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

The reactions of amidinate silylene chloride LSi(:)Cl (L = PhC(NBu)) with TMS- and Ph-ethynyl lithium salts gave rise to silacycles and , respectively. The formation of and may undergo cyclo-condensations of transient ethynylsilylene intermidiates and the activation of an amidinate backbone. The distinct structures of and 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 BH·SMe and TMSC≡CLi as well as a reaction of LSi(:)Cl with TMSC≡CLi under O exclusively obtained ethynylsilanes and , 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 . All products were characterized by NMR spectroscopy and X-ray crystallography.