A Metal-Free, Photocatalytic Method for Aerobic Alkane Iodination

Halogenation is an important alkane functionalization strategy, but O-2 is widely considered the most desirable terminal oxidant. Here, the aerobic iodination of alkanes, including methane, was performed using catalytic [(Bu4N)-Bu-n]Cl and light irradiation (390 nm). Up to 10 turnovers of CH3I were obtained from CH4 and air, using a stop-flow microtubing system. Mechanistic studies using cyclohexane as the substrate revealed important details about the iodination reaction. Iodine (I-2(-)) serves multiple roles in the catalysis: (1) as the alkyl radical trap, (2) as a precursor for the light absorber, and (3) as a mediator of aerobic oxidation. The alkane activation is attributed to Cl-center dot derived from photofragmentation of the electron donor-acceptor complex of I-2 and Cl-. The kinetic profile of cyclohexane iodination showed that aerobic oxidation of I-3(-) to produce I-2 in CH3CN is turnover-limiting.

Automated summary

In this study, the aerobic iodination of alkanes was achieved using catalytic [(Bu4N)-Bu-n]Cl and light irradiation, with up to 10 turnovers of CH3I obtained from CH4 and air. Mechanistic studies revealed the multiple roles of iodine in the catalysis, with the oxidation of I-3(-) to produce I-2 being turnover-limiting in CH3CN.