Ruthenium mixed-metal carbonyl clusters

Recent work by Ford et al. demonstrates that a variety of metal carbonyl clusters are active catalysts for the water-gas shift under the same reaction conditions used with the ruthenium cluster (104a). In particular, the mixed metal compound H2FeRu3(CO)13 forms a catalyst system much more active than would be expected from the activities of the iron or ruthenium systems alone. The source of the synergetic behavior of the iron/ruthenium mixtures is under investigation. The ruthenium and ruthenium/iron systems are also active when piperidine is used as the base, and in solutions made acidic with H2S04 as well. Whether there are strong mechanistic similarities between the acidic and basic systems remains to be determined. 

Ruthenium-Rhodium Bimetallic Catalysis. In seeking to inqprove the ethylene glycol syntheses of Table 1, one possibility that has not been extensively studied until recently (46-49), is the use of mixed metal centers with bimetallic, polymetallic or bridged-metal carbonyl clusters either as catalyst precursors, or generated in situ. 

The water-gas-shift reaction catalysed homogeneously in the presence of polynuclear metal carbonyls is of current interest. In some ruthenium systems, the principal species present in basic solutions under reaction conditions of one atmosphere pressure and at 100°C are [HRu3(CO)n] and [H3Ru4(CO)i2] . This has reasonably been taken as evidence to implicate ruthenium clusters as the probable catalysts, although it should be noted that mononuclear systems effectively promote the water-gas-shift reaction. An important finding is that mixed ruthenium-iron carbonyl clusters, e.g.. 

Then they prepared mixed-metal cluster H2FeRu3(CO)i3 and evaluated for homogeneous WGS reaction [16]. The mixed-metal cluster H2FeRu3(CO)i3 is more active than either ruthenium carbonyl or iron carbonyl individually. This synergetic behaviour of the mixed-metal system is also observed for catalyst solutions prepared initially from Ru3(CO)i2 plus FefCOls or Fe3(CO)i2 or H4Ru4(CO)i2 plus Fe(CO)5 in alkaline solution. The catalytic activity of these... 

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