Mononuclear Nickel(III) and Nickel(II) 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 νSH 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 IR studies and was quantitatively removed
by Lewis base Et3N to yield Ni(II) dimer [NiII(P(o-C6H4S)3)]22- (5). Instead of the ligand-based oxidation to
form dinuclear Ni(II) 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 [NiIII(ER)(P(o-C6H4S)3)]- (ER = SePh (3), 2-S−C4H3S (4)) accompanied by byproduct H2O identified by 1H NMR,
respectively. The 4.2 K EPR 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(III) with the odd electron in the dz2 orbital. Complex
3 undergoes a reversible NiIII/II process at E1/2 = −0.67 V vs Ag/AgCl in MeCN.

单核扭曲的方形平面[NiII(ER)(P(o-C6H4S)2(o-C6H4SH))]-(ER = SePh(1), 2-S−C4H3S(2))，其中S−H质子直接与镍和硫原子相互作用，通过[Ni(CO)(SePh)3]-/[Ni(CO)(2-S−C4H3S)3]-与P(o-C6H4SH)3的单体反应制备。通过观察红外νSH伸缩振动带（对于复合物1和2分别为2273和2283 cm-1，KBr），以及1H NMR光谱（δ 8.079 (d) (CD2Cl2) 和 8.39 (d) (C4D8O) ppm，−SH）在固态中验证了分子内[Ni−S···H−SR]/[Ni···H−SR]相互作用的组合存在，并随后通过X射线衍射研究得到确认。复合物1和2中的外硫醇质子(o-C6H4SH)通过NMR和IR研究被确认为D2O可交换质子，并由路易斯碱Et3N定量去除，从而得到Ni(II)二聚体[NiII(P(o-C6H4S)3)]22- (5)。不同于通过配体氧化形成二核Ni(II)复合物和二硫化物，复合物1和2的THF−CH3CN溶液在O2的作用下氧化，产生了单核扭曲的三角双锥[NiIII(ER)(P(o-C6H4S)3)]- (ER = SePh(3), 2-S−C4H3S(4))，伴随产物H2O的生成，该产物通过1H NMR识别。复合物3和4在4.2 K下的EPR光谱表现出高菱形性，具有三个主g值2.304、2.091和2.0，与Ni(III)的奇电子在dz2轨道上相一致。复合物3在MeCN中经历了一个可逆的NiIII/II过程，半波电位E1/2为−0.67 V vs Ag/AgCl。