Thallium trialkyls

No monomeric alkali metal alkyls or aryls are known, as those crystal structures which have been determined indicate electron-deficient, e.g. (MeLi), or ionic (K Me ) constitutions. The dialkyls of the lighter second group metals are mostly electron-deficient dimers or polymers, but those of zinc, cadmium and mercury are monomers with a linear structure as expected from participation of one (metal) s and one p orbital (with or without dji participation). In the third group the pattern is more complex. Whereas the trialkylboranes are monomeric, boron hydrides (and alkyl hydrides) and polyboron compounds form electron-deficient structures. Aluminium alkyls and alkyl hydrides are normally electron-deficient dimers or trimers gallium trialkyls are monomeric though the trivinyl is a dimer trimethylindium is a weakly associated tetramer in the solid state, otherwise all indium and thallium trialkyls appear to be monomers. 

Trimethylthallium (Figure 13(b)) has a similar crystal structure, though in solution both thallium trialkyls and triaryls are monomeric. A proton magnetic resonance study of MeaTl in PhCD3 shows that methyl exchange is second-order and consistent with an electron-deficient transition state only 6 kcal/mole above that of two monomers ... 

Whereas aluminium alkyls react with most hydroxy compounds (imless there are steric complications) with loss of all three alkyl groups, such reactions tend to stop after one or two alkyl groups have been eliminated from gallium and indium alkyls. Thallium trialkyls are hydrolysed only as far as R2TIOH, and to R2T1 cations in add solution (these are considered later). 

Exposure to neurotoxicants or neurotoxic chemical substances causes severe adverse health effects to the nervous system, which is very sensitive to organometallic compounds and sulfide compounds. These compounds disrupt the normal functioning of the central nervous system, peripheral nerves or sensory organs, and the conduction of nerve impulses. Thus, chemical substances are considered neurotoxicants when they induce a consistent pattern of neural dysfunction. The chemical substances include but are not limited to carbon disulfide, manganese, methyl mercury, organic phosphorous insecticides, tetraethyl lead, thallium, and trialkyl tin compounds. 

In its covalent compounds thallium shows no reluctance to utilizing the two 6s electrons for bond formation. Indeed monoalkyl derivatives Tl(Alk) in which the valence group would be (2, 2) are not known, whereas trialkyls (valence group 6) are known and the most stable alkyl derivatives are the dialkyl halides such as [T1(CH3)2]I. These are ionic compounds-[T1(CH3)2] OH being a strong base—and in the Tl(Alk)2 ions the thallium atom has the same outer electronic structure as mercury in CH3-Hg-CH3, viz. (4). Accordingly the (CH3-T1-CH3) ion is linear, as shown by the determination of the crystal structure of Tl(CH3)2l. In molecules such as Tl(Alk)2A, where A represents a molecule of a /3-diketone, T1 apparently has the valence group (8). 

Metallic thallium has been suggested as an intermediate in a reaction reported by Gilman and Jones.78,79). The addition of an alkyl or aryllithium compound to a mixture of the corresponding alkyl or aryliodide and thallous halide give a dark precipitate of the finely divided metal. This disappeared during the course of the reaction to give good yields of the trialkyl or aryl thallium compounds. The overall stoichiometry of these reactions was as in Eq. (1). 

Little is known so far about the alkylation of thallium compounds with trialkyl alanes, although it has been reported that thallium trichloride gives good yields of dialkyl thallium chlorides with various trialkyl alanes (268). 

The most common reagents used for this transformation are hypervalent main group oxidants such as thallium(III) [405, 406], lead(IV) [407, 408] and hypervalent iodide]III) [95, 409]. In order to avoid any a-carbonyl oxidation the reaction is usually performed in the presence of an alcohol or a combination of trialkyl orthofor-mate and a strong acid to ensure rapid acetalization. However, depending on the reaction conditions, hydroxyacids can also be isolated as major products [410, 411). 

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