LIGAND INTERCHANGE CONTROLS MANY OXIDATIONS OF DIVALENT 1ST-ROW TRANSITION-METAL IONS BY FREE-RADICALS

The volumes of activation of a series of reactions of the free radicals .CH3, CO2.-, Br2.-, and (SCN)2.-, with several Mn(II), Fe(II), and Co(II) complexes were determined. Previous data indicate that all the reactions studied proceed via the inner-sphere mechanism. The results indicate that indeed the DELTAV(double dagger) values are similar to those reported for solvent exchange and complex formation reactions of these metal cations. Thus, the results point out that mechanistically these free radicals can be considered as nucleophilic attacking ligands. The DELTAV(double dagger) values for the homolysis of the metal-carbon sigma bond in (NTA)Mn(III)-CH3- and (NTA)Fe(III)-CH3-are 4.0 and approximately 0 cm3 mol-1, respectively. When compared to the DELTAV(double dagger) values for analogous homolysis processes previously reported, the results suggest that the DELTAV(double dagger) values depend strongly on the metal-carbon bond strength.