Structure-activity relationship between some novel silica supported palladium catalysts: a study of the Suzuki reaction

A series of novel silica supported palladium catalysts bearing N-N, N-S and N-O chelating ligands have been prepared by the following reactions-(a) synthesis of 3-aminopropylsilica from activated silica and 3-aminopropyl(trimethoxy)silane; (b) synthesis of Schiff-bases from 3-aminopropylsilica and 2-acetylpyridine, 2-pyridinecarboxaldehyde, 2-thiophenecarboxaldehyde, 2-furancarboxaldehyde, 2-acetylfuran, 2-hydroxyacetopheneone, 2-aminoacetopheneone and 2-pyrrolecarboxaldehyde; (c) reaction of Schiff-bases with palladium acetate to obtain silica supported palladium catalysts. The catalysts were characterized by STA, BET, DRIFT and X-ray photoelectron spectroscopy (XPS). X-ray photoelectron spectroscopy has been found to be a useful tool for establishing the structure-activity relationship between supported palladium catalysts with different chelating atoms using Suzuki reaction as an example. The catalysts with lower binding energy for palladium in comparison to palladium acetate are more active than those with higher binding energies. The activity of the catalysts was compared on the basis of rate constants in the Suzuki reaction between bromobenzene and benzeneboronic acid using anhydrous potassium carbonate as base and o-xylene as solvent. (C) 2004 Elsevier B.V. All rights reserved.