Catalytic epoxidation of olefins by polymer-anchored amino acid ruthenium complexes

A synthetic strategy was developed to anchor an amino acid L-valine on to styrene-divinylbenzene co-polymer beads with 8% and 6% cross linking. The polymeric ligands containing bidentate N,O donor sites were treated with a solution of ruthenium(III) chloride to form the metal complex on the support. These immobilized Ru(III) complexes were characterized by elemental analysis, FT-IR, UV-visible diffuse reflectance, ESR, SEM and thermal analysis. The catalytic epoxidation of styrene, norbornylene, cyclooctene, and cyclohexene were investigated using the supported catalysts in the presence of tert.-butyl hydroperoxide as the terminal oxidant. Selective epoxide formation was observed with norbornylene and cis-cyclooctene whereas in the case of styrene the corresponding epoxide, benzaldehyde and acetophenone were obtained. Amongst the olefins screened, good activity was observed in the case of cyclohexene. The effect of various reaction parameters as well as some aspects of catalyst recycling and possible mechanistic pathways has also been investigated. (C) 2003 Elsevier B.V. All rights reserved.