Social Self-Sorting Synthesis of Molecular Knots

Abstract

We report the synthesis of molecular prime and composite knots by social self-sorting of 2,6-pyridinedicarboxamide (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 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 self-sorting 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 1 H and 13 C NMR spectroscopy, mass spectrometry, and circular dichroism 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.

Precision syntheses of molecular necklaces based on coordination interactions

“…Mechanically interlocked molecules are defined as molecules that are held together as a consequence of their topologies and possess mechanical bonds. 1 Archetypal topologies containing mechanical bonds include rotaxanes, 2-6 catenanes, [7][8][9][10][11][12][13] knots, [14][15][16] and interlocked cages [17][18][19][20] (Fig. 1a), of which cate-nanes are a representative class of mechanically interlocked molecules consisting of interlocked macrocycles 21 and are also at the forefront of creating artificial molecular machines and developing the dynamics of interlocked structures in polymers, MOFs, and other materials.…”

Formation of lanthanide luminescent di-metallic helicates in solution using a bis-tridentate (1,2,3-triazol-4-yl)-picolinamide (tzpa) ligand

“…7,8 The f-metal ions have many unique physical properties and high coordination abilities opening new avenues for the construction of supramolecular systems. 9,10 Recently, we 11,12 and several other researchers 13–16 have used lanthanide ions within these architectures. Supramolecular helicates are of particular interest as they are reminiscent of biomolecules such as the helices of polypeptides and DNA, representing the complex self-organisation found in nature.…”