Impact Of Oxidation State Of Metal On Electro-Catalyzed Hydrogen Production By Cobalt Complexes Of N-Phenylpyridin-2-Ylmethanimine

N-phenylpyridin-2-ylmethanimine, L, reacts with CoCl2 center dot 6H(2)O to form a water soluble complex, [Co-III(L)(2)Cl-2]Cl, which has been determined by X-ray diffraction analysis. Electrochemical studies show that [Co-III(L)(2)Cl-2]Cl can serve as an electrocatalyst for water or proton reduction to hydrogen from neutral water (pH 7.0) or acetic acid with a turnover frequency (TOF) of 1032.4 and 70.3 moles of hydrogen per mole of catalyst per hour (mol H-2/mol catalyst/h) at an overpotential (OP) of 837.6 mV and 941.6 mV, respectively. Compared with the previously described cobalt(II) complex, [Co-II(L)(2)Br-2] (TOF: 875.17 mol H-2/mol catalyst/h at an OP of 837.6 mV), the cobalt(III) complex, [Co-III(L)(2)Cl-2]Cl exhibits more efficient activity for hydrogen evolution. This can be attributed to Co-III/Co-II and Co-II/Co-I couples of [Co-III(L)(2)Cl-2]Cl are responsible for hydrogen production.