Search

The active template approach to interlocked molecules uses metal ions to both pre-organize reaction components and catalyse the final covalent bond formation that captures the interlocked structure. This Review looks at the history of the method, its application in the synthesis of ever more complex interlocked molecules and future directions.

Catalysts based on rotaxanes and catenanes are receiving increased attention, driven by high-profile examples with desirable properties. We survey this emerging field organized by the effect of mechanical bonding on activity, chemoselectivity and stereoselectivity to inspire future investigations and applications.

Despite mechanically axially chiral (MAC) catenanes being recognized in 1961, their stereoselective synthesis had not been disclosed until now. Closer inspection of the MAC stereogenic unit has also led to the identification of an analogous, but unremarked upon, form of rotaxane stereochemistry and the conceptualization of a general approach to prepare MAC molecules stereoselectively.

The design of synthetic systems that mimic the ability of biological systems to control chemical reactions using intricate molecular machines is a long-held dream of nanotechnology. This Review discusses how developments in controlled molecular switching and movement are being exploited in the design of catalysts that are just beginning to emulate the complexity of living systems.

A system is described in which a small macrocycle is continuously transported directionally around a cyclic molecular track when powered by irreversible reactions of a chemical fuel; such autonomous chemically fuelled molecular motors should find application as engines in molecular nanotechnology.

Catenanes are topologically non-trivial and, perhaps for this reason, molecules composed of two oriented rings have always simply been referred to as ‘topologically chiral’. Now it has been shown that the same stereogenic unit can arise in systems whose stereochemistry is Euclidean, suggesting a need to rethink this fundamental form of mechanical chirality.

A chiral [2]rotaxane in which the asymmetry is derived from the way in which the two components are mechanically interlocked — rather than being encoded in the covalent connectivity of the components themselves — has been shown to act as an enantioselective organocatalyst.

The synthesis of chiral interlocked molecules in which the mechanical bond provides the only source of stereochemistry remains challenging. Now, a chiral interlocked auxiliary approach to mechanically planar chiral rotaxanes has been developed and its potential demonstrated through the synthesis of a range of difficult targets with high enantioselectivity.

Interlocked molecules can exhibit chiral stereogenic elements that are not found in covalently bound systems. Now, the shuttling of the ring in a [2]rotaxane has been shown to result in enantiomeric co-conformations that selectively bind chiral guests.