四面体阴离子配位导向的索烃和三叶分子结的合成与性质研究

Catenanes and molecular knots have attracted great interest not only because of their charming topological structures, but also because of their potential applications in molecular machines or molecular switches. However, the construction of such systems is challenging. By using "template synthesis", catenanes and knots can be assembled in acceptable yields, and the templates used are mainly cations and neutral molecules. In principle, anions should also be applicable in templating the synthesis of these interlocking structures when proper anion binding sites are incorporated in the host. Moreover, anion-templated molecular devices could be modulated under milder conditions, which may mimic biological systems and processes more directly and closely. Yet, studies on the uses of anionic templates have been very rare. Inspired by the similarities of anion coordination to transition metal coordination chemistry, we have recently designed a series of oligourea ligands by taking advantages of the well known oligopyridine backbones. These oligourea ligands, in particular the ortho-phenylene-bridged bis- and tris-ureas, have shown excellent complementarity and high affinity to the tetrahedral sulfate and phosphate anions. In addition, a bis-bisurea ligand and phosphate ions have been successfully utilized in the assembly of the first anion triple helicate. Based on these studies, this project will aim at the self-assembly of anion-directed catenanes and molecular knots (trefoil). The tris-urea receptor will be modified by suitable spacers and functional terminal groups (eg. alkyls), and used to synthesize the anion complexes with preorganized orthogonal orientation or double helicates, which can be facilitated by the coordination properties of tetrahedral anions. Then, the terminal groups can be covalently connected by ring closing reactions such as "click" reactions. We hope to develop a new approach to the synthesis of complicated interlocking architectures by using anionic templates.

索烃和分子结无论是从拓扑美学的角度,还是分子机器的构建方面,都对化学家有巨大的吸引力和挑战性。模板合成法为获得此类物种提供了可能。虽然理论上讲，阴离子作为模板合成索烃和分子结能够在更温和条件下和更接近生命体系的条件下观察其分子机器行为，然而这方面成功的实例却还鲜见。主要原因是阴离子与配体之间的结合能力和构象控制能力较差。本申请人近年来在阴离子配位化学的研究中发现，脲基对含氧酸根离子的配位方式和吡啶对过渡金属阳离子的配位方式很相似，而且我们设计合成的邻三脲配体对四面体阴离子有高结合能力和高构象匹配性，可能作为组装单元构筑超分子体系。基于此，本项目拟通过修饰邻三脲配体，以磷酸根和硫酸根为模板组装成相互正交或双螺旋状两类阴离子配合物，进一步应用关环反应获得索烃和三叶分子结，并研究它们在环境条件改变时的分子机器行为。探索一条以阴离子为中心组装复杂的互锁和结型超分子化合物的新途径。

2016年三位化学家因在分子机器上的杰出贡献，即发明了“世界上最小的机器”，将化学发展推向了一个新的维度而获得诺贝尔化学奖。轮烷、索烃和更复杂的分子结等超分子组装体是构建分子机器的重要基础，对化学家有巨大的吸引力和挑战性。通常这类拓扑结构大多是以阳离子作为模板构建的，而基于阴离子配位的组装很少有报道。近年来阴离子配位化学的发展为阴离子诱导的超分子组装提供了可能。本课题组在阴离子配位化学的研究中发现，脲基团对含氧酸根离子的配位和吡啶对过渡金属的配位方式很相似，据此设计了一系列多脲配体，与四面体阴离子特别是磷酸根有很好的配位性质。本工作旨在利用磷酸根的高结合能力和高构象匹配性进行超分子组装，重点是轮烷、索烃及分子机器的构建，同时也进行了超分子组装体的进一步功能化及应用研究。..设计合成了一系列基于邻苯基桥联的二脲或三脲配位单元的多脲配体，如三联脲，二（联二脲），三（联二脲），四（联二脲），以及同时含有三脲和聚醚链的线状和环状配体。研究了这些配体与磷酸根的配位，得到新颖的以阴离子为配位中心的超分子组装体如三股螺旋和四面体笼等。这些结果为分子机器的构建打好了基础。利用含有三脲（阴离子结合位点）与多醚链（阳离子结合位点）的双功能线状和环状配体与磷酸根配位，得到了准轮烷和交叉配位的磷酸根配合物，进一步应用关环反应获得了索烃。同时，利用这些大环三脲配体与磷酸根配位，通过聚醚部分与阳离子的结合及体系pH值的改变，实现了可控分子转动。此外，我们还合成了聚集荧光增强模块的多脲配体，使阴离子的结合功能化，以及研究了超分子组装体的小分子包夹性质。这些结果再次证明磷酸根良好的配位性能在超分子组装中的独特优势。..项目按计划展开，研究工作取得了较好的结果。发表15篇SCI论文，包括Angew. Chem. 3篇，Chem. Commun. 2篇, Chem. Eur. J. 2篇等,另有数篇在审稿或整理阶段。