DOI: 10.1002/adsc.201100152 Cyclometalated Complexes of Ruthenium, Rhodium and Iridium as Catalysts for Transfer Hydrogenation of Ketones and Imines Nicolas Pannetier,a Jean-Baptiste Sortais,a Jean-Thomas Issenhuth,a

Abstract: A library of organometallic compounds de-rived from primary and secondary amines cyclometa-lated by ruthenium(II), rhodium ACHTUNGTRENNUNG(III) and iridi-um ACHTUNGTRENNUNG(III) was tested in the asymmetric transfer hydro-genation of a number of ketones and imines. All compounds displayed high catalytic activity for the reduction of ketones under mild conditions. The most enantioselective catalysts were based on secon-dary amines containing two asymmetric carbon atoms bound to the nitrogen atom. For the reduction of aryl alkyl ketones [Ar ACHTUNGTRENNUNG(C=O)R where R=CH3 or CH2R’] the cyclometalated ruthenium and rhodium derivatives of the (2R,5R)-2,5-diphenylpyrrolidine ligand displayed the best results with respect to ac-tivity and selectivity (ees up to 97%). However, for the reduction of aryl tert-alkyl ketones [Ar ACHTUNGTRENNUNG(C=O)R’’ in which R’ ’ is a tertiary alkyl group] the best catalyst was a ruthenium compound derived from bis[(R)-1-phenylethyl]amine, allowing the reduction of isobu-tyrophenone and cyclohexyl phenyl ketone which were both reduced with high enantioselectivities (ees up to 98%). This shows that the cyclometalated com-pounds have a high substrate specificity. In addition, acyclic and cyclic imines were reduced with good se-lectivities by both rhodium ACHTUNGTRENNUNG(III) and iridium ACHTUNGTRENNUNG(III) met-alacycles built up with (2R,5R)-2,5-diphenylpyrroli-dine