Inorg Chem. 2026 May 28. doi: 10.1021/acs.inorgchem.6c00959. Online ahead of print.
ABSTRACT
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’)2}NiX2] (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.
PMID:42206737 | DOI:10.1021/acs.inorgchem.6c00959