Template-directed syntheses of catenanes

The art and science of introducing mechanical-interlocking at the molecular level in order to generate catenanes - molecules composed of two or more macrocyclic components - offers the opportunity of constructing a new range of molecular compounds possessing intriguing properties; However, the topological features displayed by catenanes has rendered the syntheses of such molecular compounds an extremely challenging task for synthetic chemists to address. Their early syntheses were based upon either statistical approaches - the threading of a small amount of a macrocycle on to an acyclic precursor as a chance event - or directed approaches, relying upon the temporary introduction of covalent bonds in the multistep synthesis of a so-called precatenane, followed by its conversion ultimately into a catenane. These approaches afforded catenanes in very low yields overall and only after following tedious and laborious synthetic procedures. Fortunately, however, with the advent of supramolecular chemistry, template-directed methods that allow us to self-assemble [n]catenanes much more efficiently have become available. Numerous successful template-directed syntheses have now emerged - some by chance and others by design. These methods have been based upon (i) metal coordinating, (ii) hydrogen bonding, (iii) solvophobic, and/or (iv) pi-pi stacking interactions which have been found to govern self-assembly processes to catenated compounds from appropriate precursors. Their relative simplicity, the high degree of control with which they can be employed, and the remarkable efficiency with which they proceed has already provided the opportunity to synthetic chemists to self-assemble a series of [n]catenanes, incorporating from two up to five mechanically-interlocked macrocyclic components.