om3004702_si_001.cif (79.56 kB)
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
dataset
posted on 2012-09-10, 00:00 authored by Cristina Aliende, Mercedes Pérez-Manrique, Félix A. Jalón, Blanca R. Manzano, Ana M. Rodrı́guez, Gustavo EspinoThe 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– ([1]Cl), BF4– ([1][BF4]), TsO– ([1]TsO), PF6– ([1][PF6]); arene = p-cymene (p-cym), X = Cl– ([2]Cl), BF4– ([2][BF4]), TsO– ([2]TsO), PF6– ([2][PF6]); arene = 2-phenoxy-1-ethanol (phoxet),
X = Cl– ([3]Cl), BF4– ([3][BF4]), TsO– ([3]TsO), PF6– ([3][PF6])). The structures of [1]Cl, [1]TsO, [2]TsO, [2][BF4], and [2][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.