Porphyrin macrocylic structure

Even though most of the work reported has involved planar cobalt complexes nonplanar macrocylics also catalyze the reaction. For example, nonplanar cobalt tetrakis-(4-sulfonatophenyl)/ -octabromoporphyrin catalyzed the reduction of O2 via two electrons to give peroxide . Vitamin B12, which is also nonplanar, and its structure resembles that of a porphyrin (see Figure 2.4.), catalyzes the reduction of O2 via two electrons to give peroxide at low potentials and via four electrons to give water at higher overpotentials... 

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