Arylmercuric chlorides

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-... 

A different synthesis of arylmercuric chlorides (10.67) was described recently by Hu and Yu (1989). They showed that chloromercuryacetaldehyde (10.66) reacts with arenediazonium salts in aqueous acetone as shown in Scheme 10-89. The reaction is catalyzed by cupric chloride (yield 66-88% twelve substituted benzenediazonium chlorides were investigated). 

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). 

Arylmercuric chlorides are also dimerized to biaryls by this catalytic system in this case HMPT is the preferred solvent. Yields of biaryls range from 40 to 907o. 

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). 

Dichloropropene appears to be the first example of this class of compounds used in Pd-catalyzed cross-coupling. The reaction of arylmercuric chlorides with 2,3-dichloro-propene under the influence of LiPdCL-CuCL gave the CTOss-coupling products in good yields (Scheme 58).ti ]... 

Further important organometallics which offer ready access to the homo-coupling products are arylmercuric halides. This can be easily prepared by several ways, but the most convenienty from the corresponding aryldiazonium salts via the Nesmeyanov reaction, see Chapter 4. Arylmercuric chlorides derived from electron-rich arenes such as thiophene, which easily undergoes the direct mercuration reaction at 2-position, can be readily coupled with an equimolar amount of palladium(II) chloride in the presence of triethylamine as the base in high yield [35], Scheme 16. 

Ar. nitro compounds from arylmercuric chlorides HgCl- N02... 

---