Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States.
Institute for Sustainability and Energy at Northwestern, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States.
J Am Chem Soc. 2020 Mar 18;142(11):5419-5428. doi: 10.1021/jacs.0c01114. Epub 2020 Mar 5.
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 -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.
能够对外界各种刺激做出响应，实现变构调节的人工合成大环主体是超分子科学领域日益关注的焦点。在此，我们报告了一种结构可转换的四阳离子环番，其中包含两个 3,6-双（4-吡啶基）-1,2,4,5-四嗪（4-bptz）单元，它们由两个 -二甲苯桥连接在一起。该环番具有模块化的氧化还原态和结构后修饰，可以经历两次可逆的连续两电子还原，首先得到其双自由基二阳离子对应物，然后得到完全还原的物质。此外，通过盒到盒级联转化，单个母体环番可以有效地提供另外三个新类似物，利用还原或逆电子需求 Diels-Alder（IEDDA）反应。虽然所有四个新的四阳离子环番都采用刚性和对称的盒状构象，但它们的几何形状与尺寸、形状、电子性质和对多环芳烃的结合亲和力可以很容易地进行调节。由于结构后修饰，这种结构可转换的四阳离子环番可以执行各种新任务，因此可作为一种工具包，用于研究自由基性质，并通过高效发散合成快速生成一系列结构多样的环番。这项研究为将结构可转换的四阳离子环番引入机械互锁分子领域奠定了坚实的基础，并将为构建和操作智能分子机器提供一个工具包。
