M., Stein, K., BORKOWSKY, S., Waymouth, R. AMER CHEMICAL SOC. 1994: 125-ORGN

  View details for Web of Science ID A1994MY95500202

• SYNTHESIS OF FUNCTIONALIZED POLYOLEFINS USING GROUP-4 METALLOCENE CATALYSTS Coates, G., Stein, K., Fischer, D., Waymouth, R. AMER CHEMICAL SOC. 1994: 271-INOR

  View details for Web of Science ID A1994MY95403032

• MECHANISM AND STEREOCHEMISTRY OF THE ZIRCONOCENE-CATALYZED CYCLOMAGNESIATION OF DIENES JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Knight, K. S., Wang, D., Waymouth, R. M., Ziller, J. 1994; 116 (5): 1845-1854

  View details for Web of Science ID A1994NB16900028

• SUBSTITUENT EFFECTS ON UV ABSORPTION OF SIGMA-CONJUGATED POLYSILANES Symposium on Inorganic and Organometallic Polymers II - Advanced Materials and Intermediates, at the 205th National Meeting of the American-Chemical-Society Hsiao, Y. L., BANOVETZ, J. P., Waymouth, R. M. AMER CHEMICAL SOC. 1994: 55–63

  View details for Web of Science ID A1994BC69C00006

• FUNCTIONALIZATION OF POLY(PHENYL)SILANE BANOVETZ, J. P., Hsiao, Y. L., Waymouth, R. M. AMER CHEMICAL SOC. 1993: 161-POLY

  View details for Web of Science ID A1993KQ98301011

• SELECTIVE FREE-RADICAL HALOGENATION OF POLYPHENYLSILANE JOURNAL OF THE AMERICAN CHEMICAL SOCIETY BANOVETZ, J. P., Hsiao, Y. L., Waymouth, R. M. 1993; 115 (6): 2540-2541

  View details for Web of Science ID A1993KU90200077

• MODEL CATALYTIC SITES FOR OLEFIN POLYMERIZATION AND DIASTEREOSELECTIVITY IN THE CYCLOPOLYMERIZATION OF 1,5-HEXADIENE MACROMOLECULES Cavallo, L., Guerra, G., Corradini, P., RESCONI, L., Waymouth, R. M. 1993; 26 (2): 260-267

  View details for Web of Science ID A1993KH57900003

• CRYSTAL-STRUCTURES OF (ETA-5-C5ME5)(ETA-5-2,4-C7H11)CR AND (ETA-5-C5ME5)-(ETA-5-2,4-C7H11)CRCO - AN EXAMPLE OF S 2,4-DIMETHYLPENTADIENYL LIGAND GEOMETRY INORGANICA CHIMICA ACTA BOVINO, S. C., COATES, G. W., BANOVETZ, J. P., Waymouth, R. M., Straus, D. A., Ziller, J. W. 1993; 203 (2): 179-183

  View details for Web of Science ID A1993KL42200007

• ENANTIOSELECTIVE CYCLOPOLYMERIZATION OF 1,5-HEXADIENE CATALYZED BY CHIRAL ZIRCONOCENES - A NOVEL STRATEGY FOR THE SYNTHESIS OF OPTICALLY-ACTIVE POLYMERS WITH CHIRALITY IN THE MAIN CHAIN JOURNAL OF THE AMERICAN CHEMICAL SOCIETY COATES, G. W., Waymouth, R. M. 1993; 115 (1): 91-98

  View details for Web of Science ID A1993KG95400014

• STEREOSELECTIVE CYCLOMAGNESIATION OF 1,6-HEPTADIENES CATALYZED BY ZIRCONOCENES - EFFECTS OF SUBSTITUENTS, SOLVENT AND MAGNESIUM REAGENTS TETRAHEDRON LETTERS WISCHMEYER, U., Knight, K. S., Waymouth, R. M. 1992; 33 (50): 7735-7738

  View details for Web of Science ID A1992KB18200031

• CHIRAL POLYMERS VIA CYCLOPOLYMERIZATION 9TH INTERNATIONAL SYMP ON OLEFIN METATHESIS COATES, G. W., Waymouth, R. M. ELSEVIER SCIENCE BV. 1992: 189–94

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