Thallium-carbon bonds

For example, photolysis of a suspension of an arylthallium ditrifluoro-acetate in benzene results in the formation of unsymmetrical biphenyls in high yield (80-90%) and in a high state of purity 152). The results are in full agreement with a free radical pathway which, as suggested above, is initiated by a photochemically induced homolysis of the aryl carbon-thallium bond. Capture of the resulting aryl radical by benzene would lead to the observed unsymmetrical biphenyl, while spontaneous disproportionation of the initially formed Tl(II) species to thallium(I) trifluoroacetate and trifluoroacetoxy radicals, followed by reaction of the latter with aryl radicals, accounts for the very small amounts of aryl trifluoroacetates formed as by-products. This route to unsymmetrical biphenyls thus complements the well-known Wolf and Kharasch procedure involving photolysis of aromatic iodides 171). Since the most versatile route to the latter compounds involves again the intermediacy of arylthallium ditrifluoroacetates (treatment with aqueous potassium iodide) 91), these latter compounds now occupy a central role in controlled biphenyl synthesis. 

Remarkably, ArTlXj compounds also suffer nucleophilic substitution on the carbon-thallium bond with hydride ion to regenerate the parent arom-... 

Data for 2-chloro-3-butanol is unavailable, but the low glycol yield for Tl(III) oxidation is understandable on the basis of steric hindrance to Sn2 attack of water on the carbon-thallium bond. With ethylene and propylene, the thallium (III) is attached to a primary carbon while with 2-butene it is attached to a secondary carbon. The situation with 2-butene is somewhat different from that found with the other olefins. In the oxythallation adduct from this olefin. 

Thus, Criegee 11) prepared the oxythallation adduct of styrene in methanol which he decomposed at 130°C. to give products which result from solvolysis of the carbon-thallium bond with (HI) and without (IV)... 

Treatment of arylthallium(III) compounds with metal nitrites in trifluoroacetic acid affords the corresponding nitrosoarenes, which are oxidised to the nitroarenes. The reaction was suggested to occur by electrophilic attack of NO+ on the carbon-thallium bond. l ... 

The conversion of a carbon-thallium bond into a carbon-carbon bond has been performed directly only in a relatively limited number of cases formation of aiylcyanides, reaction with nitroalkane salts as well as the reaction with copper acetylides. Other carbon-carbon bond formation reactions have been reported with a carbon-thallium substrate. However, they all involve palladium catalysis, and this is beyond the scope of this book. 147... 

Alkyl and vinylthallium(in) compounds are mostly obtained by oxythallation of alkenes or alkynes. They can also be formed by transmetallation between, for example, an organomercury compound and thallium(ni) salts. Various types of reactivity have been observed for these compounds. The evolution of the carbon-thallium bond into functionalised products usually takes place homolytically or heterolytically. The ligand coupling process has also been evoked to rationalize a small number of transformations. 

The formation of a carbon-carbon bond by reaction of alkylthallium(III) compounds has been described in the a-nitroalkylation of alkanes. The reaction of alkylthallium (129) with nitroalkane anions leads to the nitroalkyl derivatives (130). In this case, radical intermediates generated by electron transfer activation of the carbon-thallium bond are involved in a non-chain substitution process. 

The term organometallic refer to compounds that contain a carbon-metal bond. [59] The term spans compounds that are primarily ionic (such as when the metal is sodium or potassium and thus should be nomenclated as the distinct ions) through compounds that are primarily covalent (such as when the metal is lead, tin, mercury or thallium for which the bonding is covalent)... 

The Grignard reagent is the best-known member of a broad class of substances, called organometallic compounds, in which carbon is bonded to a metal lithium, potassium, sodium, zinc, mercury, lead, thallium—almost any metal known. Each kind of organometallic compound has. of course, its own set of properties, and its particular uses depend on these, fiut, whatever the metal, it is jess electronegative than carbon, and the carbon-metal bond—like the one in the... 

The nature of the carbon-metal bond varies widely, ranging from bonds that are essentially ionic to those that are primarily covalent. Whereas the structure of the organic portion of the organometaiiic compound has some effect on the nature of the carbon-metal bond, the identity of the metal itself is of far greater importance. Carbon—sodium and carbon-potassium bonds are largely ionic in character carbon—lead, carbon—tin, carbon—thallium, and carbon—mercury bonds are essentially covalent. Carbon—lithium and carbon—magnesium bonds lie between these extremes. 

Efforts at C-H activation can be divided into three broad categories. The first involves C-H bonds of arenes, heteroarenes and comparable alkenes. In many cases, the formation of the carbon-metal bond may be viewed as an electrophilic substitution reaction (Scheme 3.1), following the same pathway as metallation by main-group metals such as mercury, thallium and lead, as well as classical reactions such as bromination and nitration. This is not, however, always the case. 

By heating in 0.1 M HCl the carbon-cobalt bond of adenosylcobalamin is cleaved the alkylcobalamins are relatively stable in dilute acid or alkali. Cyanide forms another threat to the adenosyl-cobalt bond, in particular at alkaline pH and at elevated temperature, by inducing dicyanocobalamin. The alkylcorrinoids are more resistant to the effect of cyanide, but are spliced through electrophilic attacks on the methyl group, for instance by ionic mercury or thallium, into aquocobalamin and the methylmercury cation, or the methylthallic dication (29). 

Thallium(III) substituents (see 36) exert even larger effects on a-caibon atoms than mercury does (141) (see 37 and 38) this has been ascribed to displacement of electrons in the carbon-metal a-bond toward the metal atom, due to its increased nuclear charge. 

The thallium complexes show somewhat different electrochemical behavior, and reversible oxidations are observed for both n-alkyl and n-aryl thallium porphyrins, indicating that the oxidized complexes have a more stable metal—carbon bond than the gallium or indium analogs. Spectroelectrochemistry revealed that the first oxidation is porphyrin ring-centered. The first reduction is reversible and ring... 

Most of the studies on organo-gallium, indium, and thallium porphyrin complexes have focused on synthesis and properties of the complexes, and rather little attention has been devoted to reaction chemistry. Two areas which have received some attention are the insertion of small molecules (SO2 or CO2) into the metal—carbon bonds and photochemical metal—carbon bond cleavage. The... 

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