Chiral (Cyclopentadienone)iron Complexes for the Catalytic Asymmetric Hydrogenation of Ketones

Three chiral (cyclopentadienone)iron complexes derived from (R)-BINOL (CK1-3) were synthesized and their structures unambiguously confirmed by X-ray analysis (CK3). Under suitable conditions for the in situ conversion into the corresponding (hydroxycyclopentadienyl)iron hydrides (Me3NO, H2), the new chiral complexes were tested in the catalytic asymmetric hydrogenation of ketones, showing moderate to good enantioselectivity. In particular, the complex bearing methoxy substituents at the 3,3-positions of the binaphthyl moiety (CK2) proved remarkably more enantioselective than the unsubstituted one (CK1) and reached the highest level of enantioselectivity (up to 77% ee) ever obtained with chiral (cyclopentadienone)iron complexes.