Fast and Versatile Functionalization of Glassy Carbon.
Langmuir : the ACS journal of surfaces and colloids
A rapid procedure for the functionalization of glassy carbon surfaces (GCSs) is disclosed. A three-step sequence of bromomethylation, azide displacement, and copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) allows ethynylated molecules to be attached covalently to the carbon surface through a methylene functional group. Redox-active ethynyl ferrocene and [RuII(Cl)(DMSO)(ethynyl-TPA)]1+ (DMSO = dimethylsulfoxide; TPA = tris(2-pyridylmethyl)amine) are attached with high coverages as assessed by cyclic voltammetry, and the elemental composition of the surface is confirmed by X-ray photoelectron spectroscopy. In less than 1 h, surface coverages of 1 × 1014 molecules/cm2 are possible that exhibit good durability in both acidic and basic media. Attached [RuII(Cl)(DMSO)(ethynyl-TPA)]1+ catalytically oxidizes alcohols, yet the currents and potentials are less impressive compared to an attachment without the intervening methylene group. The advantages of this covalent attachment procedure for GCSs are its short reaction times, mild reaction conditions, and the use of standard laboratory reagents and glassware, allowing for many types of ethynylated molecules to be attached rapidly to the surface.
View details for DOI 10.1021/acs.langmuir.2c01964
View details for PubMedID 36326209
Phenolate-bonded bis(μ-oxido)-bis-copper(III) intermediates: hydroxylation and dehalogenation reactivities.
Exogenous phenolate ortho-hydroxylation by copper oxidants formed from dioxygen is generally thought to occur through one of two limiting mechanisms defined by the structure of the active oxidant: an electrophilic μ-η2:η2-peroxo-bis-copper(II) species as found in the oxygenated form of the binuclear copper enzyme tyrosinase (oxyTyr), or an isomeric bis(μ-oxido)-bis-copper(III) species (O) with ligated phenolate(s) as evidenced by most synthetic systems. The characterization of the latter is limited due to their limited thermal stability. This study expands the scope of an O species with ligated phenolate(s) using N,N'-di-tert-butyl-1,3-propanediamine (DBPD), a flexible secondary diamine ligand. Oxygenation of the [(DBPD)Cu(I)]1+ complex at low temperatures (e.g., 153 K) forms a spectroscopically and structurally faithful model to oxyTyr, a side-on peroxide intermediate, which reacts with added phenolates to form a bis(μ-oxido)-bis-copper(III) species with ligated phenolates, designated as an A species. The proposed stoichiometry of A is best understood as possessing 2 rather than 1 bonded phenolate. Thermal decomposition of A results in regiospecific phenolate ortho-hydroxylation with the ortho-substituent as either a C-H or C-X (Cl, Br) group, though the halogen displacement is significantly slower. DFT and experimental studies support an electrophilic attack of an oxide ligand into the π-system of a ligated phenolate. This study supports a hydroxylation mechanism in which O-O bond cleavage of the initially formed peroxide by phenolate ligation, which precedes phenolate aromatic hydroxylation.
View details for DOI 10.1039/d1fd00071c
View details for PubMedID 35156114
Electrocatalytic alcohol oxidation by covalently immobilized ruthenium complex on carbon.
Journal of inorganic biochemistry
2022; 231: 111784
A dearth of discrete immobilized metal complexes exist that electrocatalytically oxidize methanol. Reported here is the covalent immobilization of a tris(2-pyridylmethyl)amine ruthenium complex [RuII(Cl)(DMSO)(ethynyl-TPA)]+ (ethynyl-TPA = (5-ethynyl-2-pyridylmethyl)bis(2-pyridylmethyl)amine) to a glassy carbon (GC) electrode through a CuI catalyzed azide-alkyne cycloaddition (click) reaction between the ethynyl-TPA ligand and an azide derivatized carbon surface forming [RuII(Cl)(DMSO)(GC-click-TPA)]+. Following water substitution for DMSO and proton coupled electron transfer, [RuIV(O)(Cl)(GC-click-TPA)]+ electrooxidizes alcohols, including methanol, efficiently relative to other immobilized metal complexes. A primary kinetic isotope effect suggests rate-limiting Cα-H bond cleavage of benzyl alcohol. Approximately 40% of the [RuII(Cl)(DMSO)(GC-click-TPA)]+ undergoes the DMSO for water exchange to form an active oxidant, consistent with the 40% distribution of the more labile Cl-cis-amine isomer before immobilization. Using the benchmark of benzyl alcohol electrocatalytic oxidation, [RuIV(O)(Cl)(GC-click-TPA)]+ operates at ca. 250 mV lower overpotential, with a 15% increase in faradaic efficiency, and at least an order of magnitude increase in average turnover frequency (0.7 s-1 TOFavg) compared to the previously best immobilized discrete ruthenium complexes.
View details for DOI 10.1016/j.jinorgbio.2022.111784
View details for PubMedID 35298933