Photo-Driven Si-C Bond Cleavage in Hexacoordinate Silicon Complexes

Hexacoordinate diorganosilicon complexes of the type (ONNO)SiRR′, with (ONNO) being a di-anionic salen-type Schiff base ligand, were shown to undergo Si–C bond cleavage and intramolecular rearrangement (1,3-shift of R’ to a former imine carbon atom) upon irradiation with UV. The course of this reaction depends on the nature of silicon-bound substituents: Whereas complexes (ONNO)SiMe2 and (ONNO)SiPh2 give rise to the rearrangement of a methyl and a phenyl group, respectively, complexes of the type (ONNO)Si(aryl)(alkyl) were found to undergo Si–C(alkyl) bond cleavage exclusively.Furthermore, such alkyl groups bearing β-hydrogen atoms may lead to β-hydride transfer to the imine carbon atom accompanied by olefin elimination. Irradiation of compounds (ONNO)SiRX, with X being a non-carbon sacrificial ligand, was shown to give rise to further side reactions: In case of X = F the unexpected formation of (ONNO)SiF2 was observed. In analogy to the photo-induced rearrangement of (ONNO)SiPh2 the heavier congenor (ONNO)GePh2 exhibits similar behavior, whereas the related tin compound (ONNO)SnPh2 proved inert under these reaction conditions applied.