Weakly Associated TFPB Anions Are Superior to PF<sub>6</sub> Anions When Preparing (Pseudo)Rotaxanes from Crown Ethers and Secondary Dialkylammonium Ions

Chen, Nai-Chia; Chuang, Chun-Ju; Wang, Liang-Yun; Lai, Chien‐Chen; Chiu, Sheng‐Hsien

doi:10.1002/chem.201103464

Cited by 28 publications

(9 citation statements)

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“…To minimize the competing interactions of solvent molecules in chelating the alkali metal ions, the assembly must generally be performed in less polar solvents (e.g., CH 2 Cl 2 , CHCl 3 ). To increase the solubility of metal ion salts in these solvents while minimizing ion pairing, the counteranions should be chosen as those that coordinate very weaklyfor example, tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (TFPB) …”

Section: Catenane Synthesismentioning

confidence: 99%

“…To increase the solubility of metal ion salts in these solvents while minimizing ion pairing, the counteranions should be chosen as those that coordinate very weaklyfor example, tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (TFPB). 14 As outlined in Scheme 6, our reaction protocol for catenane synthesis involved dynamic imino bond formation between di(ethylene glycol)-containing diamine 1 and dialdehyde 2 in the presence of NaTFPB in CHCl 3 . In the presence of 0.5 equiv of NaTFPB, this mixture contained the [2]catenane [im3• Na][TFPB] as the predominant product at equilibrium.…”

Section: Conceptmentioning

confidence: 99%

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Using Alkali Metal Ions To Template the Synthesis of Interlocked Molecules

2018

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In 1987, Pedersen, Cram, and Lehn were awarded the Nobel Prize in Chemistry to honor their achievements in, among other things, the selective recognition of alkali metal ions by synthetic hosts. Almost three decades later, the 2016 Nobel Prize went to Stoddart, Sauvage, and Feringa for the development of artificial molecular machines, in which interlocked molecules play a significant role. Surprisingly, although many rotaxane- and catenane-based molecular machines have been constructed using various templating approaches, alkali metal ions, which are good templates for crown ether synthesis, have only rarely been applied as templates for the assembly of these interlocked molecules. This paucity of examples is probably due to the less well defined coordination numbers and geometries in the complexation of alkali metal ions to common oxygen-containing ligands, resulting in much weaker metal-ligand interactions and less predictable structures for their complexes compared with those formed between transition metal ions and common pyridine-containing ligands. Nevertheless, the ease of removing alkali metal ions from interlocked compounds and their much lower toxicity compared with that of transition metal ions are attractive features that have inspired their use as templates in the synthesis of interlocked molecules. About a decade ago, we began investigating the feasibility of using alkali metal ions to template the formation of catenanes and rotaxanes, with the hope of developing facile, broadly applicable, green, and efficient methods for their construction. We noticed that the interactions between oxygen-containing ligands and alkali metal ions can be strengthened by minimizing the effects of competing interactions from solvent molecules and counteranions. Thus, to increase the solubility of the metal ion salts in less polar solvents (e.g., CHCl, CHCl) and minimize ion pairing, we chose tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (TFPB), a weakly coordinating anion, as the counteranion for the alkali metal ions applied as templates. Our strategy has been based on the association of simple and general recognition units: (i) the orthogonal arrangement of two oligo(ethylene glycol) chains around an alkali metal ion and (ii) the encircling of a single urea/amide unit by an oligo(ethylene glycol)-containing macrocycle in the presence of a templating alkali metal ion. The former recognition system has allowed the facile construction of many interesting interlocked structures, including cyclic [2]catenane trimers and tetramers; the latter has provided several rotaxanes, including some incorporating monomers of practically important (macro)molecules (e.g., peptides, polymers) and some that behave as switches with unique functions (e.g., catalysis, gelation). The components in these recognition systems possess high flexibility in terms of their structures and the choice of suitable alkali metal ion templates. This Account tells the story of the concept behind this alkali metal ion-templating approach as well as its elab...

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Section: Catenane Synthesismentioning

confidence: 99%

Section: Conceptmentioning

confidence: 99%

Using Alkali Metal Ions To Template the Synthesis of Interlocked Molecules

2018

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“…Thus, given the effectiveness of the superweak anion approach in inducing the threading of secondary ammonium ions through the annulus of scarcely preorganized and/or narrow macrocyclic hosts, , we decided to study the formation of calix[5]arene-based pseudorotaxanes in the presence of dialkylammonium TFPB salts.…”

Section: Introductionmentioning

confidence: 99%

Calix[5]arene Through-the-Annulus Threading of Dialkylammonium Guests Weakly Paired to the TFPB Anion

et al. 2017

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Through-the-annulus threading of calix[5]arene penta-O-ethers by dialkylammonium cations coupled to the loosely coordinating superweak TFPB anion has been achieved. H NMR titration data show that preorganization of the calix[5]arene scaffold leads to great thermodynamic stability of the pseudorotaxane complexes as well as to a favorable threading kinetic. Thus, calix[5]arene 1c, bearing tert-butyl groups at the wide rim, was threaded by all of the cations under study (with the exception of the dibenzylammonium 2b) more tightly than the other derivatives under investigation (K's up to 2.02 ± 0.2 × 10 M) because of its preorganized cone conformation. According to DFT calculations, van der Waals interactions between the tert-butyl groups of 1c and the alkyl chain of the cationic axle are likely responsible for the remarkable stability observed. The threading of the calix[5]arene wheels with the asymmetric pentylbenzylammonium axle 2c led to the toposelective formation of the endo-pentylpseudorotaxane stereoisomer in agreement with the known "endo-alkyl rule". Owing to the steric hindrance of the axle phenyl group, the threading of the guest was seen to occur in a unidirectional fashion through the calixarene narrow rim.

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“…We suspected that slippage rotaxanes would serve as such “locking” units because their synthesis requires only the heating of a mixture of size-complementary macrocycles and dumbbell-shaped guests at higher temperatures, with the resulting assemblies being sufficiently stable for chromatographic isolation . The stability of slippage rotaxanes arises from the thermodynamic trap generated upon complexation of the recognition unit (guest) of the dumbbell-shaped unit within the cavity (host) of the macrocycle, thereby increasing the activation energy for the deslipping process; dissociation of slippage rotaxanes can be facilitated, however, through the effect of an external stimulus (e.g., added bases, anions, light, or unpreferred solvents) to decrease the strength of the interactions between the recognition units. Because of the delicate balance required, in size and energy, between host macrocycles and guest dumbbell-shaped molecules, only a limited number of slippage systems have been reported previously .…”

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Using Slippage to Construct a Prototypical Molecular “Lock & Lock” Box

et al. 2021

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We report a new slippage system based on p-tert-butylbenzyl-terminated imidazolium ions and di(ethylene glycol)containing macrocycles and their use as linking units for the construction of a prototypical molecular "Lock & Lock" box from a resorcinarene-based cavitand "bowl" and a porphyrin "cover". The multivalent structure with four slippage linkers provided the molecular box with high stability, yet the system dissociated into its two components upon application of suitable external stimuli.

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Weakly Associated TFPB Anions Are Superior to PF₆ Anions When Preparing (Pseudo)Rotaxanes from Crown Ethers and Secondary Dialkylammonium Ions

Abstract: Making the right choice: Tetrakis(3,5-trifluoromethylphenyl)borate (TFPB) counter anions can facilitate the threading of dibenzylammonium (DBA(+)) ions through macrocycles in cases where the corresponding PF(6)(-) salts fail to exhibit complexation.

Cited by 28 publications

References 62 publications

Using Alkali Metal Ions To Template the Synthesis of Interlocked Molecules

Using Alkali Metal Ions To Template the Synthesis of Interlocked Molecules

Calix[5]arene Through-the-Annulus Threading of Dialkylammonium Guests Weakly Paired to the TFPB Anion

Using Slippage to Construct a Prototypical Molecular “Lock & Lock” Box

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Weakly Associated TFPB Anions Are Superior to PF6 Anions When Preparing (Pseudo)Rotaxanes from Crown Ethers and Secondary Dialkylammonium Ions

Abstract: Making the right choice: Tetrakis(3,5-trifluoromethylphenyl)borate (TFPB) counter anions can facilitate the threading of dibenzylammonium (DBA(+)) ions through macrocycles in cases where the corresponding PF(6)(-) salts fail to exhibit complexation.

Cited by 28 publications

References 62 publications

Using Alkali Metal Ions To Template the Synthesis of Interlocked Molecules

Using Alkali Metal Ions To Template the Synthesis of Interlocked Molecules

Calix[5]arene Through-the-Annulus Threading of Dialkylammonium Guests Weakly Paired to the TFPB Anion

Using Slippage to Construct a Prototypical Molecular “Lock & Lock” Box

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Weakly Associated TFPB Anions Are Superior to PF₆ Anions When Preparing (Pseudo)Rotaxanes from Crown Ethers and Secondary Dialkylammonium Ions