Titanium complexes cationic compounds

Titanium cesium alum, 6 50 Titanium (II) chloride from disproportionation of titanium (III) chloride, 6 56, 61 Titanium(III) chloride, 6 52, 57 Titanium (IV) chloride, reduction of, with hydrogen, 6 52, 57 Titanium complex compounds, cations, with acetylacetone, [Ti-(C.H. hTiCl, and [Ti(C6H7-0,),]FeCl , 2 119, 120 Titanium(IV) oxide, extraction of, from ilmenite, 5 79, 81 to titanium powder with calcium, 6 47... 

Hydroxycarboxylic acids, which include citric acid, malic acid, lactic acid, etc., are benign to the environment and very convenient for the solution processing. Moreover, since these reagents can form stable complexes with other cations, they rarely yield a precipitate. For several complexes single crystals of well-defined composition suitable for the X-ray structural analysis were isolated. Thus, these water-soluble titanium complexes of hydroxycarboxylic acids are promising precursors for the synthesis of ceramics from an aqueous solution and their industrial utilization is expected in the future. In this chapter we decribe the method of synthesis, structural analysis, and stability of these complexes. The examples of multicomponent oxide materials preparation using these compounds are presented. 

In addition to MAO, boron compounds based on tris(pentafluorophenyl)boron and its derivatives, typically dimethylanilinium tetrakis(pentafluorophenyl) borate, have been used as cocatalysts for sPS polymerizations (40,41). Although MAO has been used in large molar excesses relative to the titanium complex, the boron compounds may be used in roughly equimolar amounts to the titanium catalyst. The boron cocatalyst reacts with a titanium alkyl species, either by protonation in the case of dimethylanilinium tetrakis(pentafluorophenyl)borate or by alkyl group abstraction in the case of tris(pentafluorophenyl)boron, to generate a titanium cationic species with a borate counterion (74-76). The esr spectral evidence has been reported for these systems, supporting a titanium(III) cationic active species (76). 

In the inverse electron-demand (lED) HDA reaction systems, a,p-unsaturated ketones, thiones, nitroalkenes, and related compounds often serve as heterodiene units and the electron-rich olefins are usually used as dienophiles for the reaction [158]. A concerted mechanism has been suggested for the HDA reaction between an a,p-unsaturated ketone with a vinyl ether mediated by a titanium complex (Scheme 14.66), although the possibility of a stepwise, cationic pathway, particularly in the presence of a Lewis acid, cannot be completely excluded [160]. 

Electric neutraUty of the compounds, postulated as an essential prerequisite for the achievement of cytostatic properties in the case of platinum complexes is obviously not a crucial condition for cyclopentadienyl metal complexes to exhibit antitumor properties. There exist, on the one hand, numerous neutral compounds such as the metallocene diaddo complexes I-XLIU and the decasubstituted main group IV metallocenes LVn-LIX exhibiting antiproliferative properties on the other hand, marked tumor-inhibitmg potendes were also found with the charged ferricenium salts XLIX-LVI as well as with the ionic cyclopentadienyl titanium complexes Xl.IVXLVlll wherein the titanium-containing unit may either form the cationic or the anionic moiety. Because of... 

The most common oxidation state of niobium is +5, although many anhydrous compounds have been made with lower oxidation states, notably +4 and +3, and Nb can be reduced in aqueous solution to Nb by zinc. The aqueous chemistry primarily involves halo- and organic acid anionic complexes. Virtually no cationic chemistry exists because of the irreversible hydrolysis of the cation in dilute solutions. Metal—metal bonding is common. Extensive polymeric anions form. Niobium resembles tantalum and titanium in its chemistry, and separation from these elements is difficult. In the soHd state, niobium has the same atomic radius as tantalum and essentially the same ionic radius as well, ie, Nb Ta = 68 pm. This is the same size as Ti ... 

In crystals of more complex formula, such as titanium dioxide, TiC>2, a Schottky defect will consist of two anion vacancies and one cation vacancy. This is because it is necessary to counterbalance the loss of one Ti4+ ion from the crystal by the absence of two O2- ions in order to maintain composition and electroneutrality. This ratio of two anion vacancies per one cation vacancy will hold in all ionic compounds of formula MX2. In crystals like A1203, two Al3+ vacancies must be balanced by three O2- vacancies. Thus, in crystals with a formula M2X3, a Schottky defect will consist of two vacancies on the cation sublattice and three vacancies on the anion sublattice. These vacancies are not considered to be clustered together but are distributed... 

The mineral constituents of the raw cane juice persist in the final molasses. The principal difference in relative amounts of these substances in molasses arises from the use of lime in defecation which causes an increase in calcium. Egyptian cane molasses solids contained 0.66% of titanium.181 The cations are believed to complex with the sugars and to thus inhibit the crystallization of sucrose, which latter is known to form compounds with inorganic salts, such as its well known compound with sodium chloride. Decationization of cane juice with ion exchange resins greatly reduces molasses formation but sucrose inversion is a concomitant problem.182... 

Arasabenzene, with chromium, 5, 339 Arcyriacyanin A, via Heck couplings, 11, 320 Arduengo-type carbenes with titanium(IV), 4, 366 with vanadium, 5, 10 (Arene(chromium carbonyls analytical applications, 5, 261 benzyl cation stabilization, 5, 245 biomedical applications, 5, 260 chiral, as asymmetric catalysis ligands, 5, 241 chromatographic separation, 5, 239 cine and tele nucleophilic substitutions, 5, 236 kinetic and mechanistic studies, 5, 257 liquid crystalline behaviour, 5, 262 lithiations and electrophile reactions, 5, 236 as main polymer chain unit, 5, 251 mass spectroscopic studies, 5, 256 miscellaneous compounds, 5, 258 NMR studies, 5, 255 palladium coupling, 5, 239 polymer-bound complexes, 5, 250 spectroscopic studies, 5, 256 X-ray data analysis, 5, 257... 

We wish also to point out that the fact that in the above schemes only the transition metal, the last polymerized unit, and the coordinated monomer are represented does not mean that the catalysts prepared from A1(C2H5)3 and a titanium alkoxyde or from A1(C2H5)2C1 and a Co compound are pure organo-metallic compounds of Ti or Co, respectively. These catalysts are presumably complexes containing A1 and the transition metal, the latter probably being part of a cation, the A1 of an anion. In the above schemes we have represented only the transition metal for the sake of simplicity. 

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