Homogeneous Catalysis (PDF)
A practical guide filled with techniques and examples of classroom-based assessments
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A practical guide filled with techniques and examples of classroom-based assessments
Homogeneous catalysis using transition metal complexes is an area of research that has grown enormously in recent years. Many amazing catalytic discoveries have been reported by researchers both in industry and in academia.
Homogeneous Catalysis: Understanding the Art gives real insight into the many new and old reactions of importance. It is based on the author's extensive experience in both teaching and industrial practice. Each chapter starts with the basic knowledge and ends with up-to-date concepts.
The focus of this book is on concepts, but many key industrial processes and applications that are important in the laboratory synthesis of organic chemicals are used as examples. The full range of topics is covered, such as fine chemicals, bulk chemicals, polymers, high-tech polymers, pharmaceuticals, but also important techniques and reaction types among other aspects. For a few reactions the process schemes, environmental concerns and safety aspects are included, to encourage catalyst researchers to think about these topics at an early stage of their projects and to communicate with chemical engineers, customers and the end-users. There is no other book available that gives insight into so many reactions of importance. Such a resource is critical as the field of homogeneous catalysis becomes ever more central to the interests of organic chemists and academia. This book provides the background for chemists trained in different disciplines and for graduate and masters students who take catalysis as a main or secondary topic.
Piet W.N.M. van Leeuwen is Professor of Homogeneous Catalysis, University of Amsterdam, The Netherlands.
PALLADIUM CATALYSED CROSS-COUPLING REACTIONS (p. 271-272)
The new workhorse for organic synthesis
13. PALLADIUM CATALYSED CROSS-COUPLING REACTIONS
13.1 Introduction
The making of carbon-to-carbon bonds from carbocations and carbanions is a straightforward and simple reaction. Easily accessible carbanions are Grignard reagents RMgBr and lithium reagents RLi. They can be conveniently obtained from the halides RBr or RCl and the metals Mg and Li. They are both highly reactive materials, for instance with respect to water. The thermodynamic driving force for the formation of such reactive materials and their subsequent reactions is the formation of metal halides. The reactions of these carbon centred anions with polar compounds such as esters, ketones, and metal chlorides are indeed very specific and give high yields. The reaction of Grignard reagents with alkyl or aryl halides, however, is extremely slow giving many side-products, if anything happens at all. Note that this is also the key to the success of preparing Grignard type reagents(!), otherwise the partially formed RMgBr would react with the starting material RBr still present to give the "homocoupled" R-R. Exceptions are allylic and benzylic halides which react very fast amongst themselves during their synthesis. The Grignard reagents of this structure require specific practical procedures otherwise the homocoupled species are formed.
Reactions that can be expected for the reaction of an alkyl halide and a metal alkyl are depicted in Figure 13.1. The reaction may require several days at room temperature or may proceed in a few minutes, depending on the nature of the species. Many by-products may be formed. First a metal-halide exchange may occur. The resulting exchange products can give coupling products as well. Secondly, elimination reactions instead of C-C coupling can occur. Also, a radical reaction may
Figure 13.1. Products formed in a coupling reaction of a Grignard reagent and an alkyl halide
Thus, this reaction was of limited practical value until the transition metal catalysed cross-coupling reaction became known. Ever since, the "cross- coupling" reaction has found wide application in organic synthesis both in the laboratory and in industry. One might state that in any multi-step sequence for making an organic chemical, one of the steps involves a transition metal catalysed coupling reaction! The transition metal catalysts are usually based on palladium and sometimes nickel. In addition to organomagnesium and organolithium a great variety of organometallic precursors can be used. Also, many precursors can serve as starting materials for the carbocation. Last but not least, the ligand on the transition metal plays an important role in determining the rate and selectivity of the reaction. Here we will present only the main scheme and take palladium as the catalyst example, although many more metals have been found to be very useful. The reactions to be discussed are: allylic alkylation, Heck reaction, cross-coupling, and Suzuki reaction, a variant of the latter. Initially the cross-coupling chemistry focussed on carbon-tocarbon bond formation but in the last decade it has become also extremely useful for making carbon-to-heteroatom bonds. The organyl halide (or other anion used) involves in general an aryl, vinyl, or allylic species.
- Autor: Piet W. N. M. van Leeuwen
- 2006, 2004, 408 Seiten, Englisch
- Verlag: Springer Netherlands
- ISBN-10: 1402020007
- ISBN-13: 9781402020001
- Erscheinungsdatum: 02.08.2006
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