Direct Observation of Steric Hindrance in the Process of Photoisomerization of Cobaloxime Complexes

Abstract

The cobaloxime complex crystals with the β-cyanoethyl group as an axial group and the biphenylboron group substituted to the equatorial ligand were prepared. When the crystals were irradiated with a xenon lamp, the β-cyanoethyl groups were changed to the α-cyanoethyl group with retention of the single crystal forms. The produced α-cyanoethyl groups were not racemic but chiral depending on the asymmetry around the β-cyanoethyl groups in the original crystals. It was made clear from the structure analyses before and after the reaction that the steric repulsion of the biphenylboron group with the produced α-cyanoethyl group is responsible to the generation of chirality.

Key Words:

• photoisomerization
• cobaloxime complex
• X-ray crystal structure analysis
• asymmetric reaction
• solid-state reaction