Lee Eunji, Ju Huiyeong, Park In-Hyeok, Jung Jong Hwa, Ikeda Mari, Kuwahara Shunsuke, Habata Yoichi, Lee Shim Sung
Department of Chemistry and Research Institute of Natural Science , Gyeongsang National University , Jinju 52828 , S. Korea.
Department of Chemistry, Education Center, Faculty of Engineering , Chiba Institute of Technology , 2-1-1 Shibazono , Narashino , Chiba 275-0023 , Japan.
J Am Chem Soc. 2018 Aug 1;140(30):9669-9677. doi: 10.1021/jacs.8b05751. Epub 2018 Jul 19.
Chiral inversion of single molecules has been a challenging task because chirality information controls structures and functions of various molecules, artificial nanostructures, DNA, and proteins. Herein we present a pseudo[1]catenane-type molecule whose planar chiral inversion is driven by a metal ion under the control of anions for the first time. Considering an in-out equilibrium of a fused thiacrown and the soft metal binding, pillar[5]thiacrown ( rac-L) was synthesized. Two planar-chiral enantiomers of rac-L ( in-pS-L and in-pR-L) were isolated and the absolute configuration was determined by circular dichroism and single crystal X-ray analysis. The in-pS-L recognizes Hg to trigger the chiral inversion to out-pR-L, to our surprise; it takes place only in the presence of ClO or NO among the anions used. In the mercury(II) perchlorate complex solution, anion-exchange from ClO to I or removal of Hg by addition of S makes the system reversible. The crystallographic approach reveals that the anions act as coordination mode-directing species ( endo- or exo-coordination) which play a decisive role on the chiral inversion. For instance, the week coordinating ClO allows Hg to locate inside the thiacrown ( endo-coordination) which causes the chiral inversion from in-pS-L to out-pR-L due to the expansion of the thiacrown unit upon endo-mode complexation. Oppositely, the strong coordinating I takes Hg out of the thiacrown ( exo-coordination) without large conformational changes of the thiacrown, resulting in no chiral inversion. A series of experimental works was also accomplished with the other enantiomer in-pR-L, which afforded identical results. Consequently, the chiral inversion is governed by steric factors that arise from the coordination modes depending on the coordinating ability of anions. This work demonstrates the first chiral inversion induced by combination of metal ion and anion and presents a new perspective on the supramolecular coordination chemistry of pillar[ n]arenes.
单分子的手性反转一直是一项具有挑战性的任务，因为手性信息控制着各种分子、人工纳米结构、DNA和蛋白质的结构与功能。在此，我们首次展示了一种伪[1]连环烷型分子，其平面手性反转由金属离子在阴离子的控制下驱动。考虑到稠合硫杂冠醚的进出平衡以及与软金属的结合，合成了柱[5]硫杂冠醚（rac-L）。分离出了rac-L的两种平面手性对映体（in-pS-L和in-pR-L），并通过圆二色性和单晶X射线分析确定了绝对构型。令人惊讶的是，in-pS-L识别Hg会触发手性反转成为out-pR-L；在所用的阴离子中，只有在ClO或NO存在时才会发生。在高氯酸汞配合物溶液中，阴离子从ClO交换为I或通过添加S去除Hg会使系统可逆。晶体学方法表明，阴离子充当配位模式导向物种（内配位或外配位），它们在手性反转中起决定性作用。例如，配位较弱的ClO使Hg定位在硫杂冠醚内部（内配位），这由于内模式络合时硫杂冠醚单元的扩张导致了从in-pS-L到手性反转的out-pR-L。相反，配位较强的I将Hg带出硫杂冠醚（外配位），而硫杂冠醚没有大的构象变化，导致没有手性反转。还对另一种对映体in-pR-L完成了一系列实验工作，得到了相同的结果。因此，手性反转受空间因素控制，这些因素源于取决于阴离子配位能力的配位模式。这项工作展示了由金属离子和阴离子组合诱导的首次手性反转，并为柱[n]芳烃的超分子配位化学提供了新的视角。
