Hydrogenation of arenes, alkenes and alkynes catalyzed by a sol–gel entrapped mixture of [Rh(cod)Cl]2 and Na[HRu3(CO)11]

A sol–gel entrapped 1:3 mixture of [Rh(cod)Cl]2 and Na[HRu3(CO)11] catalyzes the hydrogenation of various unsaturated substrates by two distinguishable mechanisms. Under 13.8 bar H2 and 20 °C methylated arenes react rapidly to give cycloalkane derivatives. XRD and TEM studies showed that under these conditions the hydrogenation proceeds without the generation of free metal particles. The hydrogenation of non-methylated arenes, as well as that of alkenes and alkynes, require a temperature of 80–120 °C at which the entrapped complexes form metallic nano-particles of 3–5 nm. Chloroarenes are also hydrodechlorinated at 120 °C, but require a hydrogen pressure of ≥25 bar. At both temperature ranges the catalysts are reusable at least four times. The high efficiency of the hydrogenation process at 20 °C is rationalized by a synergistic effect between the two different metal atoms of the combined catalyst. This may be related to a remote control model through a hydrogen spillover mechanism.

Methylated benzenes are rapidly hydrogenated at 20 °C and 13.8 bar H2 by a catalyst composed of sol–gel co-entrapped [Rh(cod)Cl]2 and Na[HRu3(CO)11]. Under these conditions no metallic particles are formed in the reaction mixture. Other unsaturated substrate that require a temperature of 80–120 °C react via the formation of sol–gel entrapped metallic nano-particles.Figure optionsDownload as PowerPoint slide