Kinetic Studies Exploring the Role of Anion Templation in the Slippage Formation of Rotaxane‐Like Structures

Abstract

The first examples of the slippage formation of rotaxane-like structures in the presence of an anion template are reported between a macrocycle, synthesised by exploiting Eglinton coupling, and stoppered pyridinium axle components. The role of the anion template in the slippage process has been explored by kinetic studies. (1)H NMR spectroscopic investigations reveal the slippage species formed are not rotaxanes but pseudorotaxanes with some rotaxane character. The anion template significantly influences the amount of rotaxane character and the rate of slippage. Importantly, the fastest slippage rates, k(on), are achieved with the non-coordinating hexafluorophosphate anion, whereas the slowest slippage off rates, k(off), are observed in the presence of coordinating anions, such as chloride. Since the k(off) rates are significantly smaller than the k(on) rates in the presence of coordinating anions, these anions act as templates favouring formation of the slippage species thermodynamically. Consequently, the resulting pseudorotaxanes with coordinating anions have greater rotaxane character. Two strategies for converting the slippage pseudorotaxanes into rotaxanes using hydrogenation or complexation with cobalt carbonyl are investigated.

Revisiting the Formation and Tunable Dissociation of a [2]Pseudorotaxane Formed by Slippage Approach

“…Herein, we employ a slippage approach in one pot ( Figure 1 ) to yield a thermodynamically stable [ 2 ]pseudorotaxane [ 29 , 30 ] by mixing an ammonium thread (dumbbell) 1 -H·PF 6 with dibenzo[ 24 ]crown-8 ( DB24C8 ). Benzo-crown ether DB24C8 is capable to recognize with secondary ammonium ions by virtue of [N + –H···O] and [N + –C–H···O] hydrogen bonds, electrostatic interactions, and augmented with some aromatic π-π interactions [ 31 , 32 , 33 , 34 , 35 , 36 ].…”

[2]Catenane Synthesis via Covalent Templating

“…This results, in comparison to covalent approaches, in shorter and relatively higher yielding syntheses of MiMs, which explains the widespread application of these strategies in other fields, such as that of molecular machines [9] . In addition, new non‐covalent approaches are being developed, such as radical and halogen bonding templation [10, 11] . However, the structural motifs required for supramolecular recognition tend to shape a large portion of the resulting MiMs, as well as their properties.…”

“…[9] In addition, new non-covalent approaches are being developed, such as radical and halogen bondingt emplation. [10,11] However,t he structural motifs required for supramolecular recognition tend to shapealarge portion of the resulting MiMs, as well as their properties.…”

Rotaxanes and pseudorotaxanes with threads containing pyridinium units

“…75 The first examples of using slippage and anion templation to assemble rotaxanees, and investigate the role of the templating anion in the slippage process by kinetic methods, have been reported. 76 In these experiments the ring 41 was obtained from 42 by Eglinton coupling of the terminal alkyne groups with copper(II) acetate. The ring 41 has an isophthalamide anion binding cavity and contains electron rich hydroquinone units for π-π stacking interactions with the electron-deficient pyridinium unit of the thread (Scheme 10).…”