Isolable silylene, disilenes, trisilaallene, and related compounds

Abstract

Our recent studies of synthesis, structure, and reactions of an isolable silylene, stable novel cyclic and conjugated disilenes, a trisilaallene are summarized. Due to the distinctive electronic and steric effects of trialkylsilyl substituents, tetrakis(trialkylsilyl)disilenes showed interesting structural features around Si Si bonds, electronic spectra, and reactions. The tetrasilyldisilenes were useful reagents for the synthesis of novel types of organosilicon compounds such as η 2-disilene transition metal complexes and a 1,3-disilabicyclo[1.1.0]butane. Photochemical and thermal interconversion among Si 4R 6 isomers including a cyclotetrasilene, a silylcyclotrisilene, and a bicyclo[1.1.0]tetrasilane occured without apparent participation of the corresponding tetrasila-1,3-diene. The first spiropentasiladiene was thermally very stable and showed remarkable spiroconjugation between the two ring π systems. An isolable dialkylsilylene was found to be well-protected sterically from dimerization but least perturbed electronically. Using the silylene, a trisilaallene, the first stable compound with formal sp-hybridized silicon atom, was synthesized. In contrast to carbon allenes, the skeleton of the trisilaallene was significantly bent and remarkably fluxional.