NiI/RuII Model for the Ni鈥揕 State of the [NiFe]Hydrogenases: Synthesis, Spectroscopy, and Reactivity

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• 作者：Geoffrey M. Chambers ; Joyee Mitra ; Thomas B. Rauchfuss ; Matthias Stein
• 刊名：Inorganic Chemistry
• 出版年：2014
• 出版时间：April 21, 2014
• 年：2014
• 卷：53
• 期：8
• 页码：4243-4249
• 全文大小：424K
• 年卷期：v.53,no.8(April 21, 2014)
• ISSN：1520-510X

文摘

This study describes the characterization of a mixed-valence Ru^II/Ni^I complex, a structural model for the Ni鈥揕 state of the [NiFe]hydrogenases. One-electron oxidation of (cymene)Ru(渭-pdt)Ni(diphos) ([1]⁰, diphos = dppe, C₂H₄(PPh₂)₂; [2]⁰, diphos = dcpe, C₂H₄(P(C₆H₁₁)₂)₂] affords the mixed-valence cations [(cymene)Ru(pdt)Ni(diphos)]⁺ ([1]⁺ and [2]⁺). Crystallographic and spectroscopic measurements indicate that these cations are described as Ru^II/Ni^I. Although [1]⁰ and [1]⁺ are very similar structurally, the following changes are notable: the Ni鈥揚 distances elongate upon oxidation, and the Ru鈥揘i distance changes insignificantly. The molecular and electronic structures of the Ni center in [1]⁺ approaches that observed in the [NiFe]hydrogenases. Density functional theory calculations indicate that [1]⁰ is best described as Ru^II/Ni⁰, consistent with its oxidation to Ru^II/Ni^I in [1]⁺. The fast electron self-exchange rate of 10⁷ M^鈥? s^鈥? between [1]⁰ and [1]⁺ suggests minor reorganization, more consistent with a Ni⁰/Ni^I oxidation state change than a Ni^I/Ni^II couple. In solution, [1]⁺ slowly converts to [H1]⁺ and [1-H]⁺, with the latter being a complex of the thioaldehyde SCHCH₂CH₂S arising from C鈥揌 activation of the pdt backbone. Treatment of [1]⁺ with the H-atom abstracting reagent 2,2,6,6-tetramethylpiperidine-1-oxy also gives [1-H]⁺.