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.

Electrochemical reduction of Fe(2)(mu-pdt)(CO)(6) 1 (pdt = propane-1,3-dithiolate) leads initially to a short-lived species, 1-, then subsequently to two-electron reduced products, including a CO-bridged diiron compound, 1B. The assignment of the redox level of 1- is based on EPR and UV-vis spectra together with the observation that a CO-saturated solution of 1- decays to give 1 and 1B. Hydride reduction of 1 also results in formation of 1B via a relatively long-lived formyl species, 1(formyl). Despite its involvement in hydride transfer reactions, 1B is formulated as [Fe(2)(mu-S(CH(2))(3)SH)(mu-CO)(CO)(6)](-) based on a range of spectroscopic measurements together with the Fe-Fe separation of 2.527 A (EXAFS). Electrocatalytic proton reduction in the presence of 1 in moderately strong acids has been examined by electrochemical and spectroelectrochemical techniques. The acid concentration dependence of the voltammetry is modeled by a mechanism with two electron/proton additions leading to 1H(2), where dissociation of dihydrogen leads to recovery of 1. Further reduction processes are evident at higher acid concentrations. Whereas free CO improves the reversibility of the electrochemistry of 1, CO inhibits electrocatalytic proton reduction, and this occurs through side reactions involving a dimeric species formed from 1-.