Catalytically self-threading polyrotaxanes

Abstract

A mainchain polyrotaxane is formed in which polymerisation and rotaxane formation occur simultaneously, due to the presence of the catalytically-active self-threading macrocycle cucurbituril.

Reactions under the Click Chemistry Philosophy Employed in Supramolecular and Mechanostereochemical Systems

“…This type of catalysis is reminiscent of the cyclooctyne ring-strain strategy in that the inclusion of the azide and alkyne inside the cavity of CB creates a geometry similar to that of the transition state, and hence, speeds up the reaction dramatically. In 1999, the Steinke group [26] exploited this catalysis to synthesize polyrotaxanes. In the context of using electron-deficient alkynes, as early as 1996 our own group [27] has employed the use of the bulky symmetric di-tert-butyl acetylenedicarboxylate to participate in a copper-free 1,3-dipolar cycloaddition, with the steric bulk associated with the triazole ring serving as a stopper.…”

Self‐Assembled Nanoreactors

“…In more recent work, Tuncel and Steinke have shown that this cucurbituril-catalyzed Diels-Alder reaction can also be applied in the synthesis of polyrotaxanes by using diazides and diacetylenes as the substrates. 55,56 The octameric analogue cucurbit [8]uril, which has a cavity with a size comparable to that of γ-CD, can accommodate two aromatic guest molecules. The cavity was used as a nanoreactor in the [2+2]-photodimerization of (E)-diammoniumstilbene in aqueous solution.…”

pH‐Triggered Dethreading–Rethreading and Switching of Cucurbit[6]uril on Bistable [3]Pseudorotaxanes and [3]Rotaxanes

“…We know from our previous work that the nature of the spacer (i.e., shape, size, and length) affects the catalytic ability of CB6 during [3 + 2] cycloaddition reactions. [8][9][10] Therefore, one should carefully choose a spacer that has a lower affinity constant for CB6 than prop-2-ynylamine or azidoethylamine. It is known from the literature that CB6 can form fairly stable host-guest complexes with diaminoalkanes if the number of methylene units in the spacer is between three and eight.…”

“…Cucurbiturils have a hydrophobic cavity and two identical hydrophilic carbonyl portals. [6][7][8][9][10][11][12][13] CB6 binds well to protonated mono-and diaminoalkanes as a result of these structural features, mainly through ion-dipole interactions and the hydrophobic effect.…”

“…[8][9][10][11] There are also a number of examples of CB6-based bistable [2]rotaxanes that behave as molecular switches. [12] The properties of rotaxanes and pseudorotaxanes in other applications can be best exploited if their synthesis is straightforward and very efficient.…”