Highly efficient iridium catalysts based on C2-symmetric ferrocenyl phosphinite ligands for asymmetric transfer hydrogenations of aromatic ketones

Abstract

A series of chiral modular C2-symmetric ferrocenyl phosphinite ligands have been synthesized in good yields by using 1,1′-ferrocenedicarboxyaldehyde and various amino alcohols as starting materials, and applied in the iridium(III)-catalyzed asymmetric transfer hydrogenations of aromatic ketones to give the corresponding secondary alcohols with good enantioselectivities and reactivities using 2-propanol as the hydrogen source (up to 98% ee and 99% conversion). The substituents on the backbone of the ligands were found to have a significant effect on both the activity and enantiomeric excess. The structures of these complexes have been clarified by a combination of multinuclear NMR spectroscopy, IR spectroscopy, and elemental analysis.