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

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(<i>azo-up</i>) and 12(<i>azo-down</i>). 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(<i>azo-down</i>) in 25% yield after purification. Mass spectrometry and NMR spectroscopy confirmed the successful synthesis and orientation of C3(<i>azo-down</i>).