Synthesis, Structure, and Fullerene-Complexing Property of Azacalix[6]aromatics

Synthesis, structure, and fullerene-binding
property of azacalix­[6]­aromatics
were systematically studied. By means of [3 + 3] and [2 + 2 + 2] fragment
coupling protocols, a number of azacalix­[6]­aromatics containing
different combinations of benzene, pyridine, and pyrimidine rings
and various substituents on the bridging nitrogen atoms were synthesized
conveniently in moderate to good yields. The resulting macrocycles
adopt in the solid state symmetric and heavily distorted 1,3,5-alternate
conformations depending on the aromatic building units, whereas, in
solution, they exist as a mixture of conformers that undergo rapid
interchanges relative to the NMR time scale. All macrocycles were
able to form 1:1 complexes with C60 and C70 in
toluene with the association constants up to 7.28 × 104 M–1. In the crystalline state, azacalix­[6]­aromatics
form complexes with C60 and C70 with 2:1, 1:1,
and 1:2 stoichiometric ratios between host and guest. Azacalix­[6]­aromatics
interact with fullerene by forming mainly the sandwich structure in
which C60 or C70 is sandwiched by two macrocycles.
X-ray molecular structures revealed that multiple π–π
and CH−π interactions between concave azacalix­[6]­aromatics
and convex fullerenes C60 and C70 contribute
a joint driving force to the formation of host–guest complexes.

本研究系统性地探究了氮杂卡利克斯[6]芳烃的合成、结构及其与富勒烯的相互作用性质。通过[3 + 3]和[2 + 2 + 2]片段偶联策略，成功合成了多种氮杂卡利克斯[6]芳烃，这些芳烃包含苯、吡啶和嘧啶环的不同组合，以及桥连氮原子上的各种取代基，且合成效率适中至良好。在固态中，所得的大环分子根据芳环构建单元的不同，呈现对称且严重扭曲的1,3,5-交替构象；而在溶液中，它们则以构象混合物的形式存在，其构象之间的快速交换相对于核磁共振时间尺度。所有大环分子均能与C60和C70在甲苯中形成1:1的复合物，其结合常数高达7.28 × 10^4 M^-1。在晶体状态下，氮杂卡利克斯[6]芳烃与C60和C70形成复合物，主客体之间的化学计量比为2:1、1:1和1:2。氮杂卡利克斯[6]芳烃与富勒烯的相互作用主要通过夹心结构实现，其中C60或C70被两个大环分子所包围。X射线分子结构分析揭示，凹面氮杂卡利克斯[6]芳烃与凸面富勒烯C60和C70之间的多重π-π和CH-π相互作用，共同推动了主客体复合物的形成。