A New Stepwise Mechanism for Formation of a Metallacyclobutane via a Singlet Diradical Intermediate

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• 作者：Jack T. Fuller ; Daniel J. Harrison ; Matthew C. Leclerc ; R. Tom Baker ; Daniel H. Ess ; Russell P. Hughes
• 刊名：Organometallics
• 出版年：2015
• 出版时间：November 9, 2015
• 年：2015
• 卷：34
• 期：21
• 页码：5210-5213
• 全文大小：350K
• ISSN：1520-6041

文摘

Density functional calculations (M06/def2-TZVP//M06/LACVP** in THF solvent) reveal that the formation of a perfluorometallacyclobutane from tetrafluoroethylene, C₂F₄ (TFE), and the difluorocarbene complex CoCp(PPh₂Me)(CF₂) is highly exothermic and involves a stepwise [2 + 2] cycloaddition mechanism with a 1,4-singlet diradical intermediate. This pathway is significantly lower in energy than pathways involving initial 畏¹ or 畏² binding of TFE to cobalt. The stability of the singlet-diradical intermediate results from the formation of a strong CF₂鈥揅F₂ bond coupled with the radical stabilizing effect of a difluoromethylene group. A concerted [2 + 2] transition state between the 18-electron complex CoCp(PPh₂Me)(CF₂) and TFE is very high in energy and essentially forbidden.