Other catalytic reactions

Isomerizations are another category of reaction where Co complexes act as catalysts. Mixed S,P donor complexes Co(SCN)2(PR3)2 catalyze the isomerization of 1-butene to 2-butene in the presence of NaBH4, with CoH(SCN)(PR3)2 proposed as the active species.1366 A cyclopentadienyl complex (272) is active in the isomerization of quadricyclene to norbornadiene. 

Rearrangement of trivalent (5-hexenyl)Co(salen) proceeds via a radical chain process leading to the isomeric cyclopentylmethyl complex.1387 The efficiency with which this rearrangement occurs is dependent on the presence of trace impurities or 02. The selective reaction of alcohols (ROH) with arylglyoxals (ArCOCHO) to give a-aryl-a-hydroxyacetic esters ArCH(0H)C02R is catalyzed by compounds of this family.1388 

After having discussed catalytic reactions involving carbon monoxide, hydrogen, carbon monoxide and hydrogen, as well as carbon monoxide and water, this section is dedicated mainly to isomerization and rearrangement reactions and to carbon-carbon and carbon-nitrogen coupling reactions. 

The isomerization of terminal olefins to a mixture of internal olefins 

Isomerization of Olefins and Dienes Catalyzed by Various Transition Metal Clusters 

Substrate Products (%) Catalyst Conditions Time Catalytic turnover Remarks References 

Pent-l-ene ( )-Pent-2-ene, (Z)-pent-2-ene H4Ru4(CO)12 Toluene, 70°C NG NG Product composi-ton NG (333) 

We have further examined the reactions of thiolato-bridged diruthenium complexes with other unsaturated organic substrates. When the cationic Ru complex 4 is treated with cinnamyl alcohol in p-xylene, the allylated aromatic compound 18 is obtained in good yield (Equation 6). We assume a Tc-allyl intermediate because the reaction using l-phenylprop-2-en-l-ol gives, instead of cinnamyl alcohol, the same product 18 however, the detailed reaction mechanism is still obscure. This novel allylation reaction is halogen-free, and may replace the conventional Friedel-Crafts alkylation. 

The cationic Ru complex 4 also promotes silylative dimerisation of aromatic aldehydes with hydrosilanes. For example, the reaction of benzaldehyde and triethylsilane in the presence of a catalytic amount of 4 affords the dimerisation product 19 along with a small amount of the hydrosilylation product PhCH20SiEt3 (Equation 7). This type of silylative dimerisation of aldehydes is relatively scarce in the literature common ruthenium complexes such as [RuCl2(PPh3)3] and [Ru3(CO)j2] give only the hydrosilylation products. 

Even if the main use of ceria is related to develop of TWCs, ceria participates as a component in the formulation of catalyst for several reactions. A few selected examples are reported in the following sections. 

The H2S decomposition reaction has also been studied utilizing electrochemical membrane reactors. Alqahtany et al. [2.319], for example, studied the reaction in a Pt/YSZ/Pt 

Catalytic Membranes and Membrane Reactors. By J. G. Sanchez Marcano and Th. T. Tsotsis Copyright 2002 Wilcy-VCH Verlag GmbH ISBN 3-527-30277-8 

The decomposition of dilute mixtures of NH3 in a PBMR using Pd-alloy membranes was studied by Collins and Way [2.322], and by Gobina et aL [2.323]. This application is of potential interest in the treatment of coal gasification streams, and the laboratory results showed promise. It would be interesting to see, whether the same membranes prove robust in the real coal-gas environment. The use of a PBMR to study the hydrodechlorination of dichloroethane was reported by Chang et al. [2.324]. The reported potential advantage of the membrane would be in preferentially removing the by-product HCl, which deactivates the catalyst. The authors attribute the observed improved performance, however, to a dilution effect. 

HC reductant Cleaned exhaust j Exhaust Cleaned exhaust [  

Exhaust cxTDtaining 2N0+02- 2N02 NO oxidation catalyst czj reductant  

As already mentioned the catalysts show a certain isomerization activity that may become the main reaction imder certain experimental conditions. This is the only activity of the Cr(II)B species vs. olefins. The mechanism looks like an acid catalysis, using the protons from to chromium coordinated OH groups. Addition of Lewis acids supports this reaction. 

As mentioned above. Mo containing catalysts can react with olefins under metathesis [23, 27]. This shows that the carbene mechanism is at least not excluded for this type of surface compounds. 

Using mixtures of olefins and hydrogen as educts the olefins undergo hydrogenation imder mild conditions and with quantitative yields [61]. With Ru catalysts this is the typical reaction [29]. 

Finally it should be mentioned that Cr(II) surface compounds may act as catalysts in a Fischer-Tropsch system. From H2 and CO or CO2 they produce methane with some ethane and propane. The reaction pathway may foUow the mechanism given 1976 by Henrici-Olive and Olive [76]. Important steps are here the intermediate formation of a formaldehyde complex follow C carbene complex [77]. 

---

The stoichiometric reaction of allenes with Pd(II) is treated in Chapter 3, Section 9, and catalytic reactions with organic halides are in this chapter, Section 1.1,1.3 Other catalytic reactions of allenes are surveyed in this section. 

Eor the application of C2-symmetric bis-oxazoline-Lewis acids in other catalytic reactions (a) Mukaiyama-aldol reactions see, e.g., D.A. Evans, M.C. Kozlowski,... 

Some Other Catalytic Reactions Useful for Fine Chemical... 

Hoveyda in his essay on asymmetric catalysis in target-oriented synthesis (p 145). The concept of catalysis-based total synthesis, in which a series of catalytic enantioselective reactions are employed in combination with other catalytic reactions, is emerging as the desirable way to make complex natural products and medidnally-important target compounds. 

Due to many impressive advances in metal-catalyzed transformations, both asymmetric and non-asymmetric, several efforts have been directed towards designing total synthesis routes that very heavily depend on various catalytic methods. These total syntheses benefit from the economic efficiency and environmental consciousness that are two of the inherent attributes of catalytic reactions. The total synthesis of wodeshiol 133 by Corey, discussed above (Scheme 19) is one such example. Two additional catalysis-based enantioselective total syntheses are briefly discussed below. In both efforts, all centers of asymmetiy are attained by a catalytic enantioselective method, and the synthesis is completed through the use of several other catalytic reactions. 

In the chemical industry, iodine and/or iodine compounds are often used as catalysts and/or catalytic promoters for the production of value-added organic chemicals. As with other catalytic reactions, the catalyst or promoter must be removed from the products after completing the reaction. However, removing trace amounts of organic iodide contaminates from the product by conventional distillation techniques is difficult primarily due to the fact that iodine compounds are unstable and split off into various boiling ranges. 

Other catalytic reactions involving a transition-metal allenylidene complex, as catalyst precursor or intermediate, include (1) the dehydrogenative dimerization of tributyltin hydride [116], (2) the controlled atom-transfer radical polymerization of vinyl monomers [144], (3) the selective transetherification of linear and cyclic vinyl ethers under non acidic conditions [353], (4) the cycloisomerization of (V2V-dia-llyltosylamide into 3-methyl-4-methylene-(V-tosylpyrrolidine [354, 355], and (5) the reduction of protons from HBF4 into dihydrogen [238]. 

Other Catalytic Reactions via Allenylidene Complexes as Key Intermediates... 

The same effect should be expected in other catalytic reactions. In order to confirm this, disproportionation and isomerization reactions were... 

A key aspect of metal oxides is that they possess multiple functional properties acid-base, electron transfer and transport, chemisorption by a and 7i-bonding of hydrocarbons, O-insertion and H-abstraction, etc. This multi-functionality allows them to catalyze complex selective multistep transformations of hydrocarbons, as well as other catalytic reactions (NO,c conversion, for example). The control of the catalyst multi-functionality requires the ability to control not only the nanostructure, e.g. the nano-scale environment around the active site, " but also the nano-architecture, e.g. the 3D spatial organization of nano-entities. The active site is not the only relevant aspect for catalysis. The local area around the active site orients or assists the coordination of the reactants, and may induce sterical constrains on the transition state, and influences short-range transport (nano-scale level). Therefore, it plays a critical role in determining the reactivity and selectivity in multiple pathways of transformation. In addition, there are indications pointing out that the dynamics of adsorbed species, e.g. their mobility during the catalytic processes which is also an important factor determining the catalytic performances in complex surface reaction, " is influenced by the nanoarchitecture. 

Conversion of C3H6 in the ratio interval between 1 1.5 and 1 2 is decreased by 3 wt.%, whereas for epoxide this value equals 10 wt.%. These data show that the increase in yields of other oxidation products is caused by epoxide isomerization and the parallel proceeding of other catalytic reactions. It should be noted that chromatographic tests have detected only unreacted C3H6 in the gas products, whereas CO, C02 and other products of C3H6 degradation were not observed. 

Polymerization on heterogeneous catalysts differs from other catalytic reactions in the sense that the product remains on the catalyst. Several techniques can be used to study the polymer product after reaction. Figures 9.29 and 9.30 show several examples of polymer that was formed at 160 °C (i.e., above its melting point), and subsequently cooled to room temperature. During cooling, polyethylene crystallizes and is expected to develop its well-known spherulite morphology [101]. 

Other catalytic reactions carried out in fluidized-bed reactors are the oxidation of naphthalene to phthalic anhydride [2, 6, 80] the ammoxidation of isobutane to mcthacrylonitrilc [2] the synthesis of maleic anhydride from the naphtha cracker C4 fraction (Mitsubishi process [81, 82]) or from n-butane (ALMA process [83], [84]) the reaction of acetylene with acetic acid to vinyl acetate [2] the oxychlorination of ethylene to 1,2-di-chloroethane [2, 6, 85, 86] the chlorination of methane [2], the reaction of phenol with methanol to cresol and 2,6-xylenol [2, 87] the reaction of methanol to gasoline... 

In this chapter we also discuss two other catalytic reactions that involve CO as one of the reactants. These are the water-gas shift (see Section 1.2) and Fischer-Tropsch reactions. Although for these reactions homogeneous catalysts are not used industrially, for explaining the formation of by-products in the... 

In Section 5.2.5 immobilization of a thin him of an aqueous solution of Rh-TPPTS complex on high-surface-area silica has been mentioned. This general strategy for some other catalytic reactions sometimes lead to problems due to reaction of water with TPPTS-containing precatalyst. Suggest a solution to this problem. 

---