Reaction of N-Heterocyclic Silylenes with Thioketone: Formation of SiliconSulfur Three (Si-C-S)- and Five (Si-C-C-C-S)-Membered Ring Systems

Three- and five-membered rings that bear the (Si-C-S) and (Si-C-C-C-S) unit have been synthesized by the reactions of LSiCl (1; L=PhC(NtBu)2) and LSi (2; L=CH{(CCH2)(CMe)(2,6-iPr2C6H3N)2}) with the thioketone 4,4-bis(dimethylamino)thiobenzophenone. Treatment of 4,4-bis(dimethylamino)thiobenzophenone with LSiCl at room temperature furnished the [1+2]-cycloaddition product silathiacyclopropane 3. However, reaction of 4,4-bis(dimethylamino)thiobenzophenone with LSi at low temperature afforded a [1+4]-cycloaddition to yield the five-membered ring product 4. Compounds 3 and 4 were characterized by NMR spectroscopy, EIMS, and elemental analysis. The molecular structures of 3 and 4 were unambiguously established by single-crystal X-ray structural analysis. The room-temperature reaction of 4,4-bis(dimethylamino)thiobenzophenone with LSi resulted in products 4 and 5, in which 4 is the dearomatized product and 5 is formed under the 1,3-migration of a hydrogen atom from the aromatic phenyl ring to the carbon atom of the CS unit. Furthermore, the optimized structures of probable products were investigated by using DFT calculations.