Zinc and iron complexes of a helix-directing (1R,2R)-cyclohexyl salen ligand with phenanthryl sidearms

A symmetrical salen ligand is formed by the condensation of (1R,2R)-diaminocyclohexane with 4-hydroxy-3-phenanthrenecarboxaldehyde. Crystallographic characterization of the metal complexes (ZnII, FeII, and FeIII) show 1:1 mixtures of diastereomeric M and P helical molecules. ECD spectra of the ZnII complex combined with DFT simulations strongly suggest that the M conformation is dominant in solution. This is supported by 1H and 13C NMR data, which are consistent with a single species in solution.Key words: zinc, iron, ECD, DFT, salen complexes.