Kinetic resolution of the chiral iron acetyl complexes [Fe(CO) (η5-C5H5)(L)COCH3] [L= PPh 3, P(p-tolyl)3] via aldol reactions with camphor
Case-Green SC., Costello JF., Davies SG., Heaton N., Hedgecock CJR., Humphreys VM., Metzler MR., Prime JC.
The chiral iron acetyl complexes [Fe(CO)(η5-C 5H5)(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.