Influence of the solvent in the self-assembly and binding properties of [1 + 1] tetra-imine bis-calix[4]pyrrole cages

Abstract

We report the self-assembly of shape-persistent [1 + 1] tetra-imine cages 1 based on two different tetra-α aryl-extended calix[4]pyrrole scaffolds in chlorinated solvents and in a 9 : 1 CDCl3 : CD3CN solvent mixture. We show that the use of a bis-N-oxide 4 (4,4′-dipyridyl-N,N′-dioxide) as template is not mandatory to induce the emergence of the cages but has a positive effect on the reaction yield. We use 1H NMR spectroscopy to investigate and characterize the binding properties (kinetic and thermodynamic) of the self-assembled tetra-imine cages 1 with pyridine N-oxide derivatives. The cages form kinetically and thermodynamically stable inclusion complexes with the N-oxides. For the bis-N-oxide 4, we observe the exclusive formation of 1 : 1 complexes independently of the solvent used. In contrast, the pyridine-N-oxide 5 (mono-topic guest) produces inclusion complexes displaying solvent dependent stoichiometry. The bis-N-oxide 4 is too short to bridge the gap between the two endohedral polar binding sites of 1 by establishing eight ideal hydrogen bonding interactions. Nevertheless, the bimolecular 41 complex results as energetically favored compared to the 521 ternary counterpart. The inclusion of the N-oxides, 4 and 5, in the tetra-imine cages 1 is significantly faster in chlorinated solvents (minutes) than in the 9 : 1 CDCl3 : CD3CN solvent mixture (hours). We provide an explanation for the similar energy barriers calculated for the formation of the 41 complex using the two different ternary counterparts 521 and (CD3CN)21 as precursors. We propose a mechanism for the in–out guest exchange processes experienced by the tetra-imine cages 1.

Graphical abstract: Influence of the solvent in the self-assembly and binding properties of [1 + 1] tetra-imine bis-calix[4]pyrrole cages

Supplementary files

Article information

Article type
Edge Article
Submitted
23 Sep 2022
Accepted
22 Nov 2022
First published
23 Nov 2022
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY-NC license

Chem. Sci., 2022, Advance Article

Influence of the solvent in the self-assembly and binding properties of [1 + 1] tetra-imine bis-calix[4]pyrrole cages

C. F. M. Mirabella, G. Aragay and P. Ballester, Chem. Sci., 2022, Advance Article , DOI: 10.1039/D2SC05311J

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