Synthesis, Characterization, and HER Activity of Pendant Diamine Derivatives of NiATSM

A pair of bis‐thiosemicarbazonato‐Ni(II) complexes with pendant polyamines, ( N , N′ ‐(dimethylethylenediaminothiosemi‐carbazonato)‐4‐(methylthiosemi‐carbazonato)butane‐2,3‐diimine)‐nickel(II) ( 1 ) and ( N , N′ ‐bis(dimethylethyl‐enediaminothiosemi‐carbazonato)butane‐2,3‐diimine)‐nickel(II) ( 3 ), have been synthesized. Methylation at the terminal amines yields the cationic derivatives 2 and 4 . All complexes are fully characterized by spectroscopic, electrochemical, and single‐crystal X‐ray diffraction methods. Single crystal X‐ray diffraction studies on all four Ni(II) complexes confirm a square planar Ni(II) framework with no significant changes in the coordination environment as a function of the pendant groups. Spectroscopic studies are consistent with a similar electronic structure in all complexes. However, electrochemical investigations reveal significant cathodic shifts in the Ni(II)L/Ni(II)L · – and Ni(II)L · – /Ni(I)L · 2– reduction potentials of the methylated vs. non‐methylated species. The HER activity of all four nickel complexes were evaluated in acetonitrile with glacial acetic acid. The 3 complex was shown to have the highest activity with a TOF of 6.3 × 10 3 s ‐1 , an overpotential of 0.56 V, and faradaic efficiency of 100 %.