NiI/RuII Model for the Ni–L State of the [NiFe]Hydrogenases: Synthesis, Spectroscopy, and Reactivity
datasetposted on 21.04.2014, 00:00 by Geoffrey M. Chambers, Joyee Mitra, Thomas B. Rauchfuss, Matthias Stein
This study describes the characterization of a mixed-valence RuII/NiI complex, a structural model for the Ni–L state of the [NiFe]hydrogenases. One-electron oxidation of (cymene)Ru(μ-pdt)Ni(diphos) (0, diphos = dppe, C2H4(PPh2)2; 0, diphos = dcpe, C2H4(P(C6H11)2)2] affords the mixed-valence cations [(cymene)Ru(pdt)Ni(diphos)]+ (+ and +). Crystallographic and spectroscopic measurements indicate that these cations are described as RuII/NiI. Although 0 and + are very similar structurally, the following changes are notable: the Ni–P distances elongate upon oxidation, and the Ru–Ni distance changes insignificantly. The molecular and electronic structures of the Ni center in + approaches that observed in the [NiFe]hydrogenases. Density functional theory calculations indicate that 0 is best described as RuII/Ni0, consistent with its oxidation to RuII/NiI in +. The fast electron self-exchange rate of 107 M–1 s–1 between 0 and + suggests minor reorganization, more consistent with a Ni0/NiI oxidation state change than a NiI/NiII couple. In solution, + slowly converts to [H1]+ and [1-H]+, with the latter being a complex of the thioaldehyde SCHCH2CH2S arising from C–H activation of the pdt backbone. Treatment of + with the H-atom abstracting reagent 2,2,6,6-tetramethylpiperidine-1-oxy also gives [1-H]+.