Tris(perfluorotolyl)borane-A Boron Lewis Superacid

Tris[tetrafluoro-4-(trifluoromethyl)phenyl] borane (BTolF) was prepared by treating boron tribromide with tetrameric F3CC6F4-Cu-I. The F3CC6F4-CuI was generated from F3CC6F4MgBr and copper(I) bromide. Lewis acidities of BTolF evaluated by the Gutmann-Beckett method and calculated fluoride-ion affinities are 9 and 10%, respectively, higher than that of tris(pentafluorophenyl) borane (BCF) and even higher than that of SbF5. The molecular structures of BTolF and BCF were determined by gas-phase electron diffraction, that of BTolF also by single-crystal X-ray diffraction.