Easy Access to the Copper(III) Anion [Cu(CF3)4]−.

CuCl or pre-generated CuCF₃ reacts with CF₃SiMe₃/KF in DMF in air to give [Cu(CF₃)₄]⁻ quantitatively. [PPN]⁺, [Me₄N]⁺, [Bu₄N]⁺, [PhCH₂NEt₃]⁺, and [Ph₄P]⁺ salts of [Cu(CF₃)₄]⁻ were prepared and isolated spectroscopically and analytically pure in 82-99 % yield. X-ray structures of the [PPN]⁺, [Me₄N]⁺, [Bu₄N]⁺, and [Ph₄P]⁺ salts were determined. A new synthetic strategy with [Cu(CF₃)₄]⁻ was demonstrated, involving the removal of one CF₃⁻ from the Cu atom in the presence of an incoming ligand. A novel Cu^III complex [(bpy)Cu(CF₃)₃] was thus prepared and fully characterized, including by single-crystal X-ray diffraction. The bpy complex is highly fluxional in solution, the barrier to degenerate isomerization being only 2.3 kcal mol⁻¹. An NPA study reveals a huge difference in the charge on the Cu atom in [Cu(CR₃)₄]⁻ for R=F (+0.19) and R=H (+0.46), suggesting a higher electron density on Cu in the fluorinated complex. [ABSTRACT FROM AUTHOR]