Photocatalytic H2 generation based on noble-metal-free binuclear cobalt complexes using visible-light

Two new binuclear cobalt complexes, namely {[Co(dmgH)(dmgH(2))](2)L1} (I) and {[Co(dmgH)(dmgH(2))](2)L2} (II) (dmgH = dimethylglyoximate monoanion; dmgH(2) = dimethylglyoxime, L1 = 1,3-bis(4-pyridyl) propane), L2 = 1,3-bis(imidazol-1-ylmethyl) benzene), have been synthesized by the self-assembly of [Co(dmgH)(dmgH(2))] and L1 or L2, respectively. An efficient photocatalytic system was constructed by combining a noble-metal-free cobalt complex as the catalyst with Eosin Y dye (EY2-) as the photosensitizer to give an efficient H-2 generating system under visible-light irradiation (lambda > 420 nm) using triethanolamine (TEOA) as a sacrificial electron donor. The maximum amount of H-2 generated was 1013 TON for I and 1134 TON for II over a 2 h irradiation period (lambda > 420 nm) under the conditions of pH 8.0, 5% TEOA (v/v), an EY2- concentration of 4.0 x 10(-4) M and a catalyst concentration of 4.0 x 10(-4) M in the mixed solvent system of CH3CN-H2O (3 : 1, v/v). In addition, the mechanism of H-2 generation in the photolysis system was briefly discussed.