Coordination-Driven Self-Assembly of a Molecular Knot Comprising Sixteen Crossings

Molecular knots have become highly attractive to chemists because of their prospective properties in mimicking biomolecules and machines. Only a few examples of molecular knots from the billions tabulated by mathematicians have been realized and molecular knots with more than eight crossings have not been reported to date. We report here the coordination-driven [8+8] self-assembly of a higher-generation molecular knot comprising as many as sixteen crossings. Its solid-state X-ray crystal structure and multinuclear 2D NMR findings confirmed its architecture and topology. The formation of this molecular knot appears to depend on the functionalities and geometries of donor and acceptor in terms of generating appropriate angles and strong π-π interactions supported by hydrophobic effects. This study shows coordination-driven self-assembly offers a powerful potential means of synthesizing more and more complicated molecular knots and of understanding differences between the properties of knotted and unknotted structures.

A simple and highly effective ligand system for the copper(I)-mediated assembly of rotaxanes

A [2]rotaxane was produced through the assembly of a picolinaldehyde, an amine, and a bipyridine macrocycle around a Cu(I) template by imine bond formation in close-to-quantitative yield. An analogous [3]rotaxane is obtained in excellent yield by replacing the amine with a diamine, thus showing the suitability of the system for the construction of higher order interlocked structures. The rotaxanes are formed within a few minutes simply through mixing the components in solution at room temperature and they can be isolated through removal of the solvent or precipitation.