Key Factors in Controlling Stille Coupling Reactions Catalyzed by Palladium Complexes: Density Functional Theory (DFT) Calculation Analyses

Stille coupling reactions are one of the most common coupling reactions used nowadays. For many years only phosphorous ligands have been considered in the catalysts for this type of reaction but recent studies have shown that also arsenic ligands are very promising. In this study, DFT calculations were applied to the Stille coupling reaction of different systems (with various substrates and catalysts) in order to obtain the energy values associated to the various steps of the reaction. In trial 1, oxidative addition was found to be a rate-determining step (but the considered halogen atom could effectively modulate the energy levels of this step), while transmetalation was found to be a rate-determining step only with phosphorous ligands. In trial 2, different substituent groups were attached to the substrate (with a fixed halogen atom). In this trial, the energy levels of the transition states associated to the oxidative addition and the transmetalation were clearly lowered in the first considered system where an electron-withdrawing group was used as the substituent group of the substrate. The use of arsenic ligands in Stille coupling reactions is interesting because it can significantly lower the energies associated to almost every transition state of the reaction, and the use of specific substituent groups in the ligand can enhance this behavior. The study of different substrates has also found that the use of specific halogen atoms and substituent groups in the substrate can strongly influence the reaction and highly enhance the reaction yield.