Anion recognition as a method for templating pseudorotaxane formation

Abstract

Two thread-shaped cations, pyridinium nicotinamide and imidazolium, as their chloride and hexafluorophosphate salts, were studied with regards to complexation with hydrogen-bonddonating acyclic and macrocyclic ligands. In the latter case, the cations form pseudorotaxanes templated by the chloride anion but not hexafluorophosphate. This formation is a function of the coupling of ion-pairing between the cation and chloride anion and subsequent recognition of the anion by the macrocyclic diamide, which provides the driving force for interpenetration. We propose that this anion template principle is a general method for the construction of pseudorotaxanes and could be applied to other cationic threads, anions, and macrocyclic species.

Ion pair receptors

“…The formation of this latter product is evidenced by the appearance of a broad band at approximately 370 nm in the UV/Vis spectrum, features that correspond to color change from colorless to pale yellow. Consistent with this proposed mechanism, it was found that pseudorotaxane 72 is not formed in protic solvents because of competition from the solvents 83,84. In contrast, the permanently interlocked [2]- and [3]-catenanes 74 and 75 can be formed from the ion pair receptor 70 and the organic ion pair 73 by ring-closing metathesis (Fig.…”

Anion-templated assembly of [2]rotaxanes

“…The chloride anion-templated RCM reaction was also attempted with the 5-nitroisophthalamide derivative 3 and the cyclic product (14) isolated in 60% yield after purification (Fig. 4).…”

Mass spectrometric evidence for catenanes and rotaxanes from negative-ESI FT-ICR tandem-MS-experiments

“…Another important difference is that axles 19 and 20 do not have any groups that are prone to forming strong hydrogen bonds with any of the macrocycles, while the phenolate formed upon deprotonation of 21 is capable of strong hydrogen bonding to two amide groups of the macrocycles. In dichloromethane, a binding constant of K > 10 5 M −1 was determined The strong binding of phenolates and other anions to tetralactam macrocycles in solution has been utilized for designing template effects for efficient rotaxane synthesis [20][21][22][28][29][30][31][32][33]. In the gas phase, one might expect the binding to be even stronger because there is no competition with the solvent anymore.…”