SYNOPSIS
A series of chiral poly(urea)s was synthesized by solution polyaddition. The polymers are characterized by NMR, FTIR, DSC, viscosimetry, and microanalysis. After deposition of the rhodium, the insoluble chiral polymers were used as catalysts in the reduction of acetophenone by hydrogen transfer. The influence of the structure of the polymers on the catalytic activity and selectivity was investigated. The enantiomeric excesses (e.e.) obtained were up to 60%, and the polymeric catalysts were reused without loss of activity and selectivity. 0 1996 John Wiley & Sons, Inc
I N T R O DU CTlO N
Chemical synthesis of enantiomerically pure compounds plays a pivotal role in the development of pharmaceuticals, agrochemicals, flavors, and fragrances, as well as certain advanced materials. The main limitations in industrial use of the already known homogeneous catalytic reactions lies in the recovery and recycling of the catalysts. Indeed, in many cases, both the cost of the transition metal and of the chiral ligand are not negligible compared with the price of the synthesized product. This problem can be solved by fixing the ligand on a solid, insoluble support such as silica, zeolite, or a polymer. The structures of the support have to be optimized to limit the decrease of selectivity, activity, and leaching of the metal. The use of polymer-supported catalysts for asymmetric catalysis has been already reported in the literat~re.'-~ Most of the systems involve crosslinked polystyrene or polyacrylatesupported reagent^.^.^ Nitrogen-containing ligands are more and more used in asymmetric catalysis6 for reactions as different as carbonyl reduction7 or allylic alkylation.8 Recently, we reported the asymmetric homogeneous hydride transfer reduction of prochiral ketones using