A DFT study on the difference of C–H bond activation by Pd(II) and Pd(IV) complex

The reaction mechanism of Pd(II) and Pd(IV) complex catalyzed C–H bond activation was investigated by density functional theory. The difference between the two complex catalyzed reactions was uncovered. It can be concluded from the calculated results that the energy barrier difference (EAb–EAa) of Pd(II) complex catalyzed reaction is higher than that (EBb–EBa) of Pd(IV) complex catalyzed reaction in the rate-determining step, which induces the higher site selectivity of Pd(II) complex catalyzed reaction. The degree of energy barrier difference should be related to synergic effect between the steric effect of methyl and the space distribution of HOMO-C-p and LUMO-Pd-d orbitals. In other words, this synergic effect should be responsible for the different site selectivity between Pd(II) and Pd(IV) complex catalyzed C–H bond activation.