III. Summary

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Organocobalt complexes are sources of free radicals because heating, photolysis, or enzymatic reaction cleaves a carbon–cobalt bond homolytically to produce carbon-centered and cobalt-centered radicals. Cleaving the carbon–cobalt bond in this way changes the oxidation state of cobalt from Co(III) to Co(II). Complexes with cobalt in the Co(II) oxidation state exhibit radical reactivity. Cobalt-containing carbohydrates easily undergo epimerization reactions because the radicals formed by bond fragmentation readily recombine. Carbon-centered radicals produced from organocobalt complexes also undergo the characteristic radical reactions of addition and cyclization.

Organocobalt and organomercury compounds have a similarity in reactivity because each contains a carbon-metal bond that is easily cleaved by heating or photolysis. Carbon-centered radicals produced from organomercury compounds undergo hydrogen-atom abstraction and radical addition reactions. Concern about the toxicity of organomercury compounds reduces their usefulness as radical precursors.