Immobilized homogeneous catalysts Subject

Chapter 7 - Immobilized Homogeneous Catalysts, Pages 247-289 Appendix, Pages 291-293 Author Index, Pages 295-328 Subject Index, Pages 329-346... 

Although all of these fields are summarized in the literature, time after time there are different opinions on the subject of the results that may be achieved in catalysis by using MX immobilized on a tailor-made polymer. Some researchers believe this approach to be a panacea to eliminate all disadvantages of traditional homogeneous catalysts others emphasize shortcomings of such systems in comparison with typical heterogeneous catalysts. Here we try to analyze in detail the possibilities and perspectives of polymer-immobilized metal complex catalysts for a wide variety of reactions in organic synthesis. 

In the search to develop new materials for immobilization of homogeneous transition metal catalyst to facilitate catalyst-product separation and catalyst recychng, the study of dendrimers and hyperbranched polymers for application in catalysis has become a subject of intense research in the last five years [68], because they have excellent solubility and a high number of easily accessible active sites. Moreover, the pseudo-spherical structure with nanometer dimensions opens the possibility of separation and recycling by nanofiltration methods. Although dendrimers allow for controlled incorporation of transition metal catalysts in the core [69] as well as at the surface [70], a serious drawback of this approach is the tedious preparation of functionalized dendrimers by multi-step synthesis. 

For a variety of reasons, silica and alumina structures are important frameworks for the subject of heterogeneous catalysis 11-3]. Aluminas, and perhaps to a lesser extent silicas, are employed directly as cracking catalysts or as substrates for assorted catalytic systems (see Chapter 4). The silylation of silica surfaces also provides a strategy for immobilizing a catalytic center that has been found useful in the context of homogeneous catalysis [4], Furthermore, many heterogeneous catalytic systems based on zeolites, clays, or silica-aluminas have aluminosilicate frameworks for which silica and alumina structures serve as structural prototypes. 

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