Chirality Inversion Process of a Bulky Alkyl Group in the Crystalline State Photo‐Isomerization of Cobaloxime Complex Crystals

Abstract

AbstractThe complex of [(R)‐tert‐(butoxycarbonyl)ethyl][(S)‐1‐cyclohexylethylamine]bis(dimethylglyoximato)cobalt(III), (R‐bce)(S‐cha)cobaloxime, 1, showed a racemization of the R‐bce group on exposure to a xenon lamp with retention of the single crystal form. A part of the R‐bce groups gradually inverted to the opposite configuration in the P212121 cell. However, the inversion of the R‐bce group converged when the R:S ratio became ca.75:25. The shape of the reaction cavity for the disordered bce group became symmetric at the ratio. For the related complex crystal with pyridine as an axial ligand, (R‐bce)(py)cobaloxime, 2, there are two crystallographically independent molecules, A and B, which are related by a pseudo inversion center in the P21 cell. When the crystal was exposed to the xenon lamp, the R‐bce group of the A molecule was gradually inverted to the opposite configuration without decomposition of the single crystal form, whereas the R‐bce group of B remained unchanged. Finally the pseudo inversion center became a crystallographic one and the space group became P21/c. The third complex crystal with water as an axial ligand, (R‐bce)(aqua)cobaloxime, 3, showed no changed on exposure to the xenon lamp. This is well explained by the size and shape of the reaction cavities for the R‐bce groups in the three crystals.