Homogeneous catalysis, basic principles

The applications of coordination compounds in catalysis that have been shown are by no means the only important cases. In fact, there are numerous reactions in which homogeneous catalysis forms the basis for a great deal of chemistry. From the examples shown, it should be apparent that this is a vast and rapidly developing field. It is also one that is important from an economic standpoint. Although the basic principles have been described in this chapter, the literature related to catalysis is extensive. For further details and more comprehensive reviews of the literature, consult the references listed. 

In principle, more or less stable BRC structures can be obtained in heterogeneous biomimics, especially when adsorption and catalytic sites are combined, i.e. active sites perform both functions fixation and transformation of the substrate. To put it another way, the above enumerated restrictions typical of homogeneous catalysis are absent in heterogeneous mimic-substrate complexes, where acidic-basic sites are fixed in required points of the active site. 

The rise of homogeneous catalysis, as well as the understanding of the mechanistic principles of many heterogeneously catalyzed reactions, is inextricably linked to the development of organometallic chemistry.1 Catalytic reactions can be understood on the basis of a limited number of basic reaction types. This chapter will consider the fundamental reaction steps involved in transition metal catalyzed reactions the next chapter will deal with catalytic reaction types and processes. 

Phase-transfer catalysis (PTC) is the most widely used method for solving the problem of the mutual insolubility of nonpolar and ionic compounds. Basic principles, synthetic uses, industrial applications of PTC, and its advantages over conventional methods are well documented [1-3]. PTC has become a powerful and widely accepted tool for organic chemists due to its efficiency, simplicity, and cost effectiveness. The main merit of the method is its universality. It may be applied to many types of reactions involving diverse classes of compounds. An important feature of PTC is its computability with other methods for the intensification of biphasic reactions (sonolysis, photolysis, microwaving, etc.) as well as with other types of catalysis, in particular, with transition-metal-complex catalysis. Homogeneous metal-complex catalysis under PTC conditions involves the simul-... 

The basic principles of biphase catalysis is accordingly that the homogeneous catalyst is in solution in one of the phases and the reaction products are located in a second phase which is immiscible with the catalyst phase - heterogeneous -and are therefore easy to separate off (see below). 

It is clear from the basic principles (or, more correctly, the formalisms) of homogeneous catalysis just outlined that the essence of homogeneous catalysis lies in the formation of a transition-metal complex with a coordination sphere that offers an environment conducive to chemical change. These transformations may involve rearrangement or migration of ligands already present and their elimination as product(s) or insertion of an external ligand within the coordination sphere to form a product that then is eliminated from the complex. 

Discuss some basic principles of homogeneous catalysis. 

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