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(PPh 2 ) 2 ) ligands, [RN(PPh 2 ) 2 Ni(bdt)] (bdt = 1,2-benzenedithiolate; R = (CH 2 ) 3 OCH 3 ( 1 ), (CH 2 ) 3 SCH 3 ( 2 ), CH(CH 3 )C 6 H 5 ( 3 )) and [RN(PPh 2 ) 2 Ni(tdt)] (tdt = 3,4-toluenedithiolate; R = (CH 2 ) 3 OCH 3 ( 4 ), (CH 2 ) 3 SCH 3 ( 5 ), CH(CH 3 )C 6 H 5 ( 6 )), have been synthesized in moderated yields by condensations of RN(PPh 2 ) 2 NiCl 2 with 1,2-benzenedithiol or 3,4-toluenedithiol in the presence of Et 3 N at room temperature. All the complexes were fully characterized by elemental analysis, FTIR, NMR ( 1 H, 13 C, and 31 P) 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(PPh 2 ) 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 CH 2 Cl 2 solution with trifluoroacetic acid (TFA) as a proton source have been studied by cyclic voltammetry.