Pillar[ n]arene-calix[ m]arene hybrid macrocyclic structures

Abstract

To reserve planar chirality, enhance molecular recognition, and build advanced self-assemblies, hybrid macrocyclic hosts containing rigid pillar[n]arene and flexible calix[m]arene were designed, prepared and investigated for interesting applications. This review summarizes and discusses different synthetic strategies for constructing hybrid macrocyclic structures. Pillar[n]arene dimer with rigid aromatic double bridges provided the possibility of introducing calix[m]arene cavities, where the planar chirality was reserved in the structure of pillararene. The capacity for molecular recognition was enhanced by hybrid macrocyclic cavities. Interestingly, the obtained pillar[n]arene-calix[m]arene could self-assemble into "channels" and "honeycomb" in both the solid state and solution phase as well as donate the molecular architecture as the wheel for the formation of mechanically interlocked molecules, such as rotaxane. In addition, the pillar[n]arene and calix[m]arene could also be coupled together to produce pillar[n]arene embeded 1,3-alternate and cone conformational calix[m]arene derivatives, which could catalyze the oxidative polymerization of aniline in aqueous solutions. Except for building hybrid cyclophanes by covalent bonds, weak supramolecular interactions were used to prepare pillar[n]arene-calix[m]arene analogous composites with other pillar-like pillar[n]pyridiniums and calix-like calix[m]pyrroles, exhibiting reasonable performances in enhancing molecular recognition and trapping solvent molecules.

Scheme 1. Schematic presentation of the structures of pillar[n]arene and calix[m]arene.

Scheme 2. The synthetic strategy that produces a significant previous piece of P2/P5 and P3 in high yields using the nucleophilic substitution of P1/P4 with F1.

Fig. 1. Single crystal structures of P2 in stick representation indicate (a) a column-like tubular supramolecular self-assembly with (b) noncovalent interactions, as highlighted in green, as well as (c) honeycombed self-assemblies owing to the possession of π–π stacking interactions and C–H⋯π hydrogen bonds, where hydrogen atoms were omitted for clarity.

Scheme 3. Two synthesis routes from the starting molecule P4 with the assistance of F1 to prepare diverse oxacalix[4]arene-bridged pillar[5]arene dimers, such as PC1, PC2 and PC3, with different planar chirality. P5 is an important intermediate compound in one synthesis strategy.

Fig. 2. Single crystal structures of PC3 in the stick representation of (a) top view, (b) side view and (c) packing model showing a self-assembled channel-like architecture. The configurations of the two pillar[5]arenes possessed R_p and S_p rings. Solvent molecules and hydrogen atoms were omitted for clarity.

Scheme 4. Schematic illustration of the synthesis of diverse planar chirality-containing pillar[5]arene-based [2]rotaxanes, such as PC4, PC5, PC8 and PC9, as well as [3]rotaxanes, such as PC6, PC7 and PC10, by utilizing previous pieces, such as double-bridged pillar[5]arene derivatives, including PC1, PC2 and PC3, as well as functional reagents, including stopper-containing F2 and F3 for the formation of axle subunits.

Fig. 3. Single crystal structures of a pair of planar chiral enantiomers, PC6 and PC7. Hydrogen atoms were omitted for clarity.

Scheme 5. Synthesis route for producing PC11 and PC12 by coupling thiacalix[4]arene C1 and pillar[5]arene P6.

Scheme 6. Synthesis of PC13 using P7 and C2.

Scheme 7. Chemical structures of P8, P9 and C3.

Fig. 4. Expanded asymmetric unit of 1/2 P8·C3 (A), where H₂O was trapped inside the center of P8 (B) by a series of weak supramolecular interactions (C–E). Copyright© 2022 by The Royal Society of Chemistry.

Fig. 5. Asymmetric unit of 1/2 P9·C3 (A), where H₂O was trapped inside P9 (B) by a series of weak supramolecular interactions (C–E). Copyright© 2022 by The Royal Society of Chemistry.

Zhaona Liu

Bing Li

Leqian Song

Huacheng Zhang