Titanium-Based Catalyst Developments

Titanium-Based Catalyst Developments 2.2.1 Historical Developments... 

Dimerization of ethylene to butene-1 has been developed recently by using a selective titanium-based catalyst. Butene-1 is finding new markets as a comonomer with ethylene in the manufacture of linear low-density polyethylene (LLDPE). 

Union Carbide (95, 96) developed chromium catalysts that need activation by aluminum alkyls, but which have the advantage that molecular weight can be controlled with hydrogen, as in the case of the titanium-based catalysts. To prepare the catalysts, organosilanols are combined with chromium trioxide to afford silylchromate. The silylchromate is then deposited on a silica support and activated with an aluminum alkyl (see Fig. 13). 

Since the discovery of Ziegler-Natta catalysts, polyolefin industries have been developed mainly by using titanium-based catalysts. However, after the appearance of metallocene catalysts, much emphasis has been placed on those based on zirconium owing to the superiority of their performance over titano-cene catalysts. 

The large-scale production of esomeprazole is now successfully achieved by asymmetric oxidation of the same sulfide intermediate as is used in the production of omeprazole (Scheme 2.5). Using the titanium-based catalyst originally developed by K. Barry Sharpless for allyl alcohol oxidation [56] and by H.B. Kagan for certain sulfide oxidations [57], a process was developed that could achieve initial enantiomeric excesses of about 94% [53]. During the production process, the optical purity is further enhanced by the preparation of esomeprazole magnesium salt, with subsequent re-crystallization. 

A specially developed titanium-based catalyst has been used in the suspension process for EPM and EPDM where the termonomer is low-boiling. The advantages claimed, in addition to those characteristic of the suspension process, are better structural control and high catalyst efficiency, resulting in a high-purity product without requiring catalyst removal.51... 

Variants of this ethyiece oligomerization techniqi have been developed by Esso and Mitsui PetrochemicaL which use titanium base catalysts, and Shell, which uses a complex of nickel with phosphin ... 

As the fundamentals of coordination complex structure and reactivity were realized, new and exciting applications were discovered. In 1955, Ziegler and Natta and their coworkers developed a titanium-based catalyst, Figure 1.9, which catalyzes the polymerization of alkenes at atmospheric pressure and ambient temperature. The open coordination site allows an alkene ligand such as ethylene or propylene to bind to the Ti center, initiating the polymerization. Their work sparked tremendous interest in the field and garnered them the Nobel Prize in 1963. 

PIT), and so on. Recently, the developments of titanium-based catalysts make a marvelous progress (Liu et al., 2006), such as titanium dioxide based catalyst (C-94) mainly focusing on designing to be stable and having good activity and color. 

Chapters 2, 3 and 4 discuss each of the three catalyst types used today to manufacture polyethylene, with Chapter 2 devoted to titanium-based catalysts Chapter 3 to chromium-based catalysts and Chapter 4 to singlesite catalysts. These chapters would primarily appeal to scientists that are involved in developing ethylene polymerization catalysts. 

Mantegazza MA, Leofanti G, Petrini G, Padovan M, Zeccina A, Bordiga S (1994) Selective oxidation of ammonia to hydroxylamine with hydrogen peroxide on titanium based catalysts. In Cotberan VC, Bellon SV (eds) New developments in selective oxidation 11. Elsevier, New York, pp 541-550... 

Although the titanium-based methods are typically stoichiometric, catalytic turnover was achieved in one isolated example with trialkoxysilane reducing agents with titanocene catalysts (Scheme 28) [74], This example (as part of a broader study of enal cyclizations [74,75]) was indeed the first process to demonstrate catalysis in a silane-based aldehyde/alkyne reductive coupling and provided important guidance in the development of the nickel-catalyzed processes that are generally more tolerant of functionality and broader in scope. 

MPC [Mitsui Petrochemical] A continuous process for polymerizing propylene, based on the Ziegler-Natta process, but using a much more active catalyst so that de-ashing (catalyst removal) is not required. The catalyst contains magnesium in addition to titanium successive versions of it have been known as HY-HS (high yield, high stereospecifity), HY-HS II, and T-catalyst. Developed jointly by Mitsui Petrochemical Industries, Japan, and Montedison SpA, Italy, in 1975, and now licensed in 56 plants worldwide. 

Mikami et al X developed a palladium-based catalyst system 22, capable of forming quaternary centers via a carbonyl-ene reaction. This is one of the few recent examples of a carbonyl-ene reaction that uses a ketone rather than an aldehyde and affords 84% yields in the case of the five-membered ring (23, n = 1) to near quantitative yields for the six-membered ring (23, n = 2), with 96% ee or better in both cases (Equation (12)). This catalyst system also shows selectivity when other ene partners are used, giving synl anti ratios equal to or better than the titanium systems and affords linear products with complete ( )-selectivity. 

Ultra-High-Molecular-Weight PE is difficult to synthesize (since chain transfer must be almost entirely suppressed) and thus for these extremely strong materials other catalysts are needed. Figure 10.22 shows the Dow catalyst based on titanium(IY) and a competing catalyst developed by DSM based on titanium(III). 

Because of the importance of olefin metathesis in the industrial production of olefins and polymers, many different catalysts have been developed. Almost all of these are transition metal-derived, some rare exceptions being EtAlCl2 [758], Me4Sn/Al203 [759], and irradiated silica [760]. The majority of catalytic systems are based on tungsten, molybdenum, and rhenium, but titanium-, tantalum-, ruthenium-, osmium-, and iridium-based catalysts have also proven useful for many applications. 

Dialkylzincs are much less reactive than phenyl or alkynylzincs. In 2002, Kozlowski et al. developed a chiral salen-based catalyst 62 that can promote the diethylzinc addition to a-ketoesters in high yield, [Eq. (13.38)]. In their catalysis, titanium acts as a Lewis acid, and amine nitrogen acts as a Lewis base (63). The enantioselectivity was up to 78% ee ... 

Practical and efficient asymmetric allylation of aldehydes is successfully promoted by Lewis acid catalysts bearing chiral auxiliaries to afford high levels of enantioselectivity.165 The effective catalysts for asymmetric allylation to benzaldehyde are shown below (Scheme j) 166-176 The catalytic asymmetric allylation of ketones has proved to be a more challenging transformation owing to the significantly low reactivity compared to aldehydes. In 2002, a catalyst based on titanium complex was developed (Equation (51)).A ... 

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