Metal halogenide

Olefin polymerization by catalysts based on transition metal halogenides is usually designated as coordinated anionic, after Natta (194). It is believed that the active metal-carbon bond in Ziegler-Natta catalysts is polarized following the type M+ - C. The polarization of the active metal-carbon bond should influence the route of its decomposition by some compounds ( polar-type inhibitors), e.g. by alcohols. When studying polymerization by Ziegler-Natta catalysts tritiated alcohols were used in many works to determine the number of metal-polymer bonds. However, as it was noted above (see Section IV), in two-component systems the polarization of the active bond cannot be judged by the results of the treatment of the system by alcohol, as the radioactivity of the polymer thus obtained results mainly from the decomposition of the aluminum-polymer bonds. 

Because of its favorable kinetic and thermodynamic properties, norbomene can be polymerized with simple transition-metal halogenides.99 116 Even RuC13, which is not active in other metathesis reactions, is effective in the ring-opening polymerization of norbomene.117118 Developments in the early 1990s include the use of... 

An abrupt change in properties in a series of compounds, such as in the melting points or boiling points of metal halogenides, has sometimes been considered to indicate an abrupt change in bond type. Thus of the fluorides of the second-row elements,... 

This method hitherto has been the most commonly used for the synthesis of metal alkoxides the reaction is usually carried out in alcohols. That is why at first some considerations concerning interaction of metal halogenides with alcohols should be made. It has been emphasized by Tishchenko [1585] that dissolution of ZnCl2 in alcohols is accompanied by vigorous reaction leading to ZnCl (OR)2 , accompanied by evolution of HC1, and followed by further reaction ... 

This secondary reaction is especially noticeable in the presence of catalysts, metal halogenides, which are ranged by their dearylising effect as... 

Tricresylphosphate can also be obtained by the continuous technique. In this case etherification is carried out in a cascade of consequtive reactors operating at increasing temperatures the maximum temperature can reach 200 °C if the reaction is catalysed with metal halogenides. To reduce the losses of phosphorus chlorooxide with gaseous hydrogen chloride, the process should be carried out at reduced pressure. 

The homocoupling of aryl Grignard reagents triggered by organic halides in the presence of catalytic quantities of cobalt chloride or other transition metal halogenides was studied initially by Kharasch and Fields in 1941 [36]. They... 

For bulk heteroj unction solar cells made from MDMO-PPV/PCBM, measured under metal halogenide lamps, a mismatch factor of M 0.76 has been determined, while for xenon high-pressure lamps, M rs 0.9 is used. 

These are halogenated adds, metallic halogenides or a mixture of both, forming complexes with aromatics, AIO —HCl, BF3—HF, etc. They act according to the following prindple ... 

The chlorides of the transition metals can also be employed to obtain transition metal carbides (equation 4). This reaction proceeds in the gas phase at temperatures above approximately 600 °C. Because transition metal halogenides are rather volatile, this reaction is usually used for chemical vapor deposition of carbide layers on solid substrates or to produce carbide powders with very fine (submicron) grain sizes ( nanopowders ). In the latter case, the nucleation of the... 

The aluminum flakes can be coated with aluminum oxide and/or silicon dioxide in the liquid phase before the CVD process to reduce the reactivity of the metal and to create multilayer color effects. These pigments show strong angle-dependent coloristic effects (color travel) [5.158]. Metal halogenides are difficult to use as gas-phase precursors for metal oxide coating because of the reactivity of the metal flakes and the corrosion of steel in chloride atmospheres. The use of TiCU and water vapor was described about ten years ago. However, no commercial products have, as yet, been introduced. 

PTs and PATs. The dehydrohalogenation of 2-halothiophenes 101 (scheme 23d) with anhydrous metal halogenids developed by Hotta eonstitutes still another way to PATs whieh possess high molecular weight, exhibit high electrical conductivity, and contain very little metallic impurities [142],... 

A completely different kind of interaction can be observed with alkali metals, some metal halogenides and with tungsten hexafluoride In close analogy to the behavior of graphite, multiwaUed nanotubes are able to incorporate atoms or... 

Lotmar and Feitknecht investigated variations in ionic distances of bivalent basic metal halogenides with layered structures of the Cdl2 type. In this context they needed the unit cell dimensions of nickel hydroxide as well as cobalt hydroxide. 

By corresponding considerations, apparent irregularities in the lattice energies of metallic halogenides in the heats of formation and heats of reactions and in the kinetic stability of transition metal complexes can be rationalized. 

This chapter reviews the effect of alkali metal halogenides and zwitterionic form of glycine on the iodine-triiodide equilibrium in aqueous solution and the interaction of I2, and I3 with lithium halogenides (LiCl). It reveals and analyzes the results obtained by experimental studies using UV and IR spectroscopy, as well as the outcomes of theoretical investigations. Computational studies have been carried out using quantum-chemical methods of DFT-B3PW91/midi, explicit inclusion of solvent molecules, as well as by application of COSMO continuum model [30]. 

Although strong Lewis acid metal halogenides are known catalysts for cationic ROP, zinc dichloride can initiate ROP of -CL, according to a coordination-insertion mechanism in which the alkyl-oxygen bond of the monomer is cleaved (Fig. 13) (72). The mechanism was assessed by computational calculations, analysis of the two chain-ends by NMR, and agreement between A/ and the monomer/zinc dichloride molar ratio. Zinc carboxylates are ROP promoters in the presence of alcohols (71,73). Similarly to tin octanoate, zinc alkoxide is formed, which is the real initiator (72,74). Side formation of octanoate ester end groups is kinetically less favorable compared with the tin counterpart (73). 

However, the reaction proceeded only under drastic conditions (pressure 700 upward to 900 atm) in the presence of mineral acids, BFg or metal halogenides. At that time metal carbonyls had been regarded as catalyst poisons. However, Reppe could prove that olefins react with carbon monoxide and water in the presence of metal carbonyls. The reaction products are saturated carboxylic acids. Whereas Ni(CO)4 is the preferred catalyst in the carbonylation of acetylenes, cobalt, rhodium and ruthenium catalysts are equivalent or superior in olefin carbonylation. Also palladium and hydrochloric acid containing catalyst systems are of special activity in hydrocarboxylation [469-471]. Iron has an accelerating effect [472]. Addition of boric acid to Ni or Co catalysts increases the catalyst life and suppresses the formation of insoluble polymer products [473]. 

Stabilization 294 Metal halogenide lamp 180 Metal-halogenide-stabilization... 

Organometallics, metal alkoxides, metal halogenides, salts of organic acids, etc. can be attached to oxide surfaces according to this scheme. Table 7 shows several representative reactions with aluminum compounds that form Si-O-Al bonds useful for introducing Lewis acidity to the surface. 

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