Palladium-Catalyzed Cross-Coupling Reactions with Fluorinated Substrates: Mechanistic Insights into the Undesired Hydrodehalogenation of Aryl Halides

We report here that the undesired hydrodehalogenation
in cross-coupling
reactions with fluorinated substrates involves water as a possible
hydrogen source. Moreover, the product distribution (hydrodehalogenation
vs carbon–carbon coupling) can be controlled by varying the
phosphine substituents. Significant hydrodehalogenation occurs prior
to the formation of ArF–Pd­(II)–Br complexes.
DFT calculations were used to evaluate a direct hydrodehalogenation
route with a phosphine and water. These findings provide new mechanistic
insight into aryl–Br bond activation with fluorinated substrates
and selective arene functionalization.