Metal complex catalysts

Acetonitrile also is used as a catalyst and as an ingredient in transition-metal complex catalysts (35,36). There are many uses for it in the photographic industry and for the extraction and refining of copper and by-product ammonium sulfate (37—39). It also is used for dyeing textiles and in coating compositions (40,41). It is an effective stabilizer for chlorinated solvents, particularly in the presence of aluminum, and it has some appflcation in... 

Chira.lHydrogena.tion, Biological reactions are stereoselective, and numerous dmgs must be pure optical isomers. Metal complex catalysts have been found that give very high yields of chiral products, and some have industrial appHcation (17,18). The hydrogenation of the methyl ester of acetamidocinnamic acid has been carried out to give a precusor of L-dopa, ie, 3,4-dihydroxyphenylalanine, a dmg used in the treatment of Parkinson s disease. 

These siUca-supported catalysts demonstrate the close connections between catalysis in solutions and catalysis on surfaces, but they are not industrial catalysts. However, siUca is used as a support for chromium complexes, formed either from chromocene or chromium salts, that are industrial catalysts for polymerization of a-olefins (64,65). Supported chromium complex catalysts are used on an enormous scale in the manufacture of linear polyethylene in the Unipol and Phillips processes (see Olefin polymers). The exact stmctures of the surface species are still not known, but it is evident that there is a close analogy linking soluble and supported metal complex catalysts for olefin polymerization. 

Among the J ,J -DBFOX/Ph-transition(II) metal complex catalysts examined in nitrone cydoadditions, the anhydrous J ,J -DBFOX/Ph complex catalyst prepared from Ni(C104)2 or Fe(C104)2 provided equally excellent results. For example, in the presence of 10 mol% of the anhydrous nickel(II) complex catalyst R,R-DBFOX/Ph-Ni(C104)2, which was prepared in-situ from J ,J -DBFOX/Ph ligand, NiBr2, and 2 equimolar amounts of AgC104 in dichloromethane, the reaction of 3-crotonoyl-2-oxazolidinone with N-benzylidenemethylamine N-oxide at room temperature produced the 3,4-trans-isoxazolidine (63% yield) in near perfect endo selectivity (endo/exo=99 l) and enantioselectivity in favor for the 3S,4J ,5S enantiomer (>99% ee for the endo isomer. Scheme 7.21). The copper(II) perchlorate complex showed no catalytic activity, however, whereas the ytterbium(III) triflate complex led to the formation of racemic cycloadducts. 

It should be noted that by immobilizing the metal complex catalysts on carbochain polymers it is possible to prepare polymer-polymer compositions using PVC, PMMA, poly(vinyl acetate), etc., as the polymeric fillers [286-287]. 

Coordination-catalyzed ethylene oligomerization into n-a-olefins. The synthesis of homologous, even-numbered, linear a-olefins can also be performed by oligomerization of ethylene with the aid of homogeneous transition metal complex catalysts [26]. Such a soluble complex catalyst is formed by reaction of, say, a zero-valent nickel compound with a tertiary phosphine ligand. A typical Ni catalyst for the ethylene oligomerization is manufactured from cyclo-octadienyl nickel(O) and diphenylphosphinoacetic ester ... 

W02005/080456 Al, Lanxess Inc. Process for the preparation of low molecular weight hydrogenated nitrile rubber EP2028194 Al, Lanxess Deutschland GmbH Metathesis of nitrile rubbers in the presence of transition metal complex catalysts Press release Lanxess - New York Conference, New York City, USA, Monday August 28, 2006, Address by Dr. Ulrich Koemm LANXESS Concepts in Rubber ... 

The above example outlines a general problem in immobilized molecular catalysts - multiple types of sites are often produced. To this end, we are developing techniques to prepare well-defined immobilized organometallic catalysts on silica supports with isolated catalytic sites (7). Our new strategy is demonstrated by creation of isolated titanium complexes on a mesoporous silica support. These new materials are characterized in detail and their catalytic properties in test reactions (polymerization of ethylene) indicate improved catalytic performance over supported catalysts prepared via conventional means (8). The generality of this catalyst design approach is discussed and additional immobilized metal complex catalysts are considered. 

The reductive carbonylation has an advantage of low feedstock cost. A wide range of homogenous metal complexes have been tested for both reactions (1-16). The major drawback of the use of metal complex catalysts is the difficulty of catalyst recovery and purification of the reaction products (12). In addition, the gaseous reactants have to be dissolved in the alcohol/amine mixture in order to have an access to the catalyst. The reaction is limited by the solubility of the gaseous CO and 02 reactants in the liquid alcohol reactant (17). 

Three main methods of synthesis of supported metal complex catalysts can be distinguished from the literature, which we will successively analyze ... 

Kureshy developed a polymer-based chiral Mn-salen complex (Figure 21). Copolymerization of styrene, divinylbenzene, and 4-vinylpyridine generated highly cross-linked (50%) porous beads loaded with pyridine ligands at 3.8 mmol g-1. Once the polymer was charged with the metal complex catalyst, enantioselective epoxidation of styrene derivatives was achieved with ee values in the range 16 46%. 79... 

The aim of this overview is first to present the general principles of electrocatalysis by metal complexes, followed by a series of selected examples published over the last 20 years illustrating the major electrochemical reactions catalyzed by metal complexes and their potential applications in synthetic and biomimetic processes, and also in the development of sensory devices. The area of metal complex catalysts in electrochemical reactions was reviewed in 1990.1... 

Dimerization, oligomerization, and similar reactions of olefins have been reported to be catalyzed by systems involving the majority of the Group VIII metals (3). The reasons for the particular interest in nickel-containing catalysts are their exceptionally high catalytic activity (catalytic reactions have been performed at temperatures as low as - 100°C), the diversity of catalytic reactions of obvious synthetic value, as well as the possibility to direct the course and control the selectivity of a catalytic reaction by tailoring the catalyst which are perhaps without parallel among transition metal complex catalysts. 

Transition metal complexes, catalysts based on, 20 193 Transition-metal compounds cause of color, 7 326t, 328-331 Transition-metal coordination compounds, 7 582-584... 

The Ziegler-type catalysts contain also a metal-alkyl, like triethylaluminum. They work usually at moderate temperature and pressure. The most active catalysts for polymer hydrogenation are the noble metal complex catalysts, and they can also be used for reduction of elastomers in the latex phase. The most difficult task is the removal of the catalyst from the reaction mixture. The methods used are based on extraction, adsorption, absorption or on their combination. 

Chiral porphyrin metal complex catalysts have also received much attention. In this situation, the flat, symmetrical porphyrin structure must be modified dramatically in order to incorporate dissymmetry. This has been achieved through strapping techniques. " Some examples are shown in Figure 11.7. 

While such a film format is not intended for routine use in e.g. soHd phase synthesis, it has proved useful for spectroscopic mechanistic investigation of polymer-supported metal complex catalysts [49] and we, with our collaborators, are employing such films as a component in nanosecond fluorescence sensing devices [50]. 

Proteins are water-soluble biopolymers with a huge number of potential donor atoms and coordination sites which could make them useful carriers of metal complex catalysts. Indeed, a few successful attempts can be found in the literature [139] but often the interaction of proteins and metal complexes lead to a loss of catalytic activity [140]. This was not the case with human serum albumin (HSA) which formed a stable and active catalytically active complex with [Rh(acac)(CO)2]. In the hydroformylation of 1-octene and styrene the selectivity towards aldehydes was excellent, moreover styrene reacted with high regioselectivity (b/1 = 19). The activity... 

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