TetrazineBox: A Structurally Transformative Toolbox

• Published in: Journal of the American Chemical Society Vol. 142; no. 11; pp. 5419 - 5428
• Main Authors: Guo, Qing-Hui, Zhou, Jiawang, Mao, Haochuan, Qiu, Yunyan, Nguyen, Minh T, Feng, Yuanning, Liang, Jiaqi, Shen, Dengke, Li, Penghao, Liu, Zhichang, Wasielewski, Michael R, Stoddart, J. Fraser
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 18.03.2020; Amer Chemical Soc
• Subjects: binding capacity; Chemistry; Chemistry, Multidisciplinary; cycloaddition reactions; geometry; Physical Sciences; polycyclic aromatic hydrocarbons; Science & Technology; POST-ASSEMBLY MODIFICATION; MOLECULAR RECOGNITION; PI INTERACTIONS; COMPLEXES; CHEMISTRY; CRYSTAL-STRUCTURES; ROTAXANE; CUCURBITURIL HOMOLOGS; CROWN-ETHERS; BINDING
• ISSN: 0002-7863; 1520-5126; 1520-5126
• DOI: 10.1021/jacs.0c01114

Synthetic macrocycles capable of undergoing allosteric regulation by responding to versatile external stimuli are the subject of increasing attention in supramolecular science. Herein, we report a structurally transformative tetracationic cyclophane containing two 3,6-bis­(4-pyridyl)-l,2,4,5-tetrazine (4-bptz) units, which are linked together by two p-xylylene bridges. The cyclophane, which possesses modular redox states and structural post-modifications, can undergo two reversibly consecutive two-electron reductions, affording first its bisradical dicationic counterpart, and then subsequently the fully reduced species. Furthermore, one single-parent cyclophane can afford effectively three other new analogs through box-to-box cascade transformations, taking advantage of either reductions or an inverse electron-demand Diels–Alder (IEDDA) reaction. While all four new tetracationic cyclophanes adopt rigid and symmetric box-like conformations, their geometries in relation to size, shape, electronic properties, and binding affinities toward polycyclic aromatic hydrocarbons can be readily regulated. This structurally transformative tetracationic cyclophane performs a variety of new tasks as a result of structural post-modifications, thus serving as a toolbox for probing the radical properties and generating rapidly a range of structurally diverse cyclophanes by efficient divergent syntheses. This research lays a solid foundation for the introduction of the structurally transformative tetracationic cyclophane into the realm of mechanically interlocked molecules and will provide a toolbox to construct and operate intelligent molecular machines.