Tunable ferrocenyl diphosphine ligands for the Ir-catalyzed enantioselective hydrogenation of N-aryl imines

Ferrocenyl diphosphines R2PF-P(R')(2) are effective. tunable ligands for the iridium catalyzed enantioselective hydrogenation of N-aryl imines in the presence of iodide and acid promoters. Structure-activity/selectivity correlations were found for the hydrogenation of N-(2-ethyl-6-methylphenyl)-N-(1 ' -methoxymethyl)-ethylidene-amine (MEA-imine) and for 2,3,3-trimethylindolenine (TMI). Extremely high catalytic activity and moderate to good enantioselectivity were observed for the MEA imine using a catalyst generated in situ from [Ir(cod)Cl](2) and (R)-(S)-PPF-P(3,5-Xyl)(2) (xyliphos). With the same type of catalysts, several other N-aryl imines can be hydrogenated with enantioselectivities between 31 and 96%, albeit with lower catalyst activities. (C) 2001 Elsevier Science B.V. All rights reserved.