Abstract
Hexapyrrolohexaazacoronene (HPHAC) is one of the N-containing polycyclic aromatic hydrocarbons in which six pyrroles are fused circularly around a benzene. Despite the recent development of HPHAC analogues, there is no report on direct introduction of functional groups into the HPHAC skeleton. This work reports the first example of nitration reaction of decaethylHPHAC. The structures of nitrodecaethylHPHAC including neutral and two oxidized species (radical cation and dication), intramolecular charge transfer (ICT) character, and global aromaticity of the dication are discussed.
Highlights
Introduction of functional groups into π-conjugated systems is a straightforward way to tune their chemical and physical properties
DEHPHAC 1a was synthesized from N-(2,3,4,5,6-pentafluorophenyl)-1H-pyrrole via decaethylated hexapyrrolylbenzene DEHPB by SN Ar and successive Scholl reactions in accordance with the previously reported procedure [15,27]
In contrast to the cases of corrole and porphyrin [28,29], DEHPHAC 1a did not dimerize by this oxidant but was transformed into nitroDEHPHAC 2a in a 51% yield (Scheme 1)
Summary
Introduction of functional groups into π-conjugated systems is a straightforward way to tune their chemical and physical properties. When the nitro group is introduced to large π-conjugated compounds, the LUMO levels would be sufficiently lowered so that nucleophiles could directly attack the π-conjugated systems. Hexapyrrolohexaazacoronene (HPHAC) is a nitrogen-embedded PAH, consisting of circularly connected pyrroles around a benzene core and is prepared from hexapyrrolylbenzene by the Scholl oxidation using FeCl3 [15], 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) in the presence of trifluoromethanesulfonic acid [16], or N-bromosuccinimide (NBS) [17]. The HPHAC π-system consists of local π-systems of six pyrroles and one benzene and has a non-aromatic character in the whole molecule. Due to the pyrrole moieties, on the other hand, multiple oxidation levels of HPHAC are reversibly generated, and its dication shows global aromaticity owing to the cyclic conjugation of a 22π-electron system. (iii) AgPF6 (1.0 equiv.), CH2 Cl2 , rt; quant.; (iv) AgPF6 (2.0 equiv.), CH2 Cl2 , rt; quant
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