Applications catalytic

The activity of the catalyst systems increases as the dissociation energy of the labile ligand is reduced. The catalytic performance of these systems is comparable with Schrock s highly active yet very sensitive molybdenum system [45]. So even tetrasubstituted olefins are accessible by ring-closing metathesis using these optimized air- and moisture-stable ruthenium systems [46, 47]. 

Pd-catalyzed C-C-coupling reactions of the Heck type, e. g., Suzuki [48c] and Stille [49c] cross-coupling, are excellent tools for the preparation of biaryls (see also Section 3.1.9). The activity and stability of the catalyst is highly dependent on the steric and electronic properties of the ligands. Sterically demanding basic alkylphosphines e. g., tri(/-butyl)phosphine, have proven to be very effective ligands in the Heck reaction [50] as well as in the Suzuki cross-coupling [51]. NHCs resemble those basic phosphines (see above) and therefore were tested 

In contrast to the other examples, a Pd bis (NHC) complex (10) reveals the highest activity known to date in the Suzuki cross-coupling of chloroarenes [53], 

However, the problem of catalyst decomposition that was known previously only for phosphine complexes prevents quantitative yields with these catalysts. This means that in the coupling of p-chlorotoluene with phenylboronic acid with 3 % 1,3-di(t-butylimidazolin-2-ylidene Pd a conversion of 55 % is observed after only 10 min. Yet no more than 68% yields are reached due to catalyst decomposition. 

For Pd the strong electron-donor effect of the NHC seems to have a destabilizing effect on the metal center that is oversaturated with electron density. However, this high electron density facilitates the oxidative addition of the 

The X-ray diffraction analysis of the major isomer revealed that the CO anti to the CpFe fragment in complex 31 had been replaced by the bulky PPhs ligand (Fig. 1.5.7). 

Selected derivatives of the ligands and complexes described above have been tested in catalytic applications. Early tests with bidentate P,P or P,N ligands such as 4, 6, and 8 in Rh-catalyzed asymmetric hydrogenation were disappointing, with ee values below 20%. However, as was demonstrated mainly by the Fu group, phosphaferrocene derivatives do have the potential for successful applications in asymmetric catalytic reactions, provided the phosphaferrocene is endowed with sufficient steric bulk. Examples are depicted in Eig. 1.5.8 the Cp derivative 32, 

The bis(phosphaferrocene) 22 gave good results in the hydroformylation of a-olefins regarding activity and n/iso selectivity [33]. 

Calmuschi, J. Haberland, W. Hummel, A. Liese, T. Nickel, O. Stelzer, A. Salzer, Eur. J. Inorg. Chem. 2004, 2235. 

8 For a short review see C. Ganter, J. Chem. Soc., Dalton Trans. 2001, 3541. 

791 g product (mmol of M) 652g product (mmol of M) 286 g product (mmol of M) 694 g product (mmol of M) 

1280 g product (mmol of bar 907 g product (mmol of bar 1446 g product (mmol of bar 278 g product (mmol of bar  

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The applications of zeolites can be divided into tliree major categories ion exchange, adsorjDtion and catalysis. The largest amount of zeolites is used in ion exchange applications while tire largest value is derived from catalytic applications [1, 33]. 

Catalytic Applications. The PGMs are widely used as catalysts for a variety of chemical reactions, such as hydrogenation, oxidation. ... 

Table 18. Chemical Industry Catalytic Applications of Platinum-Group Metals ...

The main uses of palladium [13] are in the electronics and electrical industries, in circuitry and in dental alloys. It finds many catalytic applications in industry, as well as in diffusion cells for the synthesis of hydrogen, and in automobile catalysts. Jewellery and three way auto-catalysts are the principal uses of platinum, which fulfils a wide range of roles in the chemical industry. 

During the last decade N-heterocyclic carbene complexes of transition metals have been developed for catalytic applications for many different or-... 

Carbon-carbon bond formation reactions and the CH activation of methane are another example where NHC complexes have been used successfully in catalytic applications. Palladium-catalysed reactions include Heck-type reactions, especially the Mizoroki-Heck reaction itself [171-175], and various cross-coupling reactions [176-182]. They have also been found useful for related reactions like the Sonogashira coupling [183-185] or the Buchwald-Hartwig amination [186-189]. The reactions are similar concerning the first step of the catalytic cycle, the oxidative addition of aryl halides to palladium(O) species. This is facilitated by electron-donating substituents and therefore the development of highly active catalysts has focussed on NHC complexes. 

Coating of fine-porosity carbon for catalytic applications. 1... 

Certain aspects of catalytic applications of transition metal amidinate complexes have already been summarized in review articles. The "Chemistry of... 

Furthermore, gallium compounds can serve as model systems for aluminum congeners. Cationic gallium alkyls are of interest in synthesis and catalytic applications involving polar substituents because of the relative stability of the Ga—R bond toward hydrolysis and electrophilic cleavage compared to the otherwise superior Al-R species [11]. 

Table 2.1 Benefits of mesoporous zeolites prepared by desilication in catalytic applications with respect to the purely microporous counterparts.

Mechanism The understanding of mechanisms in catalytic reactions is sometimes crucial for the creative development of new applications. In a first approach, the main interest was to develop high surface area titanium nitride as a material for catalytic applications and, therefore, evaluation of catalysts prepared under different conditions was performed. 

Synthesis and catalytic applications of uniform-sized nanocrystals... 

As a new kind of carbon materials, carbon nanofilaments (tubes and fibers) have been studied in different fields [1]. But, until now far less work has been devoted to the catalytic application of carbon nanofilaments [2] and most researches in this field are focused on using them as catalyst supports. When most of the problems related to the synthesis of large amount of these nanostructures are solved or almost solved, a large field of research is expected to open to these materials [3]. In this paper, CNF is tested as a catalyst for oxidative dehydrogenation of propane (ODP), which is an attractive method to improve propene productivity [4]. The role of surface oxygen annplexes in catalyzing ODP is also addressed. 

Abstract The unique and readily tunable electronic and spatial characteristics of ferrocenes have been widely exploited in the field of asymmetric catalysis. The ferrocene moiety is not just an innocent steric element to create a three-dimensional chiral catalyst enviromnent. Instead, the Fe center can influence the catalytic process by electronic interaction with the catalytic site, if the latter is directly coimected to the sandwich core. Of increasing importance are also half sandwich complexes in which Fe is acting as a mild Lewis acid. Like ferrocene, half sandwich complexes are often relatively robust and readily accessible. This chapter highlights recent applications of ferrocene and half sandwich complexes in which the Fe center is essential for catalytic applications. 

Although there are some reactions that use complex 76 stoichiometrically [50-58], it was not until 1979 that Roustan et al. developed the first catalytic application of complex 76-Na (Scheme 16) [59, 60]. In his publication, he could show that catalytic amounts of complex 76-Na react with an allylic chloride or acetate to form an allyl-iron-complex, which, in a second step, is substituted with a malonate to yield 77. Most importantly, they observed a preference for the ipso-substitution-product 77a, that is, the new C-Nu-bond was formed preferentially at the carbon atom that was substituted with the leaving group before. 

Another catalytic application emanating from the Hieber base reaction was developed by Reppe and Vetter [108]. They showed that 1-propanol 126 could be generated by treatment of ethylene 125 with catalytic amounts of Fe(CO)5 78 under CO-pressure and basic reaction conditions (Scheme 33). Thereby, trimethylamine and V-alkylated amino acid derivatives mrned out to be optimal bases for this reaction. Like ethylene 125, propylene could be transferred mainly to 1-butanol diolefins like butadiene only reacted to monoalcohols. By employing these reaction conditions to olefins in the presence of ammonia, primary or secondary amines, mono-, di-, and trialkylamines were obtained whose alkyl chains were elongated with one carbon atom, compared to the olefins. 

Draganjac M, Rauchfuss TB (1985) Transition metal polysulfides Coordination compounds with purely inorganic chelate ligands. Angew Chem Int Ed Engl 24 742-757 DuBois MR (1989) Catalytic applications of transition metal complexes. Chem Rev 89 1-9 Ansari MA, Ibers JA (1990) Soluble selenides and tellurides. Coord Chem Rev 100 223-266... 

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