Formation of a Ruthenium(IV)-Oxo Complex by Electron-Transfer Oxidation of a Coordinatively Saturated Ruthenium(II) Complex and Detection of Oxygen-Rebound Intermediates in C鈥揌 Bond Oxygenation

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• 作者：Takahiko Kojima ; Kazuya Nakayama ; Kenichiro Ikemura ; Takashi Ogura ; Shunichi Fukuzumi
• 刊名：Journal of the American Chemical Society
• 出版年：2011
• 出版时间：August 3, 2011
• 年：2011
• 卷：133
• 期：30
• 页码：11692-11700
• 全文大小：1070K
• 年卷期：v.133,no.30(August 3, 2011)
• ISSN：1520-5126

文摘

A coordinatively saturated ruthenium(II) complex having tetradentate tris(2-pyridylmethyl)amine (TPA) and bidentate 2,2鈥?bipyridine (bpy), [Ru(TPA)(bpy)]²⁺ (1), was oxidized by a Ce(IV) ion in H₂O to afford a Ru(IV)-oxo complex, [Ru(O)(H⁺TPA)(bpy)]³⁺ (2). The crystal structure of the Ru(IV)-oxo complex 2 was determined by X-ray crystallography. In 2, the TPA ligand partially dissociates to be in a facial tridentate fashion and the uncoordinated pyridine moiety is protonated. The spin state of 2, which showed paramagnetically shifted NMR signals in the range of 60 to 鈭?0 ppm, was determined to be an intermediate spin (S = 1) by the Evans鈥?method with ¹H NMR spectroscopy in acetone-d₆. The reaction of 2 with various oraganic substrates in acetonitrile at room temperature afforded oxidized and oxygenated products and a solvent-bound complex, [Ru(H⁺TPA)(bpy)(CH₃CN)], which is intact in the presence of alcohols. The oxygenation reaction of saturated C鈥揌 bonds with 2 proceeds by two-step processes: the hydrogen abstraction with 2, followed by the dissociation of the alcohol products from the oxygen-rebound complexes, Ru(III)-alkoxo complexes, which were successfully detected by ESI-MS spectrometry. The kinetic isotope effects in the first step for the reaction of dihydroanthrathene (DHA) and cumene with 2 were determined to be 49 and 12, respectively. The second-order rate constants of C鈥揌 oxygenation in the first step exhibited a linear correlation with bond dissociation energies of the C鈥揌 bond cleavage.