Ethylene glycol, rhodium-catalyzed synthesis

In contrast, metal clusters have several active centers or can form multi-electron systems. Metal clusters such as Rh (CO)i6, Rh4(CO)i2, It4(CO)i2, Ru3(CO)i2, and more complex structures have been successfully tested in carbonylation reactions. Rhodium clusters catalyze the conversion of synthesis gas to ethylene glycol, albeit at very high pressures up to now. 

Another system in which intact cluster catalysis seems likely is the synthesis gas (CO/H2) production of ethylene glycol catalyzed by an anionic rhodium cluster of uncertain or undisclosed identity. From high-temperature... 

A particularly significant and useful contribution of transition metals in fine organic synthesis as well at the industrial level is based on their use as catalysts. This aspect is of course particularly important with expensive transition metals (Rh, Os, Pd, etc.). Indeed, there are numerous examples of selective processes which have never been developed up to the industrial stage because of catalyst costs, especially when some (even minor) loss of the catalyst could not be avoided. This was, for example, the case for palladium-catalyzed benzylic acetoxylation reactions, and several rhodium-catalyzed reactions, such as the direct ethylene glycol production from syngas (prohibitive pressures being an additional major drawback in this latter case). 

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