Is There BN Bond‐Length Alternation in 1, 2:3, 4:5, 6‐Tris(biphenylylene)borazines?. Issue 9 (17th May 2013)

• Record Type: Journal Article
• Authors: Müller, Matthias; Maichle‐Mössmer, Cäcilia; Sirsch, Peter; Bettinger, Holger F.
• Is Part Of: ChemPlusChem. Volume 78:Issue 9(2013:Sep.)
• Page Start: 988
• Page End: 994
• Publication Date: 2013-05-17
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1002/cplu.201300110
• Languages: English
• ISSNs: 2192-6506

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p>The alternation of the BN bonds in the central borazine ring of the overcrowded 1, 2:3, 4:5, 6‐tris(biphenylylene)borazine (<bold>2 a</bold>) and its tribromo derivative (<bold>2 g</bold>) is investigated by computational methods and compared with their experimentally obtained crystal structures. The calculations are performed with a meta‐generalized‐gradient‐approximation (GGA) density functional (Tao–Perdew–Staroverov–Scuseria (TPSS)) without and with dispersion corrections, including Becke–Johnson damping, in conjunction with a polarized triple‐ζ basis set. These data show a small bond‐length alternation (BLA) of around 0.01 Å in <bold>2 a</bold> and <bold>2 g</bold>. This outcome is in good agreement with X‐ray diffraction data for <bold>2 g</bold>, but at variance with earlier X‐ray diffraction measurements that gave a BLA of 0.06 Å for <bold>2 a</bold>. A re‐investigation of the crystal structure of <bold>2 a</bold> reveals a positional disorder that precludes a discussion of the BN bond lengths. The synthesis of <bold>2 g</bold> is the first example of an electrophilic aromatic substitution of an aryl borazine with elemental bromine. Successful bromination was also demonstrated for hexaphenylborazine.</p> </abstract>