August 7, 2025

Non-Heme Tri-Iron(II) Complex as a Precursor for Dioxygen Activation and Oxygen Reduction Reaction Catalysis

Key Points

MAIN FINDING: The triiron(II) complex shows significant activity in O2 activation and selective catalysis for H2O production in the oxygen reduction reaction.
KEY EVIDENCE: The complex generates a unique {Fe4OF5}3+ core which demonstrates high selectivity for H2O when exposed to O2 and appropriate reactants.
APPROACH: The study involved characterizing the complex in solid and solution states, and examining its behavior in acetonitrile with various reactants.
SIGNIFICANCE: This system advances the understanding of nonheme iron catalysts and opens avenues for their application in efficient chemical processes.

Abstract

Nonheme iron catalysts are attractive for bioinspired aerobic oxidations and oxygenations, as well as for the oxygen reduction reaction (ORR), although their potential in ORR remains largely underexploited. This study presents a rare example of such a system, displaying O2 activation activity and ORR catalytic selectivity toward H2O generation. The triiron (II) complex FeIIL3 (BF4) 3, where L- is a thiolate-containing N3S donor bis (2-pyridylmethyl) amine derivative, was fully characterized in the solid state and in MeCN solution, where it dissociates into the mononuclear solvent adduct FeL (MeCN) +. Upon exposure to O2 in an acetonitrile solution, FeL (MeCN) + generates a μ-oxo diiron (III), that further evolves to an adduct featuring an original Fe4OF53+ core. In the presence of 2, 6-lutidinium tetrafluoroborate (proton source), and octamethylferrocene (reducing agent), FeL (MeCN) + catalyzes the ORR with exclusive production of H2O. This system is finally discussed with respect to a few other reported nonheme Fe-based ORR catalysts operating under chemical conditions.

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