MOLECULAR IMPRINTING OF POLYMERIZED CATALYTIC COMPLEXES IN ASYMMETRICCATALYSIS

The hydride transfer reduction of prochiral ketones using rhodium base d catalysts has been studied. In homogenous catalysis, acetophenone wa s quantitatively converted to (R) phenyl ethanol 3 in 7 days, (67% ee) using two equivalent of (1S,2S)-N,N'-dimethyl-1,2-diphenylethane diam ine per Rh. We then prepared polyurea supported complex: rhodium conta ining catalyst were prepared by complexation of the metal to nitrogen ligands in the backbone. Using this catalyst, acetophenone was quantit atively converted to (S) phenyl ethanol in 1 day, enantiomeric excess was 60%. We have then polymerised preformed [rhodium(I)-(N,N'-dimethyl - 1,2-diphenylethane diamine)(2)] with di- and triisocyanates. Using t he (S,S) isomer of the diamine leads to the reduction of propiophenone into (R) in 6 days with 47% ee In order to use molecular imprinting e ffect, we have polymerised [rhodium(I)-(N,N'-dimethyl-1,2-diphenyletha ne diamine)(2)] in the presence of a chiral template: pure (R) or (S) sodium phenylethanolate. Reduction of various substrates was carried o ut. We have shown that the imprinting effect is obvious for molecule r elated in structure to the template (propiophenone, 4'-trifluoromethyl acetophenone) and it is not efficient if the substrate has a structur e too different from the template one. The studying of conversion vs. global conversion has shown that the mechanism occurs via two parallel reactions on the same site without any interconversion of the final p roducts. Phenyl ethyl ketone was reduced quantitatively in 2 days to ( R) phenyl ethanol ee 70%. (C) 1998 Elsevier Science B.V. All rights re served.