Oxidation of a Cyclometalated Pd(II) Dimer with “CF₃⁺”: Formation and Reactivity of a Catalytically Competent Monomeric Pd(IV) Aquo Complex

The reaction of [(bzq)Pd(OAc)]2 (bzq = benzo[h]quinoline) with “CF3+” reagents to afford the monomeric PdIV aquo complex (bzq)Pd(CF3)(OAc)2(OH2) is demonstrated. Heating this PdIV adduct at 60 °C for 12 h leads to highly chemoselective aryl−CF3 bond-forming reductive elimination. The rate and yield of this transformation are both significantly enhanced by the addition of Brønsted and Lewis acidic additives. The mechanism of C−CF3 bond formation from (bzq)Pd(CF3)(OAc)2(OH2) has been studied, and the major pathway is proposed to involve pre-equilibrium acetate dissociation followed by C−CF3 coupling. Finally, this monomeric PdIV complex is shown to be a kinetically competent intermediate for C−H trifluoromethylation with “CF3+” reagents. Collectively, these studies provide valuable insights about the speciation, nuclearity, and reactivity of Pd intermediates in catalytic C−H trifluoromethylation reactions.