Catalytic hydrogen evolution and hydrogen oxidation by cobalt macrocyclic glyoxime and tetra-imine complexes

Abstract

Cobalt complexes supported by diglyoxime ligands of the type Co(dmgBF_2)_2(CH_3CN)_2 and Co(dpgBF_2)_2(CH_3CN_2) (where dmgBF_2 is difluoroboryldimethylglyoxime and dpgBF_2 is difluoroboryldiphenylglyoxime), as well as cobalt complexes with1;143;-tetraene-N_4(Tim) ligands of the type 1;Co(Tim^R)X_23;^n+ (R = Me or Ph, X = Br or CH_3CN; n = 1 with X = Br and n = 3 with X = CH_3CN) have been obsd. to evolve H_2 electrocatalytically at potentials between -0.55 V and -0.20 V vs. SCE in CH_3CN. The potentials at which these cobalt complexes catalyzed H_2 evolution were close to the reported thermodn. potentials for the prodn. of H_2 from protons in CH_3CN, with the smallest overpotential being 40 mV for Co(dmgBF_2)_2(CH_3CN)_2. Consistent with these small overpotentials, some of the complexes were also able to oxidize H_2 in the presence of a suitable conjugate base.