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

Abstract

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.

Redox‐Switchable Calix[6]arene‐Based Isomeric Rotaxanes

“…[23] In arotaxane-based architecture, asymmetry can be included in both the axle and wheel components. The majority of twostationm olecular shuttles reporteds of ar is based on nonsymmetricala xles, [18,24,25] but in principle the direction of motion in ar otaxanec ould be dictated by the asymmetry of the wheel component ( Figure 1). [22,[26][27][28][29][30][31] In am inimalistic design like that showni nF igure 1a,o nw eakening the interaction between the axle and the ring the formation of two orientational isomers could be envisaged.…”

Cooperative Effects in Switchable Catalysis: Enhancing Double‐Click Reaction Yield of Symmetrical Rotaxanes

“…In previous work, we had already shown that copper(I)‐loaded phenanthrolines of type [Cu(phenAr 2 )] + were able to catalyze cyclopropanations [5b] and click reactions. [2d] Equally, the exposed copper(I) ions in the dimer [FeCu 2 ( 1 ) 2 )] 4+ (State II) should be capable of capping bis‐ethynyl terminated pseudorotaxanes with bulky stoppers via a click [16] protocol to form [2]rotaxanes. No catalytic activity was expected for complex [Cu 2 ( 1 ) 2 ] 2+ since the encapsulated copper(I) ions should be unreactive.…”

Chemically Induced Mismatch of Rings and Stations in [3]Rotaxanes

“…In particular, a deshielding is observed for all the signals related to the nuclei placed around the Tz core, whereas the Tz aryl peak remains almost unaltered and the Tz methyl group becomes shielded by 0.88 ppm. 31 , 40 , 41 These changes suggest that in Rot + both rings have moved toward the central triazolium station, with neither of them overtaking it.…”