Oriented rotaxanes composed of tris(N‐phenylureido)calix[6]arene wheel 1 and N,N′‐dialkyl viologen‐based axles were synthesized in which the span between the diphenylacetyl stoppers at the wheel upper and lower rim and the bis‐pyridinium cation portion of the axial component is different in length. A sequential synthetic pathway was followed to achieve the selective formation of orientational isomers, wherein the short (or long) chain of the axle is positioned either on the upper or lower rim of the wheel. The synthetic strategy adopted involves the upper rim threading of axles 2a–c to yield oriented pseudorotaxanes, which were then stoppered in situ. The structure of the oriented rotaxanes was unravelled by detailed NMR experiments, and their spectroscopic, electrochemical and dynamic properties were investigated by UV/Vis, cyclic voltammetry, and EPR measurements. The results were compared with those of their symmetric counterparts.

A substrate can modify its chemical features, including a change of its reactivity, as a consequence of non-covalent interactions upon inclusion within a molecular host. Since the rise of supramolecular chemistry, this phenomenon has stimulated the ingenuity of scientists to emulate the function of enzymes by designing supramolecular systems in which the energetics and selectivity of reactions can be manipulated through programmed host-guest interactions and/or steric confinement. In this paper we investigate how the engulfment of a positively charged pyridinium-based guest inside the π-rich cavity of a tris-(N-phenylureido)calix[6]arene host affects its reactivity towards a S2 reaction. We found that the alkylation of complexed substrates leads to the formation of pseudorotaxanes and rotaxanes with faster kinetics and higher yields with respect to the standard procedures exploited so far. More importantly, the strategy described here expands the range of efficient synthetic routes for the formation of mechanically interlocked species with a strict control of the mutual orientation of their non-symmetric molecular components.

We describe the active template effect of a calix[6]arene host towards the alkylation of a complexed pyridylpyridinium guest. The acceleration of the reaction within the cavity is significant and rim-selective, enabling the efficient preparation of rotaxanes with full control of the mutual orientation of their nonsymmetric components.

Understanding the role played by the nature, number, and arrangement of binding sites anchored to a macrocycle remains a topic of current interest for the synthesis of new interwoven species. We report the synthesis and detailed structural characterization of a new calix[6]arene derivative decorated with two phenylureido groups anchored at the diametrical position of the calix upper rim that adopts a 1,2,3‐alternate conformation in solution and in the solid state. Preliminary data on the ability of this host to form redox‐active pseudorotaxanes and rotaxanes are reported.

Catenanes with desymmetrized ring components can undergo co-conformational rearrangements upon external stimulation and can form the basis for the development of molecular rotary motors. We describe the design, synthesis and properties of a [2]catenane consisting of a macrocycle—the ‘track’ ring—endowed with two distinct recognition sites (a bipyridinium and an ammonium) for a calix[6]arene—the ‘shuttle’ ring. By exploiting the ability of the calixarene to thread appropriate non-symmetric axles with directional selectivity, we assembled an oriented pseudorotaxane and converted it into the corresponding oriented catenane by intramolecular ring closing metathesis. Cyclic voltammetric experiments indicate that the calixarene wheel initially surrounds the bipyridinium site, moves away from it when it is reduced, and returns in the original position upon reoxidation. A comparison with appropriate model compounds shows that the presence of the ammonium station is necessary for the calixarene to leave the reduced bipyridinium site.