The synthesis of ligands (2,9-disubstituted phenanthrolines) bearing one or two acylaminopyridine binding sites, compounds 1 and 2 respectively, is described. Each ligand can assemble on a Cu(I) template, forming two different receptors for dicarboxylic acids, Cu(1)2+BF4- and Cu(2)2+BF4–. These orange Cu(I) complexes are shown to bind (Ka > 104 M–1) to a variety of dicarboxylic acids in chloroform, with a slight preference for the C5-dicarboxylic acids, glutaric and N-CBz-glutamic acids, over shorter and longer substrates. Complexation is analyzed both by NMR chemical shift changes and UV–visible absorption changes. The data indicate formation of 1:1 complexes for Cu(1)2+BF4– and 2:1 complexes for Cu(2)2+BF4–, with the dicarboxylic acid substrate hydrogen bonding simultaneously to an acylaminopyridine binding site on each ligand. For Cu(2)2+BF4–, the complexation event results in large shifts in the visible absorption bands and a color change from orange to red. The change in the visible absorbance, and therefore the chromogenicity, was found to be substrate dependent. The chromogenic effect is explained by a conformational change in the receptors resulting from hydrogen bond formation with the substrate.
ASJC Scopus subject areas
- Colloid and Surface Chemistry