Preferential catalytic hydrogenation of aromatic compounds versus ketones with a palladium substituted polyoxometalate as pre-catalyst

A palladium-substituted polyoxometalate having a Keggin structure, supported on gamma-alumina or active carbon, was used as a catalyst precursor for catalytic hydrogenation. The catalyst system enabled fast hydrogenation of arenes at 30 bar H-2 and 230degreesC. Most interesting was the finding that arenes could be selectively reduced in the presence of distal ketone groups under similar conditions, 30 bar H-2 and 200degreesC. For example, 1-phenyl-2-propanone yielded 1-cyclohexyl-2-propanone with no reduction of the ketone moiety. Additionally, aromatic compounds with vicinal (conjugated) ketone moieties underwent complete hydrogenation to saturated hydrocarbons and catalytic McMurry coupling was observed for aliphatic aldehydes.