The chemistry of the mechanical bond

Abstract

The use of templation in the synthesis of unnatural products where two or more components are mechanically interlocked has not only raised the efficiency of their production to near quantitative levels in some instances, but the molecular recognition that aids and abets the templation is also part and parcel of the molecules after they have been prepared, purified and presented for investigation. The fact that the molecular recognition 'lives on' in mechanically interlocked molecules, following their templated formation, makes them prime candidates for applications that straddle the scientific and technical worlds from devices that could spawn new information technologies to integrated systems that could have fundamental applications in the health-care industries. The challenge to make more and more sophisticated compounds is predicated upon our fundamental understanding of the nature of the mechanical bond and how this associated knowledge base can be employed to do complex systems chemistry in very different environments where emergent phenomena become the order of the day (critical review, 104 references).

Self-assembly formation of mechanically interlocked [2]- and [3]catenanes using lanthanide ion [Eu(iii)] templation and ring closing metathesis reactions

“…4 The templating ions can be employed as an integrated part of the resulting self-assembly structure or be removed after its formation by competitive extraction/displacement, changing their oxidation states, chemical reactions, etc. 5 Many examples of such elegantly designed systems have been reported by leading scientists in this field, including those of Sauvage et al, 5 Stoddart et al 6 and Leigh et al 7 All have demonstrated the use of d-metal ion directed synthesis of interlocked molecules. 8,9 In contrast, the use of lanthanide ions (f-metal ions) in the formation of such interlocked molecules has remained relatively unexplored to date.…”

Mechanostereochemistry and the mechanical bond

“…Over the past 30 years, the mechanical bond (Stoddart 2009) has emerged as a consequence of the molecular recognition and self-assembly processes that are underpinned by noncovalent bonding interactions prior to different kinds of post-assembly covalent modifications. Molecular components can be mechanically interlocked (figure 1) in a manner such that the components cannot part company without the breaking of at least one covalent bond, giving rise to molecules (Schill 1971;Sauvage & Dietrich-Buchecker 1999) such as catenanes, where two or more rings are linked together as in a chain (catena is Latin for chain) and rotaxanes (rota is Latin for wheel, and axis is Latin for axle) where ring components are threaded onto rod whose termini are stoppered-forming dumbbell components-and thus blocking the rings from escaping.…”

Synthesis of novel [2]rotaxanes using hydrogen-bonding template

“…1 Due to their characteristic of controlling motion (pirouetting or shuttling) the [2]rotaxanes have received much scientific interest over the last decade, especially in the development of biological machines.…”