Donor/Acceptor Concepts for Developing Efficient Suzuki Cross-Coupling Catalysts Using Graphene Supported Ni, Cu, Fe, Pd, and Bimetallic Pd-Ni Clusters

First-principles theoretical studies on the electronic properties and activation energies for the three steps of the Suzuki cross-coupling reaction have been performed on 3d transitionmetal clusters and Pd/Ni bimetallic clusters supported on defected graphene. The ability of the clusters to effectively donate and accept charge is found to be critical to the activity of the catalysts, and graphene further enhances this ability. Nickel acts as the best replacement for palladium in cross-coupling catalysts for the oxidation steps but is not a good replacement in the transmetallation and reductive elimination steps which require the cluster to serve as a charge acceptor. Reducing the size of the cluster from Ni-13 to Ni-4 enhances the activity because of the cluster being more positively charged. Bimetallic Pd/Ni clusters were found to offer even lower activation energies for all three steps of the Suzuki reaction because of charge donation from the Ni atoms to the Pd atoms making the bimetallic cluster a highly active co-catalyst. This study reveals that the donor-acceptor concepts that explain the enhanced activity of Pd clusters on defected graphene can also be applied to explain lowered activation energies in bimetallic clusters acting as co-catalysts.