Ab initio study of the insertion reaction of magnesium into the carbon-halogen bond of fluoro- and chloromethane

Theoretical calculations using self-consistent field (SCF) and Moller-Plessett perturbation theory, up to fourth order (MP4), have been carried out on the gas-phase Mg+CH 3 X→CH 3 MgX Grignard reaction surface for X=F and Cl. The transition-state energies, geometries, and vibrational frequencies for both reactions are presented and compared to the smaller Mg+HX→HMgX reaction. The transition states for both X=F and X=Cl are found to process C s symmetry and to be almost identical in structure. The activation energy for the Mg + fluoromethane reaction is found to be 31.2 kcal-mol −1 , while that for the chloromethane reaction is substantially higher, at 39.4 kcal.mol −1 , calculated at the MP4SDTQ level by using the 6-311G(d,p) basis. The intrinsic reaction coordinate has been followed down from the transition state toward both reactants and product for the Mg + CH 3 F→CH 3 MgF reaction, confirming the connection of these points on the potential surface