Easy Access to Bio-Inspired Osmium(II) Complexes through Electrophilic Intramolecular C(sp2)-H Bond Cyclometalation

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• 作者：Ricardo Ceró ; n-Camacho ; David Morales-Morales ; Simon Hernandez ; Ronan Le Lagadec ; Alexander D. Ryabov
• 刊名：Inorganic Chemistry
• 出版年：2008
• 出版时间：June 2, 2008
• 年：2008
• 卷：47
• 期：11
• 页码：4988 - 4995
• 全文大小：719K
• 年卷期：v.47,no.11(June 2, 2008)
• ISSN：1520-510X

文摘

Mild electrophilic C(sp²)-H cyclometalation of 2-phenylpyridine and N,N-dimethylbenzylamine by the chloro-bridged osmium(II) dimer [OsCl(μ-Cl)(η⁶-C₆H₆)]₂ in acetonitrile affords cyclometalated pseudotetrahedral Os^II complexes [Os(C~N)(η⁶-C₆H₆)(NCMe)]PF₆ (C~N = o-C₆H₄py-κC,N (2) and o-C₆H₄CH₂NMe₂-κC,N (5), respectively) in good to excellent yields. The cyclometalation reactions are super sensitive to the nature of an external base. Sodium hydroxide is essential for cyclometalation of 2-phenylpyridine, but NaOH retards metalation of N,N-dimethylbenzylamine, the tertiary amine being self-sufficient as a base. Further reactions of compounds 2 and 5 with 1,10-phenanthroline or 2,2′-bipyridine (N~N) lead to the substitution of the η⁶-bound benzene to produce octahedral species [Os(C~N)(N~N)(NCMe)₂]PF₆ or [Os(C~N)(N~N)₂]PF₆ in MeCN or MeOH as solvent, respectively. The cis configuration of the MeCN ligands in [Os(C~N)(phen)(NCMe)₂]PF₆ has been confirmed by an X-ray crystallographic study. Electrochemical investigation of the octahedral osma(II)cycles by cyclic voltammetry showed a pseudoreversible M^III/II redox feature at (−50)−(+109) and 190−300 mV versus Ag/AgCl in water and MeCN, respectively. As a possible application of the compounds, a rapid electron exchange between the reduced active site of glucose oxidase enzyme from Aspergillus niger and the electrochemically generated Os^III species has been demonstrated. The corresponding second-order rate constants cover the range (0.7−4.8) × 10⁶ M⁻¹ s⁻¹ at 25 °C and pH 7.