Mononuclear Nickel(lll) and Nickel(ll) Thiolate Complexes with Intramolecular S -- H Proton Interacting with Both Sulfur and Nickel: Relevance to the [NiFe]/[NiFeSe] Hydrogenases.

Mononuclear, distorted square planar [NiII(ER)(P(o-C6H4S)2(o-C6H4SH))]- (ER = SePh (1), 2-S-- C4H3S (2)) with a S-H proton directly interacting with both nickel and sulfur atoms were prepared by reaction of [Ni(CO)(SePh)3]/[Ni(CO)(2-S-C4H3S)3] and P(o-C6H4SH)3, individually. The presence of combinations of intramolecular [Ni-S…H-SR]/[Ni…H-SR] interactions was verified in the solid state by the observation of an IR vSH stretching band (2273 and 2283 cm-1 (KBr) for complexes 1 and 2, individually) and ¹H NMR spectra (δ 8.079 (d) (CD2Cl2) and 8.39 (d) (C4D8O) ppm (-SH) for complexes 1 and 2, respectively) and subsequently confirmed by X-ray diffraction study. The exo-thiol proton (o-C6H4SH) in complexes 1 and 2 was identified as a D2O exchangeable proton from NMR and IA studies and was quantitatively removed by Lewis base Et3N to yield Ni(II) dimer [NiII(P(o-C6H4S)3)]62- (5). Instead of the ligand-based oxidation to form dinuclear Ni(Il) complexes and dichalcogenide, oxidation of THF-CH3CN solution of complexes 1 and 2 by O2 resulted in the formation of the mononuclear, distorted trigonal bipyramidal [NiII(ER)(P(o-C6H4S)3)y (ER = SePh (3), 2-S-C4H3S (4)) accompanied by byproduct H2O identified by ¹H NMR, respectively. The 4.2 K EPA spectra of complexes 3 and 4 exhibiting high rhombicities with three principal g values of 2.304, 2.091, and 2.0 are consonant with Ni(Ill) with the odd electron in the d22 orbital. Complex 3 undergoes a reversible NiIII/II process at E… = -0.67 V vs Ag/AgCl in MeCN. [ABSTRACT FROM AUTHOR]