Anionic vs. radical intermediates in the fragmentation reactions of dendritic polysilanes

Abstract

Fragmentation reactions during the formation of highly congested dendritic polysilanes can conceivably occur by either anionic or radical mechanisms. In the specific case of the production of [(SiMe₃)₂SiMeSiMe₂]₃SiH from the reaction of (ClSiMe₂)₄Si with (Me₃Si)₂MeSiLi, the two types of mechanisms were tested by trapping reactions. Product formation was found to be independent of the presence of proton sources, contrary to the expectations of the anionic mechanism. Homolytic fragmentation of the initial product [(SiMe₃)₂SiMeSiMe₂]₄Si was supported by the observation of products with the radical trap phenylacetylene. Evidence is presented that the reaction produced, in low yield, this dendritic polysilane, which would be the first such structure with a fourfold-substituted core.