Organosilicon-Based Reactive Intermediates: New Molecular Systems with Silicon-Silicon Multiple Bonds

Synthesis, structure, and reactions of novel cyclic and conjugated disilenes are discussed. Photochemical and thermal interconversion among Si& isomers including a cyclotetrasilene, a silylcyclotrisilene, and a bicyclo[ 1. I .O]tetrasilane occurred without apparent participation of the corresponding tetrasila- 1,3-diene. The first spiropentasiladiene derivative, which is thermally very stable in contrast to spiropentadiene, which decomposes below -1 00 "C, shows modified but significant spiroconjugation between the two ring n systems. The first stable silicon compound with a formally sp-hybridized silicon atom, trisilaallene, has a remarkably bent and fluxional kamework and exhibits a significant conjugation between the two trans-bent Si=Si bonds.