Titanium compounds precursors

MOCVD Reactions. A great deal of interest has been generated by the availability of two metallo-organic titanium compounds, tetrakis-diethylamino titanium (TDEAT) andtetrakis-dimethylamino titanium (TDMAT). These precursors make possible the deposition of TiN at lower temperature.[ " k l These compounds are liquid at room temperature. A flow of helium bubbling through the warm precursor entrains the vapor into the deposition chamber. Deposition temperature is approximately 320°C. The following reactions occur ... 

Among titanium-based precursors, monocyclopentadienyl compounds of the type CpTiCl3 or Cp TiCl3 activated by MAO or B(C6F5)3 showed the best performance, although several substituted mono-Cp or indenyl derivative and Cp-free compounds as Ti(CH2Ph)4 and Ti(OR)4 (R = alkyl, aryl) are quite active as well. In short, practically any soluble titanium compound can be used as precatalyst.154-158... 

Similarly to alkenes, alkynes react with various titanium-methylidene precursors, such as the Tebbe reagent [13,63], titanacydobutanes [9b, 64], and dimethyltitanocene [65] to form the titanium-containing unsaturated cyclic compounds, titanacydobutenes 67 (Scheme 14.29). Alternatively, 2,3-diphenyltitanacydobutene can be prepared by the reaction of the complex titanocene(II) bis(trimethylphosphine) with 1,2-diphenylcyclopropene [66]. Substituent effects in titanacydobutenes [67], the preparation of titanocene-vinylke-tene complexes by carbonylation of titanacydobutenes [68], and titanacyclobutene-vinylcar-bene complex interconversion [69] have been investigated. 

Titanium nitride films have usually been prepared by OMCVD from dialkylamido titanium compounds Ti(NR2)4 and ammonia, which plays a major role in the process as a reducing agent and source of nitrogen.12,13 Other authors have reported the use of azide compounds such as Cp2Ti(N3)2 or [Ti(NMe2)(N3)(p-NMe2)]3(p3-NH), with the former compound,14 contamination of the films by free carbon from the decomposition of the Cp group is mentioned, while with the latter,15 which occurs as a trimeric species, a lack of sufficient volatility rules out its use as a CVD precursor. 

It should be noted in this connection that, for ethylene polymerisation in the presence of a non-supported catalyst such as TiCl4-AlR3 (R = Et, z -Bu), polymerisation proceeds at the maximum rate when the average valence state of titanium is 2 [304], However, while catalysts with divalent titanium compounds as precursors are known to be highly active for the polymerisation of ethylene, their activities for the polymerisation of a-olefins are generally low [51,240],... 

Monocyclopentadienyl titanium derivatives are the most active precursors for catalysts possessing high syndiospecific polymerisation activity for styrene and ring-substituted styrenes. The polymerisation activity of biscyclopentadie-nyl titanium compounds activated with methylaluminoxane is lower than that of other soluble titanium-based catalysts [73]. 

The literature data on kinetics and mechanisms of BaTiOs formation under hydrothermal conditions are contradictory. In general, the precursor of Ba is completely soluble in aqueous solutions, while the Ti precursor usually forms solid gel-like phases with low solubility. Since Ba + is not a gel forming ion, it initially adsorbs on the particles surface and dissolves in the gel of titanium compounds, destroying Ti-O-Ti bonds. This is accompanied by dehydration, followed by crystallization of perovskite phase via heterogeneous nucleation and growth [82, 83, 89-93]. 

The synthesis of polystyrene with a liighly syndiotactic microstructure (Scheme 22.7) was achieved for the first time by Ishihara in 1986 with a catalyst consisting of a titanium precursor and aluminum activator. Roughly 98% of the polymer was insoluble in 2-butanone, and this material had an rrrr-pentad content greater that 98%. Many simple titanium catalysts activated by MAO were later shown to generate syndiotactic polystryrene. Tetrabenzyltitanium, when activated by MAO, catalyzes the polymerization of styrene to form a syndiotactic material with greater than 98% rr triads. Tetrahalo and tetraalkoxo titanium compounds also form syndiotactic polystryene when activated by MAO, but the activity of these catalysts was relatively low. 

An example of the physical impregnation method is provided by U.S. Patent 4,302,565, which was discussed above. The dissolution of a magnesium compound and a titanium compound in a suitable solvent, usually an electron donor solvent such as tetrahydrofuran (THF), can lead to the formation of a new species (catalyst precursor) that provides a highly-active Ziegler system when activated. Removing the solvent at elevated temperatures in the presence of a support material such as silica will precipitate the precursor into the pores of the silica. In this method it is necessary that... 

MAO and boron compounds are expensive chemicals that increase the cost of the SPS production. However, the cocatalyst is an indispensable compound for the titanium complexes used as styrene polymerization catalysts. The roles of the cocatalyst are supposed to reduce the valence of the titanium compounds by forming the precursor of the active site, to activate the precursor, and subsequently to stabilize the active site by weak coordination. TIBA reacts with the transition metal and reduces Tl(IV) to 11(111), and this may be the precursor of the active site. Yabunouchi found that the catalytic activity in the styrene polymerization increased by the addition of a small amount of ((R )3CO)n-Al-(R )3 n to the styrene monomer, even if the amount of MAO is decreased [17]. One of these compounds is [(C6Hs)3CO](i-C4H9)2Al (Fig. 3.8). The catalytic activitiy was increased more than two times by the addition of a small amount of [(C6H5)3CO](i-C4H9)2Al to a mixture consisting of Tl MAO TIBA = 1 50 25 in molar ratio. 

The previously described 7-deazapurine carbocyclic nucleoside synthesis (see Scheme 1) indicated that the most efficient route to 22 would be via reaction of the protected chiral amine 23 with the dimethylacetal of 2-(2-amino-4,6-dichloropyrimidin-S yl)acetaldehyde followed by ring closure, hydrolysis and dqirotection. A review of the literature revealed two enantioselective routes to cyclobutyl derivatives that had been used in the chiral synthesis of carbocyclic oxetanocins and could be employed for preparing a precursor to 23. In one case, however, the initial step involved a [2-i-2]-cycloaddition reaction of not easily obtainable reagents in the presence of a chiral titanium compound as... 

Titanium carbide may also be made by the reaction at high temperature of titanium with carbon titanium tetrachloride with organic compounds such as methane, chloroform, or poly(vinyl chloride) titanium disulfide [12039-13-3] with carbon organotitanates with carbon precursor polymers (31) and titanium tetrachloride with hydrogen and carbon monoxide. Much of this work is directed toward the production of ultrafine (<1 jim) powders. The reaction of titanium tetrachloride with a hydrocarbon-hydrogen mixture at ca 1000°C is used for the chemical vapor deposition (CVD) of thin carbide films used in wear-resistant coatings. 

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