Tetraaminopillar[5]arene Dimers: Synthesis, Structure and Properties

Abstract

Multi-macrocyclic hosts with fixed conformations provide important platforms for the construction of complicated mechanically inter-locked structures. In order to synthesize rigid multi-macrocycles, a type of oxacalix[4]arene-bridged pillar[5]arene dimers were further derivatized. Firstly, the four NO2 groups in pillar[5]arene dimer 1 were reduced under catalytic hydrogenation conditions using Raney Ni as a catalyst to give tetraamino compound 2. Unfortunately, the aromatic amino groups in compound 2 were unstable in the air and hard for next investigation of molecular recognition. Therefore, further derivatization was used to introduce more stable aliphatic amino groups. After multiple optimization attempts, the "1＋4" intermediate product 3 was obtained in a high yield of 72% from reaction of compound 2 and ten equivalents of t-butoxycarbonyl (Boc)-β-alanine 5 in the presence of dicyclohexylcarbodiimide (DCC) at room temperature. The N-Boc protection groups were further removed in the presence of trifluoroacetic acid in CH2Cl2 to afford target compound 4 with four aliphatic amino groups. The structure of 4 was thoroughly confirmed by nuclear magnetic resonance (NMR), high resolution mass spectrometry (HRMS) and X-ray single crystal analysis. X-ray single crystal analysis indicated that the tricyclic host had a shape of binoculars and the conformation was rigid, which could be slightly tuned by different substituents. With a pillar-calix-pillar structure, the host-guest properties of compound 4 were investigated subsequently. Because of its small cavity, oxacalix[4]arene unit played just a role of framework to make two pillar cavities parallel and appropriate for association with guest molecules. The dimers 4 could associate with 1,4-dicyanobutane and form the complex of 2G⸦4 with strong binding ability. The binding constants (K1＝3.9×10 4 L•mol -1 , K2＝2.4×10 4 L•mol -1 , Ka＝ 9.4×10 8 L 2 •mol -2 ) were determined by ultraviolet and visible (UV-Vis) spectroscopy. The complexation between pillar[5]arene dimer 1 with NO2 group and G was also investigated for comparison. The 1 H NMR spectrum and UV-vis spectroscopy studies indicated the binding ability for 1 was not as good as that for 4. This investigation provides a new opportunity for fabricating hierarchical supramolecular systems. Keywords macrocycle; pillar[5]arene dimer; oxacalix[4]arene; fixed conformation; host-guest chemistry 1 引言 大环主体分子的高效构筑历来是驱动超分子化学 蓬勃发展的强劲引擎 [1] . 随着分子机器领域的快速发展, 大环分子设计的结构趋于复杂化, 同时构象的固定也成 为其重要方向之一 [2] . 多环类大环分子由于具有协同效 应 [3] , 为构筑多层次自组装结构提供了很好的发展机会.

Synthesis and Characterization of a Novel Pillar[5]arene That can Undergo Single-Crystal-to-Single-Crystal (SCSC) Transformation★

“…单晶 到单晶的转变可以通过晶体对多种外部刺激(温度 [3][4] 、 光照 [5][6] 、 机械力 [6][7][8][9] 和蒸汽 [9][10][11] )的响应而实现, 已在传感 器 [12][13][14] 、吸附 [15][16][17][18] 、催化 [13] 、手性 [19] 、信息加密 [20] 和分 子机器 [21][22] 等领域展现了卓越的应用前景. 柱芳烃是一类具备柱状结构和独特空腔的大环分 子, 因其空腔结构赋予的主客体性质被广泛应用于超分 子化学和功能材料研究 [23][24][25][26][27][28][29][30][31][32][33] . 在本研究中, 为了构建具 有新型主客体功能的柱芳烃分子, 将吩噻嗪引入柱芳 烃, 成功合成了一种具有新型骨架结构的柱 [5]芳烃.…”