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. The synthesis of interlocked compounds such as catenanes and rotaxanes has undergone much development in recent years, but molecular knots are still relatively hard to make. It has now been shown that a linear bipyridine oligomer can fold around a single zinc-ion template to form a complex that can be cyclized to give a molecular trefoil knot.

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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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