Metal thallium-mercury bonds

The softness of a heavy metal indicates how toxic it is. (In this case, softness means a heavy metal ion with a low charge.) Soft, and therefore toxic, metals include mercury (Hg), lead (Pb), cadmium (Cd), and thallium (Tl). Mercury and lead in particular are strongly complexing and, therefore, very toxic in the body because they can bond in biomolecules and prevent them from working properly, as well as be difficult to remove. (See Chapter 5 for a refresher on hard and soft acids.)... 

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. 

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. 

Among some metal oxygen compounds which add, palladium and thallium ion both oxidize olefins and apparently the initial step is the addition of a metal hydroxide across the olefin double bond. The intermediates have not been isolated because they go on to other products but kinetic and other evidence indicates that the addition of the hydroxide is the initial step. In the well known mercury acetate addition to olefins in alcohol solution one can isolate the /S-hydroxv or alkoxy ethylmercury derivatives. 

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)... 

Lead, like its neighbor tin, enjoys both the -t-2 and +4 oxidation state. In this case, Pb(II) is the normal metallic cation and the Pb(IV) state is rather unstable and very often oxidizing. As such, any species that might contain a bonded Pb(IV) and an enolate anion may mimic Pb(II) and an enoxyl cation. Metal-metal exchange reactions of lead enolates show both enolate and enoxyl cation behavior , depending on what is affixed to the metal. This quasi-enolate vs. enoxyl cation dichotomy is also seen for suitable mercury-and thallium-containing species. 

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 increase in toxicity can be explained by the increasing affinity of these elements for amino, imino, and sulfhydtyl groups, which form the active centers of a number of enzymes. The metals of the sixth Period and their compounds are potentially the most toxic elements of the Periodic System. The generally poor water solubility of their salts, however, often masks their inherent high degree of toxicity. This toxicity becomes apparent in those lead, mercury, and thallium salts that are relatively soluble. The metallic ions of the fourth Period form mostly covalent bonds and complexes with biological ligands, and some form hydroxy acids in which the metal is part of the anion. 

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. 

The oxidative ring cleavage of cyclopropenes and of cyclobutenes by thallium(m), mercury(n), palladium(n), or lead(iv) bears some resemblance to the isomerizations discussed above. In particular, the first step in the oxidations is probably insertion of the metal into a carbon-carbon bond, as in isomerization. 

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