Chapter 15 - Metal Species Supported on Organic Polymers as Catalysts for the Epoxidation of Alkenes

Abstract

Recent developments in the field of immobilized metal catalysts for liquidphase alkene epoxidation are reviewed. Progress since 2000 is summarized considering organic polymers as supports with a focus on polymer types, catalyst preparation, and performance rather than physicochemical parameters of the modified polymers. A broad variety of metals including manganese, molybdenum, titanium, and calcium are considered and several immobilization strategies are described. Recent advances comprise new catalyst systems for asymmetric heterogeneous or homogeneous epoxidation, new polymeric supports, and new polymer-based epoxidation catalysts with high long-term activities in the range of months. By asymmetric epoxidation, catalytic performances of supported manganese complexes with salen-type ligands could be improved and concepts such as immobilized Katsuki-type complexes or complexes with new chiral backbones have emerged. In this context, conjugated salen-cross-linked polymers, obtained by condensation of a trialdehyde with chiral diamines in the presence of a manganese salt, are a promising approach toward active, selective, and stable catalyst systems for multiple use. In the field of supported Sharpless-epoxidation catalysts, discovery of enantioreversal as a function of the molecular weight of polymer-modified tartrate ligands could offer a new approach for control of asymmetric reactions.