Synthesis and characterization of chiral dinuclear salen complexes

Using an unreported intermediate I (comprised of (R,R)-diaminocyclohexane, 3,5-di-tert-butyl salicylaldehyde and 2,6-diformal-4-methylphenol), four novel dinuclear Salen complexes [Zn2L center dot 3H(2)O (2), Cu2L-H2O(3), Co2L (4), Ni2L (5)] have been synthesized (L is chiral dimeric Salen ligand synthesized from I and 1,2-diaminobenzene). These ligand and complexes were characterized by elemental analysis, H-1 NMR, FTIR and CD spectra. The H-1 NMR spectra were compared with those of the intermediate and the ligand. Cotton effect and Cotton split of CD spectrometer of these chiral compounds were explained by the exciton interaction theory. It was found that the direction of Cotton split depended on the configuration of diaminocyclohexane. (R,R)-diaminocyclohexane determines the negative chirality of Salen compounds.