Résultat de la recherche
Arene ruthenium oxinato complexes: Synthesis, molecular structure and catalytic activity for the hydrogenation of carbon dioxide in aqueous solution
Two families of arene ruthenium oxinato complexes of the types [(η6-arene)Ru(η2-N,O-L)Cl] and [(η6-arene)Ru(η2-N,O-L)(OH2)]+ have been synthesized from the dinuclear precursors [(η6-arene)RuCl2]2 (arene = para-cymeme or hexamethylbenzene) and the corresponding oxine LH (LH = 8-hydroxyquinoline, 5-chloro-8-hydroxyquinoline, 5,7-dichloro-8-hydroxyquinoline, 5-nitro-8-hydroxyquinoline, 5,7-dimethyl-8-hydroxyquinoline, 5,7-dichloro-2-methyl-8-hydroxyquinoline). The molecular structures of the neutral chloro complexes [(η6-C6Me6)Ru(η2-N,O-L)Cl] (LH = 8-hydroxyquinoline, 5,7-dichloro-2-methyl-8-hydroxyquinoline) and [(η6-MeC6H4Pri)Ru(η2-N,O-L)Cl] (LH = 5,7-dichloro-2-methyl-8-hydroxyquinoline) as well as those of the cationic aqua derivatives [(η6-MeC6H4Pri)Ru(η2-N,O-L)(OH2)]+ (LH = 8-hydroxyquinoline, 5,7-dimethyl-8-hydroxyquinoline), isolated as the tetrafluoroborate salts, show in all cases a piano-stool arrangement with the arene ligand, the chelating oxinato ligand and the chloro or the aqua ligand surrounding the ruthenium center in a pseudo-tetrahedral fashion. The analogous reaction of [(η6-MeC6H4Pri)RuCl2]2 with other N,O-chelating ligands such as 2-pyridinemethanol or tetrahydrofurfurylamine did not give the expected analogs but resulted in the formation of the complexes [(η6-MeC6H4Pri)Ru(η2-NC5H4CH2OH)Cl]+ and [(η6-MeC6H4Pri)Ru(η1-NHCH2C4H3O)Cl2]. The neutral and cationic complexes of the types [(η6-arene)Ru(η2-N,O-L)Cl] and [(η6-arene)Ru(η2-N,O-L)(OH2)]+ have been found to catalyze the hydrogenation of carbon dioxide to give formate in alkaline aqueous solution with catalytic turnovers up to 400.
Synthesis of a trinuclear cation [H3Ru3(Fc-arene)(C6Me6)2(O)]+ containing a ferrocenyl group tethered to an arene ligand
Ferrocene carboxylic acid 2-cyclohexa-1,4-dienyl-ethyl ester (1) is prepared from ferrocene carboxylic acid and 2-cyclohexa-1,4-dienyl-ethanol. This diene reacts with RuCl3•nH2O in refluxing ethanol to afford quantitatively [Ru(Fc-arene)Cl2]2 (2) (Fc-arene=ferrocene carboxylic acid phenethyl ester). The dinuclear complex 2 reacts with triphenylphosphine to give the mononuclear complex [Ru(Fc-arene)(PPh3)Cl2] (3). The trinuclear arene-ruthenium cluster cation [H3Ru3 (Fc-arene)(C6Me6)2(O)]+ (4) is synthesised from the dinuclear precursor [H3Ru2 (C6Me6)2]+ and the mononuclear complex [Ru(Fc-arene)(H2O)3]2+, accessible from 2 in aqueous solution. The water-soluble trinuclear cluster cation 4 catalyses the hydrogenation of benzene to give cyclohexane under biphasic conditions.