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

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)(2)SiMeSiMe2](3)SiH from the reaction of (ClSiMe2)(4)Si with (Me3Si)(2)MeSiLi, the two types of mech anisms were tested by trapping reactions. Product formation was found to be independent of the presence of proton sources, contrary to the expectation s of the anionic mechanism. Homolytic fragmentation of the initial product [(SiMe3)(2)SiMeSiMe2](4)Si was supported by the observation of products wit h the radical trap phenylacetylene. Evidence is presented that the reaction produced, in low yield, this dendritic polysilane, which would be the firs t such structure with a fourfold-substituted core.