Thallium halide complexes

Of the thallium halide complexes, the bromide complex is the most important in extraction separations. Tl(III) and Au(IlI) are extracted quantitatively from 1-3 M HBr with diethyl ether or DIPE, or MIBK. At that concentration of HBr, Fe(lII), Ga, In, Hg, and Te are extracted in small amounts. After extraction with MIBK, Ga, In, Fe(IlI), and Sn are stripped with a 1.5 iW HBr formamide solution, leaving only Tl(III) in the ketone phase [1]. The thallium(III) bromide eomplex has been extracted with TO A in benzene [2], or n-octylaniline in CHCI3 [3],... 

Thallium(i) salts have long been used in reactions with organic and organometallic halide complexes as a means of activating the halide by removal as insoluble T1X. However, the thallium ions proved not to be innocent bystanders, and numerous examples were reported in COMC (1995) where the metal-bound thallium complexes were formed. Deliberate reactions of thallium(i) and thallium(m) salts with metal carbonyl anions have yielded a variety of complexes of the form T1 MLJ3. In the past decade, new examples of metal carbonyl derivatives of thallium have been prepared (see Table 2). In addition, the propensity for Tl+ to form adducts with 16-electron noble metal complexes has been exploited. 

A large number of halide complexes of thallium(III) have been prepared by precipitation of the complexes from solution with a suitable cation, eg, H+, (C2H5)4N+, (C6H5)4As+, and K+. Both four-coordinated [HXJ" and six-coordinated [TlXJ3 ions exist in solutions and in solid states. 

In addition to the halide systems there are a number of thallium(I) salts of thallium(III) complex anions in which the overall stoichiometry implies, incorrectly, the presence of thallium(II) species. These include the sulfate, selenate,369 acetate370 and oxalate371 derivatives. An X-ray determination has confirmed that Tl(OAc)2 is indeed Tl[Tl(OAc)4], in which the anions are linked through seven-coordinate Tl+, with some evidence for a stereochemically active inert pair.370 In T1[T1(0H)(S04)2], the structure consists of sheets of linked anions with Tl+ ions.372... 

Halide complexes of this group react with carbanions to form stable alkylmetalloporphyrins.27 The thallium atom is significantly displaced (0.98 A) from the N4 plane with a large T1—N,, distance (2.29 A) in Tl(TPP)Me, formed by the reaction of H2TPP and MeTl(OCOMe)2 (Scheme 5). Monovalent thallium porphyrin complexes are also known.17 They can be prepared by treating a porphyrin with thallium(I) ethoxide in THF.29 Unlike the other Group IIIB metalloporphyrins, [Tl i Por) is easily hydrolyzed. 

Thallium(I) halides are predominantly ionic, although there is a tendency toward increasing covalent character in the series of compounds TlCl (17%), TlBr (20%), and TII (28%). This increased degree of covalency results in decreased solubility for example, TIF is soluble in water whilst the other Tl halides are only sparingly soluble. The thallium(I) halides are classical examples of incompletely dissociated 1 1 electrolytes. The stability of halide complexes of Tl is low and follows the order TIF < TlCl < TlBr < TII, where for the series of halides, Kx = -, 0.8, 2.1, 5.0 and Ki = -, 0.2, 0.7, 1.5 respectively. The fluoride ion F is preferred to perchlorate as a noncomplexing counterion. Claims have been made for T1X species with n = 3 and 4 however, the formation of complexes in aqueous solution with n > 2 seems unlikely. 

Thallium(I) forms salts with cyanide (CN ), cyanamide (NCN ), azide (Ns"), cyanate (OCN ), isocyanate (CNO"), thiocyanate (SCN"), and selenocyanate (SeCN ) however, complexes with these hgands, hke the Tl -halide complexes, are very weak. In contrast, the neutral Tl Xs species are not well known, although the Tl -pseudohahde complexes are more or less stable. 

The halide complexes of thallium(III) in aqueous solution are among the most stable of metal halide complexes, and they have been intensively studied (3, 89-92,103,118-122). There occurs a distinct break... 

Table 6.8 gives stability constants for the complexes [FeX] and [HgX] for different halide ions while the stabilities of the Fe complexes decrease in the order F > CP > Br, those of the Hg complexes increase in the order F < CP < Br < P. More generally, in examinations of stability constants by Ahrland, Chatt and Davies, and by Schwarzenbach, the same sequence as for Fe + was observed for the lighter s- and /i-block cations, other early J-block metal cations, and lanthanoid and actinoid metal cations. These cations were collectively termed class (a) cations. The same sequence as for Hg complexes was observed for halide complexes of the later J-block metal ions, tellurium, polonium and thallium. These ions were collectively called class (b) cations. Similar patterns were found for other donor atoms ligands with O- and iV-donors form more stable complexes with class (a) cations, while those with S- and F-donors form more stable complexes with class (b) cations. 

Cyclopentadienylthallium is a superior reagent for many syntheses. It is easily prepared and stored, it may be handled in air, and the insolubility of thallium halide leads to high yields of product that may be filtered easily and worked up. The reagent has been used for preparing a variety of actinide, lanthanide, and transition metal cyclopentadiene complexes. 

Cyclopentadienylthallium is a light yellow solid that decomposes at 230°. It is stable for several months if stored under N2 in a Schlenk flask kept in the dark. Slow decomposition takes place in the air and light, whereupon the solid turns brown, but pure product may be sublimed away from this material. The IR spectrum shows absorption bands at 3022, 1584, 995, and 725 cm" Cycloi>entadienylthallium is insoluble in most organic solvents. It may be handled in air, and it is normally heated at reflux in THF solution with the substrate for about 2h under an inert gas atmosphere. When allowed to react with metal halides, the insoluble thallium halide produced may be filtered from the reaction solution. Most cyclopentadienyl complexes are air- and moisture-sensitive and should be handled with appropriate techniques. ... 

Thallium is also used in low-temperature thermometers, photoelectric cells, dye pigments, and to produce various types of resistant cements. Because of the element s high refractive index it is utilized in the manufacturing of optical lenses and imitation jewelry. Thallium is included as a component of corrosion-resistant alloys, organic reaction catalysts, and fireworks. The incorporation of thallium halides into organic alkylhalides produces formation of new complexes that act as phosphors. This is the basis for using thallium in scintillation counters [Nal(Tl)]. 

Scheme 20.15). One equivalent of hydroxide or alkoxide is necessary to replace the halogen on the palladium complex I and the second equivalent is essential to form the borate II, so that the allq l group becomes more nucleophilic. According to Kishi and coworkers,the advantage of using thallium(i) hydroxide over sodium hydroxide is that the first can form insoluble thallium halide (TlX) which contributes to enhance this step and to accelerate the coupling. 

Fromherz and his colleagues began in 1927 a study of the halide complexes of the family tin(II), thallium(I), and lead(II), > > where the corresponding gaseous ions contain two s electrons. The present author has measured antimony(III), while Hume and Newman studied bismuth(III). This family became interesting to solid state physicists investigating the mixed crystals with alkali halides, and Seitz proposed, 1938, that the weaker band of T1(I) in such crystals is caused by the atomic transition Sq(6s ) —> Pi(6s6 ), while the stronger band is caused by... 

As an alternative to the toxic halide scavenging silver and thallium salts, polar solvents, capable of promoting the cationic palladium(II) intermediate from aryl halides, have been applied with great success producing the branched disubstituted alkenes selectively. In particular, Xiao [80] and Larhed [81] showed that aryl chlorides and bromides, usually resulting in strongly coordinated neutral palla-dium(II) halide complexes, could effectively be employed in the synthesis of... 

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