DFT study on the mechanism of palladium(0)-catalyzed reaction of o-iodoanilines, CO2, and CO

Abstract

The reaction mechanism of palladium(0)-catalyzed reaction of o-iodoanilines, CO2, and CO has been studied theoretically. The calculations suggest that the reaction proceeds via C(sp2)I bond oxidative addition, CO insertion, CsI·OAc cluster anion formation, NHH bond activation, ligand exchange of one PPh3 ligand with CsI·HOAc cluster, CO2 insertion, and C(sp2)O bond reductive elimination steps. The CO2 insertion involves the rate-determining transition state with a free energy barrier of 18.4 kcal/mol, consistent with the experimental reaction condition (60 °C). The influence of solvent on the product yield was analyzed. It is found that the CO2 insertion occurs with the coordination of PPh3 ligand in THF while it needs the help of base CsOAc in toluene. The role of bases KOAc and NaOAc has been calculated and compared with CsOAc. The stability of the rate-determining intermediate increases in the order of Cs < K < Na, resulting in the increase of the reaction energy barrier.