A novel strategy for heterogenisation of homogeneous and colloidal chiral catalysts and their application in enantioselective reactions

For the heterogenisation of chiral catalysts, a novel method has been developed and applied to different enantioselective reactions. The new heterogenisation method is based on the, three-dimensional entrapment of catalysts by electrostatic attraction between a polyelectrolyte and an oppositely charged catalyst. An easy preparation procedure, a simple separation and a good retention of the active metal in the polymeric material and a high long-term stability of the entrapped catalyst are the significant features of this new heterogenisation method. Applying these entrapped catalysts in the hydroformylation of vinyl acetate, an enantiomeric excess (ee) of 39% could be obtained with a rhodium diphosphine complex. The activities and selectivities in the hydrogenation of dimethyl itaconate have been found to be competitive with homogeneous catalysts. A change in the direction of enantioselectivity has been observed by using entrapped Ru catalysts in different solvents. For the entrapment of chirally stabilised Pt-colloids used in the enantioselective hydrogenation of ethyl pyruvate, different polyartions have been found to be suitable. A constant enantioselectivity and a good activity during 25 hydrogenation cycles were obtained employing alginate-entrapped Pt-colloids. (C) 2002 Elsevier Science B.V. All rights reserved.