Suzuki Chemistry-A Promising Ligand-Free Metal Catalyst System in Situ Generated from PdII Supported on MgO

Ligand-free Pd catalyst systems derived from Pd(acac)2/Mg(OH)2 and their catalytic properties toward the Suzuki coupling of bromobenzene and phenylboronic acid have been studied. Catalytic study illustrates that the catalyst system (0.2 mol% Pd) in situ generated in the Suzuki reaction is highly active in a mixture of DMA and H2O and in H2O alone at 22-50 ℃, and can be recycled at least three times. The catalysis heterogeneity tests by filtration test and catalyst poisoning with solid-bound thiols reveal that soluble leached Pd from Pd/MgO is fully responsible for the catalytic activity. Transmission electron microscopy measurements show that Pd0/MgO has a smaller mean Pd particle size than Pd0/SiO2. The relation between the size of the supported Pd particles and the catalytic activity further suggests that the size of supported Pd particles determines catalytic activity in a C-C coupling reaction although the catalysis is homogeneous in nature.