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 (Zn-II, Fe-II, and Fe-III) show 1:1 mixtures of diastereomeric M and P helical molecules. ECD spectra of the Zn-II complex combined with DFT simulations strongly suggest that the M conformation is dominant in solution. This is supported by H-1 and C-13 NMR data, which are consistent with a single species in solution.