Crystalline-state beta-alpha photoisomerization of cobaloxime complexes .1. Generation of asymmetry in chiral crystal environment

The beta-cyanoethyl groups bonded to the cobalt atoms in [beta-cyanoethyl)(3-methylpyridine)bis(dimethylglyoximato)cobalt(III) and [beta-cyanoethyl](4-methylpyridine)bis(dimethylglyoximato)cobalt(III) are isomerized to the alpha-cyanoethyl groups, at room temperature and at 346 K respectively, on exposure to visible light with retention of the single crystal form. The produced alpha-cyanoethyl group has a chiral carbon atom bonded to the cobalt atom. The crystal structures of the 3-methylpyridine complex before and after the irradiation, which were determined by X-rays, revealed that the ratio of the R and S configurations of the produced alpha-cyanoethyl group in one site was not 1:1 but about 4:7. On the other hand, the alpha-cyanoethyl group only had the R configuration in one site of the 4-methylpyridine complex crystal. The difference in shape of the reaction cavities for the produced alpha-cyanoethyl groups of the two complex crystals well explains the reason why such different degrees of asymmetry were generated in the produced alpha-cyanoethyl groups. (C) 1997 Published by Elsevier Science S.A.