Heteroleptic dmit nickel complexes with bis(diphenylphosphanyl)amine ligands as robust molecular electrocatalysts for hydrogen evolution.

Four new neutral heteroleptic dmit nickel complexes bearing bis(diphenylphosphanyl)amine ligands, [RN (PPh2)2Ni(dmit)] (where dmit2− = 1,3‐dithiole‐2‐thione‐4,5‐dithiolate; R = (CH2)4CH3 [1], (CH2)3OCH3 [2], (CH2)2CH(CH3)2 [3], and CHPhCH3 [4]), have been synthesized in moderated yields by the reactions between (n‐Bu)2Sn(dmit) and RN (PPh2)2NiCl2 at room temperature. The complexes were fully characterized by elemental analysis, spectroscopy (Fourier transform infrared [FTIR], ultraviolet–visible [UV–vis], 1H, 13C{1H}, and 31P{1H} nuclear magnetic resonance [NMR]), thermogravimetric analysis, and single crystal X‐ray diffraction. In the crystal structures of 1–3 and 4·2CH2Cl2, every nickel atom adopts a slightly distorted square‐planar coordination by two phosphorus atoms of the RN (PPh2)2 ligand and two sulfur atoms of the dmit ligand. Furthermore, the electrochemical behaviors and electrocatalytic activities of 1–4 for hydrogen evolution have also been investigated by the cyclic voltammetry using trifluoroacetic acid (TFA) as the proton source. With the addition of 120‐mM trifluoroacetic acid to 0.5‐mM 1–4 in MeCN, the turnover frequency values of these catalysts were estimated to be 2827–5149 s−1, and the relevant overpotentials were 0.72–0.79 V. Density functional theory (DFT) calculations and electrochemical investigations suggest that H2 production proceeds via a key hydride intermediate [NiH (SH)] with an adjacent protonated sulfur atom of the dmit ligand in which the chelating sulfur atoms serve as proton relays. These findings demonstrate that these heteroleptic dmit nickel complexes could serve as robust and effective molecular electrocatalysts for hydrogen evolution. [ABSTRACT FROM AUTHOR]