Electrocatalytic production of hydrogen gas by a cobalt formamidin-ate complex

A molecular cobalt complex, Co(DippF)₂ (where DippF is the anion of N,N-bis[2,6-diisopropylphenyl]-formamidine), (1), is able to electrochemically produce hydrogen gas from the reduction of organic acids in homogeneous solutions. Compound 1 has a distorted square planar structure as evidenced through X-ray crystallography studies, and an effective magnetic moment of 4.13, obtained by the Evans method, that corresponds to three unpaired electrons. Compound 1 shows an irreversible cathodic peak at - 1.59 V vs Fc/Fc⁺ which is assigned to the reduction of Co^II to Co^I. In the presence of organic acids the onset of catalytic current is observed at -1.2 V, -1.45 V and -1.89 V vs Fc/Fc⁺ with p-toluenesulfonic acid, benzoic acid and phenol as the proton source, respectively, in Me CN as the solvent. Detection of hydrogen gas was obtained by GC-Ms with Faradaic efficiencies ranging from 85% to 100%. Kinetic studies using foot-of-the-wave analysis (FOWA) reveal a linear dependence of the observed rate constant, k_obs, against acid concentration in the range of 0.065 to 10.02 s^-1. (Author)