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

Abstract

Ferrocenyl diphosphines R 2PF-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.