Block organometallic clusters as homogeneous catalysts

Over the past 30 years, much effort has been put into investigating the use of J-block organometallic clusters as homogeneous catalysts, and equations 27.27 27.29 give examples of small-scale catalytic reactions. Note that in reaction 27.27, insertion of CO is into the O—H bond. In contrast, in the Monsanto process using [Rh(CO)2l2] catalyst, CO insertion is into the C—OH bond (equation 27.15). 

Give an example of how PPh3 can be converted into a hydrophilic catalyst. 

Despite the large of amount of work that has been carried out in the area and the wide range of examples now known, it would appear that no industrial applications of cluster catalysts have yet been found to be viable. 

A promising development in the area is the use of cationic clusters. [H4(r] -C6Hg)4Ru4] catalyses the reduction of fumaric acid, the reaction being selective to the C=C bond and leaving the carboxylic acid units intact (Fig. 25.13). 

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