CH Bond Activation of Unsaturated Hydrocarbons by a Niobium Methyl Cyclopropyl Precursor. Cyclopropyl Ring Opening and Alkyne Coupling Reaction

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• 作者：Pascal Oulié ; Chiara Dinoi ; Chen Li ; Alix Sournia-Saquet ; Kane Jacob ; Laure Vendier ; Michel Etienne
• 刊名：Organometallics
• 出版年：2017
• 出版时间：January 9, 2017
• 年：2017
• 卷：36
• 期：1
• 页码：53-63
• 全文大小：577K
• ISSN：1520-6041

文摘

The transient intermediate η<sup>2sup>-cyclopropene/bicyclobutane niobium complex [Tp<sup>Me2sup>Nb(η<sup>2sup>-c-C<sub>3sub>H<sub>4sub>)(MeCCMe)] A, generated by an intramolecular β-H abstraction of methane from the methyl cyclopropyl complex [Tp<sup>Me2sup>NbMe(c-C<sub>3sub>H<sub>5sub>)(MeCCMe)] (1), is able to cleave the CH bond of a variety of unsaturated hydrocarbons RH in a selective manner to give the corresponding hydrocarbyl complexes [Tp<sup>Me2sup>NbR(c-C<sub>3sub>H<sub>5sub>)(MeCCMe)] (R = 2-furyl, 2-thienyl, 1-alkynyl, 1-cyclopentenyl, 1-ferrocenyl (Fc), pentafluorophenyl). The activation of the C–H bond occurs stereospecifically via a 1,3-CH addition across the Nb(η<sup>2sup>-cyclopropene) bond of A. Full characterization of several of these complexes includes multinuclear NMR spectroscopy, X-ray diffraction, UV/vis spectroscopy, and electrochemical data. A charge transfer between the ferrocenyl moiety and the niobium center is responsible for the characteristic purple color of the bimetallic complex [Tp<sup>Me2sup>NbFc(c-C<sub>3sub>H<sub>5sub>)(MeCCMe)]. The reactivity of these complexes with benzene follows qualitatively the strength and the pK<sub>asub> of the CH bond that is cleaved. The pentafluorophenyl complex [Tp<sup>Me2sup>Nb(C<sub>6sub>F<sub>5sub>)(c-C<sub>3sub>H<sub>5sub>)(MeCCMe)] undergoes cyclopropyl ring opening and alkyne coupling to give two isomeric η<sup>4sup>-butadienyl complexes, with [Tp<sup>Me2sup>Nb(C<sub>6sub>F<sub>5sub>)(η<sup>4sup>-CMeCMeCHCHMe)] as the major isomer.