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 [ n Bu 4 N]Cl and light irradiation (390 nm). Up to 10 turnovers of CH 3 I were obtained from CH 4 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 • 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 CH 3 CN is turnover-limiting.