Pentafluorophenylboron halides: 40 years later

The pentafluorophenylboron halides C6F5BX2 (X=Cl, F) and (C6F5)2BCl were first reported in the early 1960s. After a period of inactivity these perfluoroarylboron derivatives have been employed for the synthesis of a variety of important compounds, including monomeric iminoboranes, a highly electrophilic hydroboration reagent, strong Lewis acids (with one or two acceptor sites) that activate alkyl metallocene polymerization catalysts, and the first organoxenon(IV) compounds. These recent developments provide a cogent example of the time lag that often occurs between discovery and applications in fundamental research.