Iron(II) and zinc(II) monohelical binaphthyl-salen complexes with overlapping benz[a]anthryl sidearms

The synthesis of the polyaromatic aldehyde 1-hydroxybenz[a]anthracene-2-carboxaldehyde is reported via a seven step protocol from 9,10-dihydroanthracene, with an overall yield of 30%. Two equivalents of the aldehyde are condensed with (R)-1,1′-binaphthyl-2,2′-diamine to produce a new binaphthyl-salen ligand, which is subsequently complexed to iron(II) and zinc(II) ions. The ligand and complexes are characterized by single-crystal X-ray crystallography. The complexes have distinct helical structures with overlapping benz[a]anthryl sidearms, and only M-helices are observed. The ligand and complexes are further characterized by solution 1H and 13C NMR spectroscopy as well as UV-visible and ECD spectroscopies. These studies indicate that there is a single component in solution, consistent with the solid state characterization.