As a major class of mechanically interlocked molecules, not only are catenanes topologically intriguing targets that challenge the chemical synthesis to the efficient formation of mechanical bonds, but also the mechanical properties arising from the topology offer unique and attractive features for the development of novel functional molecular materials. Despite advancements in templated methods for different types of interlocked architectures, [ n]catenane possessing multiple numbers of interlocked macrocycles still remains a difficult synthetic target with very few reported examples. If the unique mechanical properties of catenanes are to be fully exploited, reliable, controllable, and efficient strategies for accessing [ n]catenanes will be necessary. In this Viewpoint, challenges, considerations, and strategies to [ n]catenanes are discussed.

We report here the efficient synthesis of a series of [3]catenanes featuring the use of cucurbit[6]uril to simultaneously mediate the mechanical and covalent bond formations. By coupling the mechanical interlocking with covalent macrocyclization, formation of topological isomers is eliminated and the [3]catenanes are formed exclusively in good yields. The efficient access to these [3]catenanes and the presence of other recognition units render them promising building blocks for the construction of other high-order interlocked structures.

Strategies to control building block intertwining and the efficient assembly of a linear [4]catenane are presented.

A pair of radial [5]catenanes, with either an isomeric cyclic ‐AABB‐ or ‐ABAB‐ type sequence of the interlocked β‐cyclodextrin (β‐CD) and cucurbit[6]uril (CB[6]) units, has been efficiently synthesized. Because of a marked difference in the binding strength and interlocking sequence of the peripheral macrocycles, interesting sequence‐dependent properties, characteristic of mechanically bonded macrocycles, were realized. Variable‐temperature 1H NMR studies showed that the ‐ABAB‐ isomer has a more independent β‐CD dynamic, whereas the β‐CD motions in the ‐AABB‐ isomer are coupled. Dynamics of the pH‐insensitive β‐CD can also be further modulated upon base‐triggered mobilization of the CB[6]. These unique properties of the mechanical bond expressed in a sequence‐specific fashion and the transmission of the control on the macrocycle dynamics from one interlocked component to another, highlight the potential of similar complex hetero[n]catenanes in the design of advanced, multicomponent molecular machines.