Procatalysts activation

Aluminum chloride dissolves readily in chlorinated solvents such as chloroform, methylene chloride, and carbon tetrachloride. In polar aprotic solvents, such as acetonitrile, ethyl ether, anisole, nitromethane, and nitrobenzene, it dissolves forming a complex with the solvent. The catalytic activity of aluminum chloride is moderated by these complexes. Anhydrous aluminum chloride reacts vigorously with most protic solvents, such as water and alcohols. The ability to catalyze alkylation reactions is lost by complexing aluminum chloride with these protic solvents. However, small amounts of these "procatalysts" can promote the formation of catalyticaHy active aluminum chloride complexes. 

Semicrystalline poly(ethylene-co-propylene) was prepared by the authors (1) using a Zr/Si procatalyst, (I), supported on an organic porous substrate having pore sizes of 0.1 and 2 xm. The catalyst was prepared after activating... 

A remarkable complex (33) with a C2-symmetric semicorrin ligand has been recently developed by Pfaltz and coworkers.64 A copper(II) complex was used as a procatalyst, but (33) was shown to be the active cyclopropanation catalyst. As shown in Table 3, this complex resulted in spectacular enantioselecti-vities in the range of 92-97% ee. Once again, the (15,35,4/ )-menthyl group attenuated the selectivity. Unfortunately, even though respectable yields were obtained with dienes and styrenes, the reaction with 1-heptene was rather inefficient. 

Ziegler-Natta catalysts are defined as the products formed in reactions of transition metal compounds of groups 4 to 8 (procatalysts, catalyst precursors) with organometallic compounds or metal hydrides of groups 1 to 4 (activators). These reactions are carried out in an inert medium and under inert (anaerobic) conditions ... 

Nevertheless, many vanadium-based catalysts and polymerisation systems comprising them have received much academic attention in the hope that they might provide models for heterogeneous catalysts and polymerisation systems, since the problems connected with surface properties and particle size were believed to have been overcome. It must be noted, however, that homogeneous vanadium-based catalysts appeared to be more complex than was thought. There is no decisive evidence on the structure of catalytic sites formed by reaction between the procatalyst and activator. 

In connection with the above characteristic features of metallocene methy-laluminoxane catalysts, it must be emphasised that alternative, potentially cheaper alkylaluminoxanes, such as ethyl or z-butyl derivatives, which are more soluble in aliphatic hydrocarbons than methylaluminoxane, or other alkylaluminium compounds used as activators for metallocene procatalysts, show inferior activity. 

During the last decade, a variety of new catalysts have been presented for the stereospecific polymerisation of a-olefins, based on non-bridged metallocene or stereorigid ansa-metallocene as the procatalyst and a methylaluminoxane activator [29,30,37,105-107,112-114,116-135], Apart from isotactic [118,119,124, 131,132] and syndiotactic [23,118,124,133] polypropylenes and other poly(a-olefin)s [121], hemiisotactic [112,121,124], isoblock [131,132,134], syndioiso-block (stereocopolymer) [127], stereoblock isotactic [135] and stereoblock isotactic atactic [116,128,129] polypropylenes have been obtained using these new catalysts. 

The symmetry of the metallocene and also the kind of procatalyst metal atom, the nature of the catalyst activator and the polymerisation temperature determine the polypropylene tacticity. The general stereoregulation behaviour of metallocene catalysts may be explained in terms of the local chirality, or chirotopicity, of the catalytic sites bonded to the same metal atom. For this analysis, the structure of metallocenes as catalysts should be considered. 

For the majority of olefin polymerisations with heterogeneous Ziegler Natta catalysts, the polymerisation rates, Rv, are proportional to the concentrations of procatalyst (MtX ) and monomer (M), but do not depend on the concentration of alkylaluminium activator (A) as long as a threshold concentration is maintained [37] ... 

This means that there is practically no dependence of the olefin polymerisation rate on the activator/procatalyst molar ratio over a wide range. In some... 

The rate is independent of the concentration of the activator, AlEt2Cl, (Rp [A]0) as long as a low concentration of the cobalt procatalyst and a fixed concentration of H20 are maintained. 

The Ziegler-Natta catalyst 2,6-diacetylpyridinebisiron(II) chlorotrimethylalu-minium, (I), and procatalyst 2,4- [N-(2,6-dimethylphenyl)]phenylimidoyl 6-methyl pyrimidine iron dichloride, (11), were prepared by Kimberley [1] and Gibson [2], respectively, and used as high-activity 1-olefin polymerization catalysts. 

Recent advances of the preparation of novel optically active organoselenimn compounds, mainly organic diselenides, and their application as chiral ligands to some transition metal-catalyzed reactions and also as procatalysts for asymmetric diethylzinc addition to aldehydes are reviewed. Recent results of catalytic reactions using some organoselenimn compounds such as aUylic oxidation of alkenes and its asymmetric version as well as epoxidation of alkenes are also summarized. 

Usually, a catalyst has to be synthesized or conditioned prior to its use in a catalytic reaction. However, there is an alternative to such an isolated or preformed catalyst, the so-called in-situ catalyst. The in-situ catalyst is prepared by mixing the transition metal compound (the procatalyst) and the ligand (the cocatalyst) in the solvent in which the reaction is to be carried out [79]. The use of in-situ catalysts is most appropriate in enantioselective hydrogenation reactions with Wilkinson-type catalysts. The optically active phosphines needed for optical induction have to be synthesized in multi-step syntheses [80, 81]. It is most convenient to combine them directly with the Rh-containing procatalysts. 

The procatalyst [Rh(cod)Cl]2 is an orange, air-stable solid which is commercially available, accessible in one step from RhCls and 1,5-cyclooctadiene [82], The cocatalyst DIOP (Figure 3), the most frequently used optically active phosphine, is also commercially available. A survey of the literature shows that more than half of the numerous studies on the hydrogenation of (Z)-a-acetamido-cinnamic acid have been carried out with in-situ catalysts [79, 81]. 

In the Telene process the procatalyst is a tetrakis(tridodecylammonium)-octamolybdate, activated with a mixture of Et2AlCl, propanol and SiCU. Up to 10% trimer of cyclopentadiene is added to the monomer to increase crosslinking in the polymer, while the trimer also lowers the melting point of DCPD. The of the product is typically 150 °C. BFGoodrich has licenced their process to the Japanese company Nip n Zeon Co., which produces it under the trade name Pentem. In the USA Helene RIM polymers are presently produced by APT, LLC, a joint venture of BFGoodrich and Advanced Polymer Technologies, LLC, recently renamed Cymetech, LLC. 

Both 7 and 9 are procatalysts. The active catalyst, which is likely to be a copper(I) monochelate, is generated by heating in the presence of the diazocarbonyl compound at ca. 60-80 °C for a few minutes, by reduction with phenylhydrazine (9 ) or an alkylhydrazine (7 ), or by treatment with ca. 0.25-0.5 equivalents of diisobutylaluminum hydride. ... 

A polymeric support material is prepared by reacting a,ft>-amines with 1,5-dichlorohexamethyltrisilox-ane. This is deprotonated and allowed to react with CpZrCls to afford a procatalyst which, when contacted with 1000—1500 equivalents of MAO, polymerizes ethylene with activities as high as 1100 kg/g Zr h (Scheme 23). ... 

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