Room-Temperature Conversion of Methane to Methanediol by [FeO₂]

Area of Science:

• Inorganic Chemistry
• Biomimetic Chemistry
• Physical Chemistry

Background:

• Nature utilizes high-valent Fe-oxo complexes in enzymes like P-450 and Rieske oxygenases for alkane oxidation.
• Understanding gas-phase methane oxidation mechanisms is crucial for developing artificial catalytic systems.
• Previous studies on [FeO]+ and [Fe(O)OH]+ with methane yielded different product distributions.

Purpose of the Study:

• To investigate the oxidation of methane by the high-valent iron oxide cation [FeO2]+ in the gas phase.
• To elucidate the reaction mechanism and identify key intermediates and products.
• To compare the gas-phase findings with known biological oxidation processes.

Main Methods:

• Fourier transform-ion cyclotron resonance (FT-ICR) mass spectrometry was employed to study the reaction dynamics.
• High-level quantum chemical calculations were performed to support experimental observations and explore reaction pathways.
• Analysis of product distribution, particularly the dominant formation of Fe+.

Main Results:

• The reaction of [FeO2]+ with methane predominantly yields Fe+ as the main product, unlike previous systems.
• A novel 'oxygen rebound' pathway was proposed for the liberation of methanediol.
• Theoretical calculations indicated an increase in iron valence prior to C-H activation, mirroring cytochrome P-450 activity.

Conclusions:

• This study presents the first gas-phase demonstration of methane activation by a high-valent Fe(V)-oxo species.
• The findings suggest a potential link between gas-phase model systems and condensed-phase biological oxidation mechanisms.
• The identified pathway offers insights into biomimetic methane oxidation catalysis.