Similarity catalysts

There is one other benzene to allylbenzene method that you should take a look at. Osmium sent in the article in which that magical clay and other similar catalyst add the allyl to aryl in record fashion. To read more check out ref 143. 

Dicyclopentadiene is also polymerized with tungsten-based catalysts. Because the polymerization reaction produces heavily cross-Unked resins, the polymers are manufactured in a reaction injection mol ding (RIM) process, in which all catalyst components and resin modifiers are slurried in two batches of the monomer. The first batch contains the catalyst (a mixture of WCl and WOCl, nonylphenol, acetylacetone, additives, and fillers the second batch contains the co-catalyst (a combination of an alkyl aluminum compound and a Lewis base such as ether), antioxidants, and elastomeric fillers (qv) for better moldabihty (50). Mixing two Uquids in a mold results in a rapid polymerization reaction. Its rate is controlled by the ratio between the co-catalyst and the Lewis base. Depending on the catalyst composition, solidification time of the reaction mixture can vary from two seconds to an hour. Similar catalyst systems are used for polymerization of norbomene and for norbomene copolymerization with ethyhdenenorbomene. 

The addition of allcenes to alkenes can also be accomplished by bases as well as by the use of catalyst systems consisting of nickel complexes and alkylaluminum compounds (known as Ziegler catalysts), rhodium catalysts, and other transition metal catalysts, including iron. These and similar catalysts also catalyze the 1,4 addition of alkenes to conjugated dienes, for example. 

Mukaiyama aldol reactions have been reported, usually using chiral additives although chiral auxiliaries have also been used. This reaction can also be run with the aldehyde or ketone in the form of its acetal R R C(OR )2> in which case the product is the ether R COCHR2CR R OR instead of 27. Enol acetates and enol ethers also give this product when treated with acetals and TiCLi or a similar catalyst. When the catalyst is dibutyltin bis(triflate), Bu2Sn(OTf)2, aldehydes react, but not their acetals, while acetals of ketones react, but not the ketones themselves. 

Studies on similar catalysts have suggested a rate expression of the form... 

Fig. 1(b) represents the selectivity to styrene as a ftmcfion of time fijr the above catal ts. It is observed that the selectivity to styrene is more than 95% over carbon nauofiber supported iron oxide catalyst compared with about 90% for the oxidized carbon nanofiber. It can be observed that there is an increase in selectivity to styrene and a decrease in selectivity to benzene with time on stream until 40 min. In particrdar, when the carbon nanofiber which has been treated in 4M HCl solution for three days is directly us as support to deposit the iron-precursor, the resulting catalyst shows a significantly lows selectivity to styrene, about 70%, in contrast to more than 95% on the similar catalyst using oxidized carbon nanofiber. The doping of the alkali or alkali metal on Fe/CNF did not improve the steady-state selectivity to styrene, but shortened the time to reach the steady-state selectivity. 

The electrons are transported through an outer circuit connected to the cathode, where oxygen is reduced to oxygen ions on a similar catalyst system as for the anode ... 

A similar catalyst to which 3.9% arsenic had been added in the laboratory was tested and its activity (Figure 3) compared to the activity of a fresh catalyst and also to that of the used catalyst. The activity loss of the used catalyst containing 3.6% As corresponds closely with that for the prepared sample, indicating that arsenic added by impregnation acts like that deposited under actual operating conditions. When the used catalysts were regenerated in air at 482°C, the arsenic was not removed. 

In a more comprehensive follow-up work, the selectivity on OAOR-modified silver could be raised to 65%, still without the presence of promoters such as 1,2-dichloroethane [4]. This value is by far better than most values known in the literature for the same catalyst. The best value finally obtained was 69% and approaches the industrial limit of 80% that was obtained with promoters and a different, better catalyst, kglk 20y A similar catalyst type (Aluchrom catalyst) was also tested in the micro reactor, but so far yielding lower results, the best selectivity measured being 58%. 

It was found in the 1960s that disperse platinum catalyst supported by certain oxides will in a number of cases be more active than a similar catalyst supported by carbon black or other carbon carrier. At platinum deposits on a mixed carrier of WO3 and carbon black, hydrogen oxidation is markedly accelerated in acidic solutions (Hobbs and Tseung, 1966). This could be due to a partial spillover of hydrogen from platinum to the oxide and formation of a tungsten bronze, H WOj (0 < a < 1), which according to certain data has fair catalytic properties. 

This and similar catalysts are effective with silyl ketene acetals and silyl thioketene acetals.155 One of the examples is the tridentate pyridine-BOX-type catalyst 18. The reactivity of this catalyst has been explored using a- and (3-oxy substituted aldehydes.154 a-Benzyloxyacetaldehyde was highly enantioselective and the a-trimethylsilyoxy derivative was weakly so (56% e.e.). Nonchelating aldehydes such as benzaldehyde and 3-phenylpropanal gave racemic product. 3-Benzyloxypropanal also gave racemic product, indicating that the (i-oxy aldehydes do not chelate with this catalyst. 

It would be more convenient if 12 or a similar catalyst could be made in situ from precursors which are more air-tolerant than 6 and require fewer steps to make. (Phosphine 11 is air-sensitive but no more so than PPh3, which can be weighed and transferred in open air.) Complex 1 seemed a suitable candidate, for it is air-stable and can be made in one step from ruthenium trichloride, CpH, and PPh3,(21) and ligand substitutions are facile, particularly inprotic solvents. 

The authors conducted a similar investigation of precatalysts 7 and 11 using TiBA and trityl tetrakis(pentafluorophenyl)borate as the cocatalyst. They concluded that this material contained no fraction that could be characterized as blocky. It was therefore proposed that reversible chain transfer occurred only with MAO or TMA and not with TiBA. This stands in contrast to the work of Chien et al. [20] and Przybyla and Fink [22] (vida supra), who claim reversible chain transfer with TiBA in similar catalyst systems. Lieber and Brintzinger also investigated a mixture of isospecific 11 and syndiospecific 12 in attempts to prepare iPP/sPP block copolymers. Extraction of such similar polymers was acknowledged to be difficult and even preparative temperature rising elution fractionation (TREF) [26, 27] was only partially successful. 

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. 

The nickel catalyst under the condition for the 1 1 codimerization is not known to dimerize or polymerize ethylene, although a similar catalyst system has been known to dimerize propylene (26, 27) via a w-allyl intermediate. 

While there are cases where only one of the two methods works, very often both approaches give a similar catalyst performance, and consequently the de-... 

Tetrasubstituted alkenes are among the most challenging substrates for catalytic hydrogenation reactions. Towards this end, Buchwald and co-workers recently reported efficient and highly enantioselective Zr-catalyzed hydrogenations of a range of styrenyl tetrasubstituted alkenes (Scheme 6.41) [123]. Precedents based on efficient polymerization reactions promoted by cationic zirconocenes led these workers to consider similar catalyst species, derived from dimethylzirconocene 107, for this purpose. 

Some of the practicals describe the use of similar catalysts and/or catalysts that accomplish the same task. This has been done purposely to try to get the best match between the substrate described and the one being considered by an interested reader. Moreover when catalysts can be compared, this has been done. Sometimes a guide is given as to what we found to be the most useful system in our hands. In this context, it is important to note that, except for polyleucine-catalysed oxidations and the use of a bicyclic bisphosphinite for asymmetric hydrogenation, the Liverpool group had no previous experience in... 

Similar catalysts, although not designed computationally, have been used successfully for related addition reactions. In an approach to asymmetric... 

At all calcination temperatures except the highest, the dispersion of the SEA-prepared samples is higher than similar catalysts prepared by DI. Notably, the dispersion of the 100°C dried and... 

In this chapter we will discuss some aspects of the carbonylation catalysis with the use of palladium catalysts. We will focus on the formation of polyketones consisting of alternating molecules of alkenes and carbon monoxide on the one hand, and esters that may form under the same conditions with the use of similar catalysts from alkenes, CO, and alcohols, on the other hand. As the potential production of polyketone and methyl propanoate obtained from ethene/CO have received a lot of industrial attention we will concentrate on these two products (for a recent monograph on this chemistry see reference [1]). The elementary reactions involved are the same formation of an initiating species, insertion reactions of CO and ethene, and a termination reaction. Multiple alternating (1 1) insertions will lead to polymers or oligomers whereas a stoichiometry of 1 1 1 for CO, ethene, and alcohol leads to an ester. 

Interestingly, the catalysts used here are similar to the nickel-ligand complexes used by Shell for their commercial ethene oligomerization process. Similar catalysts for making polyketone have also been patented by Keim et al. 

From these studies it is evident that the intermediates obtained during an organic synthesis will likely contain impurities at the percentage level that may make the use of similar catalyst levels necessary, unless still better catalysts that are more resistant to alcohols and water will be developed. 

---