Two mechanisms have been proposed for lithium–halogen exchange.
One proposed pathway involves a nucleophilic mechanism that generates a reversible "ate-complex" intermediate. Farnham and Calabrese crystallized an "ate-complex" lithium bis(pentafluorophenyl) iodinate complexed with TMEDA.
The "ate-complex" further reacts with electrophiles and provides pentafluorophenyl iodide and CHLi. A number of kinetic studies also support a nucleophilic pathway in which the carbanion on the lithium species attacks the halogen atom on the aryl halide. Another proposed mechanism involves single electron transfer with the generation of radicals. In reactions of secondary and tertiary alkyllithium and alkyl halides, radical species were detected by EPR spectroscopy. The mechanistic studies of lithium–halogen exchange are complicated by the formation of aggregates of organolithium species.