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.