Silicon-Assisted Direct Covalent Grafting on Metal Oxide Surfaces: Synthesis and Characterization of Carboxylate N,N′-Ligands on TiO2

The easy covalent bonding of an OH-bearing molecule onto a metal oxide surface can be done by transesterifying a trimethylsilylated hydroxy function with the surface OH groups. This results in the grafting of the organic molecule directly on the matrix, accompanied by the formation of trimethylsilanol, which can easily be eliminated as volatile hexamethyldisiloxane and water. This was accomplished on a TiO2 matrix with three carboxylic acids: acetic, isonicotinic, and 2,2'-bipyridyl-4,4'-dicarboxylic acids. The N,N'-immobilized ligand was then used for a dioxidomolybdenum entity and tested as such at room temperature and under atmospheric pressure O-2 oxidation of ethylbenzene. All intermediates and grafted species were fully characterized by (13)CMAS NMR spectroscopy, and thermogravimetric and elemental analysis.