Hückel‐ and Baird‐Type Global Aromaticity in a 3D Fully Conjugated Molecular Cage

• Published in: Angewandte Chemie 2022-02, Vol.134 (9), p.n/a
• Main Authors: Wu, Shaofei, Ni, Yong, Han, Yi, Hou, Xudong, Wang, Congyong, Hu, Wenping, Wu, Jishan
• Format: Article
• Language: English
• Subjects: 3D Aromaticity; Aromaticity; Baird Aromaticity; Cages; Chemical synthesis; Chemistry; Crystallography; Ground state; Hückel Aromaticity; NMR; Nuclear magnetic resonance; π-Conjugated Molecular Cage
• ISSN: 0044-8249; 1521-3757
• DOI: 10.1002/ange.202115571

Global aromaticity in 3D π‐conjugated molecular cages remains largely unexplored. Herein, we report the facile synthesis of a fully conjugated molecular cage (1) containing two bridged triphenylamine units and three quinoidal bithiophene arms. X‐ray crystallographic analysis, NMR/ESR measurements and theoretical calculations reveal that: 1) its dication (12+) has an open‐shell singlet ground state and is 3D globally aromatic, with individual macrocycles being 2D Hückel aromatic; 2) its tetracation (14+) has a triplet ground state and is also 3D globally aromatic, with individual macrocycles being 2D Baird aromatic; and 3) its hexacation (16+) has a closed‐shell nature and shows local aromaticity. The study demonstrated a close relationship between 2D Hückel/Baird aromaticity and 3D global π‐aromaticity. Hückel‐ and Baird‐type global aromaticity was observed in a 3D fully conjugated molecular cage at different oxidation states. The dication 12+ has an open‐shell singlet ground state and is 3D globally aromatic, with individual macrocycles being 2D Hückel aromatic; the tetracation 14+ has a triplet ground state and is also 3D globally aromatic, with individual macrocycles being 2D Baird aromatic.