Mechanistic Investigations of Palladium-Catalyzed Allylic Fluorination

A computational and experimental approach was employed to study the mechanism of the palladium(0)-catalyzed fluorination of allylic chlorides with AgF as fluoride source. Our findings indicate that an allylpalladium fluoride is a key intermediate necessary for the generation of both the nucleophile and electrophile. Evidence was also obtained to support a homobimetallic mechanism in which C-F bond formation occurs by nucleophilic attack of a neutral allylpalladium fluoride on a cationic allylpalladium electrophile (with fluoride as counterion). The high branched selectivity and unusual ligand effects observed in the regioselective fluorination are assessed in light of this mechanism and calculated transition states. These results may have important implications for the mechanism of other transition-metal-catalyzed fluorinations.