Reactivity and mechanism of stable heterocyclic silylenes with carbon tetrachloride.

The potential energy surfaces for the reactions of stable silylenes with carbon tetrachloride have been characterized in detail using density functional theory [B3LYP/6-311G(d)], including zero-point corrections. Five stable silylene species (1-5) have been chosen in this work as model reactants. The activation barriers and enthalpies of the reactions are compared to determine the relative reactivity of the stable silylenes on the reaction potential energy surface. Our theoretical findings suggest that stable silylene 5, which has two carbon atoms bonded to the silicon center and does not contain a resonance structure, is relatively unstable with respect to the reaction with haloalkanes, in comparison with the other stable silylenes (1-4). Of the three possible reaction paths, Cl abstraction (path 1), CCl3 abstraction (path 2), and CCl4 insertion (path 3), path 1 is found to be most favorable, with a very low activation energy and a large exothermicity. In short, electronic as well as steric factors play a dominant role in determining the chemical reactivity of the stable silylene species kinetically as well as thermodynamically. Furthermore, a configuration mixing model based on the work of Pross and Shaik is used to rationalize the computational results. The results obtained allow a number of predictions to be made.