Chiral Octahedral Phosphano–Oxazoline Iridium(III) Complexes as Catalysts in Asymmetric Cycloaddition Reactions

The synthesis and characterization of cationic iridium­(III) aqua complexes of the formula [IrH­(H2O)­(PN*)­(PP)]­[SbF6]2 (PN* = chiral phosphano–oxazoline ligand; PP = diphosphane) as well as that of the OPOF2-containing complex [IrH­(OPOF2)­(PNiPr)­(dppp)]­[SbF6] (10) are reported. The X-ray molecular structures of [IrH­(H2O)­(PNInd)­(dppe)]­[SbF6]2 (1), [IrH­(H2O)­(PNInd)­(dppen)]­[SbF6]2 (2), and 10a have been determined. Dichloromethane solutions of these aqua complexes efficiently catalyze the enantioselective 1,3-dipolar cycloaddition of the nitrone N-benzylidenephenylamine N-oxide to methacrolein and Diels–Alder reactions between cyclopentadiene and trans-β-nitrostyrenes. In the first case, the catalytic reaction occurs with excellent endo selectivity and ee up to 85%; the Diels–Alder reaction occurs rapidly at room temperature with good endo:exo selectivity and ee up to 90%. The dipolar cycloaddition intermediates [IrH­(methacrolein)­(PNInd)­(PP)]­[SbF6]2 (PP = (S,S)-chiraphos (11), (R)-prophos (12)) have been characterized, and the molecular structure of 11 has been determined by an X-ray structural analysis.