Immobilization of a Ligand-Preserved Giant Palladium Cluster on a Metal Oxide Surface and Its Nobel Heterogeneous Catalysis for Oxidation of Allylic Alcohols in the Presence of Molecular Oxygen

A 1,10-phenanthroline (phen) ligand-preserved five-shell giant palladium cluster, Pd5(phen), could be uniformly immobilized on a neutral TiO 2 surface while keeping its original cluster size of ca. 30 Å and local ordering around Pd atoms. The Pd5(phen)/TiO 2 acted as an efficient and reusable heterogeneous catalyst for the oxidations of primary allylic alcohols into the corresponding α,β-unsaturated aldehydes in the presence of molecular oxygen as well as the corresponding homogeneous Pd5(phen) cluster. Roles of the phen ligand in the oxidation catalysis of the giant Pd cluster are discussed in relation to electronic and geometric effects of the Pd atoms on the Pd cluster surface.