Racemizations of Alkyl Groups in Cobaloxime Complex Crystals

Abstract

The mechanism of racemization was examined with theoretical calculation and neutron diffraction. Various racemization processes were observed changing the axial base ligand and chiral alkyl group in the crystals of cobaloxime complex crystals. For racemization of the cyanoethyl group bonded to the cobalt atom, three different types of racemization were observed owing to the different structures before the reaction. The reaction process and the reaction rate are well explained by the size and shape of the reaction cavity. Moreover, the unusual racemic-to-chiral transformation was made clear using the size and shape of the reaction cavity. For the bulkier (methoxycarbonyl)ethyl groups, not only the inversion of the chiral carbon atom bonded to the cobalt atom but also the anti -to-syn transformation of the methoxyl group occurs cooperatively. Moreover, solvent molecules in a crystal play an important role in racemization.