Mechanisms of thermal decomposition of dialkylcobalt(III) complexes

Abstract

The thermal stability of a series of CoR 2(acac)(PPhMe 2) 2 complexes decreases in the order: CH 3>;C 2H 5 >C 3H 7>C 4H 9. Thermal decomposition of the alkylcobalt complex in toluene solution is first order with respect to the complex and activation energies for pyrolysis of the ethyl and propyl cobalt complexes are 30.6 and 25.5 kcal/mol, respectively. Addition of free PPhMe 2 to the solution of the ethyl cobalt complex strongly inhibits its thermal decomposition and the apparent activation energy increases with increasing the concentration of added PPhMe 2 approaching its limiting value of ca. 35 kcal/mol. Comparison of the relative rates of thermolysis of Co(C 2H 5) 2(acac)(PPhMe 2) 2 and Co(CH 2CD 3(acac)(PPhMe 2) 2 revealed the presence of a considerable isotope effect (k H/k D  2.30 ± 0.05). The slow thermolysis of the ethyl-d 3 complex below 5° in benzene or toluene, and the thermolysis at room temperature in pyridine as well as rapid thermolysis of the solid sample, predominantly liberate