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

• Published in: Organometallics Vol. 32; no. 6; pp. 1609 - 1619
• Main Authors: Carmona, Daniel, Ferrer, Joaquina, Garcı́a, Néstor, Ramı́rez, Paola, Lahoz, Fernando J, Garcı́a-Orduña, Pilar, Oro, Luis A
• Format: Journal Article
• Language: English
• Published: American Chemical Society 25-03-2013
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/om301089c

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.