Synthesis, Structure, and Properties of Oligo-tridentate Ligands; Covalently Assembled Precursors of Coordination Arrays

Hanan, Garry S.; Schubert, Ulrich S.; Volkmer, Dirk; Riviere, Emmanuel; Lehn, Jean-Marie; Kyritsakas, Nathalie; Fischer, Jean
Oligo-tridentate ligands based on alternating pyridines and pyrimidines were synthesised by Stille-type carbon–carbon bond-forming reactions. The terpyridine-like sites are designed to coalign upon metal complexation, giving rise to organized and rigidly spaced metal ions. Peripheral functionalization of the basic bis-tridentate framework was explored. The heterocycles in the ligands are in an all-trans conformation about the interannular bonds as indicated by comparison of their 1H NMR spectra. An X-ray crystal structure analysis of the nonchiral tris-tridentate ligand 2a reveals a helical structure in the solid state. The seven heterocycles form a helical structure with resulting overlap of the terminal pyridines. Their centroid-to-centroid distance is 4.523 Å with 38.8° between the planes. NMR investigations support a helical conformation in solution as well. Electrochemical and UV absorption measurements indicate that the LUMO resides on the pyrimidine moiety of the ligands.
Type of Publication:
nitrogen containing ligands; Stille coupling; helical structure; supramolecular chemistry
Canadian Journal of Chemistry
169 - 182