Titanium complexes fluorides

Other Lewis acids, such as boron trifluoride-diethyl ether complex, titanium(IV) fluoride, and triethyloxonium tetrafluoroborate, were far less effective. a, -Unsaturated esters and nitriles cannot be cyclopropanated in this manner. 

Lewis add complexes formed by the reactions of various aminoalcohols with Et2AlG [778, 824] or by the reaction of Et2Zn with a chiral sulfamide [806] have displayed a low efficiency in the asymmetric condensations of ketene and thioketene silyiacetals derived from acetic acid with aldehydes. Disappointing se-lectivities have also been observed with some binaphtol-titanium complexes [778]. However, Mikami and Matsukawa [1296] recently performed the enantioselective condensation of various aldehydes with acetic acid derivatives in the presence of a chiral binaphtol-titanium complex. Good selectivities were observed when the reaction was performed at 0°C in toluene (Figure 6.95). Quaternary ammonium fluorides derived from cinchona alkaloids have been proposed as catalysts to perform additions of enoxysilanes derived from ketones to PhCHO, but the observed selectivities are modest [1303],... 

Titanium, tetrakis(trimethysilyl)oxy-, 334 Titanium complexes alloy hydrides, 353 amino adds, 342 antimony, 345 arsenic, 345 bromides, 357 chlorides, 355, 356 fluorides, 354 Group IV derivatives, 352 halides, 354 electron spectra, 358 hexamethylphosphoramide, 335 iodides, 357... 

Aqueous, chromium-free acidic solutions have also been developed for aluminum materials that may contain complex fluorides of titanium and zirconium, phosphate, and special organic compounds. These solutions are applied by spraying or dipping (up to 60 °C) and produce thin, almost colorless conversion layers with a surface weight < 0.1 g/m. ... 

With the monodentate fluoride ion, it is difficult to have two H2O ligands in trails allowing condensation of opposed coplanar edges. This mode of condensation is possible only with a bidentate ligand ([HSO4]) which leaves only one water molecule in the coordination sphere. As a result, only anatase can form. In both cases, this mechanism may only take place if the complexes are sufficiently stable. Equilibria between various species are probably involved. Under these conditions, it is difficult to know what is the precursor of the solid. Since the oxide always contains some amount of sulfate difficult to remove, it is reasonable to speculate that the complexes are rather stable and that the formation of the solid takes place by incorporation of the sulfated titanium complexes by olation. This is also probably the case with the fluoride. Therefore, the complexing ions of titanium... 

The i5p-titanium(IV) atom is hard, ie, not very polarizable, and can be expected to form its most stable complexes with hard ligands, eg, fluoride, chloride, oxygen, and nitrogen. Soft or relatively polarizable ligands containing second- and third-row elements or multiple bonds should give less stable complexes. The stabihty depends on the coordination number of titanium, on whether the ligand is mono- or polydentate, and on the mechanism of the reaction used to measure stabihty. 

A number of attempts to produce tire refractory metals, such as titanium and zirconium, by molten chloride electrolysis have not met widr success with two exceptions. The electrolysis of caesium salts such as Cs2ZrCl6 and CsTaCle, and of the fluorides Na2ZrF6 and NaTaFg have produced satisfactoty products on the laboratory scale (Flengas and Pint, 1969) but other systems have produced merely metallic dusts aird dendritic deposits. These observations suggest tlrat, as in tire case of metal deposition from aqueous electrolytes, e.g. Ag from Ag(CN)/ instead of from AgNOj, tire formation of stable metal complexes in tire liquid electrolyte is the key to success. 

Sulphuric acid is not recommended, because sulphate ions have a certain tendency to form complexes with iron(III) ions. Silver, copper, nickel, cobalt, titanium, uranium, molybdenum, mercury (>lgL-1), zinc, cadmium, and bismuth interfere. Mercury(I) and tin(II) salts, if present, should be converted into the mercury(II) and tin(IV) salts, otherwise the colour is destroyed. Phosphates, arsenates, fluorides, oxalates, and tartrates interfere, since they form fairly stable complexes with iron(III) ions the influence of phosphates and arsenates is reduced by the presence of a comparatively high concentration of acid. 

A particulate gel breaker for acid fracturing for gels crosslinked with titanium or zirconium compounds is composed of complexing materials such as fluoride, phosphate, sulfate anions, and multicarboxylated compounds. The particles are coated with a water-insoluble resin coating, which reduces the rate of release of the breaker materials of the particles so that the viscosity of the gel is reduced at a retarded rate [205]. 

Among titanium compounds, many sit on the border of being organometallic/coordination compounds. One which is of interest in relation to the enhancing effects of F (see Section 9.5.5.2) is the titanium fluoride complex (52), which is highly active for the hydrosilylation of imines (Scheme 33).143... 

Bilinear chemometrics methods, 6 39-57 Billet products, titanium, 24 858 Bill of Material, 15 460, 470 Bills of lading, 25 330 Bimetal complexes, 16 88 Bimetallic deactivation processes, 16 93-94 Bimetallic fluorides, 15 396 Bimetallic metal nitrides, 17 199 Bimetallic organometallic uranium complexes, 25 442 Bimetallic organometallic thorium complexes, 24 773-774... 

The aldol condensation of benzaldehyde with the thioacetamide carbanion (RCHCSNRV), derived from the desilylation of the silyl-thioether with tetra-/i-buty-lammonium fluoride, is stereoselective at—80°C producing the erythro isomer of the p-hydroxy thioamide preferentially (Scheme 6.18, R = Me, erythro threo 95 5) via a conformationally mobile intermediate. However, when R is bulky, a greater amount of the threo isomer is formed. Predictably, as the reaction temperature is raised, so the stereoselectively decreases. This procedure contrasts with the corresponding condensation catalysed by titanium salts, where the complexed intermediate produces the threo isomer [47, 48],... 

Although in the recent years the stereochemical control of aldol condensations has reached a level of efficiency which allows enantioselective syntheses of very complex compounds containing many asymmetric centres, the situation is still far from what one would consider "ideal". In the first place, the requirement of a substituent at the a-position of the enolate in order to achieve good stereoselection is a limitation which, however, can be overcome by using temporary bulky groups (such as alkylthio ethers, for instance). On the other hand, the ( )-enolates, which are necessary for the preparation of 2,3-anti aldols, are not so easily prepared as the (Z)-enolates and furthermore, they do not show selectivities as good as in the case of the (Z)-enolates. Finally, although elements other than boron -such as zirconium [30] and titanium [31]- have been also used succesfully much work remains to be done in the area of catalysis. In this context, the work of Mukaiyama and Kobayashi [32a,b,c] on asymmetric aldol reactions of silyl enol ethers with aldehydes promoted by tributyltin fluoride and a chiral diamine coordinated to tin(II) triflate... 

Minerals such as euxenite, fergusonite, samarskite, polycrase and loparite are highly refractory and complex in nature. These minerals may be opened up by treatment with hydrofluoric acid. While metals such as niobium, tantalum and titanium form soluble fluorides, rare earth elements form an insoluble residue of their fluorides. Such insoluble fluorides are filtered out of solution and digested with hot concentrated sulfuric acid. The rare earth sulfates formed are dissolved in cold water and thus separated from the insoluble mineral impurities. Rare earth elements in the aqueous solution are then separated by displacement ion exchange techniques outlined above. 

The reactivity of bromine trifluoride is significantly enhanced by Lewis acids, such as tin(IV) chloride, antimony(V) chloride, titanium(IV) chloride, which are exchanged to the corresponding fluorides and give complexes with bromine trifluoride. Thus, the reaction of 2,2,2-tri-fluoroethyl or 2,2,3,3-tetrafluoropropyl 2,3-dibromopropanoate with bromine trifluoride in the presence of 1 mol% tin(IV) chloride affords the corresponding 2,3-difluoropropanoates in 85-87% yield.110... 

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