Social Self-Sorting Synthesis of Molecular Knots

We report the synthesis of molecular prime and composite knots by social self-sorting of 2,6-pyridine dicarboxamide (pdc) ligands of differing topicity and stereochemistry. Upon mixing achiral monotopic and ditopic pdc ligand strands in a 1:1:1 ratio with Lu(III), a well-defined heteromeric complex featuring one of each ligand strand and the metal ion is selectively formed.
Introducing point-chiral centers into the ligands leads to single-sense helical stereochemistry of the resulting coordination complex. Covalent capture of the entangled structure by ring-closing olefin metathesis (RCM) then gives a socially self-sorted trefoil knot of single topological handedness. In a related manner, a heteromeric molecular granny knot (a six-crossing composite knot featuring
two trefoil tangles of the same handedness) was assembled from social self-sorting of ditopic and tetratopic multi-pdc strands. A molecular square knot (a six-crossing composite knot of two trefoil tangles of opposite handedness) was assembled by social selfsorting of a ditopic pdc strand with four (S)-centers and a tetratopic strand with two (S)- and six (R)-centers. Each of the entangled
structures was characterized by 1H and 13C NMR spectroscopy, mass spectrometry, and circular dichroism (CD) spectroscopy. The precise control of composition and topological chirality through social self-sorting enables the rapid assembly of well-defined sequences of entanglements for molecular knots.