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Cyclobis(7,8‐( para ‐quinodimethane)‐4,4′‐triphenylamine) and Its Cationic Species Showing Annulene‐Like Global (Anti)Aromaticity
Author(s) -
Dong Shaoqiang,
Gopalakrishna Tullimilli Y.,
Han Yi,
Chi Chunyan
Publication year - 2019
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.201905763
Subject(s) - aromaticity , dication , chemistry , antiaromaticity , annulene , triphenylamine , singlet state , photochemistry , supramolecular chemistry , crystallography , computational chemistry , ion , excited state , molecule , crystal structure , organic chemistry , physics , nuclear physics
π‐Conjugated macrocycles containing all‐benzenoid rings usually show local aromaticity, but reported herein is the macrocycle CBQT , containing alternating para ‐quinodimethane and triphenylamine units displaying annulene‐like anti‐aromaticity at low temperatures as a result of structural rigidity and participation of the bridging nitrogen atoms in π‐conjugation. It was easily synthesized by intermolecular Friedel–Crafts alkylation followed by oxidative dehydrogenation. X‐ray crystallographic structures of CBQT , as well as those of its dication, trication, and tetracation were obtained. The dication and tetracation exhibited global aromaticity and antiaromaticity, respectively, as confirmed by NMR measurements and theoretical calculations. Both the dication and tetracation possess open‐shell singlet ground states, with a small singlet–triplet gap.