Dicatechol-diimines:: easily accessible ligands for the self-assembly of dinuclear triple-stranded helicates

Dicatechol ligands 3b-g-H-4 are simply prepared by imine formation of 2,3-dihydroxybenzaldehyde 2 with a series of different diamines 1b-g. An X-ray structural analysis was obtained for the butyl-bridged compound 3e-H4, showing an intramolecular proton transfer and the formation of a chinoidic "keto-amine" structure. The dicatechol derivatives 3b-g-H-4 form dinuclear triple-stranded helicates M-4[(3)(3)Ti-2] with titanium(IV) ions in the presence of alkali-metal carbonate. For the phenyl- and the trans-1,4-cyclohexyl-bridged complexes, K-4[(3b)(3)Ti-2] and Na-4[(3f)(3)Ti-2], X-ray structures were obtained.