title: B3N3 borazine substitution in hexa-peri-hexabenzocoronene: computational analysis and Scholl reaction of hexaphenylborazine.
abstract: The doping of graphene molecules by borazine (B(3)N(3)) units may modify the electronic properties favorably. Therefore, the influence of the substitution of the central benzene ring of hexa-peri-hexabenzocoronene (HBC, C(42)H(18)) by an isoelectronic B(3)N(3) ring resulting in C(36)B(3)N(3)H(18) (B3N3HBC) is investigated by computational methods. For comparison, the isoelectronic and isosteric all-B/N molecule B(21)N(21)H(18) (termed BN) and its carbon derivative C(6)B(18)N(18)H(18) (C6BN), obtained by substitution of a central B(3)N(3) by a C(6) ring, are also studied. The substitution of C(6) in the HBC molecule by a B(3)N(3) unit results in a significant change of the computed IR vibrational spectrum between 1400 and 1600 cm(-1) due to the polarity of the borazine core. The properties of the BN molecule resemble those of hexagonal boron nitride, and substitution of the central B(3)N(3) ring by C(6) changes the computed IR vibrational spectrum only slightly. The allowed transitions to excited states associated with large oscillator strengths shift to higher energy upon going from HBC to B3N3HBC, but to lower energy upon going from BN to C6BN. The possibility of synthesis of B3N3HBC from hexaphenylborazine (HPB) using the Scholl reaction (CuCl(2)/AlCl(3) in CS(2)) is investigated. Rather than the desired B3N3HBC an insoluble and X-ray amorphous polymer P is obtained. Its analysis by IR and (11)B magic angle spinning NMR spectroscopy reveals the presence of borazine units. The changes in the (11)B quadrupolar coupling constant C(Q), asymmetry parameter η, and isotropic chemical shift δ(iso)((11)B) with respect to HPB are in agreement with a structural model that includes B3N3HBC-derived monomeric units in polymer P. This indicates that both intra- and intermolecular cyclodehydrogenation reactions take place during the Scholl reaction of HPB.
authors.affiliation: Institut für Organische Chemie, Universität Tübingen, Auf der Morgenstelle 18, 72076 Tübingen, Germany.
authors.forename: Christina
authors.initials: C
authors.lastname: Tönshoff
authors.forename: Matthias
authors.initials: M
authors.lastname: Müller
authors.forename: Tapas
authors.initials: T
authors.lastname: Kar
authors.forename: Florian
authors.initials: F
authors.lastname: Latteyer
authors.forename: Thomas
authors.initials: T
authors.lastname: Chassé
authors.forename: Klaus
authors.initials: K
authors.lastname: Eichele
authors.forename: Holger F
authors.initials: HF
authors.lastname: Bettinger