ORR on Macrocyclic Transition Metal Complexes

1 ORR Mechanisms Catalyzed by Transition Metal Macrocyclic Complexes 

Transition metal maeroeyelie eomplexes ean eatalyze the O2 reduetion reaetion through a 2-eleetron or 4-eleetron transfer pathway to produee either FI2O2 or FI2O. Sometimes, they ean also eatalyze ORR through a mixed pathway of 2- and 4-eleetron transfer reduetion. In rare eases, transition metal maeroeyelie eomplexes ean also eatalyze a 1-eleetron O2 reduetion, produeing superoxide ions. 

The eatalytie reaetion meehanism is proposed to be a modified redox eatalysis proeedure [1, 49]. In the first step, the adduet between oxygen and the metal ion eenter of the maeroeyelie eompound is formed, followed by an intra-adduet eleetron transfer from the metal ion to the oxygen. The addition of protons from the eleetrolyte, together with the eleetron transfer, then produees FI2O2. The FI2O2 is either the final produet or ean be further redueed to produee water, depending on the individual transition metal maeroeyelie eompounds used. The meehanism ean be summarized as follows  

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