Electrochemical and photochemical-driven hydrogen evolution catalyzed by a dinuclear cobalt(II)–triazenido complex with high turnover number

Abstract

In the presence of Et3N, the reaction of CoCl2·6H2O and 1-[(2-methoxy)benzene]-3-[benzothiazole]triazene (HL) provides a dinuclear cobalt(II) complex [Co2L4] 1, a molecular catalyst. 1 can electrocatalyze hydrogen evolution both from acetic acid and purely aqueous media (pH 7.0), with a turnover frequency (TOF) of 32.1 and 137 mol of hydrogen per mole of catalyst per hour at an overpotential of 942 mV and 789 mV, respectively. Sustained proton reduction catalysis occurs at glassy carbon (GC) to give H2 over a 40 h electrolysis period with 75% Faradaic yield and no observable decomposition of the catalyst. Photocatalytic experiments indicate that complex 1 in pH 4.0 aqueous solution under air, together with [Ru(bpy)3]Cl2 and ascorbic acid, in the presence of blue light (λmax = 469 nm) can produce hydrogen with a turnover number (TON) = 4367 mol of H2 (mol of cat)−1 under air, which is significantly larger than any other reported molecular cobalt catalysts for photochemical hydrogen production.