Metastable doubly threaded [3]rotaxanes with a large macrocycle |
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Authors: | Jerald E Hertzog Vincent J Maddi Laura F Hart Benjamin W Rawe Phillip M Rauscher Katie M Herbert Eric P Bruckner Juan J de Pablo Stuart J Rowan |
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Institution: | Department of Chemistry, University of Chicago, Chicago IL 60637 USA.; Pritzker School of Molecular Engineering, University of Chicago, Chicago IL 60637 USA ; Department of Macromolecular Science and Engineering, Case Western Reserve University, 2100 Adelbert Road, Cleveland OH 44106 USA ; Chemical Science and Engineering Division and Center for Molecular Engineering, Argonne National Laboratory, 9700 S. Cass Ave., Lemont, IL 60434 USA |
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Abstract: | Ring size is a critically important parameter in many interlocked molecules as it directly impacts many of the unique molecular motions that they exhibit. Reported herein are studies using one of the largest macrocycles reported to date to synthesize doubly threaded 3]rotaxanes. A large ditopic 46 atom macrocycle containing two 2,6-bis(N-alkyl-benzimidazolyl)pyridine ligands has been used to synthesize several metastable doubly threaded 3]rotaxanes in high yield (65–75% isolated) via metal templating. Macrocycle and linear thread components were synthesized and self-assembled upon addition of iron(ii) ions to form the doubly threaded pseudo3]rotaxanes that could be subsequently stoppered using azide–alkyne cycloaddition chemistry. Following demetallation with base, these doubly threaded 3]rotaxanes were fully characterized utilizing a variety of NMR spectroscopy, mass spectrometry, size-exclusion chromatography, and all-atom simulation techniques. Critical to the success of accessing a metastable 3]rotaxane with such a large macrocycle was the nature of the stopper group employed. By varying the size of the stopper group it was possible to access metastable 3]rotaxanes with stabilities in deuterated chloroform ranging from a half-life of <1 minute to ca. 6 months at room temperature potentially opening the door to interlocked materials with controllable degradation rates.Multiple metastable doubly threaded 3]rotaxanes using a large 46 atom ring were prepared and fully characterized. Varying the stopper group size gave a range of interlocked stabilities in CDCl3 from a half-life of <1 minute to ca. 6 months. |
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