Details

Autor(en) / Beteiligte

• Hahn, Jennifer
• Krieg, Matthias
• Keck, Constanze
• Maichle-Mössmer, Cäcilia
• Fink, Reinhold F
• Bettinger, Holger F

Titel

Thermal dehydrochlorination in the 4-fluoroaniline-trichloroborane system: identification of reactive intermediates involved in the formation of B,B′,B′′-trichloro-N,N′,N′′-tri((4-fluoro)phenyl)borazineElectronic supplementary information (ESI) available. CCDC 1535682, 1535683 and 1590012. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c8dt03954b

Erscheinungsjahr

2018-12

Link zum Volltext

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• Borazines are used in chemical vapor deposition processes to produce hybrid graphene-boron nitride nanostructures. As the knowledge on the mechanism of borazine formation is scarce, we studied the mechanism of formation of B , B ′, B ′′-trichloro- N , N ′, N ′′-tri( p -fluorophenyl)borazine ( 3a ) from p -fluoroaniline and boron trichloride employing NMR spectroscopy, X-ray single crystal structure analysis, trapping experiments, and computational chemistry methods up to the coupled cluster CCSD(T) level of theory. These studies suggest the initial formation of the 1 : 1 adduct 1a (ArNH 2 BCl 3 , Ar = 4-fluorophenyl) with a dative B-N bond that could be fully characterized including single crystal X-ray diffraction. Adduct 1a undergoes unimolecular hydrogen chloride elimination with a first-order rate constant of k 1 = 3.03(7) × 10 −2 min −1 in toluene at 100 °C. This rate constant is in very good agreement with the one derived ( k 1 = 3.18 × 10 −2 min −1 ) from computed activation parameters (Δ H ‡ 373.15 = 28.1 kcal mol −1 , Δ S ‡ 373.15 = 1.56 eu, Δ G ‡ 373.15 = 27.6 kcal mol −1 ). The product of the first hydrogen chloride evolution is anilinodichloroborane ArNHBCl 2 ( 2a ). Compound 2a cannot be isolated in a pure form due to instability, but its presence as a transient reactive intermediate can be derived from NMR spectroscopy. Reactive intermediates other than anilinodichloroborane cannot be assigned by NMR spectroscopy. We propose that the mechanism of formation of borazine 3a involves the reaction of 2a with 4-fluoroaniline as the rate determining step. The mechanism of borazine formation from 4-fluoroaniline and trichloroborane is investigated.