American Chemical Society, Journal of the American Chemical Society, 32(137), p. 10437-10442, 2015
DOI: 10.1021/jacs.5b07069
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We report on the assembly of 2,6-pyridinedicarboxamide ligands (1) with point chirality about lanthanide metal ion (Ln3+) templates, in which the helical chirality of the resulting entwined 3:1 ligand:metal complexes is covalently captured by ring-closing olefin metathesis to form topologically chiral molecular trefoil knots of single handedness. The ligands do not self-sort (racemic ligands form a near-statistical mixture of homoleptic and heteroleptic lanthanide complexes); but the use of only (R,R)-1 leads solely to a trefoil knot of Λ-handedness whereas (S,S)-1 forms the Δ-trefoil knot with complete stereoselectivity. The knots and their isomeric unknot macrocycles were characterized by NMR spectroscopy, mass spectrometry and X-ray crystallography, and the expression of the chirality that results from the topology of the knots studied by circular dichroism.