title: Proton electroreduction catalyzed by cobaloximes: functional models for hydrogenases.
abstract: Cobaloximes have been examined as electrocatalysts for proton reduction in nonaqueous solvent in the presence of triethylammonium chloride. [Co(III)(dmgH)2pyCl], working at moderate potentials (-0.90 V/(Ag/AgCl/3 mol x L(-1) NaCl) and in neutral conditions, is a promising catalyst as compared to other first-row transition metal complexes which generally function at more negative potentials and/or at lower pH. More than 100 turnovers can be achieved during controlled-potential electrolysis without detectable degradation of the catalyst. Cyclic voltammograms simulation is consistent with a heterolytic catalytic mechanism and allowed us to extract related kinetic parameters. Introduction of an electron-donating (electron-withdrawing) substituent in the axial pyridine ligand significantly increases (decreases) the rate constant of the catalytic cycle determining step. This effect linearly correlates with the Hammet coefficients of the introduced substituents. The influence of the equatorial glyoxime ligand was also investigated and the capability of the stabilized BF2-bridged species [Co(dmgBF2)2(OH2)2] for electrocatalyzed hydrogen evolution confirmed.
authors.affiliation: Laboratoire de Chimie et Biochimie des Centres Rédox Biologiques, UMR 5047 CEA/CNRS/Université Joseph Fourier, CEA-Grenoble, DRDC/CB, Bat K', 17 rue des Martyrs, 38054 Grenoble Cedex 09, France.
authors.forename: Mathieu
authors.initials: M
authors.lastname: Razavet
authors.forename: Vincent
authors.initials: V
authors.lastname: Artero
authors.forename: Marc
authors.initials: M
authors.lastname: Fontecave
mesh_terms: D002244:Carbon / Q000737:chemistry; D002384:Catalysis; D003035:Cobalt / Q000737:chemistry* / Q000494:pharmacology; D003038:Cobamides / Q000737:chemistry* / Q000494:pharmacology; D004563:Electrochemistry; D004566:Electrodes; D004583:Electrons; D006863:Hydrogen-Ion Concentration; D006864:Hydrogenase / Q000737:chemistry* / Q000378:metabolism; D008024:Ligands; D008956:Models, Chemical; D009942:Organometallic Compounds / Q000737:chemistry* / Q000494:pharmacology; D010084:Oxidation-Reduction; D010091:Oximes / Q000737:chemistry* / Q000494:pharmacology; D011522:Protons; D011725:Pyridines / Q000737:chemistry; D000644:Quaternary Ammonium Compounds / Q000737:chemistry
chemical_list: D003038:Cobamides; D008024:Ligands; D009942:Organometallic Compounds; D010091:Oximes; D011522:Protons; D011725:Pyridines; D000644:Quaternary Ammonium Compounds; D003035:Cobalt; D002244:Carbon; D006864:Hydrogenase; C023666:pyridine