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 Pd-IV aquo complex (bzq)Pd(CF3)(OAc)(2)(OH2) is demonstrated. Heating this Pd-IV adduct at 60 degrees 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 Bronsted 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 Pd-IV 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.