INSERTIONS OF METHYLIDYNE AND SILYLIDYNE INTO METHANE AND SILANE

Ab initio molecular orbital calculations have been carried out to stud y the insertion reactions of methylidyne and silylidyne into methane a nd 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 6-31C(d,p), 6-311G(d,p) and 6-311++G(d,p) basis sets; (ii) MP2/6-31G(d,p) frequenc y calculations to characterize the stationary points; (iii) MP2/6-31G( d,p) intrinsic reaction coordinate (IRC) calculations to trace the ins ertion paths; and (iv) MP4/6-311++G(2d,p) single point calculations pl us the corrections with the zero point energies to check the stability of energetic results. In the reaction path of the silylidyne insertio n 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 sigma-b onding molecular orbital of silane. The energetic results indicate tha t the insertion channel for the SiH + SiH4 reaction is feasible, and t he predicted insertion reaction path of the SiH + SiH4 reaction confir ms kinetic experimental observations. The reaction path of the silylid yne insertion into methane is predicted to be somewhat similar to that of the silylidyne insertion into silane,but the energy well is very s hallow and the barrier is significantly high. The insertions of methyl idyne into SiH4 and CH4 are predicted to occur with no energy barriers .