Solid state-specific and chiral lattice-controlled asymmetric photoisomerization of 3-substituted propyl cobalt complexes, and direct observation of the intermediate complex

Solid state-specific and chiral lattice-controlled asymmetric photoisomerization of 3-cyanopropyl cobaloxime complexes coordinated with chiral axial ligand, 1a–h, was found to occur with moderate to relatively high enantioselectivities (∼91%ee), even though the reaction proceeds through radical species. The enantioselectivities at a lower temperature (−78 °C) are extremely enhanced as compared to those at room temperature, in most cases. The configuration of the major enantiomer of the isomerized product is predictable from the shape of the reaction cavity, drawn based on the crystal structure of the starting material. The structure (including absolute configuration) of the intermediate 2-cyanopropyl complex was directly observed by X-ray crystallographic analyses of a single-crystal-to-single-crystal reaction of (S)-1-cyclohexylethylamine-coordinated 3-cyanopropyl cobaloxime, 1e.