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

This Communication describes studies of Ph–R_F (R_F = CF₃ or CF₂CF₃) coupling at Pd complexes of general structure (P^tBu₃)­Pd^II(Ph)­(R_F). The CF₃ analogue participates in fast Ph-CF₃ 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^II complex. Furthermore, they show that this undesired pathway can be circumvented by changing from a CF₃ to a CF₂CF₃ ligand. Ultimately, the insights gained from stoichiometric studies enabled the identification of Pd­(P^tBu₃)₂ as a catalyst for the Pd-catalyzed cross-coupling of aryl bromides with TMSCF₂CF₃ to afford pentafluoroethylated arenes.