Mercury salts aromatic mercuration

The use of mercury has the merit of easy preparation of the aryl mercury compounds directly from the aromatic compound and an inorganic mercury salt, sometimes in complete regioselective manner. Preparation of the other metallated species generally involves more synthetic steps. An example of a radiofluorode-mercuration reaction (Scheme 29) is the synthesis of 6-p F]fluorometaraminol... 

The mechanism of mercuration is shown in Scheme 2. In the first step, the mercury salt forms a Jt-complex with the aromatic substrate [15, 16]. In 1982, Lau, Huffman, and Kochi [17] reported the first isolation and full characterization (including X-ray molecular and crystal structure) of such an intermediate, a complex of hexamethylbenzene with Hg(TFA)2. The X-ray structure revealed a Hg2( -TFA)i framework with a molecule of C6Me6 -coordinated to each of the Hg atoms. Analogous Jt-complexes have also been observed and studied by Dean and co-workers [18] and more recently by Barron s [19] and Gabbai s [20] groups. The Jt-complex intermediate can rearrange to the ej-complcx (a Wheland intermediate) directly, or sometimes via electron transfer, to produce a radical ion pair which then collapses (Scheme 2) [21,22]. 

It is rather important to note that if an aromatic nitro compound is the substance being nitrated, addition of mercuric nitrate to the nitric acid has no effect on the reaction. For example, nitrobenzene is nitrated to dinitrobezene in the same yield both in the presence of a mercury salt and in its absence. This can be explained by the fact that nitro compounds such as nitrobenzene do not yield addition product with mercuric salts. 

Arylmercuric salts can be obtained with extraordinary ease by mercuration of aromatic compounds with mercury salts, the reaction involving direct replacement of hydrogen by mercury ... 

The ratio of the two products is primarily affected by the nature of the mercury(II) salt and also by the reaction conditions. Since the formation of these compounds could result from either a kinetically or a thermodynamically controlled mercuration process, a study of the mercuration of 3 in the presence of aromatic amines using various mer-cury(II) salts has been more recently carried out in order to determine the conditions under which aminomercuration is reversible, and the results have been compared to those of the oxymercuration170. 

Mercuration of polyalkylbenzenes with mercuric trifluoroacetate [e.g. durene -< 2,3,5,6-tetramethyl-p-phenylenedimercury bis(trifluoroacetate)] has been noted during spectroscopic (u.v., n.m.r.) examination of solutions of alkylated aromatics in trifluoroacetic acid both in the presence and absence of its mercury(ii) salt. Mono- and di-mercuration of 1,2,4,5-tetrafluoro-benzene can be achieved by heating it with mercuric trifluoroacetate... 

The formation of organomercury compoimds by the use of halides and sodium amalgam, diazo compounds, diaizonium salts, decarboxylation reactions, mercuration of aromatic compoimds, and reactions between mercury halides (or acetates) and olefins or acetylenes has been discussed in Chapter 2 and is not further elaborated here. 

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