Activation of Metal-Carbonyl Clusters by their Encapsulation Within Alumina Sol-Gel Matrices

Abstract

Abstract. Entrapment of Ru 3 (CO) 12 and Os 3 (CO) 12 within alumina sol-gel matrices, (obtained by hydrolysis and polycondensation of a THF solution of aluminum isopropoxide) converts these clusters into highly active, leachproof and recyclable hydrogen transfer catalysts. Likewise Rh 2 Co 2 (CO) 12 which, in its silica sol-gel entrapped form, neither promotes the isomerization of allylbenzene nor the disproportionation of dihydroarenes, becomes upon its entrapment in an alumina sol-gel matrix, an efficient and recyclable catalyst for these reactions. While the entrapped osmium cluster promotes at 100-110• C and 20 bar only the hydrogenation of alkenes, the ruthenium analog catalyzes also the saturation of the aromatic C C bonds. The hydrogenations take place via the hydride mechanism. XPS and TEM studies revealed that the carbonyl clusters do not decompose to give detectable amounts of (entrapped) metal particles during the encapsulation as well as during the catalytic processes.

NHC-stabilized ruthenium nanoparticles as new catalysts for the hydrogenation of aromatics

“…The chemoselective reduction of aromatic ketones to benzylalcohols can be carried out effectively by direct hydrogenation and hydrogen transfer reactions, both employing homogeneous catalysts, 36 but the selective hydrogenation of the aromatic ring is more complicated. This reaction has been studied in detail, 28,[32][33][34][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51] usually producing a mixture of the three products when heterogeneous catalysts are used and the reaction is not complete. The effect of several parameters on acetophenone hydrogenation activity and selectivity was studied.…”

Spectroscopic Study of Sol–Gel Entrapped Triruthenium Dodecacarbonyl Catalyst Reveals Hydride Formation

“…Sol–Gel Formation. Ru 3 (CO) 12 alumina sol–gels were prepared according to a previous procedure . Approximately 0.02 mmol of Ru 3 (CO) 12 was dissolved in 1 mL of THF and stirred.…”

“…This spectrum is consistent with previous reports and the features have been assigned to the E′ (axial), A2′ (axial), and E′ (radial) vibrational modes of the carbon monoxide ligands on the complex. − During the sol–gel synthesis, Al­(O- i -Pr) 3 was hydrolyzed to form a nanoporous alumina (Al 2 O 3 ) network with entrapped Ru 3 (CO) 12 . Previous work utilizing N 2 –BET analysis reported pore sizes to be on the order of 5 nm . Upon entrapment, the spectral peaks of Ru 3 (CO) 12 decrease while new features that are red-shifted appear.…”

“…In the realm of heterogeneous catalysis, it is common to find reports of performance enhancement by encapsulating homogeneous catalysts in metal oxide sol–gels . One recent study showed that entrapping Ru 3 (CO) 12 in an alumina sol–gel greatly increased its catalytic activity toward alkene hydrogenation reactions . Curiously, in the same study, it was reported that entrapment of the same catalyst in silica did not affect its catalytic behavior.…”

Entrapping homogeneous catalysts by sol–gel methods: the bottom-up synthesis of catalysts that recycle and cascade

“…The sol-gel method allows a wide range of possible supports. Blum, Avnir and co-workers 33 have demonstrated the entrapment of metal complexes in alumina for the preparation of isomerisation catalysts.…”