Collect. Czech. Chem. Commun. 2007, 72, 1037-1045

Transfer Hydrogenation of Carbonyl Compounds and Alkenes Catalyzed by Ruthenium(II)-N-Heterocycle Carbene Complexes

Marianna Feketea and Ferenc Joób,*

a Research Group of Homogeneous Catalysis, Hungarian Academy of Sciences, Debrecen, H-4010 Hungary
b Institute of Physical Chemistry, University of Debrecen, Debrecen 10, P.O. Box 7, H-4010 Hungary


The Ru(II)-N-heterocycle carbene complexes [RuCl26-p-cymene)L] (L = 1-butyl-3-methylimid- azol-2-ylidene) and [RuCl(η6-p-cymene)L(pta)]Cl (pta = 1,3,5-triaza-7-phosphaadamantane) showed excellent catalytic activities (with turnover frequencies up to 1116 h-1) in the hydrogen transfer reduction of cinnamaldehyde and several ketones using propan-2-ol/KOH as a H-donor. Similar hydrogenations of trans-stilbene and cyclohexene were characterized by low conversions. The hydrogenation of 4-phenylbut-3-en-2-one and cinnamaldehyde proceeded with moderate selectivities of the formation of the saturated alcohol or of the of C=C hydrogenation (giving saturated ketone or saturated aldehyde). In the case of cinnamaldehyde, the unsaturated alcohol is initially formed; however, subsequent redox isomerization to the saturated aldehyde with the same catalyst diminishes its yield. The hydrogen transfer from formate to 4-phenylbut-3-en-2-one in an aqueous-organic two-phase mixture was also demonstrated.

Keywords: Aldehydes; Carbene complexes; Hydrogen transfer; Ketones; Ruthenium; Catalytic hydrogenation; Reductions.

References: 20 live references.