Determination of Co-C bond dissociation energies for organocobalt complexes related to coenzyme B12 using photoacoustic calorimetry

Photolysis of organocobalt complexes with Schiff base equatorial ligand, bis(salicylidene)ethylenediamine (salen), has been investigated by pulsed, time-resolved photoacoustic calorimetry in methanol at ambient temperature. The observed enthalpy changes and measured cobalt-carbon bond dissociation energies for the above compounds lie within the range 80-170 kJ mol(-1). The influence of the steric and electronic factors of both the alkyl group and trans base ligand on Co-C bond strength is discussed. It is interesting to note that we obtain the highest Co-CH3 bond dissociation energy (BDE) value of 168 kJ mol(-1) for CH3Co(salen)H2O compared with those for coenzyme B-12 and its model compounds.