Characterization of Fused Mn and Cu Corroles and Their Potency as ORR Electrocatalysts

Given the rather poor activity of regular copper and manganese corroles as electrocatalysts for the oxygen reduction reaction (ORR), we now report the synthesis, structural characterization, and catalytic activity of binuclear manganese and copper complexes coordinated to β-β dimeric corrole frameworks. X-ray crystallographic analysis reveals distinct coordination environments and structural flexibility in these bimetallic systems: an almost perfect square geometry for the 4-coordinate (no axial ligands) bis-copper complex, while 5- and 6-coordinate structures were fully characterized for manganese with varying degrees of corrole planarity and metal displacement. The conjugation between the corrole subunits differs quite meaningfully for the copper and manganese complexes, which comes into play by much shorter near-IR bands in the electronic spectrum of the former, significantly longer C-C bond lengths in the bridging moiety of the latter, and differences in their redox potentials relative to the respective mononuclear complexes. Examination of porous carbon electrodes modified by these molecular ORR catalysts uncovered the superior performance of the binuclear manganese corrole dimer.