Electrocatalytic production of hydrogen gas by a cobalt formamidinate complex

Abstract

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 CoII to CoI. 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 MeCN 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, kobs, against acid concentration in the range of 0.065 to 10.02 s-1.