Catalyst preparation compounds

Another group of isoprene polymerization catalysts is based on alanes and TiCl. In place of alkyl aluminum, derivatives of AlH (alanes) are used and react with TiCl to produce an active catalyst for the polymerization of isoprene. These systems are unique because no organometaHic compound is involved in producing the active species from TiCl. The substituted alanes are generally complexed with donor molecules of the Lewis base type, and they are Hquids or soHds that are soluble in aromatic solvents. The performance of catalysts prepared from AlHCl20(C2H )2 with TiCl has been reported (101). 

An unusual method for the preparation of syndiotactic polybutadiene was reported by The Goodyear Tire Rubber Co. (43) a preformed cobalt-type catalyst prepared under anhydrous conditions was found to polymerize 1,3-butadiene in an emulsion-type recipe to give syndiotactic polybutadienes of various melting points (120—190°C). These polymers were characterized by infrared spectroscopy and nuclear magnetic resonance (44—46). Both the Ube Industries catalyst mentioned previously and the Goodyear catalyst were further modified to control the molecular weight and melting point of syndio-polybutadiene by the addition of various modifiers such as alcohols, nitriles, aldehydes, ketones, ethers, and cyano compounds. 

Al Ti in the range of 0.9—1.0 appeared optimum for i7j -l,4-polyisoprene yield (20). Other factors such as catalyst preparation temperature, influence of the R group in the alkyl aluminum compound (R Al), and catalyst aging have been extensively studied (16,17). Another variable studied was the effect of... 

Both of these structures are open-chained compounds corresponding to crown ethers in function if not exactly in structure (see Chap. 7). They have repeating ethyleneoxy side-chains generally terminated in a methyl group. Montanari and co-workers introduced the polypodes 22 as phase transfer catalysts . These compounds were based on the triazine nucleus as illustrated below. The first octopus molecule (23) was prepared by Vogtle and Weber and is shown below. The implication of the name is that the compound is multiarmed and not specifically that it has eight such side-chains. Related molecules have recently been prepared by Hyatt and the name octopus adopted. For further information on this group of compounds and for examples of structures, refer to the discussion and tables in Chap. 7. 

The data obtained up to the present time show that the method of catalyst preparation by the reaction of organometallic compounds with surface reactive groups may be applied to generate both isolated ions of transition metals (in various valent states) or superfine metal particles on the surface of the support. 

The Ullman reaction has long been known as a method for the synthesis of aromatic ethers by the reaction of a phenol with an aromatic halide in the presence of a copper compound as a catalyst. It is a variation on the nucleophilic substitution reaction since a phenolic salt reacts with the halide. Nonactivated aromatic halides can be used in the synthesis of poly(arylene edier)s, dius providing a way of obtaining structures not available by the conventional nucleophilic route. The ease of halogen displacement was found to be the reverse of that observed for activated nucleophilic substitution reaction, that is, I > Br > Cl F. The polymerizations are conducted in benzophenone with a cuprous chloride-pyridine complex as a catalyst. Bromine compounds are the favored reactants.53,124 127 Poly(arylene ether)s have been prepared by Ullman coupling of bisphenols and... 

The hydration of triple bonds is generally carried out with mercuric ion salts (often the sulfate or acetate) as catalysts. Mercuric oxide in the presence of an acid is also a common reagent. Since the addition follows Markovnikov s rule, only acetylene gives an aldehyde. All other triple-bond compounds give ketones (for a method of reversing the orientation for terminal alkynes, see 15-16). With allqmes of the form RC=CH methyl ketones are formed almost exclusively, but with RC=CR both possible products are usually obtained. The reaction can be conveniently carried out with a catalyst prepared by impregnating mercuric oxide onto Nafion-H (a superacidic perfluorinated resinsulfonic acid). ... 

Combined analyses by XRD and TEM showed that the aurichalcite mineral was sufficiently similar to the synthetic aurichalcite to be used as a model compound, to study the microstructural changes occurring during the catalyst preparation procedures. Calcination of the mineral and synthetic samples led to highly preferred orientations of ZnO. ZnO electron diffraction patterns with [lOlO] and [3031] zone... 

In order to confirm the hypothesis made on the role of catalyst components, we carried out the reaction with a ratile-type V/Sb/0 catalyst, having V/Sb atomic ratio equal to 1/1 (Table 40.1). This catalyst was prepared with the conventional sluny method, and therefore had a surface area of 10 mVg, lower than that obtained with the Sn/V/Nb/Sb/0 catalysts prepared with the co-precipitation method. However, despite this difference, with V/Sb/0 the conversion of n-hexane was similar to that one obtained with Sn/V/Nb/Sb/0. This is shown in Figure 40.7, which reports the conversion of n-hexane, the selectivity to CO2, to / -containing compounds and the carbon balance as a function of the reaction temperature. 

Prochiral aryl and dialkyl ketones are enantioselectively reduced to the corresponding alcohols using whole-cell bioconversions, or an Ir1 amino sulfide catalyst prepared in situ.695 Comparative studies show that the biocatalytic approach is the more suitable for enantioselective reduction of chloro-substituted ketones, whereas reduction of a,/ -unsaturated compounds is better achieved using the Ir1 catalyst. An important step in the total synthesis of brevetoxin B involves hydrogenation of an ester using [Ir(cod)(py) P(cy)3 ]PF6.696... 

Various carbon-based catalysts were tested in the investigated air gas-diffusion electrodes pure active carbon [6], active carbon promoted with silver [7] or with both silver and nickel. Catalysts prepared by pyrolysis of active carbon impregnated with a solution of the compound Co-tetramethoxyphenylporphyrine (CoTMPP) are also studied [8],... 

One way in which cobalt dispersion can be increased is the addition of an organic compound to the cobalt nitrate prior to calcination. Previous work in this area is summarized in Table 1.1. The data are complex, but there are a number of factors that affect the nature of the catalyst prepared. One of these is the cobalt loading. Preparation of catalysts containing low levels of cobalt tends to lead to high concentrations of cobalt-support compounds. For example, Mochizuki et al. [37] used x-ray photoelectron spectroscopy (XPS) and temperature-programmed reduction (TPR) to identify cobalt silicate-like species in their 5% Co/Si02 catalysts modified with nitrilotriacetic acid (NTA). The nature of the support also has... 

There can be little doubt that the active species involved in most or even all of the various combinations described in Section II is HNi(L)Y (see below), because the different catalysts prepared by activating the nickel with Lewis acids have been shown to produce, under comparable conditions, dimers and codimers which have not only identical structures but identical compositions. On modification of these catalysts by phosphines, the composition of dimers and codimers changes in a characteristic manner independent of both the method of preparation and the nickel compound (2, 4, 7, 16, 17, 26, 29, 42, 47, 76). Similar catalysts are formed when organometallic or zero-valent nickel complexes are activated with strong Lewis acids other than aluminum halides or alkylaluminum halides, e.g., BFS. 

Evidence has been collected over the years which strongly indicates that the active species in the oligomerization reactions are nickel-hydride and nickel-alkyl complexes. [This is not necessarily true for catalysts prepared from nickel(II) compounds and organoaluminum compounds having low Lewis acidity, e.g., (C2H5)2A10C2H5 (44).] The majority of the evidence is circumstantial and is discussed below. 

Cyclic imines 8 and 9 are intermediates or models of biologically active compounds and can be reduced with ee-values of 88 to 96% using Ti-ebthi, Ir-bcpm or Ir-binap in the presence of additives (entries 5.7, 5.9), as well as with the transfer hydrogenation catalyst Ru-dpenTs (entries 5.8, 5.10-5.12). As pointed out earlier, Ru-diphosphine-diamine complexes are also effective for imines, and the best results for 7 and 8a were 88% and 79% ee, respectively [36]. Azirines 10 are unusual substrates which could be transfer-hydrogenated with a catalyst prepared in situ from [RuCl2(p-cymene)]2 and amino alcohol L12, with ee-values of 44 to 78% and respectable TOFs of up to 3000 (entry 5.13). 

From the results obtained in this study [205], it was concluded that the catalyst prepared by extrusion of a paste containing the TiOz precursor together with natural silicates, is more active in the photocatalytic mineralization of organic compounds than the coated film. 

Recently Togni et al. [19] focussed on the preparation of asymmetric dendrimer catalysts derived from ferrocenyl diphosphine ligands anchored to dendritic backbones constructed from benzene-1,3,5-tricarboxylic acid trichloride and adamantane-l,3,5,7-tetracarboxylic acid tetrachloride (e.g. 11, Scheme 11). In situ catalyst preparation by treatment of the dendritic ligands with [Rh(COD)2]BF4 afforded the cationic Rh-dendrimer, which was then used as a homogeneous catalyst in the hydrogenation reaction of, for example, dimethyl itaconate in MeOH. In all cases the measured enantioselectivity (98.0-98.7%) was nearly the same as observed for the ferrocenyl diphosphine (Josiphos) model compound (see Scheme 11). 

For practical hydrogenation of olefins four classes of metal complexes are preferred (a) Rh complexes, the RhCl(PPh3)3, the so-called Wilkinson catalyst and the [Rh(diene)-(PR3)2]+ complexes, (b) a mixture of Pt and Sn chlorides, (c) anionic cyanocobalt complexes and (d) Ziegler catalysts, prepared from a transition metal salt and an alkylaluminum compound. 

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