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 (SM,RC)-[(η5-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 α,β-unsaturated nitriles with low-to-moderate enantioselectivity. The involved catalysts [(η5-C5Me5)M{(R)-Prophos}(α,β-unsaturated nitrile)](SbF6)2, isolated as mixtures of the (SM,RC)- and (RM,RC)-diastereomers, have been fully characterized, and the molecular structure of the complexes (SRh,RC)-[(η5-C5Me5)Rh{(R)-Prophos}(cis-2-pentenenitrile)](SbF6)2 and (SIr,RC)-[(η5-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 (SM,RC)-[(η5-C5Me5)M{(R)-Prophos}(α,β-unsaturated nitrile)](SbF6)2 complexes catalyze the above-mentioned DCR in a stoichiometric manner with up 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.

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(SRhRc)-(Acrilonitrile)(η5-pentamethylcyclopentadienyl)(prophos)rhodium(III) hexafluoroantimoniateC40H44F12NP2RhSb2Ee = 100[α]D27=-26.7 (c 0.5, CH2Cl2)Source of chirality: (R)-prophosAbsolute configuration: (SRhRC)

(SRhRc)-(Methacrilonitrile)(η5-pentamethylcyclopentadienyl)(prophos)rhodium(III) hexafluoroantimoniateC41H46F12NP2RhSb2Ee = 100[α]D27=-20.8 (c 0.5, CH2Cl2)Source of chirality: (R)-prophosAbsolute configuration: (SRhRC)

(SRhRc)-(cis-2-Pentenenitrile)(η5-pentamethylcyclopentadienyl)(prophos)rhodium(III) hexafluoroantimoniateC42H48F12NP2RhSb2Ee = 100[α]D27=-31.2 (c 0.6, CH2Cl2)Source of chirality: (R)-prophosAbsolute configuration: (SRhRC)

(SRhRc)-(trans-Cinnamonitrile)(η5-pentamethylcyclopentadienyl)(prophos)rhodium(III) hexafluoroantimoniateC46H48F12NP2RhSb2Ee = 100[α]D24=-90.2 (c 0.6, CH2Cl2)Source of chirality: (R)-prophosAbsolute configuration: (SRhRC)

(SRhRc)-(1-Cyclohexen-1-nitrile)(η5-pentamethylcyclopentadienyl)(prophos)rhodium(III) hexafluoroantimoniateC44H50F12NP2RhSb2Ee = 100[α]D27=-28.9 (c 0.5, CH2Cl2)Source of chirality: (R)-prophosAbsolute configuration: (SRhRC)

(SIrRc)-(Acrilonitrile)(η5-pentamethylcyclopentadienyl)(prophos)iridium(III) hexafluoroantimoniateC40H44F12IrNP2Sb2Ee = 100[α]D26=-46.3 (c 0.6, CH2Cl2)Source of chirality: (R)-prophosAbsolute configuration: (SIrRC)

(SIrRc)-(Methacrilonitrile)(η5-pentamethylcyclopentadienyl)(prophos)iridium(III) hexafluoroantimoniateC41H46IrF12NP2Sb2Ee = 100[α]D27=-36.9 (c 0.7, CH2Cl2)Source of chirality: (R)-prophosAbsolute configuration: (SIrRC)

(SIrRc)-(cis-2-Pentenenitrile)(η5-pentamethylcyclopentadienyl)(prophos)iridium(III) hexafluoroantimoniateC42H48IrF12NP2Sb2Ee = 100[α]D25=-48.9 (c 0.6, CH2Cl2)Source of chirality: (R)-prophosAbsolute configuration: (SIrRC)

(SIrRc)-(trans-Cinnamonitrile)(η5-pentamethylcyclopentadienyl)(prophos))iridium(III) hexafluoroantimoniateC46H48IrF12NP2Sb2Ee = 100[α]D26=-90.1 (c 0.6, CH2Cl2)Source of chirality: (R)-prophosAbsolute configuration: (SIrRC)

(SIrRc)-(1-Cyclohexen-1-nitrile)(η5-pentamethylcyclopentadienyl)(prophos))iridium(III) hexafluoroantimoniateC44H50IrF12NP2Sb2Ee = 100[α]D26=-48.0 (c 0.7, CH2Cl2)Source of chirality: (R)-prophosAbsolute configuration: SIrRC)