Insertions of methylidyne and silylidyne into methane and silane

Abstract

Ab initio molecular orbital calculations have been carried out to study the insertion reactions of methylidyne and silylidyne into methane and silane. The calculations included: (i) optimization calculations to locate the stationary points along the insertion paths at the second-order Moller–Plesset perturbation theory level (MP2) with 6-31G(d,p), 6-311G(d,p) and 6-311++G(d,p) basis sets; (ii) MP2/6-31G(d,p) frequency calculations to characterize the stationary points; (iii) MP2/6-31G(d,p) intrinsic reaction coordinate (IRC) calculations to trace the insertion paths; and (iv) MP4/6-311++G(2d,p) single point calculations plus the corrections with the zero point energies to check the stability of energetic results. In the reaction path of the silylidyne insertion into SiH₄ an intermediate complex separating the reactants from the transition state exists and it is stabilized owing to the interaction between the empty silicon p-orbital of silylidyne and the Si–H σ-bonding molecular orbital of silane. The energetic results indicate that the insertion channel for the SiH+SiH₄ reaction is feasible, and the predicted insertion reaction path of the SiH+SiH₄ reaction confirms kinetic experimental observations. The reaction path of the silylidyne insertion into methane is predicted to be somewhat similar to that of the silylidyne insertion into silane, but the energy well is very shallow and the barrier is significantly high. The insertions of methylidyne into SiH₄ and CH₄ are predicted to occur with no energy barriers.