Synthesis of the Catalysts

Ugi and coworkers investigated the reactivity of the lithiation of iV,iV-dimethyl-1-ferrocenylethylamine 1 at the ferrocene ring and found that the stereochemistry 

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Simplifying the synthesis of the catalysts (e.g., the highly optimized convergent synthesis of monometallic series 2 metalloporphyrins required between 14 and 17 steps [Collman et al., 2002d]—FeAc (Fig. 18.21a) is available in 7 steps). 

The same concept of using mutually interfering acid and base catalysts was achieved by Frechet s group through the use of star polymer systems [30]. The synthesis of the catalysts is outlined in Scheme 5.13. The arms of the star polymers prevent the catalysts from interfering with each other and allow the cascade reaction to proceed unhindered. 

To obtain a good enantiomeric excess, the ligand synthesis and the reduction reaction need to be carried out under strictly anhydrous conditions. The addition of the substrate needs to be as slow as possible. Table 11.3 gives some examples of the different substrates that can be reduced by the hydro-xysulfoximine-borane catalyst described. Other examples are given in the comparative Table 11.4. Concerning the synthesis of the catalyst, the yield can dramatically decrease if the reaction conditions are not strictly anhydrous. 

The solids analysis described above can be taken to yet another level by correlating the color measurement to chemical properties. An excellent model system is vanadium pyrophosphate (VPO), which is a well-known catalyst for butane oxidation to maleic anhydride. During the synthesis of the catalyst precursor, solid V2O5 particles are dispersed in a mixture of benzyl alcohol and i-butanol. In this slurry phase, the vanadium is partly reduced. Addition of phosphoric acid leads to a further reduction and the formation of the VPO structure. With a diffuse reflectance (DR) UV-vis probe by Fiberguide Ind., the surface of the suspended solid particles could be monitored during this slurry reaction. Four points can be noted from Figure 4.4 ... 

An unsaturated compound in the course of its isomerization in magnesium-containing films performs two functions (i) it forms a catalyst when the Mg4 cluster is inserted into the activated C-H bond, and (ii) it acts as a reaction substrate. The stages of the synthesis of the catalyst and isomerization can be separated. For example, anthracenyltetramagnesium hydride can be preliminarily obtained in anthracene-magnesium films, and then it can be used as a catalyst. The introduction of this cluster compound into a solution of allylbenzene or methylindene at room temperature ensures high yields of multiple bond migration products. 

This article is focused on HDN, the removal of nitrogen from compounds in oil fractions. Hydrodemetallization, the removal of nickel and vanadium, is not discussed, and HDS is discussed only as it is relevant to HDN. Section II is a discussion of HDN on sulfidic catalysts the emphasis is on the mechanisms of HDN and how nitrogen can be removed from specific molecules with the aid of sulfidic catalysts. Before the discussion of these mechanisms, Section II.A provides a brief description of the synthesis of the catalyst from the oxidic to the sulfidic form, followed by current ideas about the structure of the final, sulfidic catalyst and the catalytic sites. All this information is presented with the aim of improving our understanding of the catalytic mechanisms. Section II.B includes a discussion of HDN mechanisms on sulfidic catalysts to explain the reactions that take place in today s industrial HDN processes. Section II.C is a review of the role of phosphate and fluorine additives and current thinking about how they improve catalytic activity. Section II.D presents other possibilities for increasing the activity of the catalyst, such as by means of other transition-metal sulfides and the use of supports other than alumina. 

One of the main advantage of this method is that it allows different possibilities of synthesis of metallic particles deposited on a carbon support (1) synthesis of the catalysts with a controlled atomic ratio by coreduction, which consists in mixing different metal salts before their reduction leading to colloid formation and deposition on carbon (2) synthesis of the catalysts with a controlled atomic ratio by codeposition, which consists in mixing colloids of different... 

From a practical standpoint, it is of interest to devise a one-step synthesis of the catalyst. Since both reactions 2 and 3 are ligand substitution reactions, it is quite conceivable that both steps can be carried out at the same time. When we reacted [Ru(COD)Cl2]n with BINAP and sodium acetate in acetic acid, we indeed obtained Ru(BINAP)(OAc)2 in good yields (70-80%). Interestingly, when the reaction was carried out in the absence of sodium acetate, no Ru(BINAP)(OAe)2 was obtained. The product was a mixture of chloro-ruthenium-BINAP complexes. A 3ip NMR study revealed that the mixture contained a major species (3) (31P [ H] (CDCI3) Pi=70.9 ppm P2=58.3 ppm J = 52.5 Hz) which accounted for more than 50% of the ruthenium-phosphine complexes (Figure 2). These complexes appeared to be different from previously characterized and published Ru(BINAP) species (12,13). More interestingly, these mixed complexes were found to catalyze the asymmetric hydrogenation of 2-(6 -methoxy-2 -naphthyl)acrylic acid with excellent rates and enantioselectivities. 

The potassium complex of the hydroxyethyl functionalised carbene, once formed, can then be used as a carbene transfer agent. Patel et al. employed this compound in the synthesis of titanium(lV) complexes used as catalysts in the polymerisation of lactides [38]. Synthesis of the catalyst is facile and involves the reaction of the potassium complex of the hydroxyethyl functionaUsed carbene with [TiCOFV) ] (see Figure 4.7). Although the activity of the titanium(lV) carbene complex is considerably less then that of the potassium complex, the titanium complex acts as a masked NHC and thus a highly moisture and air stable NHC source [38]. 

An important and significant amount of work has also been done on the asymmetric polymerization of epoxides. Much of this work was carried out with catalysts derived from diethylzinc and diethylmagnesium. The asymmetry was introduced by using optically active alcohols in the synthesis of the catalyst species. Alternately, optically active monomers were polymerized using optically inactive catalysts. A detailed discussion of these studies is beyond the scope of this chapter and the reader is referred to reviews of the subject [9, 14]. 

Due to the increasing industrial demand, a laboratory pilot-plant synthesis of the catalyst was developed. In the period of 1993-2000, a total of 189 papers and patents on MTO applications have appeared, showing the great interest in both academia and industry. 

Catalyst. The catalyst studied in this work was a platinum (0.205% wt) supported on an amorphous mesoporous silica-alumina, MSA (Si02/Al203=100) extrud with 50% wt alumina. The synthesis of the catalyst and the metal deposition procedure were described in detail [9]. A used catalyst, prepared as the former and containing 0.186% wt of Pt, was studied after the hydroisomerization of an n-paraffin feed containing 10 ppm S. 

The synthesis of the catalysts has been carried out by incipient wetness impregnation the support (A1F3, Ausimont) is treated with a volume of impregnating solution (solutions of metal chlorides) equal to the total volume of the pores and every impregnation is followed by drying (120°C, 1 h) in order to remove the water. The samples prepared are reported in Table 1. 

We have reported that (Al,Sb,V)204 is the active phase for propane ammoxidation in Al-rich Al-Sb-V-0 catalysts [5]. Figure 7 shows for a slurry preparation with Al Sb V = 21 5 1 the dependence of the catalytic performance with time-on-stream. The propane conversion and the selectivities show almost constant behaviour, indicating that the active structure is formed in the synthesis of the catalyst. Characterisation with FTIR, FT-Raman, XPS and X-ray diffraction before and after use in ammoxidation showed no difference [5]. 

In the present conditions, the catalytic activity of palladium species is developed only in the contact with a proper promoter. The effective contact of palladium with the second component is provided when complexes with the heteropolytungstates are applied for the synthesis of the catalysts. The method is appeared powerful in both situations when heteropolytungstate anion is a promoter by itself and when it serves as a matrix to assemble together Pd(II) with promoting Fe(III) ions. 

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