Synthesis of (R)-BINOL-derived (cyclopentadienone)iron complexes and their application in the catalytic asymmetric hydrogenation of ketones

A family of chiral (cyclopentadienone)iron complexes, featuring an (R)-BINOL-derived backbone, and their application in the asymmetric hydrogenation of ketones are described. The complexes differ from each other in the substituents at the 3,3-positions of the binaphthyl residue (H, OH, OR, OCOR, OSO2R) or at the 2,5-positions of the cyclopentadienone ring [trimethylsilyl (TMS) or Ph]. Remarkably, eight precatalysts with different 3,3-binaphthyl substitution [(R)-1c–1j] were synthesized from a common parent complex [(R)-1b] through direct functional group interconversion reactions of the complexes. The 3,3-(bis)methoxy-substituted precatalyst (R)-1b gave the best catalytic performance, and its application scope was assessed in the hydrogenation of several ketones. The observed ee values (up to 77%) are much higher than those previously reported for other chiral (cyclopentadienone) iron complexes.