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Insertion of Silylenes into Si–H and Si–Cl Bonds. Comparison of Mechanism and Substituent Effects

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journal contribution
posted on 27.06.2011, 00:00 by Zheng Xu, Juan Jin, Haixia Zhang, Zhifang Li, Jianxiong Jiang, Guoqiao Lai, Mitsuo Kira
Electronic and steric substituent effects on the insertion reactions of dimethylsilylene (1) and 2,2,5,5-tetrasilylsilacyclopentane-1,1-diyl (2′) into Si–H bonds are compared with those into Si–Cl bonds using DFT calculations at the B3LYP/6-31++G(d,p) level. For both 1 and 2′, the ΔG value for the insertion into a Si–H bond of SiH4 is close to and only ca. 1.5 kcal mol–1 lower than that into the Si–Cl bond of H3SiCl. Effects of in-plane substituents on the ΔG values for both Si–H and Si–Cl insertion reactions are mainly electronic and electron-withdrawing substituents lower the ΔG values. Sensitivity of the Si–H insertion to the substituent effects is similar to that of the Si–Cl insertion. Effects of out-of-plane substituents are largely steric, and their sensitivity for the Si–H insertion is close to that for the Si–Cl insertion. The ΔG values for the insertion reactions of sterically bulky 2′ are significantly larger than those of 1. The puzzling prior observation that a bulky isolable silylene inserts into the Si–Cl bond of H2SiCl2 and the Si–H bond of Me2SiHCl is explained on the basis of the substituent effects on the insertion reactions.