Kinetics and mechanism of cyclohexane oxidation catalyzed by supramolecular manganese(III) porphyrins

We report the kinetics of cyclohexane oxidation with iodosylbenzene, catalyzed by two supramolecular manganese(III) porphyrin isomers, containing four [Ru(bpy)2Cl]+ complexes attached to the pyridyl groups of meso-tetra(3-pyridyl)porphynatemanganese(III) or meso-tetra(4-pyridyl)porphynatemanganese(III) centers. An unusual pseudozero-order mechanism was observed by monitoring the formation of the cyclohexanol and cyclohexanone products, and a consistent oxygen-transfer mechanism, activated by the manganese center, was proposed on the light of the kinetic behavior. The kH/kD values suggested that in Mn(3-TRPyP) catalysis, the kinetics are favored by the stereochemical environment provided by the out-of-plane ruthenium complexes, whereas for the coplanar Mn(4-TRPyP) catalyst, the favorable electronic interaction of the ruthenium complexes with the metalloporphyrin center is the most relevant factor enhancing reactivity.