Substituent Effects in Thermal Reactions of a Silene with Silyl-Substituted Alkynes: A Theoretical Study

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• 作者：Hiromasa Tanaka ; Yoshihito Shiota ; Kazunori Hori ; Akinobu Naka ; Mitsuo Ishikawa ; Kazunari Yoshizawa
• 刊名：Organometallics
• 出版年：2012
• 出版时间：July 9, 2012
• 年：2012
• 卷：31
• 期：13
• 页码：4737-4747
• 全文大小：626K
• 年卷期：v.31,no.13(July 9, 2012)
• ISSN：1520-6041

文摘

Thermal reactions of a silene derivative (Me₃Si)₂Si鈺怌(OSiMe₃)(t-Bu) (1) with silyl-substituted acetylenes, bis(trimethylsilyl)butadiyne, tert-butyldimethylsilylacetylene, and bis(trimethylsilyl)acetylene have been investigated with density functional theory calculations for the understanding of substituent effects in the reactivity of the silene. The first critical reaction step for determining the final product is the formation of a biradical intermediate from 1 and the acetylenes. A stepwise [2 + 2] cycloaddition via the biradical intermediate gives a silacyclobutene derivative, which is the precursor of the final product. The activation energy for this reaction step as well as thermodynamic stability of the biradical intermediate is governed by an interplay between geometric and electronic factors. The biradical intermediate is destabilized by steric hindrance between bulky substituents on 1 and acetylene, while it can be stabilized by delocalization of an unpaired electron in the acetylene moiety. Silacyclobutene derivatives undergo Si鈥揅 bond cleavage to give silabutadiene derivatives. The second critical reaction step is the attack of the OSiMe₃ group on the silene Si atom in the silabutadienes. If the substituent on one of the acetylene C atoms does not easily migrate, the SiMe₃ group of the OSiMe₃ group rebounds to the silene C atom to form an oxasilacyclopentene derivative. If this substituent migrates easily, on the other hand, it migrates to the silene C atom with a simultaneous migration of the OSiMe₃ group, resulting in the formation of an allene derivative.