Neutral heteroleptic nickel complexes incorporating maleonitriledithiolate and bis(diphenylphosphanyl)amine as robust molecular electrocatalysts for hydrogen evolution.

Five heteroleptic maleonitriledithiolate nickel complexes bearing bis(diphenyl-phosphanyl)amine ligands, RN(PPh 2) 2 Ni(mnt), have been synthesized and structurally characterized. The coordination geometry around the nickel atom is a slightly distorted square-planar configuration. All complexes can electrocatalyze reduction of protons to hydrogen in the presence of trifluoroacetic acid in MeCN. • The nickel atom in the crystal structure of the complexes adopts a slightly distorted square-planar coordination environment. • The complexes are stable under acidic and electrochemical conditions. • The complexes can be used as low-cost robust molecular eletrocatalysts for hydrogen evolution. • ECEC mechanism for electrocatalytic hydrogen evolution has been proposed. Five neutral heteroleptic maleonitriledithiolate nickel complexes [RN(PPh 2) 2 Ni(mnt)] bearing bis(diphenylphosphanyl)amine ligands (where mnt2− = maleonitriledithiolate; R = CH 3 O(CH 2) 3 (1), CH 3 S(CH 2) 3 (2), (S)-CH 3 CHPh (3), (CH 3) 2 CH(CH 2) 2 (4), and p- CH 3 C 6 H 4 (5)) have been synthesized and fully characterized by elemental analysis, FTIR, NMR (1H, 13C, and 31P) spectroscopy, UV–Vis spectrum, single crystal X-ray diffraction, thermogravimetric analysis, and density functional theory (DFT) calculation. The nickel atom in 1 , 2 , 4 , and 5 ⋅1.5CH 2 Cl 2 adopts a slightly distorted square-planar coordination environment with two phosphorus atoms of RN(PPh 2) 2 and two sulfur atoms of mnt2−, respectively, while the nickel atom in 3 exhibits a pseudo square pyramid with HP 2 S 2 chromophore. Furthermore, the electrochemical properties for 1 – 5 were also investigated by cyclic voltammetry. With the addition of 120 mM trifluoroacetic acid (TFA) to 1 – 5 in MeCN, the turnover frequency (TOF) values are estimated to be 368.59–585.17 s−1 with the corresponding overpotential (η) values of 0.59–0.73 V. The electrochemical studies indicate that all complexes can be used as low-cost robust molecular eletrocatalysts for the reduction protons to hydrogen in the presence of TFA and a possible ECEC mechanism for electrocatalytic hydrogen evolution has been also proposed. [ABSTRACT FROM AUTHOR]