An iron variant of the Noyori hydrogenation catalyst for the asymmetric transfer hydrogenation of ketones

We report the design of a new iron catalyst for the asymmetric transfer hydrogenation of ketones. This type of iron catalyst combines the structural characteristics of the Noyori hydrogenation catalyst (an axially chiral 2,2 '-bis(phosphino)-1,1 '-binaphthyl fragment and the metal-ligand bifunctional motif) and an ene(amido) group that can activate the iron center. After activation by 8 equivalents of potassiumtert-butoxide, (S-A,R-P,SS)-7aand (S-A,R-P,SS)-7bare active but nonenantioselective catalysts for the transfer hydrogenation of acetophenone and alpha,beta-unsaturated aldehydes at room temperature in isopropanol. A maximum turnover number of 14480 was observed for (S-A,R-P,SS)-7ain the reduction of acetophenone. The right combination of the stereochemistry of the axially chiral 2,2 '-bis(phosphino)-1,1 '-binaphthyl group and the carbon-centered chiral amine-imine moiety in (S-A,R-P,RR)-7b ' afforded an enantioselective catalyst for the preparation of chiral alcohols with moderate to good yields and a broad functional group tolerance.