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

Abstract

Dicatechol ligands 3b–g-H₄ 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-H₄ form dinuclear triple-stranded helicates M₄[(3)₃Ti₂] with titanium(IV) ions in the presence of alkali-metal carbonate. For the phenyl- and the trans-1,4-cyclohexyl-bridged complexes, K₄[(3b)₃Ti₂] and Na₄[(3f)₃Ti₂], X-ray structures were obtained.