Substitution reactions on metal complexes

A chemical bond, represented in terms of shared pairs of electrons, can be broken homolytically or heterolytically, as shown by the following equations  

In homolysis, both fragments hold one electron each. If neither A nor B are transition metals, homolysis will lead to formation of free radicals. For instance, molecular chlorine, CI2, whose dissociation energy is relatively low = 242.67 kJmor = 58 kcalmoF ) will yield free radicals under the influence of light, or at elevated temperatures  

Radicals formed in this way can, even in small quantities, initiate chain reactions  

Methyl radical reacts further with chlorine  

Chlorine atom proceeds to react in the chain reaction. In practice, the chain reaction stops after some 10000 cycles. The reason why the chain reaction discontinues is destruction of the chain carrier, as in eq. (2.1.7), when two radicals collide  

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F. Basolo, Coord. Chem. Rev., 100, 47 (1990), A retrospective on studies of ligand substitution reactions on metal complexes. 

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