Sulfonate-tagged 1,4-diazabutadiene (DADS) ligands and their noble-metal complexes – synthesis, characterization and immobilization in ionic liquids

Abstract

A series of sulfonate-tagged 1,4-diazabutadiene (DAD^S) ligands was prepared as salts with typical ionic liquid (IL) cations ([EMIM]⁺, [BMIM]⁺, [BMMIM]⁺, Bu₄N⁺, Bu₃PMe⁺, [Gua-4,4-4,4-4,1]⁺). Complexation behaviour of the ligands was investigated by preparing complexes of the types [BMMIM]₂[MCl₂(DAD^S)] (M = Pd, Pt), [BMMIM][Rh(COD)(DAD^S)] and [BMMIM]₂[Mo(CO)₄(DAD^S)]. Using UV-Vis spectroscopy, the latter sulfonate-tagged chromophore was shown to be well soluble in the sulfonate IL [BMIM]OTf and completely insoluble in toluene, resulting in perfect immobilization. The crystal structures of [HNEt₃]₂[2,6-Me₂-Me-DAD^S], [BMIM]₂[2,6-Me₂-Me-DAD^S], [BMMIM]₂[2,4,6-Me₃-Me-DAD^S], [BMMIM]₂[2,6-iPr₂-Me-DAD^S] and [HNEt₃]₂[PdCl₂(2,6-Me₂-Me-DAD^S)] were determined. Regarding the diimine fragment, they show geometries similar to the respective non-sulfonated parent compounds.