With arylmercury chlorides

Diaryltellurium dichlorides (general procedure) TeCl4 (10.8 g, 40 mmol) and arylmercury chloride (80 mmol) are heated under reflux in anhydrous dioxane (100 mL) for 2 h. 

The solution is cooled at 10°C and the HgCl2.dioxane precipitate filtered off and washed with cold dioxane (15 mL). The filtrate is poured while stirring into 1% ice-cold HCl (400 mL). The dichlorides precipitate as crystalline solids (yields 90%), and are recrystallized from benzene/petroleum ether 30-60°C (Ar=Ph, m.p. 160-162°C p-MeCgH4, m.p. 165-166°C). 

It mnst be pointed out that the reaction of tellurium tetrachloride with aryl Grignard or lithium reagents is inappropriate for the preparation of diorganyltellnrium dichlorides owing to the difficulty of stopping the reaction at the 1 2 stage. 

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Bisorganomercury compounds with carbonyl groups in the P- and P -positions (10.68) give arylmercury chloride (10.67) together with the dimer (10.69) of the organic residue that is bounded to mercury in the starting material (Hu et al., 1991 yields 10.67 64-98%, 10.69 50-63%). 

Aryl derivatives of the heavier group 6 derivatives can also serve for the synthesis of arylmercury compounds.52 For instance, treatment of the diaryltellurium complex 30 with HgCl2 leads to the formation of a coordination complex which undergoes a slow dismutation reaction to afford the arylmercury chloride derivative 31 and the corresponding tellurium species (Scheme 3).53... 

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. ... 

The formed mercury dichloride is separated as a crystalline complex with dioxane. Since the starting arylmercury chlorides are easily prepared from diazonium salts, this method allows the conversion of anilines into aryltellurium trichlorides. 

Another reaction of considerable preparative value for thiophenes is mercuriation (with mercuric chloride or mercuric acetate), the lower selectivity here (especially with the acetate) giving significant yields of (3-substituted derivatives. These arylmercurial derivatives are readily converted into other compounds. Mercuric chloride substitutes in the 2- and then the 5-position [1892LA(267)172 14LA(403)50], and the OR and SR substituents direct into the 5- and then the 3-position [32LA(495)166]. 

Arylpalladium salts ArPdX prepared from arylmercury compounds and lithium palladium chloride couple with allylic chlorides in moderate yields,... 

Unsymmetrical diorganyltellurium dihalides are formed upon condensation of aryltellurium trichlorides with activated aromatic compounds and with ketones. The addition of the trichloride across carbon-carbon double bonds in alkenes, as well as the reaction with aryl (trimethyl)silane, hexaphenyldilead, and arylmercury chlorides leads to the transfer of the aryl group to the tellurium atom. 

Mercuric acetate and mercuric trifluoroacetate are the usual reagents. 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 chloride or nitrosonium tetrafluoroborate as the electrophile. Arylmercury compounds are also useful in certain palladium-catalyzed reactions, as discussed in Section 8.2. 

Historically, the first report of the Pd-catalyzed cross-coupling reaction with acyl halide used organomercury compounds. Although alkyl- and arylmercury chlorides did not work, the use of dialkyl- and diarylmercury compounds gave the desired ketones in good yields. Acyl bromides are necessary to bring about fruitful results. The use of HMPA as the solvent is also unavoidable (Scheme 9). 

Arylmercury chlorides can also be coupled with acyl chloride in the presence of iodine and a catalytic amount of Pd(PPh3)4. In this case, not only HMPA but also acetone and THF can be used as the solvent. More recently, the Pd-catalyzed conpling reaction of... 

One of the earliest reports of microwave-assisted organometallic synthesis involved the preparation of arylmercuric chlorides. Heating an ethanol solution of diphenyldiazene and 2-phenylpyridine with Hg(OAc>2 inside a sealed Teflon vessel led to the formation of the desired arylmercury complexes. Yields were a little lower than conventional approaches, but reaction times were at least 30-times shorter. This chemistry was extended 10 years later when a solvent-free method was developed. Arylmercuric chlorides together with benzoquinone, barbituric acid, or thiobarbituric acid were adsorbed on basic alumina before being exposed to microwave irradiation for 1-3 min to produce derivatives (YIF = 1.3-1.5). 

With the exception of arylmercury compounds (like thiomersal) as a stabilizing addition to some eyedrops and the application of one drop of a mercury chloride solution in the eyes of newborns for syphilis prophylaxis, mercury-containing pharmaceutical preparations are obsolete today. But in many countries with dark-skinned people, skin-lightening creams and soaps are sold containing up to 3% mercury iodide or 10% mercury amidochloride. Despite a prohibition of the distribution of these products in the European Community, in Northern America, and in many African states, they are still exported from several European countries as germicides to the third world and reimported illegally to European cities with a substantial black population like London, etc. [8]. 

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