Superparamagnetic Core-Shell-Type Fe3O4/Ru Nanoparticles as Catalysts for the Selective Hydrogenation of an Unconstrained α,β-Unsaturated Ketone

Selective hydrogenation of the carbon-oxygen bond in α,β-unsaturated carbonyl compounds is a synthetic challenge, since C=C bond reduction is thermodynamically more favorable (35 kJ mol–1) than C=O bond reduction.[1] This problem becomes even more complicated by the presence of an aromatic substituent in such systems because of possible ring hydrogenation.[2] Moreover, the transformation of unsaturated ketones into unsaturated alcohols is more difficult than that of unsaturated aldehydes, because ketones are sterically more hindered.[3] In addition, the “promoter effect” to enhance selectivity is also absent in the case of unsaturated ketones.[4] In a pioneering study, Szöllosi et al. evaluated the potential of different metals such as Pt, Pd, Rh, Ru, Cu, and Ni supported on silica for the selective hydrogenation of α,βunsaturated ketones.[5] Later, von Arx et al. were able to attain 90% chemoselectivities for a sterically hindered C=O bond in ketoisophoron over alumina-supported Pt and Pd catalysts.[6] Such a remarkable selectivity might be attributed to steric effects,[1b,3] because the presence of bulky substituents at the olefin double bond presumably hampers its adsorption at catalytic sites.[8] Milone et al. and Mertens et al. showed that unsaturated alcohols can be obtained from different α,β-unsaturated ketones with a selectivity higher than 60% at a conversion of 90 % by using a gold catalyst.[4,8] Recently, Wang et al. also used gold supported on mesostructured CeO2 to hydrogenate trans-4Institut de Chimie, Université de Neuchâtel, Avenue de Bellevaux 51, 2000 Neuchâtel, Switzerland Fax: +41-32-7182511 E-mail: [email protected]