TiCl3 formation

The formation of surface defects of a crystal lattice. It was observed while using crystal compounds of transition metals as catalysts [e.g. as was shown by Arlman (171, 173), for a TiCl3 surface defects appear on the lateral faces of the crystal]. In this case low surface concentration of the propagation centers should be expected, as is illustrated in the case of polymerization by titanium dichloride (158). The observed... 

Pd(0)-catalyzed substitution reaction, a novel, mild reduction of a-nitro ester to an amino acid ester with TiCl3, and an improved procedure for uracil ring formation. 

Another interesting lithium-based system is Li3N/Li2NH [53]. Lithium nitride can be hydrogenated to lithium imide and lithium hydride (5.4 wt% H2). The latter reaction can be used for reversible storage at 250°C. The formation of ammonia can be completely avoided by the addition of 1% TiCl3 to the system, which has the positive additional effect to improve the kinetics [54]. Very fast kinetics has been reported for a partially oxidized lithium nitride [55]. 

Pinacols are also obtained using TiCl3 in conjunction with Zn-Cu as the reductant.165 This reagent is capable of forming normal, medium, and large rings with comparable efficiency. The macrocyclization has proven useful in the formation of a number of natural products.166 (See entry 3 in Scheme 5.11.)... 

Titanium forms three series of salts in which the element is respectively tetra-, tri-, and mono-valent. Thus, titanium and chlorine form titanium tetrachloride, TiCl4, titanium trichloride, TiCl3, and titanium monochloride, TiCl. The two last are unstable and readily pass into the higher chloride. Titanium tetrachloride shows a marked resemblance to tin tetrachloride it unites easily with hydrochloric acid in solution, with formation of the complex acid, ehloro-titanic acid, [TiCl6]tI2, and forms many crystalline products with other chlorides. It also unites with ammonia, forming ammines. 

The compounds of elements of the first three columns of the periodic system are not reduced by hydrogen, and those in the subsequent columns only partly so. At high temperatures TiCl4 is easily reduced to TiCl3, but the reaction proceeds no farther because the charge of the titanum ion is reduced. Further complications can occur in the reaction of a metal with a compound if the two metals can, themselves, combine to give a compound. In such instances the reaction will proceed in quite a different way from that expected from the stability rules. Because of the different heats of formation of halides and chalcides it can happen that a given element, for example Na, can reduce a chloride but not an oxide. 

Reaction of a purple suspension of TiCl3 in THF with two mol equivalent of HMPA (HMPA = hexamethylphosphoramide) under argon resulted in the formation of a turquoise suspension attributed to TiCl3(HMPA)2. This suspension was stable to argon, but exposure to air or dioxygen caused the formation of a crystalline yellow solid, (9). This contains Ti , and a Raman band at 970 cm-1 is assigned to the O—O stretch.73... 

Quinolines have also been prepared on insoluble supports by cyclocondensation reactions and by intramolecular aromatic nucleophilic substitution (Table 15.26). Entry 10 in Table 15.26 is an example of a remarkable palladium-mediated cycloaddition of support-bound 2-iodoanilines to 1,4-dienes. Reduction of the nitro group of polystyrene-bound 2-nitro-l-(3-oxoalkyl)benzenes with SnCl2 (Entry 11, Table 15.26) leads to the formation of quinoline /Y-oxides. These intermediates can be reduced to the quinolines on solid phase by treatment with TiCl3. 4-Quinolones have been prepared by thermolysis of resin-bound 2-(arylamino)methylenemalonic esters [311]. 

On TiCl2 and TiCl3, H- and CH3- also bind to the titanium centre, in spite of the exothermicity of ligand abstraction. The formation ofHCl or CH3CI is weakly exothermic ... 

The halide y-TiCl3, which offers only one coordination site at the active center, promotes the formation of trans-1,4-polymers, whereas /3-TiCl3, which provides more sites, favors the formation of a mixture of homo-cis- and homo-trans-polymers. Questions about the nature of TiCl3 structures may be answered by referring to references (6, 67) and (68) for polymerization on catalyst surfaces, refer especially to (69) and (70). 

Yermakov and Zakharov (13) reported comprehensive work on the difficulties associated with specific quenching techniques which make sure that only the active metal-carbon bond is quenched. There is evidence that surface determinations by the BET method can give incorrect results, but a strong correlation of polymerization rate to crystallite surface (determined by X-ray techniques) was found (see Fig. 12). The authors conclude that the formation of propagation centers in the case of unsupported TiCl3 proceeds with participation of only those surface titanium ions that are situated in special surface regions as outcrops of growth spirals, or on lateral faces (65-69, 85, 86). 

In another recent development Kojima et al. [103] mechanically milled LiH and Al without and with the TiCl3 additive for 24 h in a H2 gas atmosphere at a pressure of 1 MPa at room temperature. They found that a small amount of LiAlH4 could be directly synthesized by the mechanochemical reaction with concomitant formation of Li3AlH6. The latter can be relatively easily formed by mechanochemical synthesis of FiAlH4 and LiH as originally reported by Zaluski et al. [71] and later by Balema et al. [104],... 

The precipitated brown / -TiCl3 undergoes, in certain spots of its surface, an alkylation reaction with the organoaluminium compound present in the reaction system, which results in the formation of active species with a Ti-C bond (or with a Ti-H bond in the case of a metal hydride activator (in these spots, scheme (8) shows the activation of a catalyst precursor such as TiCl3 with AIR3 as the catalyst activator ... 

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