Component catalytic

By quenching the polymerization with C1402 or Cl40 the determination of the number of propagation rate constants was found to be also possible for the two-component catalytic system TiCl2 + AlEt2Cl 158, 159). In contrast to alcohols, carbon dioxide and carbon monoxide under polymerization conditions react only with titanium-carbon active bonds and do not react with inactive aluminum-polymer bonds. 

Abstract Recent advances in the metal-catalyzed one-electron reduction reactions are described in this chapter. One-electron reduction induced by redox of early transition metals including titanium, vanadium, and lanthanide metals provides a variety of synthetic methods for carbon-carbon bond formation via radical species, as observed in the pinacol coupling, dehalogenation, and related radical-like reactions. The reversible catalytic cycle is achieved by a multi-component catalytic system in combination with a co-reductant and additives, which serve for the recycling, activation, and liberation of the real catalyst and the facilitation of the reaction steps. In the catalytic reductive transformations, the high stereoselectivity is attained by the design of the multi-component catalytic system. This article focuses mostly on the pinacol coupling reaction. 

The above-mentioned multi-component catalytic systems are of synthetic potential in radical reactions. The generated ketyl radicals are able to undergo the inter- and intra-molecular coupling with a variety of radical acceptors. 

The application of ionic liquids as a reaction medium for the copper-catalyzed aerobic oxidation of primary alcohols was reported recently by various groups, in attempts to recycle the relatively expensive oxidant TEMPO [150,151]. A TEMPO/CuCl-based system was employed using [bmim]PF6 (bmim = l-butyl-3-methylimodazolium) as the ionic liquid. At 65 °C a variety of allylic, benzylic, aliphatic primary and secondary alcohols were converted to the respective aldehydes or ketones, with good selectiv-ities [150]. A three-component catalytic system comprised of Cu(C104)2, dimethylaminopyridine (DMAP) and acetamido-TEMPO in the ionic liquid [bmpy]Pp6 (bmpy = l-butyl-4-methylpyridinium) was also applied for the oxidation of benzylic and allylic alcohols as well as selected primary alcohols. Possible recycling of the catalyst system for up to five runs was demonstrated, albeit with significant loss of activity and yields. No reactivity was observed with 1-phenylethanol and cyclohexanol [151]. 

Shibasaki et al. described the first direct three-component catalytic enantioselec-tive Mannich reaction [3], wherein propiophenone 1, paraformaldehyde 2 and pyrrolidine 3 were reacted using (R)-LaLi tris(binaphthoxide) [(R)-LLB, 4] as catalyst to form Mannich product 5 with 64% ee and in 16% yield (Scheme 9.2). 

Scheme 2.49 Enders three-component catalytic asymmetric domino reaction.

Sintering of the Active Components. Catalytic scientists go to great lengths to disperse the active catalytic species over the surface of a carrier to maximize the number of sites available to the reactants. Small particles or crystallites have a high surface-to-volume ratio that is a highly unstable thermodynamic... 

Overall, evaluation of catalysts on resid feedstocks requires sophisticated and well integrated catalyst deactivation, catalyst stripping and cracking systems. It is important to determine not only the coke yield, but each of its components (Catalytic coke, contaminant coke, CCR coke and stripper (soft) coke). This paper provides details on how each of the components of the coke yield may be experimentally determined using catalyst metallation by cyclic deactivation, catalyst strippability measurements and modified catalytic cracking techniques. 

Interesting properties may also be obtained when using a mixed addenda system in the presence of a co-catalyst The best known system [34d] is the V-substituted phosphomolybdate in conjunction with Pd for the oxidation of olefins to carbonyl compounds. This is analogous to the Wacker oxidation process based on CUCI2 and Pd. Unlike the Wacker process, the HPA system works at very low chloride concentration, or even in its absence. In addition the HPA is more active and selective and less corrosive. Other examples of such two-component catalytic systems include TF /TP, PT /Pt ", Ru"7Ru ", Br 7Br" and l /h-... 

The two-component catalytic systems used for olefin polymerization (Ziegler-Natta catalysts) are combinations of a compound of a IV-VIII group transition metal (catalyst) and an organometallic compound of a I-III group non-transition element (cocatalyst) An active center (AC) of polymerization in these systems is a compound (at the surface in the case of solid catalysts) which contains a transition metal-alkyl bond into which monomer insertion occurs during the propagation reaction. In the case of two-component catalysts an AC is formed by alkylation of a transition metal compound with the cocatalyst, for example ... 

Studying the influence of operating conditions on the MWD of polypropylene obtained with three-component catalytic systems. Combs et al. observed that it narrows at high monomer concentrations or at low conversions, especially for low monomer concentrations. 

Fiq. 2. Model of a two-component catalytic solid, consisting of separate particles of catalyst compounds X and Y. 

Key Words Styrene, Active site, Ultrafine titania particles, Process improvement, SMPO, Trace components, Catalytic dehydration, Computational flow dynamics, Quantum mechanical calculations, Oxygen starvation. Sharpless mechanism, Titanium peroxide, Oxygen transfer, Proton parking place. Leaching, Peroxolysis, Reactive distillation. 2008 Elsevier B.v. 

Another three-component catalytic system including CuCl, TEMPO, and a base was developed for the oxidation of alcohols with molecular oxygen in the ionic liquid [bmim][PFJ by Lin et al. (Scheme 14.31) [29]. 

Preparation of a titanium-aluminium (Ti-Al) catalytic system without modifying diene additives (piperylene) results in the formation of relatively large catalyst particles (with an average radius of about 3-4 micrometres). The turbulent mode hydrodynamic impact on a two-component Ti-Al catalytic system does not influence the size of catalyst particles (and therefore its specific surface) compared with traditional process technology (Figure 3.12, curves 1 and 2). Preparation of Ti-Al with piperylene additives (three-component catalytic system) results in a decrease of the catalyst particles size to r 1.5 micrometres... 

In 2011, WulfTdescribed the first three-component catalytic asymmetric aziridi-nation reaction of an aldehyde 92, bis(dimethylanisyl)methylamine (163), and ethyl diazoacetate (164) to provide the corresponding chiral aziridine-2-carboxylic esters (165) [55]. When promoted by a chiral boroxinate catalyst in situ generated from B(OPh)3 and chiral Hgand (S)-VAPOL (2,2 -diphenyl-(4-biphenanthrol)), the reaction afforded products 165 with good yields and excellent diastereoselectivities and enantioselectivities (Scheme 11.36). This novel methodology furnished an effective solution to the problem of unstable imines derived from aliphatic aldehydes that cannot be purified. 

Scheme 11.36 First three-component catalytic, asymmetric, aziridination reaction [55],...

A multi-component catalytic asymmetric aziridination of aldehydes employs a protected amine and ethyl diazoacetate as reactants and an (5)-VAPOL boroxinate catalyst, giving aziridine-2-carboxylic esters in up to 99% ee. It works for some cases where preformed imines failed. ... 

All polymers discussed in this section have unimodal molecular weight distribution, which implied single-component catalytic systems. Also in most cases the polymer chain molecular weights were lower than estimation, which showed the presence of exchange and/or backbiting processes. This could be the reason of macrocycle detection in some cases. 

A second chapter describes the successful photopolymerization of mono- and disubstituted acetylenes with a one component catalytic system. Simple dialkyl-tungsten complexes, exposed to UV- or visible light, form metal-carbenes in situ by a Ha-abstraction. Some substituted poly(acetylenes) show the highest oxygen permeability known for polymers. 

The successful PROMP of cycloolefins, like 2-norbornene and dicyclopentadiene, with simple dialkyl-tungsten complexes by irradiation with UV- or visible light leads to the in situ formation of metal-carbenes by a Ha-abstraction reaction [20]. Metal carbenes have proven to be the active ROMP-initiators [21] and are supposed to be intermediates in the polymerization of substituted acetylenes as well [22]. Nevertheless, to the best of our knowledge, a one component catalytic system for the photopolymerization of mono- and disubstituted acetylenes has not yet been reported before our work [23]. 

The formal similarity between the COER and the olefin metathesis (OM) is in the replacement of one of the carbon atoms in the scheme of the OM with an oxygen atom, Scheme 3. Another similarity is that WCle is a representative of the mono-component catalytic systems for OM reactions. 

S. Lin, L. Deiana, G. Zhao, A. Cordova, J. Sun, Angew. Chem. Int. Ed 2011, 50, 7624-7630. Dynamic one-pot three-component catalytic asymmetric transformation hy comhination of hydrogen-bond-donating and amine catalysts. 

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