Formation of Metallo-Polymers and -Macrocycles by Complexation of Alkyl-Linked Di-Terpyridines with Iron(II) Ions

The complexation of bridged di-terpyridine ligands with iron(II) leads to new metallo-supramolecular assemblies. Di-terpyridine ligands were synthesized using nucleophilic substitution of 4′-chloro-2,2′:6′,2′′-terpyridine with different dialcoholate alkyl and dithiolate alkyl nucleophiles. Upon addition of iron(II) chloride the formation of metallo-polymeric structures via metal-to-ligand complexation is observed. The metallo-polymeric assemblies presented here contain low molar mass (cyclo)-alkyl bridged di-terpyridine ligands of which one is achiral and two others are enantiomers. For both cases, characterization using NMR and UV/Vis spectroscopy shows complex formation and indicates the formation of metallo-supramolecular polymers. For the non-polymeric system, formed at room temperature, it could be shown that upon heating exchange takes place and that the thermodynamically favored product is formed. Using column chromatography, the first two major fractions of the mixture could be separated and analyzed. MALDI-TOF mass spectrometry and 1H NMR spectroscopy confirmed the formation of metallo-macrocyclic assemblies. For the chiral system, circular dichroism (CD) experiments showed the formation of an optically active material, with the spectra of the enantiomeric assemblies being mirror-symmetric.