Mesoionic Triazolylidene Nickel Complexes: Synthesis, Ligand Lability, and Catalytic C鈥揅 Bond Formation Activity

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• 作者：Yingfei Wei ; Ana Petronilho ; Helge Mueller-Bunz ; Martin Albrecht
• 刊名：Organometallics
• 出版年：2014
• 出版时间：October 27, 2014
• 年：2014
• 卷：33
• 期：20
• 页码：5834-5844
• 全文大小：473K
• ISSN：1520-6041

文摘

A set of triazolylidene (trz) nickel(II) complexes [NiCpX(trz)] was synthesized by a direct metalation of the corresponding triazolium salt with nickelocene, NiCp₂. While at short reaction times and in the presence of a coordinating anion X the mono-carbene complex is preferably formed, long reaction times induce the gradual transformation of [NiCpX(trz)] to the bis-carbene complexes [Ni(Cp)(trz)₂]⁺. Kinetic analyses lend strong support to a consecutive pathway involving triazolylidene dissociation from [NiCpX(trz)] en route to the bis-carbene complex. Similar carbene transfer is observed in a solid-state reaction upon heating the complex [NiCpI(trz)] in vacuo, which induces disproportionation to [NiI₂(trz)₂] and NiCp₂, confirming that the Ni鈥揅(trz) bond is kinetically labile. The complexes [Ni(Cp)(trz)₂]⁺ and [NiCpX(trz)] were both efficient catalyst precursors for Suzuki鈥揗iyaura cross-coupling of aryl bromides and phenylboronic acid, with turnover frequencies exceeding 228 h^鈥?. Complex degradation after short reaction times, identified in separate experiments, prohibits high turnover numbers, and for high conversions, repetitive additions of triazolylidene nickel complex and phenylboronic acid are necessary.