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Organothallium compounds are compounds that contain thecarbon-thallium bond. The area is not well developed because of the lack of applications and the high toxicity of thallium. The behavior of organothallium compounds can be inferred from that oforganogallium andorganoindium compounds. Organothallium(III) compounds are more numerous than organothallium(I) compounds.[1]
Organothallium(I) compounds remain obscure and limited scope. Attempts to generate the simple compound thallium methyl results indisproportionation, giving thallium(III) derivatives. With the bulky tris(trimethylsilyl)methyl substituent, a tetramer has been crystallized.[3]
Similarly, thallium(I) aryl compounds require steric bulk for their isolation.[4]
A well-known organothallium(I) species isthallium cyclopentadienide. It arises by treatment of thallium(I) salts, such asthallium sulfate, with cyclopentadiene. Thallium(I) cyclopentadienide adopts a zig-zag chain structure of cyclopentadienide and thallium.[5]
In the gas and liquid phase, trialkyl organothallium compounds aremonomeric and planar. In the solid phase, there is significant intermolecular interactions between the monomers.[6]
Trialkyl thallium compounds, like those of indium and gallium, can be prepared from thallium trihalides andGrignard reagents ororganolithium reagents, though the former may yield the ether complex of the product.[6] However, unlike that of gallium and indium, trialkyl thallium compounds cannot be prepared from dialkyl mercury and thallium trihalides, in which case R2TlX will be obtained.[6] Trimethyl thallium can be prepared frommethyl iodide,methyl lithium, andthallium(I) iodide.[6] Triethyl thallium can be similarly prepared.
Trialkyl thallium compounds can undergo alkyl exchange with itself and some acidichydrocarbons likealkynes andcyclopentadiene. Some trialkyl thallium compounds arephotosensitive.[7]
R2TlX has ionic properties, such that they are water soluble and that R2TlOH is strongly basic. The structure of the dialkyl thallium anion resembles that of dialkyl mercury.[7][8][9] However, dimeric or polymeric structures may exist in inert solvents orcrystalline structures.
Dialkyl Organothallium Halides can be prepared from two equivalents of Grignard reagents andthallium trihalides, or the reaction of trialkylthallium compounds with protonic compounds.[7][9] Another preparation involves the oxidation of thallium metal witharyldiazonium tetrafluoroborate salts. They are formed from dialkyl mercury and thallium trihalides instead of trialkyl thallium compounds.
Dialkyl Organothallium Compounds are mostly stable to air and moisture.[7] The halide atom can be substituted bynucleophiles, and the alkyl group can be abstracted bymercury acetate. (C5F6)2TlBr can act as alkyl donors for low-valent metal halides, performing oxidative alkyl insertions onto the metals with itself being reduced tothallium(I) bromide.
Arylthallium dichloride can be prepared fromTlCl3 andaryl boronic acids.[10] Excess boronic acid will result in diarylthallium chloride formation. Thallium(III) trifluoroacetate canoxidize aromatic rings to form ArTl(OCOCF3)2.[7] Alkenes can also react with thallium(III) salts in a fashion analogous tooxymercuration to yield monoalkyl organothallium compounds.
Phenylthallium dihalides are prone to eliminatinghalobenzene, with the tendency increasing from chlorine to iodine, to the point that the iodide derivative is unknown.[10] They areLewis acidic in nature. Nucleophile treatment can displace the halide atom, and substituent self-exchange to form thallium(III) halides and diphenylthallium halides is also possible. The dichloride can undergotransmetallation withmercuric chloride.[10]
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The most prominent contribution of organothallium chemistry toorganic synthesis centers onthallium(III) trifluoroacetate with arenes. Moreso than Hg(II), thallium(III) is a potent electrophile, delivering arylthallium(III) derivatives:[11]
The resulting aryl thallium compounds react with nucleophiles such as halides, pseudohalides, and certain acetylides.
The first organothallium compound, diethylthallium chloride, was prepared in 1870, shortly after the discovery of the elementthallium.[12]
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