Direct observation of steric hindrance in the process of photoisomerization of cobaloxime complexes

The cobaloxime complex crystals with the beta -cyanoethyl group as an axial group and the biphenylboron group substituted to the equatorial ligand wer e prepared. When the crystals were irradiated with a xenon lamp, the beta - cyanoethyl groups were changed to the alpha -cyanoethyl group with retentio n of the single crystal forms. The produced alpha -cyanoethyl groups were n ot racemic but chiral depending on the asymmetry around the beta -cyanoethy l groups in the original crystals. It was made clear from the structure ana lyses before and after the reaction that the steric repulsion of the biphen ylboron group with the produced alpha -cyanoethyl group is responsible to t he generation of chirality.