Immobilization of Small-Molecule Ligands Containing Secondary or Tertiary Amine Groups onto TiO2-Supported Ru Catalysts Driven by the Hydrophobic Effect

A strategy for effectively immobilizing small-molecule ligands onto TiO2-supported Ru catalysts is described. The immobilization was based on a simple two-phase centrifugation technique and driven by the hydrophobic effect, likely leading to the formation of hydrophobic clusters of small-molecule ligands. By using this strategy, a library of ligands containing secondary or tertiary amine groups and hydrophobic chains were successfully immobilized onto TiO2-supported Ru catalysts. Of these ligands, ligands containing 2,2,6,6-tetramethyl-1-piperidine-N-oxyl (TEMPO) moieties significantly improved the selectivity for aldehyde at high conversion in aerobic oxidation of alcohols, resulting from the inhibition of auto-oxidation of aldehydes. This strategy can generate diversity in preparation of organic/inorganic hybrid catalysts.