Metal clusters in catalysis: Hydrocarbon reactions*

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A set of metal carbonyl clusters, Ru3(CO)12, Os3(CO)12, and Ir4(CO)12, has been evaluated as catalysts for a series of hydrocarbon reactions which comprise skeletal rearrangement, metathesis, dehydrogenation, hydrogenation, isomerization, and H-D exchange. None was especially effective as a hydrogenation catalyst even for olefins. Os3(CO)12 was a catalyst for H-D exchange between C6H6 and D2 at 195° but the ruthenium congener was inactive at temperatures below 175°, a temperature where ruthenium metal formed at an appreciable rate. Deuterium incorporation in the benzene was a single-step process. Ir4(CO)12 was an effective catalyst for the conversion of cyclohexadiene to cyclohexene and benzene. A similar reaction occurred with cyclohexene but the rate was extremely low at 160°. The ruthenium and osmium clusters catalyzed the isomerization of linear hexenes, with the former the more active. Relative rates for the hexenes were 1 > 2 > 3. At high temperatures, the osmium and iridium clusters catalyzed skeletal reactions of 2-hexene, as evidenced by the formation of pentenes, heptenes, heptanes, and small amounts of propane.

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