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

摘要

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.