The Role of Electron‐Donor Substituents in the Family of OPBAN‐Cu Water Oxidation Catalysts: Effect on the Degradation Pathways and Efficiency

The efficiency of the OPBAN‐Cu (OPBAN= tetraanionic derivative of 1,2‐phenylene bis(oxamic acid)) water oxidation catalyst family has been studied by DFT calculations. We have explored four different tetraamidate copper complexes [(L1–4)Cu]^2– (where L1 is N1,N1′‐(1,2‐phenylene)bis(N2‐methyloxalamidate) and L2–4 are variations of the same ligand with electron donating groups in the ring backbone), determining the redox active character of the ligand in the activation process and the Single Electron Transfer‐Water Nucleophilic Attack (SET‐WNA) mechanism for the O–O bond formation step. Interestingly, the stability of the two‐center three‐electron (2c3e^–) intermediate, common in the four reactions, correlates with the experimental efficiency. Additionally, we explored two pathways of catalyst degradation: the attack of a hydroxyl anion to the phenyl cation radical of the ligand and the degradation by protonation of the amidate groups when pH decreases. This last step is supported by cyclic voltammetry pH‐dependent experiments.