Synthesis of Imidazolium-Tethered Ruthenium(II)-Arene Complexes and Their Application in Biphasic Catalysis

Reaction of RuCl3 with 1-[2-(1,4-cyclohexadiene-1-yl)alkyl]-3-methylimidazolium chloride (alkyl = ethyl, butyl) and 1-[2-(1,4-cyclohexadiene-1-yl)ethyl]-2,3-dimethylimidazolium chloride affords a series of dimeric ruthenium complexes of the type [RuCl2(η6-arene)]2Cl2. Treatment of these dimeric salts with phosphine ligands leads to the highly water-soluble monomeric complexes [RuCl2PR3(η6-arene)]Cl (PR3 = PPh3, PCy3). Reaction of [RuCl2(η6-1-(2-benzylethyl)-3-butylimidazolium)]Cl with Ag2O gives rise to a η6-arene-carbene chelate complex. The phosphine complexes have been tested as catalysts in the hydrogenation of styrene immobilized in water or an ionic liquid and in the aqueous reduction of CO2/CO32-. A carbonate-hydride complex has been identified as intermediate by high-pressure NMR measurements. The solid-state structures of several of the new imidazolium-functionalized arene complexes including the arene-carbene chelate complex are reported.