Effects of Fluorination on Methylene Insertion Reactions

Abstract

The potential energy surfaces for the insertion reactions of methylene and fluorinated methylenes into the H2, HF, and F2 molecules were studied by density functional, many body perturbation, and coupled-cluster theories. These methods predict the barrier for the CF2 insertion into the hydrogen molecule to be about 33 kcal/mol, that is, significantly lower than previous estimates. A new transition state was found in this system for the reaction path which leads to CHF + HF. However the transition state for this metathesis channel is about 25 kcal/mol higher than that of the insertion channel. For the fluoromethylene insertion into H2 the predicted activation energy is about 8 kcal/mol. The CH2 insertion into F2 proceeds without a barrier. The peculiarity of the insertion reactions between carbenes and HF involves formation of a hydrogen-bonded complex. The CH2···HF complex is bound by about 10 kcal/mol relative to CH2 + HF. Coupled-cluster methods predict a small (ca. 3 kcal/mol) barrier for transformatio...