Iron‐Catalyzed Water Oxidation: O–O Bond Formation via Intramolecular Oxo–Oxo Interaction

Abstract

AbstractHerein, we report the importance of structure regulation on the O−O bond formation process in binuclear iron catalysts. Three complexes, [Fe2(μ‐O)(OH2)2(TPA)2]4+(1), [Fe2(μ‐O)(OH2)2(6‐HPA)]4+(2) and [Fe2(μ‐O)(OH2)2(BPMAN)]4+(3), have been designed as electrocatalysts for water oxidation in 0.1 M NaHCO3solution (pH 8.4). We found that1and2are molecular catalysts and that O−O bond formation proceeds via oxo–oxo coupling rather than by the water nucleophilic attack (WNA) pathway. In contrast, complex3displays negligible catalytic activity. DFT calculations suggested that theantitosynisomerization of the two high‐valent Fe=O moieties in these catalysts takes place via the axial rotation of one Fe=O unit around the Fe‐O‐Fe center. This is followed by the O−O bond formation via an oxo–oxo coupling pathway at the FeIVFeIVstate or via oxo–oxyl coupling pathway at the FeIVFeVstate. Importantly, the rigid BPMAN ligand in complex3limits theantitosynisomerization and axial rotation of the Fe=O moiety, which accounts for the negligible catalytic activity.