Tris(perfluorotolyl)borane—A Boron Lewis Superacid

Tris[tetrafluoro‐4‐(trifluoromethyl)phenyl]borane (BTolF) was prepared by treating boron tribromide with tetrameric F 3 CC 6 F 4 ‐Cu I . The F 3 CC 6 F 4 ‐Cu I was generated from F 3 CC 6 F 4 MgBr 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 SbF 5 . The molecular structures of BTolF and BCF were determined by gas‐phase electron diffraction, that of BTolF also by single‐crystal X‐ray diffraction.