Intermolecular vs. Intramolecular Reduction of Cobalt(III) Centers by Coordinated Pyridinyl Radicals

Four pentaamminecobalt(III) complexes, bound via a nonconjugated carboxylate to a pyridinyl derivative, were reduced by aliphatic free radicals. The primary site of reduction is shown to be the pyridinyl group. In one of the complexes studied an intramolecular electron transfer from the free radical to the cobalt center is observed, kIET = 4 X 10 s. Surprisingly the coordinated pyridinyl radicals in the other complexes reduce another cobalt(III) center via an intermolecular process. The origin of the different patterns of behavior is discussed.