Oxidative addition of Pd to C-H, C-C and C-Cl bonds: Importance of relativistic effects in DFT calculations

The relativistic effects for the quantum mechanical oxidative addition reactions of palladium on C-H, C-C and C-Cl bonds was studied using density functional theory (DFT). Relativistic stabilization of transition states for oxidative insertion was studied by analyzing activation energies in terms of activation strain and the transition interaction between deformed reactants in the activated complex. The discrepancies in experimental and theoretical values of activation energy was attributed to the combined effect of an underestimation of barriers by DFT and the uncertainty of a few kcal/mole in the ab initio calculations.