title: Neutral Diboron Analogues of Archetypal Aromatic Species by Spontaneous Cycloaddition.
abstract: Among the numerous routes organic chemists have developed to synthesize benzene derivatives and heteroaromatic compounds, transition-metal-catalyzed cycloaddition reactions are the most elegant. In contrast, cycloaddition reactions of heavier alkene and alkyne analogues, though limited in scope, proceed uncatalyzed. In this work we present the first spontaneous cycloaddition reactions of lighter alkene and alkyne analogues. Selective addition of unactivated alkynes to boron-boron multiple bonds under ambient conditions yielded diborocarbon equivalents of simple aromatic hydrocarbons, including the first neutral 6 π-aromatic diborabenzene compound, a 2 π-aromatic triplet biradical 1,3-diborete, and a phosphine-stabilized 2 π-homoaromatic 1,3-dihydro-1,3-diborete. DFT calculations suggest that all three compounds are aromatic and show frontier molecular orbitals matching those of the related aromatic hydrocarbons, C6 H6 and C4 H4 (2+) , and homoaromatic C4 H5 (+) .
authors.affiliation: Institut für Anorganische Chemie, Julius-Maximilians-Universität Würzburg, Am Hubland, 97074, Würzburg, Germany.
authors.forename: Merle
authors.initials: M
authors.lastname: Arrowsmith
authors.affiliation: Institut für Anorganische Chemie, Julius-Maximilians-Universität Würzburg, Am Hubland, 97074, Würzburg, Germany.
authors.forename: Julian
authors.initials: J
authors.lastname: Böhnke
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: Mehmet Ali
authors.initials: MA
authors.lastname: Celik
authors.affiliation: Institut für Anorganische Chemie, Julius-Maximilians-Universität Würzburg, Am Hubland, 97074, Würzburg, Germany.
authors.forename: Christina
authors.initials: C
authors.lastname: Claes
authors.affiliation: Institut für Anorganische Chemie, Julius-Maximilians-Universität Würzburg, Am Hubland, 97074, Würzburg, Germany.
authors.forename: William C
authors.initials: WC
authors.lastname: Ewing
authors.affiliation: Institut für Anorganische Chemie, Julius-Maximilians-Universität Würzburg, Am Hubland, 97074, Würzburg, Germany.
authors.forename: Ivo
authors.initials: I
authors.lastname: Krummenacher
authors.affiliation: Institut für Anorganische Chemie, Julius-Maximilians-Universität Würzburg, Am Hubland, 97074, Würzburg, Germany.
authors.forename: Katharina
authors.initials: K
authors.lastname: Lubitz
authors.affiliation: Institut für Anorganische Chemie, Julius-Maximilians-Universität Würzburg, Am Hubland, 97074, Würzburg, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Schneider
keywords: aromaticity; biradicals; boron; cycloaddition; multiple bonds