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An Iron Pincer Complex in Four Oxidation States
Lisa Gravogl1, Frank W Heinemann1, Dominik Munz1
1Department of Chemistry and Pharmacy, Inorganic Chemistry, Friedrich-Alexander University Erlangen-Nürnberg, Egerlandstraße 1, 91058 Erlangen, Germany.
Inorganic Chemistry
|April 10, 2020
Summary
This study presents new iron complexes with a benzimidazolin-2-ylidene pincer ligand. The research explores iron oxidation states and ligand behavior, revealing a unique iron(IV) complex and challenging assignments for iron(V).
Area of Science:
- Coordination Chemistry
- Organometallic Chemistry
- Materials Science
Background:
- Pincer ligands offer unique coordination environments for metal centers.
- Understanding iron complex redox behavior is crucial for catalysis and materials.
- Homoleptic complexes with tridentate ligands are of significant interest.
Purpose of the Study:
- To synthesize and characterize novel homoleptic iron complexes supported by a benzimidazolin-2-ylidene pincer ligand.
- To investigate the electronic structures and redox properties of these iron complexes.
- To explore the stability and reactivity of different iron oxidation states within these complexes.
Main Methods:
- Synthesis of iron complexes using ferrous and ferric iron precursors with the benzNHCOCO2- ligand.
- Characterization techniques including single-crystal X-ray diffraction (SC-XRD), EPR, Mössbauer spectroscopy, and SQUID magnetometry.
- Computational studies using DFT and multi-reference ab initio methods (NEVPT2/CASSCF).
Main Results:
- Isolation of a coordination polymer [Fe(benzNHCOCOK)2] (1) and mononuclear complexes K[Fe(benzNHCOCO)2] (2) and [K(18c6)(THF)2][Fe(benzNHCOCO)2] (3).
- Synthesis of charge-neutral [Fe(benzNHCOCO)2] (4) and cationic [Fe(benzNHCOCO)2]PF6 (5) via electrochemical oxidation.
- Complex 4 (iron(IV)) shows stabilization of the metal center, while complex 5 (formally iron(V)) exhibits covalent ligand-metal bonds, challenging oxidation state assignment.
- Complex 5 electronic structure is described as iron(IV) antiferromagnetically coupled to a ligand radical.
Conclusions:
- The benzimidazolin-2-ylidene pincer ligand stabilizes high oxidation states in iron complexes.
- Reductive elimination of the pincer ligand from the iron(IV) complex yields a metal-free spirocyclic imidazolone ketal.
- The electronic structure of the formally iron(V) complex is complex, suggesting significant covalent character and radical behavior.
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