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

Abstract

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.