Stoichiometric and Catalytic Aryl–Perfluoroalkyl Coupling at Tri-<i>tert</i>-butylphosphine Palladium(II) Complexes

This Communication describes studies of Ph–R<sub>F</sub> (R<sub>F</sub> = CF<sub>3</sub> or CF<sub>2</sub>CF<sub>3</sub>) coupling at Pd complexes of general structure (P<sup><i>t</i></sup>Bu<sub>3</sub>)­Pd<sup>II</sup>(Ph)­(R<sub>F</sub>). The CF<sub>3</sub> analogue participates in fast Ph-CF<sub>3</sub> coupling (<5 min at 80 °C). However, the formation of side products limits the yield of this transformation as well as its translation to catalysis. DFT and experimental studies suggest that the side products derive from facile α-fluoride elimination at the 3-coordinate Pd<sup>II</sup> complex. Furthermore, they show that this undesired pathway can be circumvented by changing from a CF<sub>3</sub> to a CF<sub>2</sub>CF<sub>3</sub> ligand. Ultimately, the insights gained from stoichiometric studies enabled the identification of Pd­(P<sup><i>t</i></sup>Bu<sub>3</sub>)<sub>2</sub> as a catalyst for the Pd-catalyzed cross-coupling of aryl bromides with TMSCF<sub>2</sub>CF<sub>3</sub> to afford pentafluoroethylated arenes.