# Synthesis and Characterization of a Two-Station Two-Gate Calix[6]arene-Based [2]Catenane

## TL;DR

This paper describes the synthesis and characterization of a complex molecular machine with two gates and two stations, built using a calix[6]arene-based structure.

## Contribution

The novelty lies in integrating two functional gates into a two-station molecular catenane for potential use in molecular machines.

## Key findings

- A two-station two-gate calix[6]arene-based [2]catenane was successfully synthesized.
- The final [2]catenane was confirmed using mass spectrometry and NMR spectroscopy.
- A supramolecular-assisted approach was used to overcome challenges in the synthesis process.

## Abstract

The design, construction, and operation of devices and machines at the molecular scale using the bottom-up approach captivates a lot of interest in nanoscience. Particularly intriguing are interlocked molecular architectures, which are ideal candidates for these aims. [n]Pseudorotaxanes, [n]rotaxanes, and [n]catenanes serve as versatile prototypes for constructing molecular machines because they can be engineered to execute a diverse range of functions, including mechanical-like movements in response to chemical, photochemical, or electrochemical stimuli. The study explores the synthesis and characterization of a two-station two-gate calix[6]arene-based [2]catenane. Building on prior work with calix[6]arene-based Mechanically Interlocked Molecules (MIMs), this research integrates two functional gates—an azobenzene unit and a stilbene unit —into a two-station “track” ring. The synthesis employed threading and capping strategies to prepare the precursor [2]rotaxane isomers 12(azo-up) and 12(azo-down). Challenges in the deprotection of TBS groups led to the adoption of a supramolecular-assisted approach for the direct synthesis of the desired pseudorotaxane. The final catenation reaction, using a trans-stilbene-based bisacyl chloride as the “clipping unit”, afforded the [2]catenane C3(azo-down) in 25% yield after purification. Mass spectrometry and NMR spectroscopy confirmed the successful synthesis and orientation of C3(azo-down).