Strategic Exploration of Quinoline-Based Materials

我们设计并合成了一类新的共轭大环--TEQ(TEQ)，它含有四个向内取向的氮原子，具有刚性的马鞍形结构和特殊的化学和物理性质。在Tf2O和吡啶衍生物的存在下，由喹啉酰胺底物的环状二聚体和炔烃合成了TEQ。C2对称取代的TEQ具有相当高的翻转能垒以确保其手性，实验证实了这一点，即使在240℃下，对映体过剩也没有受到侵蚀。TEQ可以容纳各种类型的过渡金属阳离子，如Fe2+、Co2+、Ni2+、Cu2+、Zn2+和Pd2+，形成相应的金属络合物，表现出很高的阳离子交换和质子化动力学稳定性。这些配合物的结构无疑得到了X射线结晶学的证实，TEQ-Fe(II)配合物在催化剂负载量低至0.1mol%的情况下对脱氢反应表现出催化活性。TEQ显示出固有的弱荧光，质子化或添加质子化或添加锌(II)阳离子时，它会变得强烈发射，这表明它可能作为结构健壮的pH或锌探针应用。

We have designed and synthesized TEtraQuinoline (TEQ), a new family of conjugated macrocycles containing four inwardly oriented nitrogen atoms, which exhibit a rigid saddle-shape structure and special chemical and physical properties. TEQ is synthesized from a cyclic dimer of quinoline-amide substrate and an alkyne in the presence of Tf2O and pyridine derivatives. DFT calculations are carried out to gain a deeper understanding of the reaction mechanism.The C2-symmetric substituted TEQ has a considerably high energy barrier for flipping to secure its chirality, which has been experimentally confirmed by no erosion of the enantiomeric excess even at 240 °C. TEQ accommodates various types of transition metal cations, such as Fe2+, Co2+, Ni2+, Cu2+, Zn2+ and Pd2+, to form corresponding metal complexes, which displayed high kinetic stability toward cation exchange and protonation. The structure of these complexes are undoubtedly confirmed by X-ray crystallography, and a TEQ-Fe(II) complex exhibits catalytic activity in dehydrogenation reactions with catalyst loadings as low as 0.1 mol%. TEQ shows inherently weak fluorescence, and it becomes strongly emissive upon protonation or addition of upon protonation or addition of Zn(II) cations, suggesting potential application as structurally robust pH or Zn probes.