Wilhelm Keim

Bio: Wilhelm Keim is an academic researcher from RWTH Aachen University. The author has contributed to research in topics: Catalysis & Ethylene. The author has an hindex of 48, co-authored 200 publications receiving 12493 citations.

Ionic Liquids-New "Solutions" for Transition Metal Catalysis.

Abstract: Ionic liquids are salts that are liquid at low temperature (<100 degrees C) which represent a new class of solvents with nonmolecular, ionic character. Even though the first representative has been known since 1914, ionic liquids have only been investigated as solvents for transition metal catalysis in the past ten years. Publications to date show that replacing an organic solvent by an ionic liquid can lead to remarkable improvements in well-known processes. Ionic liquids form biphasic systems with many organic product mixtures. This gives rise to the possibility of a multiphase reaction procedure with easy isolation and recovery of homogeneous catalysts. In addition, ionic liquids have practically no vapor pressure which facilitates product separation by distillation. There are also indications that switching from a normal organic solvent to an ionic liquid can lead to novel and unusual chemical reactivity. This opens up a wide field for future investigations into this new class of solvents in catalytic applications.

Ionische Flüssigkeiten - neue 'Lösungen' für die Übergangsmetallkatalyse

Abstract: Ionische Flussigkeiten sind bei niedrigen Temperaturen (<100 °C) schmelzende Salze, die eine neuartige Klasse von Losungsmitteln mit nichtmolekularem, ionischem Charakter darstellen. Auch wenn einige bereits seit 1914 bekannt sind, wurden ionische Flussigkeiten erst in den letzten zehn Jahren intensiv als Losungsmittel fur die Ubergangsmetallkatalyse untersucht. Die seither erschienenen Veroffentlichungen belegen, dass der Ersatz organischer Losungsmittel durch eine ionische Flussigkeit zu bemerkenswerten Verbesserungen bekannter Verfahren fuhren kann: Mit vielen organischen Produktgemischen bilden ionische Flussigkeiten zwei Phasen. Daraus ergibt sich die Moglichkeit einer mehrphasigen Reaktionsfuhrung zur problemlosen Abtrennung homogener Katalysatoren. Auserdem haben ionische Flussigkeiten praktisch keinen Dampfdruck, was eine destillative Produktabtrennung stark vereinfacht. Daruber hinaus gibt es Hinweise, dass der Ubergang von einem „ublichen“ organischen Losungsmittel zu einer ionischen Flussigkeit zu einer neuartigen und ungewohnlichen chemischen Reaktivitat fuhren kann. Dies offnet ein weites Feld fur zukunftige Untersuchungen dieser neuartigen Losungsmittelklasse in katalytischen Anwendungen.

Nickel: An Element with Wide Application in Industrial Homogeneous Catalysis

Abstract: The efficiency and future development of the chemical industry are closely linked to catalysis. It has been estimated, for example, that 60 to 70% of all industrial chemicals have involved the use of a catalyst at some point during their manufacture. In the past two decades the share of the market credited to homogeneous transition metal catalysis increasead to 10–15%. Besides cobalt, which is used mainly in hydroformylation reactions, nickel is the most frequently used metal. Many carbon–carbon bond formation reactions can be carried out with high selectivity if catalyzed by organonickel complexes. Such reactions include, inter alia, carbonylation reactions, cyclic and linear oligomerization and polymerization reactions of monoenes and dienes, and hydrocyanation reactions. It was Reppe and Wilke who pioneered and shaped the field of homogeneous nickel catalysis. Great impetus was also given to the development of organonickel chemistry by Wilke and his students. Research in this area has contributed immensely towards an understanding of the reactions involved in catalysis.—This review is primarily concerned with nickel-catalyzed reactions which are of interest both preparatively and industrially; some mechanistic aspects are also dealt with.

Oligomerization of ethylene to α-olefins: discovery and development of the shell higher olefin process (SHOP).

Abstract: Ethylene oligomerization for the manufacture of a-olefins is one of the most significant processes of homogenous transition-metal catalysis. Over one million tonnes of a-olefins are currently manufactured every year using the Shell Higher Olefin Process (SHOP). SHOP was discovered in 1968 in the laboratories of Shell Development Company in Emeryville, California, and even after 45 years it has not lost its significance. Indeed, just recently Shell announced that a further production plant with a capacity of 200 000 tonnes will be constructed in Qatar. When the author started at Shell Development in Emeryville in 1965 the following economic environment existed: 1. Shell Chemicals had just commissioned a hydroformylation plant to manufacture fatty alcohols (Neodol) in Geismar, Louisiana. Due to ecological requirements a change away from “hard” detergents with branched chains to “soft” detergents with linear fatty alcohols was emerging. The lack of biological degradation of the branched surfactants had resulted in the accumulation of foam on rivers and seas. Furthermore, the detergents based on Neodol showed good washing performance in hard water and could be used at low washing temperatures. They also worked well in formulations with low phosphate content, which reduced the eutrophication of surface waters. The fatty alcohols produced by Shell were then in high demand, and the market developed high growth rates. 2. The olefins used in Geismar for hydroformylation were produced by the halogenation of alkanes with chlorine and elimination of HCl. This process had considerable disadvantages, as the monoolefins produced in this way shorten the lifetime of the cobalt phosphane catalyst. 3. Shell planned the construction of a large-scale gas oil cracker. A market was still needed for a major portion of the generated ethylene. Against this background, a-olefins and linear monoolefins with an internal double bond were in demand at Shell Chemicals for hydroformylation. The research division of Shell Development Company was instructed to work on the oligomerization of ethylene to linear a-olefins and linear monoolefins. At that time a-olefins were primarily produced by cleavage of wax and the Ziegler polymerization of ethylene. The wax splitting and the Ziegler process are very expensive and give lower quality products for the manufacture of detergents. As a chemist who had completed his dissertation under the supervision of K. Ziegler and G. Wilke, I was very familiar with the transition-metal-catalyzed C C coupling of olefins. Numerous homogenous transition-metal catalysts with monodentate phosphane ligands had been described by which the direction of the C C linkage could be influenced. The use of ligands containing polydentate phosphane was hardly described; hence it seemed appropriate to investigate bidentate phosphane ligands. The concept described in Figure 1 shows the basis of the underlying considerations. The bidentate chelate ligand XY should exhibit the following properties: it should force square-planar coordina-

Ionic Liquids-New "Solutions" for Transition Metal Catalysis.

Abstract: Ionic liquids are salts that are liquid at low temperature (<100 degrees C) which represent a new class of solvents with nonmolecular, ionic character. Even though the first representative has been known since 1914, ionic liquids have only been investigated as solvents for transition metal catalysis in the past ten years. Publications to date show that replacing an organic solvent by an ionic liquid can lead to remarkable improvements in well-known processes. Ionic liquids form biphasic systems with many organic product mixtures. This gives rise to the possibility of a multiphase reaction procedure with easy isolation and recovery of homogeneous catalysts. In addition, ionic liquids have practically no vapor pressure which facilitates product separation by distillation. There are also indications that switching from a normal organic solvent to an ionic liquid can lead to novel and unusual chemical reactivity. This opens up a wide field for future investigations into this new class of solvents in catalytic applications.

Ionic liquid (molten salt) phase organometallic catalysis.

Abstract: For economical and ecological reasons, synthetic chemists are confronted with the increasing obligation of optimizing their synthetic methods. Maximizing efficiency and minimizing costs in the production of molecules and macromolecules constitutes, therefore, one of the most exciting challenges of synthetic chemistry.1-3 The ideal synthesis should produce the desired product in 100% yield and selectivity, in a safe and environmentally acceptable process.4 It is now well recognized that organometallic homogeneous catalysis offers one of the most promising approaches for solving this basic problem.2 Indeed, many of these homogeneous processes occur in high yields and selectivities and under mild reaction conditions. Most importantly, the steric and electronic properties of these catalysts can be tuned by varying the metal center and/or the ligands, thus rendering tailor-made molecular and macromolecular structures accessible.5,6 Despite the fact that various efficient methods, based on organometallic homogeneous catalysis, have been developed over the last 30 years on the laboratory scale, the industrial use of homogeneous catalytic processes is relatively limited.7 The separation of the products from the reaction mixture, the recovery of the catalysts, and the need for organic solvents are the major disadvantages in the homogeneous catalytic process. For these reasons, many homogeneous processes are not used on an industrial scale despite their benefits. Among the various approaches to address these problems, liquidliquid biphasic catalysis (“biphasic catalysis”) has emerged as one of the most important alternatives.6-11 The concept of this system implies that the molecular catalyst is soluble in only one phase whereas the substrates/products remain in the other phase. The reaction can take place in one (or both) of the phases or at the interface. In most cases, the catalyst phase can be reused and the products/substrates are simply removed from the reaction mixture by decantation. Moreover, in these biphasic systems it is possible to extract the primary products during the reaction and thus modulate the product selectivity.12 For a detailed discussion about this and other concepts of homogeneous catalyst immobilization, the reader is referred elsewhere.6,7 These biphasic systems might combine the advantages of both homogeneous (greater catalyst efficiency and mild reaction conditions) and heterogeneous (ease of catalyst recycling and separation of the products) catalysis. The advent of water-soluble organometallic complexes, especially those based on sulfonated phosphorus-containing ligands, has enabled various biphasic catalytic reactions to be conducted on an industrial scale.13-15 However, the use of water as a * Corresponding author. Fax: ++ 55 51 3316 73 04. E-mail: dupont@iq.ufrgs.br. 3667 Chem. Rev. 2002, 102, 3667−3692

Deep eutectic solvents: syntheses, properties and applications

Abstract: Within the framework of green chemistry, solvents occupy a strategic place. To be qualified as a green medium, these solvents have to meet different criteria such as availability, non-toxicity, biodegradability, recyclability, flammability, and low price among others. Up to now, the number of available green solvents are rather limited. Here we wish to discuss a new family of ionic fluids, so-called Deep Eutectic Solvents (DES), that are now rapidly emerging in the current literature. A DES is a fluid generally composed of two or three cheap and safe components that are capable of self-association, often through hydrogen bond interactions, to form a eutectic mixture with a melting point lower than that of each individual component. DESs are generally liquid at temperatures lower than 100 °C. These DESs exhibit similar physico-chemical properties to the traditionally used ionic liquids, while being much cheaper and environmentally friendlier. Owing to these remarkable advantages, DESs are now of growing interest in many fields of research. In this review, we report the major contributions of DESs in catalysis, organic synthesis, dissolution and extraction processes, electrochemistry and material chemistry. All works discussed in this review aim at demonstrating that DESs not only allow the design of eco-efficient processes but also open a straightforward access to new chemicals and materials.