Kinetic resolution of the chiral iron acetyl complexes [Fe(CO)(η5-C5H5)(L)COCH3][L = PPh3, P(p-tolyl)3]via aldol reactions with camphor

Abstract

The chiral iron acetyl complexes [Fe(CO)(η⁵-C₅H₅)(L)COCH₃][L = PPh₃, P(p-tolyl)₃] have been kinetically resolved via aldol reactions involving their derived lithium enolates and camphor in the presence of lithium chloride. With (1R)-(+)-camphor the faster reacting iron acetyl enantiomer had the (S)-configuration allowing the (R)-iron acetyls to be obtained after recovery of starting material and crystallisation. The corresponding (S)-iron acetyls can be obtained by a base-promoted reverse aldol reaction of the isolated products. A mechanistic rationale for the high enantiomeric discrimination is proposed which involves a chelation-controlled chair transition state with a disfavourable 1-methyl to cyclopentadienyl interaction in the mismatched pairing.