‘Ab initio’ calculations on methane interacting with the fourteen-electron Ni(PH 3 ) 2 fragment

Ab initio restricted Hartree–Fock and configuration interaction calculations have been carried out on the system Ni(PH3)2+ CH4 in order to study the energetics and the mechanism of the oxidative-addition reaction of CH4 and to model the activation of the C–H bond by zerovalent, co-ordinatively unsaturated transition-metal complexes. Energy-gradient optimizations and transition-state localizations have been performed on reactants and products in various constrained geometries. The results indicate that the oxidative addition of methane to Ni(PH3)2 is endothermic by 7.0 kcal mol–1 and the planar trans product is the most stable, being lower in energy than the cis isomer by 3.4 kcal mol–1.