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Two new cryptands were synthesized from bis(5‐bromomethyl‐1,3‐phenylene)‐32‐crown‐10 (4). The third arms, containing 19 or 21 atoms, were installed via Williamson ether syntheses with bisphenols containing 2,6‐disubstituted pyridines. 2,6‐Diaminopyridine was converted into the bis(p‐hydroxybenzoyl) derivative 3 for the first cryptand (5) and 2,6‐dicarboxypyridine was converted into the bis(p‐hydroxybenzylamide) 9 for the second cryptand (10). Cryptand 5 did not complex viologen derivatives 11–13 to an extent detectable by 1H NMR. We attribute the lack of complexation between viologen derivatives and 5 to its lack of conformational flexibility that prevents π‐stacking, a necessary component for complexation of viologens. In contrast longer and more flexible cryptand 10 did complex dimethyl paraquat (11) with Ka = 1.6 (±0.2) × 103m–1 in acetone at 23 °C, probably by π‐stacking with the p‐oxybenzyl moieties of the host, made available by its enhanced flexibility. [ABSTRACT FROM AUTHOR]

Abstract: A pseudocryptand-type [2]pseudorotaxane was formed via the self-assembly of a dipyridyl bis(meta-phenylene)-32-crown-10 (BMP32C10) derivative and a paraquat derivative. Due to the basicity of the pyridyl group, which forms the third pseudo-bridge of the pseudocryptand, this pseudorotaxane possesses two finite acid–base adjustable association constants. [Copyright &y& Elsevier]

The first dual component pseudocryptand-type [2]pseudorotaxanes were designed and prepared via the self-assembly of synthetically easily accessible bis(meta-phenylene)-32-crown-10 pyridyl, quinolyl, and naphthyridyl derivatives with paraquat. The formation of the pseudocryptand structures in the complexes remarkably improved the association constant by forming the third pseudobridge via H-bonding with the guest and π-stacking of the heterocyclic units. [ABSTRACT FROM AUTHOR]

Three new hydroxyl-functionalized secondary benzyl ammonium salts were synthesized and complexed with dibenzo-24-crown-8. Three [2]semirotaxanes and then their two [2]rotaxanes each with two different stoppers were prepared successfully by reactions of the hydroxyl groups with bulky reagents. X-ray analysis of a single crystal of a [2]semirotaxane confirmed its structure. The formation of the [2]semirotaxanes can be reversibly controlled by adding KPF6 and 18-crown-6 sequentially. These new unsymmetrical [2]rotaxanes afford a way to prepare planar chiral rotaxanes and related supramolecular systems. [ABSTRACT FROM AUTHOR]

Attempts to incorporate a tetralactam (3a) into aside-chain polyrotaxane by formation of its complex with p-tritylphenolate and reaction with poly(vinybenzyl chloride) failed,probably due to steric hindrance. However, three new small moleculemodel rotaxanes (acetal 11aand ethers 14aand 14b) were prepared based on this macrocycle, andone (14b) was characterized by X-ray crystallography.Attempts to prepare poly(ether rotaxane)s such as 18and 20bvia polymerizations in the presence of this tetralactamfailed because the mild conditions required for complexation (nonpolarsolvent, room temperature) are not sufficient for effective step-growthpolymerizations, resulting in only oligomer formation. In an alternativeapproach, clipping of the tetralactam 23onto a preformedpoly(urethane rotaxane) (27) in CH2Cl2was successful, and the original biphasic segmented polymerwas converted to a single-phase polyrotaxane (28) witha significantly lower glass transition temperature. [ABSTRACT FROM AUTHOR]

Abstract: 1,2-Bis[N-(N′-alkylimidazolium)ethane salts form complexes presumed to be pseudorotaxanes with crown ether and cryptand hosts. The association constants of 1,2-bis[N-(N′-butylimidazolium)]ethane bis(hexafluorophosphate) with dibenzo-24-crown-8 and a dibenzo-24-crown-8-based pyridyl cryptand were estimated as 24 (±1) and 348 (±30)M−1, respectively, in acetonitrile at 25°C. The pseudorotaxane-like structure of the 1:2 complex of the N′-methyl analog with the cryptand was observed by X-ray crystallography. Replacement of the ethylene spacer with propylene and butylene spacers resulted in K a values an order of magnitude smaller. [ABSTRACT FROM AUTHOR]