Catalysis summary

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. 

In summary, water is clearly an extremely bad solvent for coordination of a hard Lewis acid to a hard Lewis base. Hence, catalysis of Diels-Alder reactions in water is expected to be difficult due to the relative inefficiency of the interactions between the Diels-Alder reactants and the Lewis-acid catalyst in this medium. 

In summary, the effects of a number of important parameters on the catalysed reaction between 2.4 and 2.5 have been examined, representing the first detailed study of Lewis-acid catalysis of a Diels-Alder reaction in water. Crucial for the success of Lewis-acid catalysis of this reaction is the bidentate character of 2.4. In Chapter 4 attempts to extend the scope of Lewis-acid catalysis of Diels-Alder reactions in water beyond the restriction to bidentate substrates will be presented. 

In summary, ligands tend to diminish the affinity of the substrate for the Lewis-acid catalyst as well as the extent of activation by this catalyst, once the ternary complex is formed. Only a few examples of ligand-accelerated catalysis " have been described... 

In summary, for the most active of catalysts, the copper(II) ion, the diamine ligands that were investigated seriously hamper catalysis mainly by decreasing the efficiency of coordination of the dienophile. With exception of the somewhat deviant behaviour of N,N -dimethylethylenediamine, this conclusion also applies to catalysis by Ni" ions. Hence, significant ligand-accelerated catalysis using the diamine ligands appears not to be feasible. 

In summary, the groups of Espenson and Loh observe catalysis of Diels-Alder reactions involving monodentate reactants by Lewis acids in water. If their observations reflect Lewis-acid catalysis, involvirg coordination and concomitant activation of the dienophile, we would conclude that Lewis-acid catalysis in water need not suffer from a limitation to chelating reactants. This conclusion contradicts our observations which have invariably stressed the importance of a chelating potential of the dienophile. Hence it was decided to investigate the effect of indium trichloride and methylrhenium trioxide under homogeneous conditions. 

In summary, we have demonstrated that it is possible to extend the scope of Lewis-acid catalysis of Diels-Alder reactions in water, by employing a chelating auxiliary. We envisage that analogues of 4.39 capable of undergoing a Mamrich reaction with 4.50 can be treated with reactive dienes in the presence of a Lewis-acid catalyst in water. 

In summary, the work in this thesis provides an overview of what can be achieved with Lewis-acid and micellar catalysis for Diels-Alder reactions in water as exemplified by the reaction of3-phenyl-l-(2-pyridyl)-2-propene-l-ones with cyclopentadiene. Extension of the observed beneficial effect of water on rates and particularly enantioselectivities to other systems is envisaged. 

A brief summary of current and potential processes is given in Table 8.1. As shown in the table, most of the reactions are hydrolysis, hydrogenolysis, hydration, hydrogenation, oxidation, and isomerization reactions, where catalysis plays a key role. Particularly, the role of heterogeneous catalysts has increased in this connection in recent years therefore, this chapter concerns mostly the application of heterogeneous solid catalysts in the transformation of biomass. An extensive review of various chemicals originating from nature is provided by Maki-Arvela et al. [33]. 

In summary, we found that Ugands indeed coordinate at the surface of nanoparticles and that they can be firmly or loosely attached to this surface according to their chemical nature. Furthermore, the hgands influence the reactivity of the metal nanoparticles. This is important in catalysis but, as we will see later in this paper, is also important for the control of the growth of metal nanoparticles of defined size and shape. 

In summary, we have described our approach towards the synthesis of novel nano-objects consisting of a metal core and a surface that may be functionalized by addition of organic ligands. TEM pictures of the metal core of these nanoparticles appear similar to those of particles commonly used in heterogeneous catalysis or to colloids prepared by well-known reduction methods. However, the organometallic approach displays several specificities which can be summarized as follows ... 

In summary, these results demonstrate that air-stable POPd, POPdl and POPd2 complexes can be directly employed to mediate the rate-limiting oxidative addition of unactivated aryl chlorides in the presence of bases, and that such processes can be incorporated into efficient catalytic cycles for a variety of cross-coupling reactions. Noteworthy are the efficiency for unactivated aryl chlorides simplicity of use, low cost, air- and moisture-stability, and ready accessibility of these complexes. Additional applications of these air-stable palladium complexes for catalysis are currently under investigation. 

The photoadsorption effect as such does not constitute the subject matter of the present article. We shall consider it very briefly, only to the extent necessary to allow one to draw analogies between the mechanisms of the photoadsorptive and photocatalytic effects. The photoadsorptive effect has been studied sufficiently well. A brief summary of the experimental data will be given below. The mechanism of the phenomenon has been thoroughly discussed in a number of theoretical works from the standpoint of the electronic theory of chemisorption and catalysis C3,4,6-8). 

In summary, although subtle conformational differences between the various cycloamyloses and the effect of intramolecular hydrogen bonds on their solution conformations remain to be accurately resolved, overall structural features have been clearly defined. This is particularly advantageous and, in fact, a prerequisite if the cycloamyloses are to be profitably used as models for enzymatic or other catalytic processes. In subsequent sections of this article, various aspects of binding and catalysis will be explained on the basis of the chemical nature and geometrical dimensions of the cycloamylose cavity which is, in fact, their active site. 

A summary of the research activities of the last four years reveals three different important trends (a) The design of new ionic ligands for excellent catalyst immobilisation in ionic liquids and high regioselectivity (b) the successful application of cheap, halogen-free ionic liquids in the biphasic Rh-catalysed hydroformylation (c) the successful development of unusual multiphasic reaction concepts for Rh-catalysed hydroformylation, namely catalysis in ionic liquid/supercritical C02 and SILP-catalysts. 

In reference 44 the authors found that the [Cu2(p-0)2]2+ core with either the LlPr3 or LBn3 ligand system will activate C-H bonds for cleavage and oxidation, again having important implications for oxygenation catalysis. These authors provide a useful summary for the two core structures, which are replicated in Table 5.7. 

One of the first applications of the then newly developed Ru-binap catalysts for a,/ -unsaturated acids was an alternative process to produce (S)-naproxen. (S)-Naproxen is a large-scale anti-inflammatory drug and is actually produced via the resolution of a racemate. For some time it was considered to be one of the most attractive goals for asymmetric catalysis. Indeed, several catalytic syntheses have been developed for the synthesis of (S)-naproxen intermediates in recent years (for a summary see [14]). The best results for the hydrogenation route were obtained by Takasago [69] (Fig. 37.15), who recently reported that a Ru-H8-binap catalyst achieved even higher activities (TON 5000, TOF 600 h 1 at 15 °C, 50 bar) [16]. 

The forty-eighth volume of Advances in Catalysis includes a description of a new and increasingly well understood class of catalysts (titanosilicates), a review of transmission electron microscopy and related methods applied to catalyst characterization, and summaries of the chemistry and processes of isobutane-alkene alkylation and partial oxidation and C02 reforming of methane to synthesis gas. 

Enzymatic transformations of alkaloids by peroxidases most probably occur by single-step oxidations catalyzed by the HRP-I and HRP-II forms of the enzyme. The catalysis of one-electron oxidations of compounds containing aromatic hydrocarbon, hydrazine, phenol, hydroxamic acid, and amine functional groups has been recently reviewed (45, 58, 82). A brief summary of those HRP reactions that involve functional groups most commonly occurring in alkaloids is presented below. 

For a review of the use of palladium catalysis in heterocycle synthesis, with a good summary of the authors work, see Sakamoto, T. Kondo, Y. Yamanaka, H. Heterocycles 1988,27,2225-49. 

Resources to help others use and promote Catalysis, including short presentations to educate fellow modelers, designers, and managers summary white papers that can be handed out on Catalysis and so on. 

This chapter takes you through the principal stages of a Catalysis development, covering the main features. We recommend that if you read a single chapter of this book, this should be the one. For a greatly abbreviated sound-bite version of the tour, see Section 1.15, Summary. 

The factors — or at least some of them — which control reactivity in intramolecular reactions are relevant to enzyme catalysis, which also involves reactions between functional groups brought together in close and precisely defined proximity (Kirby, 1980). This has been an area of lively discussion in the recent literature [for a brief summary and leading references see Paquette et al. (1990)]. The main difficulty in making generalizations about the dependence of reactivity on geometry based on results from systems in which proximity is covalently enforced lies in the constraints imposed by particular systems. These may well affect reactivity... 

The first example of biphasic catalysis was actually described for an ionic liquid system. In 1972, one year before Manassen proposed aqueous-organic biphasic catalysis [1], Par shall reported that the hydrogenation and alkoxycarbonylation of alkenes could be catalysed by PtCh when dissolved in tetraalkylammonium chloride/tin dichloride at temperatures of less than 100 °C [2], It was even noted that the product could be separated by decantation or distillation. Since this nascent study, synthetic chemistry in ionic liquids has developed at an incredible rate. In this chapter, we explore the different types of ionic liquids available and assess the factors that give rise to their low melting points. This is followed by an evaluation of synthetic methods used to prepare ionic liquids and the problems associated with these methods. The physical properties of ionic liquids are then described and a summary of the properties of ionic liquids that are attractive to clean synthesis is then given. The techniques that have been developed to improve catalyst solubility in ionic liquids to prevent leaching into the organic phase are also covered. 

In summary, water appears as an extremely unsuitable solvent for coordination of hard Lewis acids to hard Lewis bases, as it strongly solvates both species and hinders their interaction. Hence, catalysis of Diels-Alder reactions in water is expected to be difficult due to the relative inefficiency of the interactions between the Diels-Alder reactants and the Lewis acid catalyst. On the other hand, the high stereoselectivities and yields observed in biosyntheses, with water as the solvent, indicate that these rationalizations cannot entirely be true. As a matter of fact, we will demonstrate in the following that Lewis acid catalysis in water is not only possible, but also allows for effective as well as environmentally friendly reaction conditions. 

In summary, we hope to have demonstrated that aqueous media for organic reactions, specifically the Diels-Alder reaction, are neither a curiosity only applicable to unusual transformations nor are they a limitation for catalysis. It is more than likely that the potential of water as an environmentally friendly and safe solvent will be used more effectively in the future for a large number of different reactions. 

Here we have discussed only very few of the many ligands that have been studied. Many variations of substituents at the cyclopentadienyl ligand have been studied, and there are more to come as well as variation in the structure of the bridge, the anions, and the central metal. In summary, the toolbox is quite extensive prediction of properties of new polymers to be made can guide the catalysis research in the design of new catalysts. 

In summary, we have demonstrated the first efficient enantio-selective alkylation via phase transfer catalysis. This alkylation was expanded to include an enantioselective Robinson annulation. The methodology was developed for the preparation of either enantiomer. Finally, our kinetic studies have provided additional mechanistic insight into the chiral PT alkylation. 

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