title: Crystal Structure Determination of the Pentagonal-Pyramidal Hexamethylbenzene Dication C6(CH3)62.
abstract: In contrast to the well-known 2-norbornyl cation, the structure of which was a matter of long debate until its pentacoordinated nature was recently proven by an X-ray structure, the pentagonal-pyramidal dication of hexamethylbenzene has received considerably less attention. This species was first prepared by Hogeveen in 1973 at low temperatures in magic acid (HSO3F/SbF5), for which he proposed a non-classical structure (containing a hexacoordinated carbon) based on NMR spectroscopy and reactivity studies, but no X-ray crystal structure has been reported. C6(CH3)62+can be obtained through the dissolution of hexamethyl Dewar benzene epoxide in HSO3F/SbF5and crystallized as the SbF6-salt upon addition of excess anhydrous hydrogen fluoride. The crystal structure of C6(CH3)62+(SbF6-)2⋅HSO3F confirms the pentagonal pyramidal structure of the dication. The apical carbon is bound to one methyl group (distance 1.479(3) Å) and to the five basal carbon atoms (distances 1.694(2)-1.715(3) Å).
authors.affiliation: Freie Universität Berlin, Institut für Chemie und Biochemie-Anorganische Chemie, Fabeckstraße 34-36, 14195, Berlin, Germany.
authors.forename: Moritz
authors.identifier: 0000-0002-6756-2951
authors.initials: M
authors.lastname: Malischewski
authors.affiliation: Freie Universität Berlin, Institut für Chemie und Biochemie-Anorganische Chemie, Fabeckstraße 34-36, 14195, Berlin, Germany.
authors.forename: K
authors.initials: K
authors.lastname: Seppelt
keywords: carbocations; electron-deficient compounds; hypercoordination; oxidation; superacids