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

The reactions of amidinate silylene chloride LSi(:)Cl (L = PhC(N t Bu) 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 BH 3 ·SMe 2 and TMSC≡CLi as well as a reaction of LSi(:)Cl with TMSC≡CLi under O 2 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.