Hydride-Bridged Heteronuclear Complexes for Hydrogen Evolution: Electrocatalytic and Theoretical Studies

To investigate metal effects on electrocatalytic hydrogen evolution, a series of selenolate-bridged heterobimetallic hydride complexes were synthesized. Irradiation of [M2(CO)10] (M = Mn or Re) with NaSePh, followed by reaction with [Cp*IrCl2]2 or [Cp*CoCl]2, respectively, afforded trichalcogenate-bridged heterodinuclear complexes [{M(CO)3}(μ-SePh)3(M'Cp*)] (M = Mn, M' = Ir) (1) and (M = Re, M' = Co) (2). Subsequent treatment with LiBH4·THF yielded corresponding hydride-bridged heterobimetallic complexes [(CO)3M(μ-SePh)2(μ-H)(M'Cp*)] (M = Mn, M' = Ir) (3) and (M = Re, M' = Co) (4). Similarly, hydride complexes [(CO)3Mn(μ-ER)2(μ-H)(CoCp*)] (E = Se, R = naphthyl) (8), (E = Te, R = naphthyl) (9), and (E = Se, R = 4-dimethylaminophenyl) (10) were synthesized from the corresponding trichalcogenate complexes [(CO)3Mn(μ-ER)3(CoCp*)] (E = Se, R = naphthyl) (5), (E = Te, R = naphthyl) (6), and (E = Se, R = 4-dimethylaminophenyl) (V). The complexes were characterized by multinuclear NMR, IR spectroscopy, and single-crystal X-ray diffraction. Electrocatalytic hydrogen evolution by complexes 3, 4, and 8-10 using HBF4 was evaluated by cyclic voltammetry, spectroelectrochemistry, and Faradaic yield measurements. Cyclic voltammetry studies suggest higher activity of complex 3 compared to 4. DFT studies revealed that differences in electron density distribution modulate the metalloradical character, accounting for the observed catalytic performance.