Stereoselective recognition of an aziridine with a Co(III) complex: a potential transition-state analogue for catalytic epoxidation.

Reversible and stereoselective coordination of 1-(R)-phenyl-2-(S)-methylaziridine to (S,S)L-Co(III) and (R,R)L-Co(III) (where L represents a salen ligand obtained from diamino cyclohexane and 2,4-di-tert-butyl salicylaldehyde) has been investigated. 1H NMR data indicate that the aziridine binds about three times more tightly to (S,S)L-Co(III) than to (R,R)L-Co(III). Crystal structures of two molecules of the aziridine coordinated to the Co(III) complexes have been determined. These structures together with molecular mechanics computation provide insight into the origin of stereoselective recognition of the aziridine to the Co(III) complexes.