Polymer-immobilized chiral catalysts

Polymer immobilization of chiral catalysts has progressed extensively over the past years. Recent intensive development of chiral organocatalysts resulted in the identification of numerous highly active catalysts, which are, however, still far less effective than transition metal catalysts. Separation of relatively large amounts of organocatalysts from the reaction mixture causes problems during product isolation. In the case of chirally modified metal catalysts, recovery of valuable metal species and suppression of metal leaching are perpetually important requirements in the design of environmentally friendly chemical processes. Various types of chiral organocatalysts and metal catalysts have been immobilized as pendant groups onto the side chains of polymer supports. Another important polymer immobilization technique is the incorporation of a chiral catalyst into its main chain, with several types of chiral catalyst monomers having been copolymerized with achiral monomers for their production. Recently, the synthesis of chiral main-chain polymeric catalysts has progressed extensively. Moreover, many examples of polymer-immobilized catalysts exhibit higher enantioselectivities in comparison to those of the corresponding low-molecular-weight catalysts. The development of these polymer-immobilized chiral catalysts, which have largely been reported in the last five years, is reviewed in this article.