Mechanistic study of silver-catalyzed decarboxylative fluorination

Abstract

The silver-catalyzed fluorination of aliphatic carboxylic acids by Selectfluor in acetone/water provides access to fluorinated compounds under mild and straightforward reaction conditions. Although this reaction provides efficient access to fluorinated alkanes from a pool of starting materials that are ubiquitous in nature, little is known about the details of the reaction mechanism. We report spectroscopic and kinetic studies on the role of the individual reaction components in decarboxylative fluorination. The studies presented herein provide evidence that Ag(II) is the intermediate oxidant in the reaction. In the rate-limiting step of the reaction, Ag(I)-carboxylate is oxidized to Ag(II) by Selectfluor. Substrate inhibition of the process occurs through the formation of a silver-carboxylate. Water is critical for solubilizing reaction components and ligates to Ag(I) under the reaction conditions. The use of donor ligands on Ag(I) provides evidence of oxidation to Ag(II) by Selectfluor. The use of sodium persulfate as an additive in the reaction as well as NFSI as a fluorine source further supports the generation of a Ag(II) intermediate; this data will enable the development of a more efficient set of reaction conditions for the fluorination.