Homogeneous Catalysis by Cluster Compounds

The tetrameric iron cluster [Fe(77 -C5H5)(/i3-CO)]4 catalyses the selective hydrogenation of terminal aUcynes to alkenes in the presence of internal alkynes and alkenes, Internal alkynes are themselves slowly reduced to 

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.. 

The main conclusion to be drawn from these recent developments con- 

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