Developing Efficient Suzuki Cross-Coupling Catalysts by Doping Palladium Clusters with Silver

It is shown that doping of a Pd duster by Ag atoms can provide an efficient catalyst for the Suzuki-Miyaura cross-coupling reactions. We demonstrate this intriguing possibility by considering a model reaction involving bromobenzene and phenylboronic acid as reagents where the reaction involves oxidation, transmetallation, and reduction steps. We have examined the reaction barriers of all three steps for a conventional ligated Pd catalyst, a nearly icosahedral Pd-13 cluster, and a monosilver-doped Pd12Ag duster using gradient-corrected density functional theory. It is observed that the reaction carried out on the Pd sites adjacent to an Ag atom in a Pd12Ag cluster shows substantially lower barriers for the oxidation and reduction steps compared to the conventional ligated Pd catalyst and the pure Pd-13 cluster. A detailed analysis indicates that the Ag site donates charge to the neighboring Pd site. While such a donation may have been expected to reduce the barrier for the oxidative step, the lowering of the barrier for the reduction step indicates that the respective sites not only act as a donor but can also serve as an acceptor for the reduction step. Furthermore, because of the differential donor-acceptor characteristic of the Ag and Pd atoms, it is observed that the barrier heights of the redox steps are primarily dependent on the chosen active site. The calculated results show that by altering the atom (Ag or Pd) at the active site of the reaction, the activation energies of the redox steps can either be reduced or increased. This shows that the active sites of a bimetallic cluster-like Pd12Ag can be utilized to control the barrier heights of suitable chemical reactions. The relative trend of the barrier heights for both clusters is also observed to be predictable by the conceptual density functional theory. Previous studies in our group have indicated that the reaction barriers for Pd-n clusters can be lowered by supporting them on reduced graphene. We, therefore, propose that silver-doped Pd-n clusters may provide an even better catalyst.

Automated summary

The doping of a Pd cluster with Ag atoms enhances the efficiency of Suzuki-Miyaura cross-coupling reactions by reducing the barriers for oxidation and reduction steps. The Ag atom adjacent to Pd sites in a Pd12Ag cluster donates charge to lower the barriers, demonstrating a unique donor-acceptor characteristic between Ag and Pd atoms. This study shows that altering the active site atom can control the activation energies of redox steps, suggesting the potential of silver-doped Pd-n clusters as catalysts.