Synthesis of catalytically active polymer-bound transition metal complexes for selective epoxidation of olefins

Abstract

Catalytically active metal-complexing polymers containing Mn(III) moieties were synthesized for use in the selective epoxidation of olefins. For this purpose two different monomers, 1b and 2b, bearing the Mn^(III)-Salen moiety (known to be a good candidate for catalyzing olefin epoxidation) were synthesized and subsequently copolymerized with ethylene glycol dimethacrylate, producing insoluble cross-linked polymer networks possessing a macroporous morphology. Metal-containing polymers were also obtained by chemical modification of cross-linked polymers bearing the Salen units (obtained by polymerizing 1a and 2a). The catalytic activities of all these polymers were evaluated during epoxidation of olefins. The polymers were able to catalyze the epoxidation of a variety of olefins at room temperature in the presence of iodosylbenzene (PhIO) as the terminal oxidant. The rates of epoxidations using these polymeric catalysts were relatively slow compared to that of the corresponding homogeneous system. However, the epoxidation reactions were selective with predominant formation of the desired epoxides over other side oxidation products. No significant influence of the spacer length between the polymer backbone and metal-complexing sites on the rate of epoxidation was observed.