Enhanced Four‐Electron Oxygen Reduction Selectivity of Clamp‐Shaped Cobalt(II) Porphyrin(2.1.2.1) Complexes

The molecular structure, electrochemistry, spectroelectrochemistry and electrocatalytic oxygen reduction reaction (ORR) features of two CoII porphyrin(2.1.2.1) complexes bearing Ph or F5Ph groups at the two meso‐positions of the macrocycle are examined. Single crystal X‐ray analysis reveal a highly bent, nonplanar macrocyclic conformation of the complex resulting in clamp‐shaped molecular structures. Cyclic voltammetry paired with UV/Vis spectroelectrochemistry in PhCN/0.1 M TBAP suggest that the first electron addition corresponds to a macrocyclic‐centered reduction while spectral changes observed during the first oxidation are consistent with a metal‐centered CoII/CoIII process. The activity of the clamp‐shaped complexes towards heterogeneous ORR in 0.1 M KOH show selectivity towards the 4e− ORR pathway giving H2O. DFT first‐principle calculations on the porphyrin catalyst indicates a lower overpotential for 4e− ORR as compared to the 2e− pathway, consistent with experimental data. Clamp‐shaped cobalt(II) porphyrin(2.1.2.1) complexes were investigated as to their electrochemical, spectroelectrochemical, and electrocatalytic ORR. Electrochemistry indicates that the first oxidation corresponds to a CoII/CoIII process. The ORR capacities of both complexes show higher selectively for the 4e− ORR and DFT calculations suggest a lower overpotential for the 4e− ORR pathway than for the 2e− pathway.