Merging the oxidative prowess of Ag(II) with the Lewis acidity and halophilicity of Ag(I) provides access to reactivity modes orthogonal to previously reported Ag(II) electrophotocatalytic schemes. Herein, we demonstrate that the dual reactivity of Ag across its accessible oxidation states facilitates the direct fluorocarbonylation of arenes. First, CF2X radicals (X = Cl, Br) are generated via photoinduced ligand-to-metal charge transfer (LMCT) of Ag(II) carboxylates in an undivided electrochemical cell. Ag(II) turnover is sustained by utilizing stoichiometric Ag(I), which undergoes electrochemical disproportionation into the active Ag(II) photocatalyst and Ag(0). Second, the presence of excess Ag(I) leads to in situ formation of synthetically valuable acyl fluorides from aryl–CF2X radical addition products through a halide abstraction process, enabling the direct conversion of aryl–H to aryl–COF. Mechanistic studies indicate that acyl fluorides form either via an SN1-like pathway featuring the intermediacy of a rare difluoro-carbocation, which was trapped and characterized crystallographically, or via SN2-like, Ag(I)-assisted nucleophilic displacement of X by the carboxylate, depending on the electronic properties of the arene. With reaction conditions tailored to the electronic nature of each arene, acyl fluorides were synthesized directly from electronically diverse (hetero)arene precursors. Furthermore, the reaction conditions developed for acyl fluoride synthesis may be extended to the perfluoroalkylation (X = F, CF3, CF2CF3) of a broad range of (hetero)arenes in moderate-to-excellent yields. The reaction is tolerant of air and wet solvents, no supporting electrolyte is required, and the deposited Ag(0) can be quantitatively recovered as the AgNO3 precatalyst to maintain Ag atom economy.
Raguram et al. (Fri,) studied this question.