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Aromaticity in Fully π-Conjugated Open-Cage Molecules

Authors :
Wu, Shaofei
Ni, Yong
Han, Yi
Xin, Shan
Hou, Xudong
Zhu, Jun
Li, Zhengtao
Wu, Jishan
Source :
Journal of the American Chemical Society; December 2022, Vol. 144 Issue: 50 p23158-23167, 10p
Publication Year :
2022

Abstract

Although aromaticity in 2D π-conjugated monocyclic and polycyclic molecules has been intensively studied, aromaticity in 3D fully π-conjugated molecular cages remains largely unexplored mainly due to the synthetic challenges. Herein, we report the facile synthesis of a π-conjugated molecular cage (1) containing four dimethylmethylene-bridged triphenylamine (DTPA) units via platinum-mediated assembly of four molecules of a pinacol borate trisubstituted DTPA derivative, followed by reductive elimination. 1has an open-cage structure, consisting of two isomeric trimers in trans- and cis-configurations, and an additional macrocycle across four DTPA units. Accordingly, the trans- (2) and cis- (3) macrocyclic trimers were also synthesized for comparison. 1–3can be facilely oxidized into their respective cations in which electrons are effectively delocalized at two or three dimensions. The detailed experimental measurements and theoretical calculations reveal that (1) the neutral cage 1shows localized aromaticity in individual benzene rings; (2) the dication 12+·2SbF6–displays bicyclic (anti)aromaticity with one macrocycle being aromatic (38π) and another macrocycle being antiaromatic (28π); on the other hand, the dications of the model compounds 2and 3are globally antiaromatic and nonaromatic, respectively; (3) the tetracation 14+·4SbF6–exhibits dominant 2D Hückel antiaromaticity in one of the macrocycles (36π). In addition, 12+·2SbF6–, 14+·4SbF6–, and 22+·2SbF6–possess open-shell singlet ground state with significant diradical character, while 32+·2SbF6–adopts a triplet ground state to release strain.

Details

Language :
English
ISSN :
00027863 and 15205126
Volume :
144
Issue :
50
Database :
Supplemental Index
Journal :
Journal of the American Chemical Society
Publication Type :
Periodical
Accession number :
ejs61310597
Full Text :
https://doi.org/10.1021/jacs.2c10859