An iron(IV)-oxo intermediate on a carbanionic ligand framework: reactivity and decay pathways

Area of Science:

• Organometallic Chemistry
• Bioinorganic Chemistry
• Catalysis

Background:

• Iron-oxo intermediates are crucial in biological oxidation processes.
• Understanding their reactivity requires stable synthetic models.
• Carbanionic ligands offer unique electronic properties for stabilizing high-valent metal species.

Purpose of the Study:

• To synthesize and characterize a novel iron(IV)-oxo intermediate stabilized by a carbanionic ligand.
• To investigate the reactivity of this intermediate in hydrogen atom transfer (HAT) and oxygen atom transfer (OAT) reactions.
• To explore the electronic and structural properties influencing its catalytic activity.

Main Methods:

• Synthesis of an iron(II) precursor complex with a tris(2-pyridylthio)methanido ligand (L1).
• Oxidation of the iron(II) complex to generate the iron(IV)-oxo intermediate using isopropyl 2-iodosylbenzoate.
• Spectroscopic characterization (e.g., UV-Vis, Mössbauer) and Density Functional Theory (DFT) calculations to determine structure and properties.
• Kinetic studies to assess reactivity in HAT and OAT reactions.

Main Results:

• Generation of a stable S=1 iron(IV)-oxo intermediate, [(L1)FeIV(O)(CH3CN)]+ (2), supported by the electron-rich carbanionic ligand.
• Spectroscopic and DFT data indicate a cis disposition of the oxo unit relative to the carbanionic donor.
• The intermediate exhibits moderate efficiency in OAT reactions but low yields in HAT reactions, especially with strong C-H bonds.
• Self-quenching via dinuclear iron(III) formation limits productive substrate oxidation.

Conclusions:

• The study presents a unique organometallic iron(IV)-oxo intermediate stabilized by an unconventional carbanionic ligand framework.
• The strong ligand field is crucial for stabilizing the high-valent iron species.
• While capable of oxidation, the intermediate's reactivity profile highlights limitations in C-H bond activation and stability, offering insights into catalyst design.