Ligand-dependent formation of ion-pair CuI/CuIII trifluoromethyl complexes containing bisphosphines

Abstract

We report novel ion-pair bisphosphine Cu^I/Cu^III trifluoromethyl complexes [(P₂)₂Cu^I]⁺[Cu^III(CF₃)₄]⁻ (P₂ = DPPE, BINAP or Xantphos) featuring tetrahedral Cu^I and square planar Cu^III units that are prepared via oxidative trifluoromethylation of CuI with CF₃SiMe₃ in the presence of AgF. The bisphosphine Cu^I/Cu^III CF₃ complexes are highly reactive for aerobic trifluoromethylation of arylboronic acids to produce trifluoromethylated arenes in good to quantitative yields, which is in sharp contrast to the Cu^I/Cu^III complex with phen/PPh₃ ligands (1′). These results not only provide strong evidence that both the neutral and ion-pair Cu^III CF₃ complexes are competent catalytic species for Cu-mediated oxidative trifluoromethylation reactions, but also have important mechanistic implications that the active catalyst and reaction mechanism should be distinct and ligand-dependent for trifluoromethylation reactions with different types of ancillary ligands.