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

Abstract

Herein, 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 NaHCO3 solution (pH 8.4). We found that 1 and 2 are molecular catalysts and that O−O bond formation proceeds via oxo–oxo coupling rather than by the water nucleophilic attack (WNA) pathway. In contrast, complex 3 displays negligible catalytic activity. DFT calculations suggested that the anti to syn isomerization 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 FeIVFeIV state or via oxo–oxyl coupling pathway at the FeIVFeV state. Importantly, the rigid BPMAN ligand in complex 3 limits the anti to syn isomerization and axial rotation of the Fe=O moiety, which accounts for the negligible catalytic activity.

Heterobimetallic NiFe Cooperative Molecular Water Oxidation Catalyst

“…Structurally well‐defined molecular platform is a good choice for detailed mechanistic understanding. However, most reported molecular catalysts are mononuclear [3b, d, f, 11] and homonuclear complexes, [4c, d, 12] while heteronuclear catalysts are much less established due to synthetic challenges [13]…”

Iron–N-heterocyclic carbene complexes as efficient electrocatalysts for water oxidation under acidic conditions

“…42,43 This relationship indicates that the electron transfer rate in the redox process is sufficiently fast and reversible. 44 There was no sign of precipitation or film formation on the working electrode.…”

“…S18b†) analysis indicated that no new species were deposited on the electrode surface after electrolysis under 1.70 V ( vs. NHE) for 1 h. These results rule out the formation of heterogeneous deposits on the electrode during the catalytic reaction. 44…”

“…S18b †) analysis indicated that no new species were deposited on the electrode surface after electrolysis under 1.70 V (vs. NHE) for 1 h. These results rule out the formation of heterogeneous deposits on the electrode during the catalytic reaction. 44 To explore any possible formation of heterogeneous species in the solution during catalysis, the electrolyte before and after CPE under 1.70 V (vs. NHE) for 1 h was detected by DLS. Fig.…”

A new hexanuclear Fe(iii) nanocluster: synthesis, structure, magnetic properties, and efficient activity as a precatalyst in water oxidation

“…31,32 To date, various iron coordination compounds have been investigated that can act as water oxidation catalysts. [33][34][35][36] However, studies show that some Fe complexes cannot behave as homogeneous molecular electrocatalysts for the oxygen evolution reaction (OER). Designing unique ligands that allow the production of high-valent iron compounds in the catalytic cycle is one of the significant challenges in this area.…”