Effects of metal centers of complexes supported by S,S-bis(2-pyridylmethyl)-1,2-thioethane on catalytic activities for electrochemical- and photochemical-driven hydrogen production

S,S '-bis(2-pyridylmethyl)-1,2-thioethane (bpte) reacts with MCl2 (M = Co, Ni, and Fe) to give three complexes, namely, [Co-II(bpte)Cl-2] (1), [Ni-II(bpte)Cl-2] (2), and [Fe-II(bpte)Cl-2] (3), respectively. They all act as catalysts for proton or water reduction to dihydrogen via electrolysis or photolysis. Under an overpotential of 837.6 mV, the electrolysis of a neutral buffer with complex 1, 2, or 3 can provide 418 (+/- 3), 555 (+/- 3), and 243 (+/- 3) moles of hydrogen per mole of catalyst per hour (mol H-2/mol catalyst/h), respectively. Under blue light, together with a photosensitizer and ascorbic acid (H(2)A) as a sacrificial electron donor, the photolysis of an aqueous solution (pH 4.5) containing complex 1, 2, or 3 can afford 9060 (+/- 5), 24,900 (+/- 5), and 10,630 (+/- 5) moles H-2 per mole of catalyst (mol of H-2 [mol of cat](-1)) during 83-h irradiation with an average apparent quantum yield of 7.1%, 24%, and 10%, respectively. The results show that the nickel complex [Ni-II(bpte)Cl-2] exhibits a more efficient activity for hydrogen generation than the iron or cobalt species. These findings may offer a new chemical paradigm for the design of efficient catalysts.