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), h ave been tested as homogeneous catalysts for the hydrogenation-isomeri zation of 1,3- and 1,4-cyclohexadiene. Catalytic activity was found bu t there is evidence for metal species rather than intact dusters to ac count 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 an alyses, mass spectrometry and, in some instances, by independent synth esis. Their role in the hydrogenation reactions is discussed. Deuterat ion experiments showed that hydrogen adds first to the cluster metals and is then transferred to the coordinated substrate.