Terminal {Ni(II)-SH} complex promoted anaerobic catalytic sulfur atom transfer reaction: implication to the sulfide oxidase function of Cu/Zn-superoxide dismutase

In mitochondria, the detoxification of molar excess H₂S as polysulfide proceeded via an oxidation process promoted by Cu/Zn containing superoxide dismutase (SOD1) enzyme, which has been very recently reported as the alternative enzyme for cytosolic H₂S oxidation. Herein, we present Ni(II) complexes bearing the terminal SH group as a synthetic functional analogue for the sulfide oxidase function of SOD1. Synthesis, crystal structure and complete spectroscopic characterization of two sets of complexes, [NiL^OMe/(PPh₃)] (2OMe/tBu) and tetraethyl salt of [NiL^OMe/(SH)]^-1 (3OMe/tBu), were described (LOMe = (E)-2-methoxy-6-(((2-sulfidophenyl)imino)methyl)phenolate and LtBu = (E)-2,4-di-tert-butyl-6-(((2-sulfidophenyl)imino)methyl)phenolate). Under anaerobic conditions, 3OMe/tBu responded to a catalytic sulfur atom transfer (SAT) reaction with PPh₃ to produce SPPh₃. The SAT reaction was analyzed using detailed studies of ¹H and ³¹P NMR spectra. Finally, the SAT reactivity pattern was compared with the same in the native enzyme of SOD1.