Cluster catalysis mononuclear ruthenium complexes

Although ruthenium is significantly less expensive than rhodium and although its use has been recommended since 1960 (7) for the oxo synthesis, complexes of this metal have not been developed as catalysts. However, many papers and patents have referred to the results obtained employing various ruthenium complexes. The purpose of this article is to analyze the work done involving ruthenium compounds, restricting the scope only to the hydroformylation reaction and not to the carbonylation reaction, which would demand to too lengthy an article. In this review we examine successively mononuclear ruthenium complexes, ruthenium clusters as precursors, photochemical activation, and supported catalysis. 

The mechanism of this interesting reaction is also discussed. Since kinetic studies suggest that the rate-determining step of the catalysis is C H activation of pyridine, this reaction requires an excess of pyridine. An active key intermediate depicted below is isolable (Figure 10.3). Although a mononuclear ruthenium complex cannot be ruled out as the active catalyst, the cluster framework remains intact during the course of the catalysis. 

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