Arylmercury reagents

Unsymmetrical coupling of vinylic, alkynyl, and arylmercury compounds was achieved in moderate-to-good yields by treatment with alkyl and vinylic dialkylcopper reagents (e.g., PhCH=CHHgCl -t- Mc2CuLi PhCH=CHMe). Unsymmetrical biaryls were prepared by treating a cyanocuprate ArCu(CN)Li (prepared from ArLi and CuCN) with an aryllithium Ar Li. ... 

The conversion of diarylthallium trifluoroacetates to aromatic iodides by treatment with molecular iodine is thus analogous to the well-known conversion of diarylmercury derivatives with iodine to a mixture of an aromatic iodide and an arylmercury iodide (134), but it is much more effective as a synthetic tool because of the spontaneous disproportionation to product of the intermediate arylthallium trifluoroacetate iodide. The present procedure thus provides a practical synthetic method for the ultimate conversion of aryl Grignard reagents to aromatic iodides. 

Aromatic compounds react with mercuric salts to give arylmercury compounds.69 Mercuric acetate or mercuric trifluoroacetate are the usual reagents.70 The reaction shows substituent effects that are characteristic of electrophilic aromatic substitution.71 Mercuration is one of the few electrophilic aromatic substitutions in which proton loss from the a complex is rate determining. Mercuration of benzene shows an isotope effect kB/kD = 6,72 which indicates that the [Pg.1026]

Arylmercury compounds are also often used as starting materials for the synthesis of palladium(ll) complexes. These reactions, whose reagents and products are compiled in Table 3, typically involve the use of chloromercurio derivatives with palladium chloride complexes (entries a-d). 93>95>179-i8i Similar procedures have been applied to the synthesis of ruthenium(ll) and gold(m) complexes (entries e and f).181,182... 

Arylmercury chlorides are valuable reagents for the preparation of aryltellurium trichlorides because they are used when the aromatic substrate is not sufficiently reactive for an easy direct condensation with tellurium tetrachloride. ... 

Mercuric acetate and mercuric trifluoroacetate are the usual reagents.66 The synthetic utility of the mercuration reaction derives from subsequent transformations of the arylmercury compounds. As indicated in Section 7.3.3, arylmercury compounds are only weakly nucleophilic, but the carbon-mercury bond is reactive toward various electrophiles. The nitroso group can be introduced by reaction with nitrosyl chloride67 or nitrosonium tetrafluoroborate68 as the electrophile. Arylmercury compounds are also useful in certain palladium-catalyzed reactions, as discussed in Section 8.2. 

Unactivated aryl iodides undergo the conversion Arl — ArCHj when treated with tris(diethylamino)sulfonium difluorotrimethylsilicate and a palladium catalyst.131 A number of methods, all catalyzed by palladium complexes, have been used to prepare unsymmetrical biaryls (see also 3-16). In these methods, aryl bromides or iodides are coupled with aryl Grignard reagents,152 with arylboronic acids ArB(OH)2,153 with aryltin compounds Ar-SnR3,154 and with arylmercury compounds.155 Unsymmetrical binaphthyls were synthesized by photochemically stimulated reaction of naphthyl iodides with naphthoxide ions in an SrnI reaction.156 Grignard reagents also couple with aryl halides without a palladium catalyst, by the benzyne mechanism.157 OS VI, 916 65, 108 66, 67. 

The example shown in Scheme 2.4.2 is particularly important in that, as illustrated in Scheme 4.1.3, aryl mercury reagents were shown to produce comparable results. Consequently, research into the nature of the aryl groups useful in these reactions have provided interesting results. Specifically, in addition to unactivated aryl groups, aryltin, arylmercury, and halogen substituted aryl compounds may be used. In the remainder of this section, examples utilizing these groups will be presented. 

Arylmercury(II) is a typical soft organometalhc reagent whose metal-carbon bond is reactive due to the labile d metal center [119,120]. The reaction of ArHgX (X = Cl, OAc) with alkene catalyzed by Li2PdCl4 leads to the arylation of alkene (Eq. 5.28). 

Additionally, symmetric ketones have also been produced by the carbonylative homo-coupling of organometallic reagents [94-99]. Under the assistant of palladium catalysts and under the pressure of carbon monoxide, ketones were produced from alkenyl- and arylborates and boronic acids, diaryliodonium salts, organolead compounds and arylmercuric salts. [Rh(CO)2Cl]2 was also applied as a catalyst for the carbonylative homo-coupling of vinyl- and arylmercurials. 

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