Isolation of Silacycles from the Reactions of a Monochlorosilylene LSi(:)Cl (L = PhC(NtBu)2) with Ethynyl Lithium Salts

The reactions of amidinate silylene chloride LSi(:)Cl (L = PhC(NtBu)2) with TMS- and Ph-ethynyl lithium salts gave rise to silacycles 1 and 4, respectively. The formation of 1 and 4 may undergo cyclo-condensations of transient ethynylsilylene intermidiates and the activation of an amidinate backbone. The distinct structures of 1 and 4 may be derived from the different electronic or steric properties of ethynyl substituents, and their formation mechanisms were investigated by density functional theory (DFT) calculations. Moreover, a sequential reaction of LSi(:)Cl with BH3 center dot SMe2 and TMSC-CLi as well as a reaction of LSi(:)Cl with TMSC-CLi under O2 exclusively obtained ethynylsilanes 2 and 3, respectively, which indicated that either blocking a lone pair of a Si(II) atom or oxidizing Si(II) to Si(IV) prevents the further conversion of ethynylsilylenes to silacycle 1. All products were characterized by NMR spectroscopy and X-ray crystallography.

Automated summary

This study investigated the reactions of amidinate silylene chloride with TMS- and Ph-ethynyl lithium salts, resulting in the formation of silacycles. The different structures of the products were attributed to the electronic or steric properties of the ethynyl substituents, and the formation mechanisms were analyzed using DFT calculations. Additionally, sequential reactions and reactions under O2 led to the exclusive formation of ethynylsilanes, indicating a prevention of further conversion of ethynylsilylenes to silacycles.