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

This Communication describes studies of Ph-RF (RF = CF3 or CF2CF3) coupling at Pd complexes of general structure (PtBu3)PdII(Ph)(RF). 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 PdII 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(PtBu3)2 as a catalyst for the Pd-catalyzed cross-coupling of aryl bromides with TMSCF2CF3 to afford pentafluoroethylated arenes.