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Molecular catalysts built from earth-abundant metals for hydrogen evolution reaction (HER) often struggle to combine high activity, extended lifetimes, and well-defined mechanisms. We reported three nickel (II) complexes, dmit (Py′) 2NiX2 (where X is Cl (1), Br (2), and NCS (3), while dmit (Py′) 2 is 4, 5-bis ( (3, 4-dimethoxypyridin-2-yl) methylthio) -1, 3-dithiole-2-thione), that share an S2N2 ligand framework integrating proton-relaying pyridyl groups into the redox-active dmit backbone. X-ray crystallography confirmed a distorted octahedral geometry at nickel. These complexes catalyzed proton reduction with overpotentials (η) of 0. 67–0. 79 V in 53. 80 mM trifluoroacetic acid (TFA), as determined by cyclic voltammetry. Controlled potential electrolysis (CPE) of complex 2 for 8 h achieved a turnover number (TON) of 16. 8 with 85. 61% Faradaic efficiency. An inverse kinetic isotope effect (KIE = 0. 70–0. 74) suggested the formation of Ni–H intermediates, while DFT calculations supported a ligand-assisted, metal-centered ECEC mechanism. UV–vis monitoring, postelectrolysis voltammetry, and SEM imaging all pointed to homogeneous catalysis and robust complex stability. These results demonstrate that embedding both proton-shuttling sites and redox noninnocence within the ligand structure enables the development of high-performance HER catalysts, providing a rational design framework for bioinspired catalysts.
Zheng et al. (Thu,) studied this question.