Thallium species

R = CH2C6H4) withM = silver or thallium. The luminescent properties ofthe silver or thallium species are sensitive to the temperature and the metallic ion M+ [337-339]... 

Although the earliest syntheses of the Corey lactone, using a cyclopentadienyl-thallium species, were not very attractive, it was soon found that the lactone could be usefully generated by a Baeyer-Villiger reaction on a bicycloheptenone.8 In turn, this derives from an easy [2 + 2] cycloaddition reaction between dichloroketene and cyclopentadiene (Scheme 30.2).9 Additionally, an intermediate of the lactone could be resolved by way of the a-methylbenzylamine salt of its opened hydroxyacid, bringing the resolution step earlier in the synthesis than previously.10... 

The synthesis of 7-methoxyindole was accomplished starting from 1-acetylindoline (34). Regioselec-tive intr uction of iodine was achieved using thallium trifluoroacetate, then potassium iodide. Deacetylation and oxidation to the indole (35), followed by reaction with sodium methoxide in DMF, gave the 7-methoxyindole (36) in 48% overall yield (Scheme 13). More recently, Somei et al have reported that treating the intermediate thallium species with copper(II) sulfate pentahydrate gives directly the l-acetyl-2,3-dihydro-7-hydroxyindole (37) in 42% yield (Scheme 14). It remains to be seen whether this is a general process. 

Marko and co-workers recently found a unique property of triorganothallium compounds (TOT) their ability to react preferentially with enones (Scheme 2-24) [54], One of the most striking observations is that selectivity of the process increases as the substrate becomes more conjugated and the intrinsic reactivity of the carbonyl function decreases. This chemical event can be interpreted by the single electron transfer from the thallium species to enones, followed by recombination of the resulting radical species 1-5 and 1-6. 

Oxidation of As"1 by Tl111 in HC104 solution is inhibited by CT, and the reactivity of the various thallium species is in the order Tl3+>TlCl2+> T1CL>T1C13 >T1C14.579 Oxidation proceeds by way of an intermediate complex between Tlni and As"1. 

Most chemical reactions in the natural surroundings and in the chemical industrial processes take place in solution, and this aggregation state constitutes the main field of interest for the majority of chemists and biochemists. However, in contrast to the large number of detailed crystal structures, the amount of available structural information for species in solution is limited. The reason for this situation is certainly the inherent disorder of the solution state, from which follows the lack of an experimental method as hard as the single-crystal X-ray diffraction technique. Certainly, spectroscopic methods can be used for studies of symmetry and bonding properties, but in order to obtain accurate interatomic distances diffraction techniques (or EXAFS, extended X-ray absorption fine structure) have to be used. These techniques are not always easily accessible and have some weak points however, they are the only ones able to provide the latter type of structural data. In the following, the few reported (and one unpublished) studies of this type of thallium species in aqueous solution will be discussed. 

Fig. 16. NMR 2D-EXSY spectrum of an acidic aqueous solution containing the thallium species Tl(OH2)g, TKCN), and T1(CN)2, showing the dominating cyanide...

Methyl thallium species have been discovered in natural water quite recently but thallium was reported to undergo biomethylation in vitro already more than two decades ago [32]. While the total thallium levels in oceans and lakes vary between 1.6 and 20.1 ng/L, levels exceeding 1000 ng/L have been found in industrial waste waters [33]. The proportion of [(CH3)2T1]+ to total thallium ranged up to 48%. The stability of the monomethyl derivatives varies in the order mercury(II) > thallium(III) 2> lead(IV) bismuth(V) [3b]. 

Heterogeneous catalysts containing thallium species have heen developed over the years to promote a number of different transformations. Table 20.1 shows examples for the use of thallium-based solid catalysts in different organic transformations. 

Salt elimination between a transition metal anion and a Group 13 halide is the most extensively exploited route into the formation of transition metal-Group 13 bonds in which the Group 13 element is in the -1-3 oxidation state. Most initial work focused on indium and thallium species and their reactions with mono-anionic carbonylmetaUates. Early examples indude [CpMo(CO)3]3Tl formed via the reaction of TljSO with 3 equiv. of Na[CpMo(CO)3] [202-204]. 

Reduction. Thallium(III) is reduced to Tl by Fe SnCl2, and so on. Metallic Mg, Zn, or A1 will reduce various thallium species to Tl. 

Table 13.28 Thermodynamic data for thallium species at 25 °C and comparison with data availaUe in the literature.

Data for the thermodynamic parameters of thallium species (both thallium(I) and thallium(III) are listed in Table 13.28). Also listed in the table are thermodynamic data for Tl", TP" and Tl(s) taken from Bard, Parsons and Jordan (1985). The table also contains thermodynamic data reported by Bard et al. for the oxide phases of thallium and some hydrolysis species. There is good agreement between the data presented by Bard et al. for Tl20(s) and those accepted in the present review. However, there is much poorer agreement for the hydrolysis species of thallium(I) and the oxide phase of thallium(III). 

---