A Study of the Kinetic Resolution of Dl -Propylene Oxide with Optically Active Co(I)(salen) Type Complexes

An optically active Co(I)(salen) type complex, lithium N,N′-bis-(salicylaldehyde)-1(R),2(R)-1,2-trans-cyclohexanediiminatocobaltate (I), was prepared by reducing the Co(II) complex, N,N′-bis-(salicylaldehyde)-1(R),2(R)-1,2-trans-cyclohexanediiminatocobalt(II), with butyllithium. The structure of the Co(I) complex was determined by means of its absorption and circular dichroism (CD) spectra. d-Propylene oxide was found to react preferentially (e.g., < >=68% in a dioxane solution) in a kinetic resolution of Dl-propylene oxide using the above Co(I) complex as a catalyst. On the contrary, l-propylene oxide reacted selectively when Lewis acids were added to the system of the lithium Co(I) complex. The Lewis acids were demonstrated to interact with the Co(I) complex and to play a significant role in the asymmetric selectivity of the Co(I) species.