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

CuCl or pre-generated CuCF3 reacts with CF3 SiMe3 /KF in DMF in air to give [Cu(CF3 )4 ](-) quantitatively. [PPN](+) , [Me4 N](+) , [Bu4 N](+) , [PhCH2 NEt3 ](+) , and [Ph4 P](+) salts of [Cu(CF3 )4 ](-) were prepared and isolated spectroscopically and analytically pure in 82-99% yield. X-ray structures of the [PPN](+) , [Me4 N](+) , [Bu4 N](+) , and [Ph4 P](+) 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.