title: Experimental assessment of the strengths of B-B triple bonds.
abstract: Diborynes, molecules containing homoatomic boron-boron triple bonds, have been investigated by Raman spectroscopy in order to determine the stretching frequencies of their central B≡B units as an experimental measure of homoatomic bond strengths. The observed frequencies between 1600 and 1750 cm(-1) were assigned on the basis of DFT modeling and the characteristic pattern produced by the isotopic distribution of boron. This frequency completes the series of known stretches of homoatomic triple bonds, fitting into the trend established by the long-known stretching frequencies of C≡C and N≡N triple bonds in alkynes and dinitrogen, respectively. A quantitative analysis was carried out using the concept of relaxed force constants. The results support the classification of the diboryne as a true triple bond and speak to the similarities of molecules constructed from first-row elements of the p block. Also reported are the relaxed force constants of a recently reported diborabutatriene, which again fit into the trend established by the vibrational spectroscopy of organic cumulenes. As part of these studies, a new diboryne with decreased steric bulk was synthesized, and a computational study of the rotation of the stabilizing ligands indicated alkyne-like electronic isolation of the central B2 unit.
authors.affiliation: Julius-Maximilians-Universität Würzburg , Am Hubland, 97074 Würzburg, Germany.
authors.forename: Julian
authors.initials: J
authors.lastname: Böhnke
authors.forename: Holger
authors.initials: H
authors.lastname: Braunschweig
authors.forename: Philipp
authors.initials: P
authors.lastname: Constantinidis
authors.forename: Theresa
authors.initials: T
authors.lastname: Dellermann
authors.forename: William C
authors.initials: WC
authors.lastname: Ewing
authors.forename: Ingo
authors.initials: I
authors.lastname: Fischer
authors.forename: Kai
authors.initials: K
authors.lastname: Hammond
authors.forename: Florian
authors.initials: F
authors.lastname: Hupp
authors.forename: Jan
authors.initials: J
authors.lastname: Mies
authors.forename: Hans-Christian
authors.initials: HC
authors.lastname: Schmitt
authors.forename: Alfredo
authors.initials: A
authors.lastname: Vargas
mesh_terms: D001895:Boron / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D013059:Spectrum Analysis, Raman
chemical_list: D001895:Boron