Aromatic dithiolate nickel complexes bearing N-substituted bis(diphenylphosphanyl)amine: Synthesis, characterization, and electrocatalytic performance for hydrogen evolution

Abstract

Six aromatic dithiolate nickel complexes bearing N-substituted bis(diphenylphosphanyl)amine (RN(PPh2)2) ligands, [RN(PPh2)2Ni(bdt)] (bdt = 1,2-benzenedithiolate; R = (CH2)3OCH3 (1), (CH2)3SCH3 (2), CH(CH3)C6H5 (3)) and [RN(PPh2)2Ni(tdt)] (tdt = 3,4-toluenedithiolate; R = (CH2)3OCH3 (4), (CH2)3SCH3 (5), CH(CH3)C6H5 (6)), have been synthesized in moderated yields by condensations of RN(PPh2)2NiCl2 with 1,2-benzenedithiol or 3,4-toluenedithiol in the presence of Et3N at room temperature. All the complexes were fully characterized by elemental analysis, FTIR, NMR (1H, 13C, and 31P) spectroscopy, UV–Vis spectrum, and thermo-gravimetric analysis. The crystal structures of complexes 1, 2, 3, and 5 have been investigated by single crystal X-ray diffraction. The nickel atom adopts a slightly distorted square-planar coordination by two phosphorus atoms of RN(PPh2)2 and two sulfur atoms of aromatic dithiolate ligands in their structures. Furthermore, the electrochemical behaviors of complexes 1–6 and their catalytic activities for electrochemical hydrogen evolution in CH2Cl2 solution with trifluoroacetic acid (TFA) as a proton source have been studied by cyclic voltammetry.