Transition metal compounds as catalysts

Tetralin, hydrogenation of, 12 Titanium compounds as catalysts, 188 Titanium dichloride, 192, 193 number of propagation centers, 198-200 Titanium trichloride, 193, 194 Toluene in exhaust gases, 67 Transalkylation, 141, 142 Transalkylidenation, 142 Transition metal compounds as catalysts, 174... 

Catalyst Effect. The effectiveness of various transition metal compounds as catalysts for the epoxidation reaction was studied (Tables I and II). A mixture of catalyst, cumene hydroperoxide, and 2-methyl-2-pentene in methanol reacted at 110°C. in a series of sealed tubes. In the... 

This reaction has been extensively modified by the use of different transition metal compounds as catalysts, as described in section A. 

In recent years, the liquid phase oxidation of organic substrates using transition metal compounds as catalysts has become a profitable means of obtaining industrially important chemicals. Millions of tons of valuable petrochemicals are produced in this manner annually [1]. Typical examples of such processes are the production of vinyl acetate or acetaldehyde via the Wacker process, equations (1) and (2) the Mid-Century process for the oxidation of methyl aromatics, such as p-xylene to tereph-thalic acid, equation (3) and the production of propylene oxide from propylene using alkyl hydroperoxides, equation (4). 

Inoue, N. Jinno, M. Shiomura, T. Preparation of transition metal compounds as catalysts for polymerization of a-olefins. Jpn. Kokai Tokkyo Koho. JP 04275293A2 (Mitsui Toatsu Chemicals, Inc.), September 30, 1992. 

Transition Metal Compounds as Catalysts with Metal-containing Compounds as Cocatalysts... 

The term hydrosilation can be used to describe an addition reaction in which compounds with one or more Si—H bonds add to any reagent. This review will describe marvelously numerous ways in which soluble complexes of transition metals act as catalysts for the hydrosilation of organic compounds, especially substituted and unsubstituted unsaturated hydrocarbons. 

An important focus of organometallic research has been the development and study of transition metal complexes as catalysts for transformations of organic compounds. These systems enable chemical reactions to occur under conditions that are often milder and more environmentally benign than more traditional routes, such as Lewis acid-catalyzed reactions, Grignard... 

The presence of transition metal compounds as oxidation catalysts can cause rapid degradation of calcium carbonate-alkalized papers under humid conditions. Magnesium carbonate offers better protection than calcium carbonate. 

In most experiments the catalyst was prepared by a two-step mixing procedure. In a first step a reduced transition metal compound was produced a 0.1 M solution of an alkylaluminum compound reacted with a similar solution of a transition metal compound at a predetermined Al/ transition metal molar ratio for 2 hours at 80° C. in isooctane or for 1 hour at 170° C. in n-decane. To avoid local overreduction of the transition metal compound as much as possible, the solution of the alkylaluminum compound was added to the solution of the transition metal compound thus ensuring the presence of an excess of the latter during the mixing stage. 

Numerous chemical, electrochemical, and photochemical processes have been used to reduce C02, the most abundant C, feedstock on Earth, to CO or to organic compounds using transition metal complexes as catalysts, but no large-scale production method has been developed yet. 

Platinum compounds and complexes are the most important and commonly used catalysts for hydrosilylation processes [7 - 9]. Platinum catalysts tolerate a variety of functional groups, but some impurities may interact with them leading to catalyst poisoning [10]. This has stimulated much research aimed at employing other transition metal compounds as potential catalysts. For example, Rh(I) complexes are selective and active hydrosilylation catalysts [11] and more resistant to poisoning than the platinum ones [12]. 

Structures of Organolithium Compounds, 3, 365 Supported Transition Metal Complexes as Catalysts, 15, 189 Transition Metal-Carborane Complexes, 8, 87 Transition Metal-lsocyanide Complexes, 11, 21... 

Triisobutylaluminum is used as a reducing agent. It is also used in combination with transition metal compounds as a Ziegler-Natta catalyst in polymerization and hydrogenation reactions. A dilute solution of the compound is employed in commercial applications. 

Transesterification of methyl methacrylate with the appropriate alcohol is often the preferred method of preparing higher alkyl and functional methacrylates. The reaction is driven to completion by the use of excess methyl methacrylate and by removal of the methyl methacrylate—methanol a2eotrope. A variety of catalysts have been used, including acids and bases and transition-metal compounds such as dialkjitin oxides (57), titanium(IV) alkoxides (58), and zirconium acetoacetate (59). The use of the transition-metal catalysts allows reaction under nearly neutral conditions and is therefore more tolerant of sensitive functionality in the ester alcohol moiety. In addition, transition-metal catalysts often exhibit higher selectivities than acidic catalysts, particularly with respect to by-product ether formation. 

HDPE resias are produced ia industry with several classes of catalysts, ie, catalysts based on chromium oxides (Phillips), catalysts utilising organochromium compounds, catalysts based on titanium or vanadium compounds (Ziegler), and metallocene catalysts (33—35). A large number of additional catalysts have been developed by utilising transition metals such as scandium, cobalt, nickel, niobium, molybdenum, tungsten, palladium, rhodium, mthenium, lanthanides, and actinides (33—35) none of these, however, are commercially significant. 

This chemical bond between the metal and the hydroxyl group of ahyl alcohol has an important effect on stereoselectivity. Asymmetric epoxidation is weU-known. The most stereoselective catalyst is Ti(OR) which is one of the early transition metal compounds and has no 0x0 group (28). Epoxidation of isopropylvinylcarbinol [4798-45-2] (1-isopropylaHyl alcohol) using a combined chiral catalyst of Ti(OR)4 and L-(+)-diethyl tartrate and (CH2)3COOH as the oxidant, stops at 50% conversion, and the erythro threo ratio of the product is 97 3. The reason for the reaction stopping at 50% conversion is that only one enantiomer can react and the unreacted enantiomer is recovered in optically pure form (28). 

The oxidation reaction between butadiene and oxygen and water in the presence of CO2 or SO2 produces 1,4-butenediol. The catalysts consist of iron acetylacetonate and LiOH (99). The same reaction was also observed at 90°C with Group (VIII) transition metals such as Pd in the presence of I2 or iodides (100). The butenediol can then be hydrogenated to butanediol [110-63-4]. In the presence of copper compounds and at pH 2, hydrogenation leads to furan (101). 

Section 14.15 Coordination polymerization of ethylene and propene has the biggest economic impact of any organic chemical process. Ziegler-Natta polymerization is canied out using catalysts derived from transition metals such as titanium and zirconium. ir-Bonded and a-bonded organometallic compounds aie intennediates in coordination polymerization. 

At the present time the concept of catalytic (or ionic-coordination ) polymerization has been developed by investigating polymerization processes in the presence of transition metal compounds. The catalytic polymerization may be defined as a process in which the catalyst takes part in the formation of the transition complexes of elementary acts during the propagation reaction. 

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