Reactions of an Isolable Dialkylsilylene with Carbon Dioxide and Related Heterocumulenes

An isolable dicoordinate dialkylsilylene, 2,2,5,5-tetrakis(trimethylsilyl)silacyclopentane-1,1-diyl (6), was found to react with CO2 and ArN?C?X (X = O, S) smoothly to give the corresponding bis(silyl)carbonate, 4-imino-1,3-dioxasiletane and 4-imino-1,3-dithiasiletane derivatives in high yields, respectively. The molecular structures of these products were determined by X-ray crystallography. All these reactions are parallel to those of a hypercoordinate silylene with ?5-pentamethylcyclopentadienyl ligands, decamethylsilicocene, reported by Jutzi et al. and are suggested to involve similarly the formation of the corresponding Si?X doubly bonded compounds (X = O, S) at the initial steps. Mechanistic details of the multistep reaction of a model dialkylsilylene with CO2 were investigated using DFT calculations.