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Synthesis of a molecular trefoil knot by folding and closing on an octahedral coordination template

Abstract

The advent of template-directed synthesis has provided access to a range of new interlocked molecular architectures. Although many syntheses of molecular catenanes and rotaxanes have been reported, molecular knots are a class of molecules with topologically non-planar graphs that are rather rare. Here we report a synthetic strategy for the preparation of a molecular trefoil knot from a flexible bipyridine oligomer and a zinc(II) octahedral coordination template. The oligomer folds into a stable open-knot conformation in the presence of the template, and trapping of this arrangement through esterification or ring-closing metathesis produces the closed-knot complex. Subsequent removal of the template from the metathesis product results in a molecular trefoil knot.

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Figure 1: Template synthesis of a molecular trefoil knot by the folding–threading–closing strategy.
Figure 2: Synthesis of the knot coordination complexes 3, 8a and 8b, and of the molecular trefoil knot 9b.
Figure 3: 1H NMR spectra of key intermediates in the synthesis of the molecular trefoil knot 9b.
Figure 4: 1H NMR chemical shift changes associated with the supramolecular organization of the knot architecture.
Figure 5: Molecular mechanics models of the three-dimensional structures of the closed-knot complex and the molecular trefoil knot.

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Acknowledgements

We thank the Engineering and Physical Sciences Research Council, the Committee of Vice-Chancellors and Principals and AstraZeneca for financial support.

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C.A.H. conceived and designed the experiments, J.G. and P.C.M. carried out the experiments, C.A.H. and J.G. co-wrote the paper and all authors helped to analyse the data and commented on the manuscript.

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Correspondence to Christopher A. Hunter.

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The authors declare no competing financial interests.

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Guo, J., Mayers, P., Breault, G. et al. Synthesis of a molecular trefoil knot by folding and closing on an octahedral coordination template. Nature Chem 2, 218–222 (2010). https://doi.org/10.1038/nchem.544

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