endo-Cavity Complexation and Through-the-Annulus Threading of Large Calixarenes Induced by Very Loose Alkylammonium Ion Pairs

Abstract

A general mode to obtain endo-complexation and through-the-annulus threading of scarcely efficient macrocyclic hosts was obtained by exploiting the inducing effect of the weakly coordinating tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (TFPB) anion that gives free "naked" cations. This method works very well with simple, conformationally mobile calix[6-7]arene ethers, which give conformationally blocked endo-calix or [2]pseudorotaxane complexes.

Calix[6]arene-based atropoisomeric pseudo[2]rotaxanes

“…As expected [ 40 ], no evidence of interaction between 2 + and 1 was detected by NMR, when 2 + was added as its chloride salt to a CDCl 3 solution of 1 . However, when 2 + was added as its TFPB − salt to a CDCl 3 solution of 1 , then dramatic changes were observed in the 1 H NMR spectrum of 1 ( Fig.…”

“…At the end of our screening, we focused our attention on hexahexyloxycalix[6]arene 1 as the wheel and bis(4-biphenylmethyl)ammonium ( 2 + ) and bis(4-trifluoromethylbenzyl)ammonium ( 3 + , TFPB – salts) as the threads. The synthetic pathway to 2 + ·TFPB − and 3 + ·TFPB − salts is outlined in Scheme 1 , while calix[6]arene 1 was obtained following a known procedure [ 40 ].…”

Alkylammonium Guest Induced‐Fit Recognition by a Flexible Dihomo­oxacalix[4]arene Derivative

“…In particular, a new set of slowly exchanging signals appeared, which include the n ‐butyl resonances in the upfield negative region of the spectrum as a result of n BuNH 3 + ⊂ 1c complex formation (Figure 3). This is a clear indication that linear n ‐butylammonium cation 2a + gives endo ‐cavity complexation with the alkyl chain shielded by the aromatic rings 5g. Complex formation was also confirmed by an MS (ESI + ), which gave a base peak value of 809 m / z , which corresponds to supramolecular ion n BuNH 3 + ⊂ 1c .…”

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

“…[17] This finding suggests that using only PF 6 À salts to investigate the binding of DBA + derivatives with macrocycles can result in the omission of possible-and potentially useful-recognition systems.…”