PREPARATION OF OPTICALLY-ACTIVE (1-METHOXYCARBONYL)ETHYL)COBALOXIMES COORDINATED WITH VARIOUS AXIAL LIGANDS AND THEIR PHOTORACEMIZATION - REMARKABLE STERIC EFFECT OF AXIAL LIGAND ON THE CO-C BOND HOMOLYSIS

Optically active [1-(methoxycarbonyl)ethyl]cobaloximes coordinated with various axial bases were prepared and their photoracemization rates were measured in a solution state. It was found that although the electronic effect of the axial ligand was negligible on the rate of photochemical Co-C bond homolysis, the steric bulkines accelerated the rate remarkably. These results had a similar tendency to those observed in a previously reported reaction with 1-cyanoethyl cobaloximes, though the degree of rate enhancement due to the steric bulkiness of the axial ligand was extremely enlarged. The reason is also discussed.