Monomeric Fe(III)-Hydroxo and Fe(III)-Aqua Complexes Display Oxidative Asynchronous Hydrogen Atom Abstraction...

Area of Science:

• Inorganic Chemistry
• Bioinorganic Chemistry
• Reaction Mechanisms

Background:

• Iron complexes are crucial in biological systems and catalysis.
• Understanding ligand effects on iron reactivity is key for catalyst design.
• Hydrogen atom abstraction (HAA) is a fundamental reaction in oxidation processes.

Purpose of the Study:

• To synthesize and characterize novel monomeric aqua-ligated iron(III) complexes.
• To investigate the hydrogen atom abstraction (HAA) reactivity of these iron(III) complexes.
• To elucidate the reaction mechanism and the influence of ligand substituents on reactivity.

Main Methods:

• Synthesis and characterization of iron(III) aqua and hydroxo complexes using spectroscopic and analytical techniques.
• Electrochemical and magnetic measurements for complex analysis.
• Kinetic studies of linoleic fatty acid HAA with varying iron(III) complexes and Hammett analyses.

Main Results:

• Novel iron(III) aqua ([Fe^III(L^5R)(OH₂)]²⁺) and hydroxo ([Fe^III(L^5R)(OH)]¹⁺) complexes were successfully synthesized and characterized.
• Electron-withdrawing groups on the L^5R ligand enhanced HAA reactivity.
• Aqua complexes exhibited higher HAA rates than hydroxo complexes, attributed to greater CPET asynchronicity.

Conclusions:

• The study reveals that iron(III) aqua complexes are more reactive in HAA than their hydroxo counterparts.
• A higher degree of asynchronous concerted proton-electron transfer (CPET) in aqua complexes leads to increased reaction rates.
• Ligand design, particularly the electronic nature of substituents, significantly impacts the HAA reactivity of iron complexes.