title: The Triboracyclopropenyl Dianion: The Lightest Possible Main-Group-Element Hückel π Aromatic.
abstract: Hückel π aromaticity is typically a domain of carbon-rich compounds. Only very few analogues with non-carbon frameworks are currently known, all involving the heavier elements. The isolation of the triboracyclopropenyl dianion is presented, a boron-based analogue of the cyclopropenyl cation, which belongs to the prototypical class of Hückel π aromatics. Reduction of Cl2 BNCy2 by sodium metal produced [B3 (NCy2 )3 ](2-) , which was isolated as its dimeric Na(+) salt (Na4 [B3 (NCy2 )3 ]2 ⋅2 DME; 1) in 45 % yield and characterized by single-crystal X-ray diffraction. Cyclic voltammetry measurements established an extremely high oxidation potential for 1 (Epc =-2.42 V), which was further confirmed by reactivity studies. The Hückel-type π aromatic character of the [B3 (NCy2 )3 ](2-) dianion was verified by various theoretical methods, which clearly indicated π aromaticity for the B3 core of a similar magnitude to that in [C3 H3 ](+) and benzene.
authors.affiliation: Institut für Anorganische Chemie, Julius-Maximilians Universität Würzburg, Am Hubland, 97074 Würzburg (Germany).
authors.forename: Thomas
authors.initials: T
authors.lastname: Kupfer
authors.affiliation: Institut für Anorganische Chemie, Julius-Maximilians Universität Würzburg, Am Hubland, 97074 Würzburg (Germany). h.braunschweig@uni-wuerzburg.de.
authors.forename: Holger
authors.initials: H
authors.lastname: Braunschweig
authors.affiliation: Institut für Anorganische Chemie, Julius-Maximilians Universität Würzburg, Am Hubland, 97074 Würzburg (Germany).
authors.forename: Krzysztof
authors.initials: K
authors.lastname: Radacki
keywords: aromaticity; boron; density functional therory; multiple bonding