A Metal-Free, Photocatalytic Method for Aerobic Alkane Iodination

Area of Science:

• Organic Chemistry
• Photocatalysis
• Alkane Functionalization

Background:

• Halogenation is a key method for modifying alkanes.
• Oxygen (O2) is the preferred oxidant, but alternative methods are sought.
• Efficient alkane functionalization remains a challenge in synthetic chemistry.

Purpose of the Study:

• To develop a novel aerobic iodination method for alkanes.
• To investigate the mechanism of light-driven alkane iodination.
• To utilize air as a terminal oxidant for alkane functionalization.

Main Methods:

• Aerobic iodination of alkanes using catalytic tetrabutylammonium chloride ([Bu4N]Cl) and 390 nm light irradiation.
• Utilized a stop-flow microtubing system for reactions involving methane.
• Mechanistic studies employed cyclohexane as a model substrate.

Main Results:

• Achieved up to 10 turnovers of methyl iodide (CH3I) from methane (CH4) and air.
• Identified multiple roles for iodine (I2) in the catalytic cycle: alkyl radical trapping, light absorption precursor, and aerobic oxidation mediator.
• Determined that the aerobic oxidation of triiodide (I3-) to I2 is the rate-limiting step in acetonitrile (CH3CN).

Conclusions:

• The photofragmentation of an iodine-chloride electron donor-acceptor complex generates chlorine radicals (Cl•) for alkane activation.
• This work presents a new strategy for alkane C-H functionalization using visible light and air.
• The findings provide insights into the complex mechanistic pathways of aerobic halogenation reactions.