Cyclobis(7,8‐(para‐quinodimethane)‐4,4′‐triphenylamine) and Its Cationic Species Showing Annulene‐Like Global (Anti)Aromaticity

• Published in: Angewandte Chemie International Edition Vol. 58; no. 34; pp. 11742 - 11746
• Main Authors: Dong, Shaoqiang, Gopalakrishna, Tullimilli Y., Han, Yi, Chi, Chunyan
• Format: Journal Article
• Language: English
• Published: WEINHEIM Wiley 19.08.2019; Wiley Subscription Services, Inc
• Edition: International ed. in English
• Subjects: Alkylation; annulenes; Aromaticity; Chemistry; Chemistry, Multidisciplinary; Conjugation; Crystal structure; Crystallography; Dehydrogenation; Low temperature; macrocycles; Nitrogen atoms; NMR; Nuclear magnetic resonance; Physical Sciences; porphyrinoids; radicals; Rigidity; Science & Technology; porphyrinoids; radicals; macrocycles; PI; annulenes; aromaticity; CHARACTERS; macrocycle, annulene, porphyrinoid, aromaticity, diradicaloid
• ISSN: 1433-7851; 1521-3773; 1521-3773
• DOI: 10.1002/anie.201905763

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. It's dynamic: The π‐conjugated macrocycle CBQT, containing alternating para‐quinodimethane and triphenylamine units, shows a temperature‐dependent dynamic process. It displays [32]annulene‐like antiaromaticity at low temperatures. Its dication and tetracation exhibit global aromaticity and anti‐aromaticity, respectively.