Diarylmercurials

The procedure described here serves to illustrate a new, general method for effecting the < -arylation of g-dicarbonyl compounds by means of an aryllead triacetate under very mild conditions. Although the first synthesis of an aryllead triacetate was reported relatively recently, a wide range of these compounds can now be readily prepared. The most direct route to these compounds is plumbation of an aromatic compound with lead tetraacetate, and in the procedure reported here p-methoxyphenyllead triacetate has been prepared in this way. It may also be obtained by reaction of the diarylmercury with lead tetraacetate, a longer, but more general method of synthesis of aryllead triacetates. 

We return now to the mercuro-de-diazoniation. Nesmeyanov s school continued the work on metallo-de-diazoniations from 1929 to 1953 (see summary by Nesmeyanov, 1972). A major discovery was made at the very beginning, namely the influence of copper powder (Nesmeyanov, 1929 b Nesmeyanov and Kahn, 1929). With this addition metallic mercury was not required instead the double salt of the diazonium chloride and mercuric chloride was used. The copper reacts stoichiometrically as an electron donor. Therefore, either arylmercuric chlorides (Scheme 10-87) or diarylmercury compounds (Scheme 10-88) can be obtained. These reactions are called Nesmeyanov reactions. Specific examples are the syntheses of di-2-naphthyl-... 

Diarylhydrazines, from ArNJ 195 Diarylmercury compounds 273 f. 1,4-Diazabicyclo [2.2.2]octane (DABCO) 360 Diazenes 6, 126, 192, 195, 211, see also Azo compounds... 

Protodemercuration was first studied kinetically by Kharasch et al.604, who measured, qualitatively, the rates of cleavage of diarylmercury compounds by acids, viz. 

A further kinetic investigation of the rates of cleavage of diphenylmercury (and some dialkylmercurials) showed similar kinetic features608. The first-order rate for the reaction of diphenylmercury with acetic acid at 25 °C was 4.98 x 10", which agreed quite well with the value from the above determination (2 x 10-4 at 42 °C with dioxan). In the presence of perchloric acid, second-order kinetics were found to be obeyed (for dineophyl mercury and presumably for diarylmercurials as well) for a twofold concentration change in both mercurial and perchloric acid. Two separate mechanisms were proposed for the reactions in the absence, and presence, of perchloric acid. Under the former conditions an SEi process (244) was... 

The kinetics of the cleavage of a wide range of diarylmercurials by hydrochloric acid in 90 vol. % aqueous dioxan have been studied by Nesmeyanov et a/.614 The second-order rate coefficients are gathered in Table 185, and are correlated... 

The kinetics of the hydrochloric acid-catalysed cleavage of diarylmercurials in... 

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. 

Similarly, dilithiation of 2-(4-bromophenoxy(ethanol in the presence of magnesium 2-ethoxyethoxide followed by reaction with 0.5 equiv. of HgCl2 afforded the corresponding diarylmercury compound 4-(H0(CH2)20)-C6H4)2Hg 26 whose crystal structure has been determined (Equation (12)).47 In addition to these alcohol and ether derivatives, thio- and phosphinoaryl mercury compounds have also been prepared. Thus, the dilithium salt... 

Studies of interactions between tetranitromethane and aryl derivatives of magnesium, tin, and mercury in sulfolane (Shevelyov et al. 1974, 1975) confirm that NO2 radical has some slight activity. For example, the reaction of diarylmercury with tetranitromethane passes through a transient step with the formation of radicals Ar and NO2. These radicals almost do not interact ... 

The reaction of diarylmercurials with elemental tellurium under heating, one of the oldest methods for the preparation of diaryl tellurides, " has been later employed in some specific cases. " ... 

A well-known reaction in organomercury chemistry consists of the conversion of arylmercuric chlorides to diarylmercury compounds by means of solutions of sodium iodide or sodium thiosulfate. Treatment of chloromercuriferrocene readily produces diferrocenylmercury (XXIX) under these conditions (63, 90). 

Razuvaev and Savitskii33 report that the action of iodine on a number of dialkyl- and diarylmercurys in solvent carbon tetrachloride follows second-order kinetics. Norate coefficients were given, but values of Ea and log A were recorded. Kinetics were presumably carried out under normal laboratory condtions, but Lord and Pritchard34 report that the iodinolysis of dimethylmercury by iodine in a number of solvents was subject to catalysis by light. 

Arylmercuric halides may be used in place of diarylmercurials. Excellent yields, often 90-98%, were obtained in many cases. Table III lists some examples. Oxidative degradation studies of selected products showed that the aryl carbon atom originally attached to mercury was the one that became bonded to the apical carbon atom of the cluster. This reaction was much less useful in the preparation of alkyl derivatives, because of very long reaction times (1-2 weeks) giving at best moderate yields (Table III). The reaction of a-haloalkylmercurials with HCCo3(CO)9 occurred... 

In 1942, Nad and Kocheshkov1161 studied in detail the reaction of Pb(OOCMe)4 with diarylmercury in CHCI3 at room temperature. This appeared to be a useful method for the preparation of diaryldiacetoxyplumbane. In 1948, Nesmeyanov and coworkers1195,1196 used it for the synthesis of (ClCH=CH)2Pb(OOCMe)2. 

The dialkyl- and diarylmercury compounds are very useful for the preparation of other organo compounds by reactions of the general type ... 

Although there are numerous examples of dimerizations of organo-metallic reagents by copper(II) salts, one particularly interesting example concerns 2,2 -dilithiobiphenyl 304). Wittig and Klar have proposed several transient copper(II) ate complexes and a stable copper(I) complex to account for the high yields of biphenylene and o-tetraphenyl-ene. Diarylcopper(II) compounds were supposedly isolated, and characterized by elemental analysis, from diarylmercury compounds and copper at 120°C 11, 197) an unlikely reaction. 

Much less attention was devoted to organometallic liquid crystals, even though the first examples, diarylmercury derivatives, were described as early as 1923 by Vorlander [6]. Recently, Ziminski and Malthete [7] reported the first mesomorphic (butadiene)iron-tricarbonyl derivatives. 

Aromatic boranes are synthesized from diborane and arylmagnesium halides [i 5], arylmercury halides [iS5], or diarylmercury compounds [/S i]. Their oxidation furnishes phenols in variable yields. A large excess (up to 16 mol) of BH3 is necessary for high yields (equations 604 and 605). 

The reactions between dialkenyl- or diarylmercury derivatives and (ejco-5-acetoxy-tricyclo[2.2.1.0 ]hept-enmercury derivatives with an enrfo-5-alkenyl or an endo-S-aryX substituent, respectively. The best results were obtained in methanol much less satisfactory results were obtained in acetonitrile. Yields above 50% were obtained when diphenylmercury and bis(2-methylprop-l-enyl)mercury were employed giving 6 and 7, respectively. 

Pure diarylzincs, including nuclear-substituted ones, are best prepared either by this method, heating zinc and the diarylmercury in, e.g., boiling xylene,146 147 or from zinc chloride and phenyllithium.148 Diarylzincs can, however, also be obtained by transmetallation, e.g, by interaction of diethylzinc and the appropriate triarylboron.149... 

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