A Metal-Free, Photocatalytic Method for Aerobic Alkane Iodination

Halogenation is an important alkane functionalization strategy, but O2 is widely considered the most desirable terminal oxidant. Here, the aerobic iodination of alkanes, including methane, was performed using catalytic [nBu4N]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 (I2) 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• derived from photofragmentation of the electron donor-acceptor complex of I2 and Cl-. The kinetic profile of cyclohexane iodination showed that aerobic oxidation of I3- to produce I2 in CH3CN is turnover-limiting.