Unprecedented Boron-Functionalized Carborane Derivatives by Facile and Selective Cobalt-Induced B鈥揌 Activation

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• 作者：Zhaojin Wang ; Hongde Ye ; Yuguang Li ; Yizhi Li ; Hong Yan
• 刊名：The Journal of the American Chemical Society
• 出版年：2013
• 出版时间：July 31, 2013
• 年：2013
• 卷：135
• 期：30
• 页码：11289-11298
• 全文大小：626K
• 年卷期：v.135,no.30(July 31, 2013)
• ISSN：1520-5126

文摘

The 16-electron complex CpCoS₂C₂B₁₀H₁₀ (1) is found to react with the alkynes HC鈮C(O)R [R = methyl (Me), phenyl (Ph), styryl (St), ferrocenyl (Fc)] at ambient temperature to give two types of 17-electron cobalt complexes 2a鈥?b>d and 3a鈥?b>d containing unique B(3)/B(6)-norbornyl carborane moieties. A formation mechanism via a tandem sequence of metal-induced B鈥揌 activation, B鈥揅p formation, Cp delivery and Diels鈥揂lder addition is proposed on the basis of DFT calculations. The reactivity of these paramagnetic 17-electron complexes has been studied: Exposed to a combination of air, moisture and silica, complexes 2a鈥?b>d undergo alkyl C鈥揝 cleavage to give 16-electron complexes 4a鈥?b>c containing a boron-norbornadienyl moiety, and simultaneous carboranyl C鈥揝 cleavage to afford cobalt-free carborane derivatives 5a鈥?b>d containing a boron-norbornyl unit. Both 2a鈥?b>d and 3a鈥?b>d allow further alkyne insertion into the Co鈥揝 bond to generate cobalt-free boron鈥搉orbornyl carborane derivatives (Z/E)-7a鈥?b>d and (Z/E)-8a鈥?b>d, both containing a vinyl sulfido group. Addition of AlCl₃ not only promotes the conversion of 2a鈥?b>d, but also leads predominantly to (E)-9a鈥?b>d as retro-Diels鈥揂lder products. Upon heating, the isomerization from E to Z-configuration of the vinyl group and reorganization of the norbornyl moiety of (Z/E)-7a鈥?b>d occur to lead to (Z)-9a鈥?b>d as well as the unexpected [1,2]-H shifted products (Z)-10b,c. Thus, the 17-electron complexes 2a鈥?b>d and 3a鈥?b>d serve as intermediates for synthesis of variety of boron-functionalized carborane derivatives. In this study, efficient routes have been developed through cobalt-mediated B鈥揌 activation to prepare boron-functionalized carborane derivatives that are unavailable by conventional routes.