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A Structurally Authenticated Closed-Shell Iron(IV) Oxo Ferryl Complex: Synthesis, Properties, and Reactivity.
Weiqing Mao1, Zihan Zhang1, Martin Keilwerth1
1Department of Chemistry and Pharmacy, Inorganic Chemistry, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Egerlandstraße 1, 91058 Erlangen, Germany.
Journal of the American Chemical Society
|March 19, 2026
Summary
Researchers synthesized a stable iron(IV) oxo complex using a tripodal tris-N-heterocyclic carbene ligand. This nonmagnetic complex exhibits a short iron-oxygen bond and mediates oxygen-atom transfer reactions.
Area of Science:
- Inorganic Chemistry
- Organometallic Chemistry
- Coordination Chemistry
Background:
- Iron-oxo complexes are crucial in biological and catalytic oxidation reactions.
- Stabilizing high-valent iron species is challenging due to their reactivity.
- N-heterocyclic carbene (NHC) ligands offer robust coordination for stabilizing reactive metal centers.
Purpose of the Study:
- To synthesize and characterize a closed-shell, nonmagnetic iron(IV) oxo complex.
- To investigate the structural, spectroscopic, and electronic properties of the iron(IV) oxo species.
- To explore the reactivity of the synthesized complex in oxygen-atom transfer reactions.
Main Methods:
- Synthesis of iron complexes using tris-N-heterocyclic carbene (NHC) ligands.
- Oxidation reactions using N₂O, [Cp₂Fe][PF₆], and trimethylamine N-oxide (TMAO).
- Photolysis of ferrous sulfoxide isotopomers.
- Comprehensive characterization including X-ray crystallography, NMR, IR, UV-vis, Mössbauer spectroscopy, and elemental analysis.
- Computational analyses (DFT) and cyclic voltammetry.
Main Results:
- Successful synthesis and isolation of a diamagnetic iron(IV) oxo complex, [(Me₂TIMMNMeS)FeIV(O)](PF₆)₂, stabilized by a tripodal NHC ligand.
- Characterization revealed a short Fe-O bond (1.576 Å) and Mössbauer isomer shift indicative of the Fe(IV) state.
- Computational studies supported an Fe≡O triple bond.
- The complex demonstrated intermolecular oxygen-atom transfer capabilities.
- Cyclic voltammetry suggested a reversible redox event corresponding to an Fe(V) oxo species.
Conclusions:
- A stable, nonmagnetic iron(IV) oxo complex has been synthesized and fully characterized.
- The complex features a short Fe-O bond and likely possesses an Fe≡O triple bond.
- This iron(IV) oxo complex shows potential as an oxidant in catalytic oxygen-atom transfer reactions.
- The study provides insights into the stabilization and reactivity of high-valent iron-oxo species.
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