Elementary Steps in Homogeneous Catalysis

Since homogeneous catalytic reactions are kinetically complex, detailed understanding requires prior investigation of various steps in the catalytic cycles. A few papers likely to be of value in the elucidation of catalytic kinetics are 

Homogeneous Catalysis of Organic Reactions by Complexes of Metal Ions 

This section outlines the elementary steps in homogeneous catalysis using organometallic complexes, showing the role that these steps play in various catalytic cycles and industrial processes. 

Every catalytic cycle is a sequence of simple chemical reactions. These elementary steps are the building blocks from which you can construct the story behind the reaction (better known as the reaction mechanism). Understanding these steps is often easier in homogeneous catalysis than in heterogeneous catalysis and 

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Figure3.2 The main elementary steps in homogeneous catalysis.

General Reviews and Elementary Steps in Homogeneous Catalysis... 

In the following, we turn our attention to reactivities which involve cleavage of the L M-H bond, inducing hydrogen or hydride transfer reactions. These processes can normally be viewed as insertion reactions into the metal-hydride bond and represent valuable elementary steps of homogeneous catalysis. It is very important to note at this point that such insertions do not require precoordination of the inserting substrate. 

Note that, while this reaction (as well as alkane hydrogenolysis) involves known elementary steps of molecular organometallic chemistry, it has not been discovered in homogeneous catalysis. One reason might be that highly... 

In stark contrast to the transport considerations, typical time-scales for elementary and non-elementary steps in organometallic chemistry and homogeneous catalysis range from vibrational motions of ca. 10 s or less [44], to ca. hours or even days for the formation of products and side products. Moreover, the three pri-... 

Essentially, two broad types of elementary reactions occur in homogeneous catalysis coordination and addition. Although these are reactions and we designate them so, they should more appropriately be viewed as steps in a catalytic cycle that activate the substrate prior to reaction. 

Central to catalysis is the notion of the catalytic site. It is defined as the catalytic center involved in the reaction steps, and, in Figure 8.1, is the molybdenum atom where the reactions take place. Since all catalytic centers are the same for molecular catalysts, the elementary steps are bimolecular or unimolecular steps with the same rate laws which characterize the homogeneous reactions in Chapter 7. However, if the reaction takes place in solution, the individual rate constants may depend on the nonreactive ligands and the solution composition in addition to temperature. 

The book presents a review of sixteen important topics in modem homogeneous catalysis. While the focus is on concepts, many key industrial processes and applications that are important in the laboratory synthesis of organic chemicals are used as real world examples. After an introduction to the field, the elementary steps needed for an understanding of the mechanistic aspects of the various catalytic reactions have been described. Chapter 3 gives the basics of kinetics, thus stressing that kinetics, so often neglected, is actually a key part of the foundation of catalysis. 

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