Base–acid-induced translational isomerism in a branched [4]rotaxane

Threading of three rings on two stations: a convergent approach to [4]rotaxane

A novel approach to efficient and selective construction of [4]rotaxane was proposed to demonstrate the superiority of H-bonded azo-macrocycles in forging higher order rotaxanes. The single crystal structure reveals the importance of the interplay of multiple non-covalent bonding interactions, particularly π-stacking interactions, in stabilizing the host-guest complex. This may open an avenue to the synthesis of oligomeric mechanically interlocked molecules containing fewer stations but more rings.

Distinguishing Two Ammonium and Triazolium Sites of Interaction in a Three-Station [2]Rotaxane Molecular Shuttle

This paper reports on the synthesis of a tri-stable [2]rotaxane molecular shuttle, in which the motion of the macrocycle is triggered by either selective protonation/deprotonation or specific carbamoylation/decarbamoylation of an alkylbenzylamine. The threaded axle is surrounded by a dibenzo[24]crown[8] (DB24C8) macrocycle and contains three sites of different binding affinities towards the macrocycle. An N-methyltriazolium moiety acts as a molecular station that has weak affinity for the DB24C8 macrocycle and is located in the centre of the molecular axle. Two other molecular stations, arylammonium and alkylbenzylammonium moieties, sit on either side of the triazolium moiety along the molecular axle and have stronger affinities for the DB24C8 macrocycle. These two ammonium moieties are covalently linked to two different stopper groups at each extremity of the thread: a tert-butylphenyl group and a substituted DB24C8 unit. Owing to steric hindrance, the former does not allow any π-π stacking interactions with the encircling DB24C8 macrocycle, whereas the latter residue does; therefore, this allows the discrimination of the two ammonium stations by the surrounding DB24C8 macrocycle in the fully protonated state. In the deprotonated state, the contrasting reactivity of the amine functional groups, as either a base or a nucleophile, allows for selective reactions that trigger the controlled shuttling of the macrocycle around the three molecular stations.

Ferrocene-containing [1]-, [2]-, [3]- and [4]rotaxanes synthesized from a common precursor

[1]-, [2]-, [3]- and [4]rotaxanes were synthesized by reaction of azide compounds with dialkylammonium with ferrocenyl and alkynyl terminal groups.