Homogeneous Catalysis by Transition Metal Complexes

Homogeneous catalysis by transition metal complexes has been thoroughly presented in monographs and monographic articles.  

Importance of homogeneous catalysis in industry can be seen from Table 11.3.1. 

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A discussion of the different types of solute-solute and solute-solvent interactions acting in homogeneous catalysis by transition metal complexes. E. Cesarotti, R. Ugo and L. Kapan, Coord. Chem. Rev., 1982,43, 275-298 (47). 

This chapter focuses exclusively on microwave heterogeneous catalysis. Microwave homogeneous catalysis by transition metal complexes is treated in Chapt. 11, phase transfer catalysis in Chapt. 5, catalytic reactions on graphite in Chapt. 7, photocataly-tic reactions in Chapt. 14, and catalytic synthesis oflabeled compounds in Chapt. 13. 

Homogeneous catalysis by transition metal complexes almost always involves processes in which product-catalyst separation and catalyst recycling are important issues. For years, researchers have worked to find effective ways to isolate metal-complex catalysts in phases separate from those containing the catalyst, usually by anchoring the metal complex to a solid surface. As summarized by Driessen-Holscher, it is now evident that the method that has met with most practical success in this direction involves the use of multiple liquid phases. For example, rhodium complexes with water-soluble sulfonated ligands are used to catalyze alkene hydroformyla-tion, and the aqueous-phase catalyst and the organic products are easily separated as insoluble liquid phases. 

Spectrophotometry. The theory of spectra is far advanced. In many cases, compounds can be unambiguously identified by their ultraviolet, visible, or infrared spectra (e.g., see Smith s book [43]). As an example, the double bond of a CO ligand in a complex has a strong characteristic infrared vibration frequency whose exact value depends on the electronic properties of the coordinating metal these, in turn, are affected by the other substituents. In homogeneous catalysis by transition-metal complexes in particular, foremost among them hydrogenation, hydroformylation, and hydrocyanation, spectra have contributed much to the identification of reaction intermediates and thus of pathways. 

Information on ligand substitution mechanisms should aid us to understand more profoundly homogeneous catalysis by transition metal complexes, where probably consecutive substitution and transfer reactions of ligands from metal to a substrate and back take place continuously. 

Hydrogenation has been the prototype reaction of homogeneous catalysis by transition metal complexes [l].The number of papers and patents on homogeneous hydrogenation is enormous and this reaction is treated in detail in numerous reviews and monographs [2—4]. 

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