Chiroptical probing of self-assembly with ligands formed in one-pot ‘click’ reaction from chiral amines (Chem. Eur. J.)

Chiroptical probing of self-assembly with ligands formed in one-pot 'click' reaction from chiral amines (Chem. Eur. J.)

After a lot of work, we finally got these results off my bench and into the literature. In our new article in “Chemistry – A European Journal” (Wiley), we present a convenient one-pot approach to synthesising chiral bis(triazolyl)pyridine ligands from enantiopure amines with the stereochemistry retained. This approach is broadly applicable.

Molecular structures of ligands 1a and 1b derived from X-ray crystallography
Molecular structures of ligands 1a and 1b derived from X-ray crystallography showing noteworthy dimer formation between the bis(triazolyl)pyridine cores

The beautiful mirror-image crystal structures were obtained by Dr Miguel Martínez-Calvo (now in Santiago) and show interesting supramolecular hydrogen bonding interactions between the ligands which we will exploit in the future.

Dr Bob Peacock in Glasgow performed circularly polarised luminescence spectroscopic measurements on the coloured lanthanide(III) complexes of these ligands, illustrating their optically active nature.

CD titrations for both enantiomers of 1 (a,b) and recalculated spectra arising from fitting of the titration of 1b with Eu(III) in acetonitrile

In this article, we were able to show interesting behaviour which has only really been studied so far by researchers in Prof Thorri Gunnlaugsson’s lab (with two other examples published recently in projects led by Dr Oxana Kotova and Sam Bradberry, respectively). This behaviour was the notable changes in the circular dichroism (CD) spectra of these chiral molecules upon addition of lanthanide(III) ions. These spectral changes could be fit to determine binding constants of this self-assembly. These clear chiroptical spectra are in contrast to a dissapointing aspect of results we published earlier this year in Inorganic Chemistry (with remote amino acid substituents giving rise to weak CPL and CD) and shows that placing the chiral centre nearer to the metal ion binding location enhanced the effect on the chiroptical properties of such systems.

URL: http://onlinelibrary.wiley.com/doi/10.1002/chem.201504257/full

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