Thallium ligand exchange reactions

The utility of thallium(III) salts as oxidants for nonaromatic unsaturated systems is a consequence of the thermal and solvolytic instability of mono-alkylthallium(III) compounds, which in turn is apparently dependent on two major factors, namely, the nature of the associated anion and the structure of the alkyl group. Compounds in which the anion is a good bidentate ligand are moderately stable, for example, alkylthallium dicar-boxylates 74, 75) or bis dithiocarbamates (76). Alkylthallium dihalides, on the other hand, are extremely unstable and generally decompose instantly. Methylthallium diacetate, for example, can readily be prepared by the exchange reaction shown in Eq. (11) it is reasonably stable in the solid state, but decomposes slowly in solution and rapidly on being heated [Eq. (23)]. Treatment with chloride ion results in the immediate formation of methyl chloride and thallium(I) chloride [Eq. (24)] (55). These facts can be accommodated on the basis that the dicarboxylates are dimeric while the... 

The kinetic characteristics of ligand exchange of thallium complexes in solution have been little explored, in contrast to the numerous equilibrium studies (4-6,41,57,61,66,67,90,92,93,96,97,112,214-246) and a large number of studies of redox reactions involving thallium (81, 100, 103, no, 246-288). 

Far more surprising was the fact that the anation reactions constituted only a minor part of the chloride exchange in this chemical system. Instead, up to the Cl/Tl ratio 3, the dynamics is dominated by a direct ligand exchange between two thallium complexes. 

Reaction of the anion 21 with Cp or Cp metal fragments provides further metallocene-type complexes with a pendant phosphaferrocene side-chain. For example, the reaction of the thallium derivative T1 21 with [Cp RhCl2]2 yields the cationic pentamethylrhodocenium 24 as its chloride (Scheme 1.5.10). This is an interesting species because it is a chiral water-soluble P ligand. The chloride anion can be exchanged by PF,s to make the compound more soluble in organic solvents. 

Cation exchange chromatography is almost always required to ensure complex purity.9-11 28-36 It is also possible to use thallium(I) salts of phenylcyanamide ligands and react them with complex halides in a metathesis reaction.1-3,37... 

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