METAL-CARBONYL CLUSTERS IN HOMOGENEOUS CATALYSIS - HYDROGENATION AND ISOMERIZATION OF CYCLIC DIENES IN THE PRESENCE OF [H4RU4(CO)(12)], [H2RU4(CO)(13)], [H2FERU3(CO)(13)] AND [FE2RU(CO)(12)] - IDENTIFICATION OF ORGANOMETALLIC PRODUCTS AND A DISCUSSION OF THEIR ROLE

The hydridic tetrahedral clusters [H4Ru4(CO)(12)] (1), [H2Ru4(CO)(13)] (2) and [H2FeRu3(CO)(13)] (3), and the related [Fe2Ru(CO)(12)] (4), have been tested as homogeneous catalysts for the hydrogenation-isomerization of 1,3- and 1,4-cyclohexadiene. Catalytic activity was found but there is evidence for metal species rather than intact dusters to account for the observed behaviour. After the hydrogenation experiments, diene- and arene-substituted clusters and organometallic derivatives were found in solution. Their nature was confirmed by spectroscopic analyses, mass spectrometry and, in some instances, by independent synthesis. Their role in the hydrogenation reactions is discussed. Deuteration experiments showed that hydrogen adds first to the cluster metals and is then transferred to the coordinated substrate.