The Electric Field as a "Smart" Ligand in Controlling the Thermal Activation of Methane and Molecular Hydrogen.

While pristine [TaO2 ]+ is rather inert in its thermal reactions with both methane and molecular hydrogen, the cluster oxide becomes reactive upon ligation with the closed-shell ligand CO2 . While the presence of CO2 increases the intrinsic barriers of the C-H and H-H bond activation steps, the efficiency of the overall reaction to generate the insertion product [Ta(R)(OH)O]+ (R=CH3 , H) is greatly enhanced by the superb leaving-group properties of CO2 . The ligand effect of CO2 has been well mimicked by the electric field of a negative point charge, and mechanistic aspects are addressed by high-level quantum chemical calculations.