Evaluation of the Steric Bulk of Substituents Utilizing the Shuttling Behavior of [2]Rotaxanes with N‐Arylpyrrole Moieties

Abstract

The activation energies of the shuttling of [2]rotaxanes with various N‐arylpyrrole moieties were determined by variable temperature (VT) 1H NMR experiments. The value provided a new quantitative scale for the estimation of the steric bulk of the substituents. The rigidity and the electronic effect of the substituents, which could inadequately influence the estimation of the steric bulk, were minimized in the method we presented.

Regulation of Macrocycle Shuttling Rates in [2]Rotaxanes by Amino‐Acid Speed Bumps in Organic–Aqueous Solvent Mixtures

“…(Note: variants with significantly faster or slower ring shuttling rates than the examples measured herein are incompatible with NMR analysis). barrier vs steric parameter S 0 (see refs [30,40] for definition of S 0 ). Further evidence of the small/negligible alanine steric speed bump effect can be obtained by comparing the 13.4…”

“…[29] In this work we developed designer rotaxane systems building on a benchmark system, namely Leigh's fumaramide rotaxane (Figure 1 top), by incorporating steric barriers to control the macrocycle shuttling rate in both non-polar organic solvents and organic aqueous mixtures. [30,31] For this propose, we synthesized degenerate molecular shuttles containing specific amino-acid units in the thread which are able to act as speed bumps to control the macrocycle shuttling speed (Figure 1, bottom) and sought to generalize this approach for a range of amino-acid units. In these systems, which have two identical stations, the macrocycle would have an equal probability of residing on each station and stochastic macrocycle shuttling would be operational.…”

Challenges and Opportunities in the Post‐Synthetic Modification of Interlocked Molecules

“…Azumaya, Saito,a nd co-workers described in 2016 an elegant intramolecular activation of an encircled conjugated dialkyne that was mediated by am echanical bond. [79] More precisely,t hey successfully performed the post-interlocking conversion of the encircled 1,3-diynyl moiety of 150 [80] into the N-phenylpyrrole-containing [2]rotaxanes 151 by using aniline and copper chloride at 120 8 8C( Scheme 29). The reaction was possible with aw ide range of other aniline derivatives.U nexpectedly,t he formation of the pyrrole moiety occurred much faster in the rotaxane species than in the non-interlocked analogue.T he authors had expected al ow reactivity of the 1,3-diynyl moiety in the interlocked structure because of the steric hindrance brought by the macrocycle.Infact, the phenanthroline moiety of the macrocycle quickly complexed the copper catalyst.…”

Conformational Control of [2]Rotaxane by Hydrogen Bond

“… 6 Assuming that the Cu complex could mediate coupling reactions such as the oxidative dimerization of alkynes (Glaser coupling), we reported the synthesis of [2]rotaxanes from macrocyclic phenanthroline–Cu complex and alkynes with bulky substituents ( Scheme 1 ). 7 Interlocked compounds with polyyne structures have been synthesized by this method, and the properties of these compounds have been studied by several research groups. 8 …”