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Open AccessArticle

NMR Studies on Li+, Na+ and K+ Complexes of Orthoester Cryptand o-Me2-1.1.1

Department of Chemistry and Pharmacy, Friedrich-Alexander University Erlangen-Nürnberg (FAU), Henkestr. 42, 91054 Erlangen, Germany
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Academic Editor: John Hardy
Int. J. Mol. Sci. 2015, 16(9), 20641-20656; https://doi.org/10.3390/ijms160920641
Received: 10 July 2015 / Revised: 6 August 2015 / Accepted: 24 August 2015 / Published: 31 August 2015
(This article belongs to the Special Issue Supramolecular Interactions)
Cryptands, a class of three-dimensional macrobicyclic hosts ideally suited for accommodating small guest ions, have played an important role in the early development of supramolecular chemistry. In contrast to related two-dimensional crown ethers, cryptands have so far only found limited applications, owing in large part to their relatively inefficient multistep synthesis. We have recently described a convenient one-pot, template synthesis of cryptands based on O,O,O-orthoesters acting as bridgeheads. Here we report variable-temperature, 1H-1D EXSY and titration NMR studies on lithium, sodium, and potassium complexes of one such cryptand (o-Me2-1.1.1). Our results indicate that lithium and sodium ions fit into the central cavity of the cryptand, resulting in a comparably high binding affinity and slow exchange with the bulk. The potassium ion binds instead in an exo fashion, resulting in relatively weak binding, associated with fast exchange kinetics. Collectively, these results indicate that orthoester cryptands such as o-Me2-1.1.1 exhibit thermodynamic and kinetic properties in between those typically found for classical crown ethers and cryptands and that future efforts should be directed towards increasing the binding constants. View Full-Text
Keywords: supramolecular chemistry; cryptands; orthoesters; dynamic covalent chemistry; NMR spectroscopy; host-guest complexes supramolecular chemistry; cryptands; orthoesters; dynamic covalent chemistry; NMR spectroscopy; host-guest complexes
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Brachvogel, R.-C.; Maid, H.; Von Delius, M. NMR Studies on Li+, Na+ and K+ Complexes of Orthoester Cryptand o-Me2-1.1.1. Int. J. Mol. Sci. 2015, 16, 20641-20656.

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