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(H ₂O)(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.