title: Formation of an Isolable Divinylborinium Ion through Twofold 1,2-Carboboration between a Diarylborinium Ion and Diphenylacetylene.
abstract: Borinium ions, that is, two-coordinate boron cations, are the most electron-deficient isolable boron compounds. As borinium ions have only four formal valence electrons on boron, they should show a strong tendency to accept electron pairs on the boron atom to fill its valence shell. Thus chemical reactions of borinium ions are expected to give products in which the coordination number of boron is increased from two to three or four. However, contrary to this expectation, we found that the dimesitylborinium ion (Mes2B+) undergoes twofold 1,2-carboboration reactions with two equivalents of diphenylacetylene to yield an unprecedented borinium ion (1+) with two substituted vinyl groups on the boron center. NMR spectroscopy and X-ray diffraction analysis of 1+, together with electronic-structure calculations, revealed that the positive charge is delocalized over the entire π-conjugated system. The fact that the chemical transformation of a borinium ion gives rise to a different borinium ion without a change in the coordination number is remarkable and should provide new insight into the chemistry of the Group 13 elements.
authors.affiliation: Laboratory for Chemistry and Life Science, Institute of Innovative Research, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama, 226-8503, Japan.
authors.forename: Naoki
authors.initials: N
authors.lastname: Tanaka
authors.affiliation: Laboratory for Chemistry and Life Science, Institute of Innovative Research, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama, 226-8503, Japan.
authors.forename: Yoshiaki
authors.identifier: 0000-0001-8437-1965
authors.initials: Y
authors.lastname: Shoji
authors.affiliation: Materials Characterization Support Unit, RIKEN Center for Emergent Matter Science (CEMS), 2-1 Hirosawa, Wako, Saitama, 351-0198, Japan.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Hashizume
authors.affiliation: Faculty of Advanced Science and Technology, Kumamoto University, 2-39-1 Kurokami, Chuo-ku, Kumamoto, 860-8555, Japan.
authors.forename: Manabu
authors.initials: M
authors.lastname: Sugimoto
authors.affiliation: Laboratory for Chemistry and Life Science, Institute of Innovative Research, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama, 226-8503, Japan.
authors.forename: Takanori
authors.identifier: 0000-0001-5586-9238
authors.initials: T
authors.lastname: Fukushima
keywords: 1,2-carboboration; borinium ions; boron; boron cations; π-conjugated systems