Polyatomic Anion Assistance in the Assembly of [2]Pseudorotaxanes

Abstract

We describe the use of polyatomic anions for the quantitative assembly of ion-paired complexes displaying pseudorotaxane topology. Our approach exploits the unique ion-pair recognition properties exhibited by noncovalent neutral receptors assembled through hydrogen-bonding interactions between a bis-calix[4]pyrrole macrocycle and linear bis-amidepyridyl-N-oxides. The complexation of bidentate polyatomic anions that are complementary in size and shape to the receptor's cavity, in which six NH hydrogen-bond donors converge, induces the exclusive formation of four particle-threaded assemblies.

Ion-pair recognition by a neutral [2]rotaxane based on a bis-calix[4]pyrrole cyclic component

“…At room temperature, the 1 H NMR spectrum of the equimolar mixture (1 mM) of 1 and 2a showed broadening beyond detection for some of the signals of the protons of the two binding partners. Based on 1 H NMR titrations we determined that the stability constant of the 1·2a complex was 800 M –1 at 298 K. 14 Taken together, these results indicate that at this concentration only around 30% of the binding partners are involved in the interwoven 1·2a or 1·2b complexes and that the equilibrium process is intermediate/fast on the proton chemical shift timescale.…”

“…of OCNTBA to a 1 mM equimolar mixture of 1 and 2a in CDCl 3 solution yielded the quantitative assembly of the 3a ⊂ 1·2a complex ( K a ∼ 10 11 M –2 ) featuring [2]pseudorotaxane topology (Scheme 1). 14 This result highlighted the important role played by the ion-pair in templating and stabilizing the interwoven structure of the complex formed between 1 and 2a in solution. We expected that the concentration increase experienced by the synthetic intermediate with [2]pseudorotaxane topology (from 30% to almost 100% in the presence of an equimolar amount of 3a ) could be translated in a significant improvement of the isolated yield of [2]rotaxane 5 .…”

“…macrocycle 1 , 14 linear component 2b and stopper 4 , 24 Fig. 1) were performed by following or adapting synthetic procedures described in literature (see ESI† for experimental details).…”

“…11–13 In 2012, we reported the use of polyatomic anions for the quantitative assembly of [2]pseudorotaxane-like architectures without involving ion-pairing in the linear component. 14 Our approach exploited the exceptional recognition properties exhibited by a neutral interwoven self-assembled receptor 1·2a towards ion-pairs (Fig. 1 and Scheme 1).…”

Ion and Molecular Recognition Using Aryl–Ethynyl Scaffolding

“…Interestingly, host 13 also assembles into a pseudorotaxane by hydrogen bonding with 3,5-pyridinecarboxamide- N -oxide. [75] The smaller binding pocket still provides six hydrogen bond donors and is selective for linear anions, cyanate or azide. In this case, three distinct binding modes have been demonstrated with a single rigid host molecule.…”