Arene Ruthenium Complexes as Versatile Catalysts in Water in both Transfer Hydrogenation of Ketones and Oxidation of Alcohols. Selective Deuterium Labeling of rac-1-Phenylethanol
2012-09-10T00:00:00Z (GMT) by
The preparation of three series of arene Ru(II) half-sandwich compounds with the functional ligand 4,4′-dimethoxy-2,2′-bipyridine (dmobpy) is described. The new cationic derivatives have the general formula [(η6-arene)RuCl(κ2-N,N-dmobpy)]X (arene = benzene, X = Cl– (Cl), BF4– ([BF4]), TsO– (TsO), PF6– ([PF6]); arene = p-cymene (p-cym), X = Cl– (Cl), BF4– ([BF4]), TsO– (TsO), PF6– ([PF6]); arene = 2-phenoxy-1-ethanol (phoxet), X = Cl– (Cl), BF4– ([BF4]), TsO– (TsO), PF6– ([PF6])). The structures of Cl, TsO, TsO, [BF4], and [PF6] were determined by X-ray crystallography. All of the complexes except the PF6– salts were water-soluble, and they behaved as active catalysts in two different processes: the transfer hydrogenation of water-soluble and -insoluble ketones to the corresponding alcohols, using HCOONa as the hydrogen source at pH 4, and the oxidation of rac-1-phenylethanol to acetophenone with tBuOOH at pH 7, both in aqueous solution. For the transfer hydrogenation with p-cymene complexes the aqua, formato, and hydride species were detected by means of 1H NMR experiments in D2O. It was found that the cationic hydrido complex was [(η6-p-cymene)RuD(dmobpy)]+. The reversible and pH-dependent formation of the hydroxo derivative was also observed. When the catalytic transfer hydrogenation was performed in D2O, the 1-phenylethanol obtained was selectively deuterated at the benzylic carbon. Mechanistic proposals are also included.