Mercury bonds

The occurrence of a hydrogen isotope effect in an electrophilic substitution will certainly render nugatory any attempt to relate the reactivity of the electrophile with the effects of substituents. Such a situation occurs in mercuration in which the large isotope effect = 6) has been attributed to the weakness of the carbon-mercury bond relative to the carbon-hydrogen bond. The following scheme has been formulated for the reaction, and the occurrence of the isotope effect indicates that the magnitudes of A j and are comparable ... 

The bicyclic amine 11-methyl-l l-azabicyclo[5.3.1]hendecanc (71) provided a model system in which the hydrogens on the equivalent a-tertiary-carbon atoms cannot be trans to the nitrogen-mercury bond in the mercur-ated complex and in which epimerization at these a carbons is impossible (77). This bicyclic system is large enough to accommodate a... 

The relative case of cleavage of the aryl-mercury bond yielded a so-called scale of electronegativities (the group Ar in reaction (242) being considered the more electronegative ) though this scale is the exact reverse of the true electro-... 

The synthetic utility of the mercuration reaction derives from subsequent transformations of the arylmercury compounds. As indicated in Section 7.3.3, these compounds are only weakly nucleophilic, but the carbon-mercury bond is reactive to various electrophiles. They are particularly useful for synthesis of nitroso compounds. The nitroso group can be introduced by reaction with nitrosyl chloride73 or nitrosonium tetrafluoroborate74 as the electrophile. Arylmercury compounds are also useful in certain palladium-catalyzed reactions, as discussed in Section 8.2. 

Voltammetric peaks, especially those of UDP and UTP, were sharper than those of the third compound, as they were adsorbed at the electrode surface. Coulometric studies (at — 1.0 V, electroreduction) at mercury pool electrode (also glassy carbon) and analysis of the obtained products have shown that for all three compounds, the two-electron reductive cleavage of the carbon-mercury bond occurs. The electrode... 

The first observation was that substances containing mercury bonded to the unusual carbomethoxyl group,... 

The development of the second class of compounds with gold-mercury bonds, that is, Hg-containing, Au-rich clusters, was mainly the contribution of Pignolet and coworkers [41-43]. Such compounds were generally obtained by addition of mercury... 

Nesmeyanova and Perevalova in related studies involving diferrocenylmercury and palladium black obtained similar result (58). Their yields of biferrocenyl amounted to only 1 to 6%, however. It is postulated that the reactions proceed via homolytic scission of the carbon-mercury bond with the formation of ferrocenyl radicals. 

Organic mercury compounds, especially phenyl and methoxyethyl mercury may also be biotransformed into inorganic mercury by cleavage of the carbon-mercury bond. Although such compounds are more readily absorbed than inorganic mercury compounds, the toxicity is similar. 

The existence of the mercury-mercury bond in the mercurous ion, Hg ++ and in molecules such as mercurous chloride, Cl—Hg—Hg—Cl,... 

They act on the kidney by depressing the mechanisms that govern the active reabsorption of sodium and chloride ions. They are rapidly excreted by the kidney but their use is hazardous because their action is believed to be due to inorganic mercury ions released by rupture of the carbon-to-mercury bond, probably followed by the firm attachment of the mercury ion to a sulphydryl group of a renal enzyme. The administration of dimercaprol (SO), a strong chelating agent for mercury, removes mercury from the kidney and terminates the diuretic action. It is of interest that Paracelsus used calomel (mercurous chloride) as a diuretic. 

This photocyclization proceeds in a one pot reaction with photolytic cleavage of the intermediate carbone-mercury bond and subsequent hydrogen abstraction through a probable hypoiodite intermediate 6 [15 a]. With secondary alcohols (R = H), the reaction is less efficient than with primary ones (R = H), and mainly undergoes a retention of configuration at the anomeric carbon [15 b] by abstraction of the a-anomeric hydrogen. 

At C-2 position, carbohydrate radicals were formed starting from unsaturated sugars by acetoxymercuration followed by reduction of the carbon-mercury bond... 

Kreevoy et al., 1966a). A comparison with the values in Table 7 suggests some progress away from covalent carbon-mercury bonds in the transition states, but certainly does not permit any formulation which requires... 

Acetyl hypofluorite also cleaves the carbon-mercury bond which provides an easy entry to many fluoroethers. Since the electrophilic fluorine attacks the electrons of the C—Hg bond, the reaction proceeds with a full retention of configuration. Several l-fluoro-2-methoxy derivatives were prepared from the corresponding olefins271, formally accomplishing the addition of the elements of MeOF across a double bond (equation 153)272. Such reactions were also used for the fluorination of very activated aromatic compounds (equation 154)273. 

---