Mechanistic Investigations of Cu-Catalyzed Fluorination of Diaryliodonium Salts: Elaborating the CuI/CuIII Manifold in Copper Catalysis

A combination of experimental and density functional theory (DFT) investigations suggests that the Cu-catalyzed fluorination of unsymmetrical diaryliodonium salts with general structure [Mes(Ar)I] + in N , N '-dimethylformamide proceeds through a Cu I /Cu III catalytic cycle. A low concentration of fluoride relative to combined iodonium reagent plus copper ensures that [Mes(Ar)I] + is available as the reactive species for oxidative "Ar + " transfer to a Cu I center containing one or two fluoride ligands. A series of different possible Cu I active catalysts (containing fluoride, triflate, and DMF ligands) have been evaluated computationally, and all show low-energy pathways to fluorinated products. The oxidation of these Cu I species by [Mes(Ar)I] + to form cis -Ar(F)Cu III intermediates is proposed to be rate-limiting in all cases. Ar-F bond-forming reductive elimination from Cu III is computed to be very facile in all of the systems examined. The conclusions of the DFT experiments are supported by several experimental studies, including tests showing that Cu I is formed rapidly under the reaction conditions and that the fluoride concentration strongly impacts the reaction yields/selectivities.