Two Plus Four Equals Three-Iron(II)/Iron(IV) Comproportionation as an Additional Pathway for Iron(IV)-Oxido Reactions

Area of Science:

• Bioinorganic Chemistry
• Organometallic Chemistry
• Enzyme Mimicry

Background:

• Iron enzymes with iron-oxygen cofactors are crucial for numerous biological reactions.
• Iron(III)-hydroxido and iron(IV)-oxido species are catalytically active in these enzymes.
• Synthetic model complexes are vital for understanding the reactivity of these iron species.

Purpose of the Study:

• To synthesize and characterize iron complexes across oxidation states II-IV using pentapyridyl ligands.
• To investigate the reactivity of iron(IV)-oxido complexes as models for enzymes like TET and lipoxygenases.
• To identify and understand potential side reactions in synthetic iron enzyme models.

Main Methods:

• Synthesis of pentapyridyl iron complexes ([Fe^IV(O)(Py₅Me₂)]²⁺ and [Fe^III(OH)(Py₅(OH)₂)]²⁺).
• Spectroscopic and spectrometric investigations of iron complexes in oxidation states II, III, and IV.
• Analysis of reaction pathways, including comproportionation reactions.

Main Results:

• Iron(II) and iron(IV)-oxido complexes readily undergo (cross-)comproportionation to form iron(III)-hydroxido species.
• This comproportionation represents a significant side reaction that can complicate mechanistic studies.
• The oxidative reactivity of a novel iron(IV)-oxido complex was investigated.

Conclusions:

• The facile comproportionation of iron(II)/iron(IV)-oxido to iron(III)-hydroxido is a critical consideration for synthetic models.
• Understanding these side reactions is essential for accurately interpreting the reactivity of iron enzyme mimics.
• Further studies on the oxidative capabilities of iron(IV)-oxido complexes are warranted.