The aqua complexes [(η5-C5Me5)M(PP*)(H2O)][SbF6]2 (M = Rh, Ir; PP* = chiral diphosphane) have been tested as catalysts for the asymmetric 1,3-dipolar cycloaddition of nitrones to α,β-unsaturated aldehydes. Quantitative conversions with very high regioselectivity, perfect endo selectivity and excellent enantioselectivity (up to 99% ee) were achieved. The stereochemical outcome was analyzed on the basis of the stereoelectronic properties of the intermediate enal complexes of the formula [(η5-C5Me5)M(PP*)(enal)][SbF6]2.We thank the Ministerio de Economía y Competitividad of Spain (CTQ2012-32095) and Gobierno de Aragón (Grupo Consolidado: Catalizadores Organometálicos Enantioselectivos) for financial support. A. A. acknowledges IUCH for a grant. R. R. acknowledges CSIC and European Social Fund for a JAE grant. M. C. acknowledges Gobierno de Aragón and CSIC for a DGA grant.Peer Reviewe
