Construction of a molecular prime link by interlocking two trefoil knots

Simple and efficient synthetic routes to topologically complex mechanically interlocked molecules remain scarce owing to the sophisticated three-dimensional entanglement of their structures. We report herein the coordination-driven self-assembly from a trefoil knot to a structure comprising two interlocked homochiral trefoil knots by increasing the length of the ligands. The quadruple interlocking of two trefoil knots of the same handedness gives the resulting molecular prime double trefoil link with a total of 14 crossings. Molecular trefoil knots of single topological chirality are formed via enantiopure ligands. Likewise, a pair of topological enantiomers of the double trefoil link are separately and stereoselectively constructed through chirality transfer from the constituent ligands. The synthesis and topological chirality of the trefoil knot and the double trefoil link have been confirmed using single-crystal X-ray diffraction, mass spectrometry, NMR spectroscopy and circular dichroism spectroscopy. Construction of molecular links from non-trivial knots rather than just trivial macrocycles provides a synthetic strategy for topologically complex mechanically interlocked molecules.