Metal clusters in catalysis: Hydrocarbon reactions

A set of metal carbonyl clusters, Ru(3)(CO)(12), Os(3)(CO)(12), and Ir(4)(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. Os(3)(CO)(12) was a catalyst for H-D exchange between C(6)H(6) and D(2) at 195 degrees but the ruthenium congener was inactive at temperatures below 175 degrees , a temperature where ruthenium metal formed at an appreciable rate. Deuterium incorporation in the benzene was a single-step process. Ir(4)(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 degrees . 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.