Dinuclear zinc(II) complexes of symmetric Schiff-base ligands with extended quinoline sidearms†‡

The synthesis of two 2-formylquinolines is reported via the Skraup method followed by SeO2 oxidation. Each aldehyde is condensed with (1R,2R)-diaminocyclohexane and (R)-BINAM, yielding four enantiomerically-pure bis(imine–quinoline) ligands. The neutral ligands are reacted with ZnCl2 to give complexes with bis(bidentate) coordination of ZnCl2 units. X-Ray structural characterization of three complexes shows them to have a single-stranded helical motif, with M helicity, except in one case where a 1 : 1 mixture of M and P helices is seen. The ligands and complexes are further characterized spectroscopically by solution 1H and 13C NMR, UV-vis and ECD.