Asymmetric 1,3-dipolar cycloaddition reaction of α,β-unsaturated nitriles with nitrones catalyzed by chiral-at-metal rhodium or iridium complexes

The aqua complexes (S-M,R-C)-[(eta(5)-C5Me5)M{(R)-Prophos}(H2O)](SbF6)(2) (M = Rh, Ir; (R)-Prophos = 1,2-bisdiphenylphosphino propane) catalyze the 1,3-dipolar cycloaddition reaction (DCR) of nitrones with alpha,beta-unsaturated nitriles with low-to-moderate enantioselectivity. The involved catalysts [(eta(5)-C5Me5)M{(R)-Prophos}(alpha,beta-unsaturated nitrile)](SbF6)(2), isolated as mixtures of the (S-M,R-C)- and (R-M,R-C)-diastereomers, have been fully characterized, and the molecular structure of the complexes (S-Rh,R-C)-[eta(5)-C5Me5)Rh{(R)-Prophos}(cis-2-pentenenitrile)](SbF6)(2) and (S-Ir,R-C)-[eta(5)-C5Me5)Ir{(R)-Prophos}(acrylonitrile)](SbF6)(2) has been determined by X-ray diffraction. The (R)-at-metal epimers isomerize to the (S)-at-metal counterparts. Diastereopure (S-M,R-C)-[(eta(5)-C5Me5)M{(R)-Prophos)(alpha,beta-unsaturated nitrile)](SbF6)(2) complexes catalyze the above-mentioned DCR in a stoichiometric manner with Lip to 97% ee. The results make clear the influence of the metal configuration on the catalytic stereochemical Outcome. The catalysts can be recycled without significant loss of either activity or selectivity. (C) 2009 Elsevier Ltd. All rights reserved.