Catalysis by organometallics complexes

Vacancies were later called coordinately unsaturated sites (cus). This is more in line with terminology used in organometallic chemistry. In view of the present understanding of the nature of the active sites, SBMS or Co(Ni)-Mo-S, the following discussion describes mechanisms in terms of catalysis by organometallic complexes. The references available on this topic are too numerous to mention, and the mechanisms are very well understood. A particularly useful reference is the book by Candlin, Taylor, and Thompson (90), although there are many others that can be consulted. 

Blaser, H.-U., Indolese, A., Schnyder, A. Applied homogeneous catalysis by organometallic complexes. Curr. Sci. 2000, 78, 1336-1344. 

Blaser HU, Pugin B, Spindler F (1996) In CornUs B, Herrmann WA (eds) Applied Homogeneous Catalysis by Organometallic Complexes. Verlag Chemie, Weinheim, p 992... 

Catalysis by organometallic complexes often involves as a first step the loss of the ligand from the catalyst (Figure 5.19). It results in freeing the coordinative site which is then able to bind the reactants... 

Comils B, Herrmann WA (eds) (2002) Applied homogeneous catalysis by organometallic complexes, 2nd edn. Wiley-VCH, Weinheim... 

A concise summary of chemistry of technologically important reactions catalysed by organometallic complexes in solution. Cornils B and Herrmann W A (eds) 1996 Applied Homogeneous Catalysis with Organometallio Compounds (Weinheim VCH) A two-volume, multiauthored account with emphasis on industrial applications. 

A chapter written in 1996 covers hydroformylation catalyzed by organometallic complexes in detail,219 whereas a review written 5 years later gives a summary of the advances on hydroformylation with respect to synthetic applications.220 A selection of papers in a special journal issue has been devoted to carbonylation reactions.221 A major area of the research has been the development of fluorous biphasic catalysis and the design of new catalysts for aqueous/organic biphasic catalysis to achieve high activity and regioselectivity of linear or branched aldehyde formation. 

While the term homogeneous catalysis pertains to all those reaction systems where the catalyst and the substrate are in the same phase, many chemists identify it with liquid-phase reactions catalyzed by organometallic complexes. Indeed, this fastgrowing field attracts most of the research effort in homogeneous catalysis. New... 

Reactions of Oiganoinetallic Complexes 686 Catalysis by Organometallic Compounds 705 Slereochenvcally Nmrigid Molecules 723 Conclusion 730... 

Carborane-metal complexes, 8, 87-113 Catalysis by organometallics carbonylation, 6, 158-163 hydroformylation, 6, 128-136 olefin reactions, 7, 199-202 organic syntheses by nickel compounds, 8, 48-83 reviews, 10, 331-336 Cationic metal carbonyls, 8, 117-159 Chromium carbonyls, 8, 133-159, see also Benchrotrenes Cobaloximes, 7, 161, 203 Cobalt carbonyl, 6, 119-163 8, 152-155 Cotton-Kraihanzel method, 10, 213-214 Coupling reactions, on nickel, 8, 30-39, 82-83... 

The electrochemical incorporation of CO2 into perfluoroalkyl derivatives has been explored in the case of (perfluoroalkyl)alkyl iodides and (perfluoroalkyl)alkenes, with an electrochemical system based on the use of consumable anodes combined with organometallic catalysis by nickel complexes. Iodide derivatives have been functionalized to the corresponding carboxylic acids by reductive carboxylation. Interesting and new results have been obtained from the fixation of CO2 into perfluoroalkyl olefins. Good yields of carboxylic acids could be reached by a carefull control of the reaction conditions and of the nature of the catalytic system. The main carboxylic acids are derived from the incorporation of carbon dioxide with a double bond migration and loss of one fluorine atom from the CF2 in a position of the double bond. 

On the basis of these results, the polyurethane catalysis by organometallic compounds can hardly be explained by an activated binary complex as proposed by Entelis. Ternary or quaternary complexes are more realistic catalytic pathways but their present description is not necessarily the best one (16). All the complexation possibilities are not taken into account. 

Numerous reviews, special journal editions and books have been already devoted to the topic of aqueous organometallic catalysis especially in the last 5-8 years. All these publications, however, comprise of detailed reviews or accounts on particular topics written by leading specialists. While this is certainly beneficial for those who themselves work in the same direction, non-specialists, students or those who are just to enter this field of research may be better served by a monograph of the style and size of the Catalysis by Metal Complexes series. In 1994, in Volume 15 of this series, a chapter was published on aqueous organometallic hydrogenations - with the aim of giving a complete description of what had been done before in that respect. After only seven years such an aim of all-inclusivity is irrealistic, and this had to bring with itself a selection of the literature used. 

Catalysis by organometallic compounds is based on activation of the substrates by coordinating it to the metal, which lowers the activation energy of the reaction between substrates. As in other types of catalysis the use of a homogeneous catalyst in a reaction provides a new pathway, because the reactants interact with the metallic complex first. Homogeneous transition metal catalysts are increasingly being applied in industrial processes to obtain bulk chemicals, fine chemicals and polymers. 

Organometallic catalysis is very diverse and many different mechanisms have been proposed in the literature for various reactions. Interestingly it is rather seldom that kinetic models are derived for the proposed catalytic cycles and the kinetic equations are even compared qualitatively with experimental observations. We will discuss several examples which represent typical cases in homogeneous catalysis by metall complexes. 

To explore the catalytic chemistry of metal surfaces, and in particular of small metal particles, we shall have to seek the help of adjacent areas of science. These will include the study under UHV conditions of chemisorbed hydrocarbons, concerning which much is now known homogeneous catalysis by metal complexes, and catalysis by complexes adsorbed on surfaces (to a more limited extent) organometallic chemistry in general and of course theoretical chemistry. 

Scheme 11 Desulfurization of thiols on Co-Mo-S clusters. Reproduced from Organometallic modeling of the hydrodesulfurization and hydrodenitrogenation, by R. A. Sanchez-Delgado in Catalysis by Metal Complexes] B. R. James and P. W. N. M. van Leeuwen, Eds. Kluwer Academic Publishers Dordrecht, Vol. 24, p. 126 (2002). With kind permission of Springer Science and Business Media.

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