Silicon−Fluorine and Silicon−Carbon Bond Cleavage in Organofluorosilicates:  A Molecular Orbital Study

The mechanism of silicon−fluorine and silicon−carbon bond cleavage in organofluorosilanes and -silicates is analyzed with the aid of molecular orbital calculations. The optimized geometries of reactants and intermediates are calculated, and these calculations support the view that cleavage of Si−F bonds occurs by way of fluorine-bridged Si--F--Si intermediates. Cleavage of a Si−C bond in PhSiF3 takes place in the presence of fluoride ion and oxidizing agents, and the calculations are in agreement with the formation of PhSiF4 - and PhSiF5 2-, followed by oxidation to a radical anion PhSiF5 •-. The latter species, however, is predicted to decompose rapidly to give anionic SiF5 -, and phenyl radicals. These calculations and the proposed mechanisms of bond cleavage are in agreement with experimental data, where available.