Attenuated LMCT photocatalysis enables C─H allylation of methane and other gaseous alkanes

The functionalization of methane, ethane, and other gaseous alkanes represents a central goal in chemistry, though synthetic tools that allow their straightforward conversion into high-value products are still rare. Here we report a general and mild photocatalytic methodology for the direct C─H allylation of gaseous alkanes. This protocol provides an efficient tool to convert these raw materials into synthetically versatile products, as illustrated by its application to the telescoped conversion of methane and ethane into important pharmaceutical intermediates and the nonsteroidal estrogen dimestrol. Successful implementation of the method requires the use of a FeCl₃·6H₂O/collidine system that serves as an efficient ligand-to-metal charge transfer (LMCT) photocatalyst. Mechanistic studies highlight the crucial role of an in situ formed L_nFeCl₄^- (L = collidinium) species in which stabilizing hydrogen bond interactions are key to prevent competing alkane C─H chlorination by attenuating the Fe─Cl bond reactivity, securing a kinetically compatible catalytic regime that provides an efficient platform for the C─H allylation reaction.