Decarboxylation of heavy B-metal salts

Nesmeyanov has extended this reaction to the synthesis of aryl derivatives of the heavier B-elements, but the yields are often low. Often the double salts of the metal halide with the diazonium salt are first isolated and then decomposed by a metal such as copper or zinc, e.g. 

In this way an aromatic amine is converted regiospecifically into the corresponding mercurial. An alternative method of preparation, electrophilic mercuration of an arene, however, leads to a mixture of position isomers (p. 62). 

The decarboxylation of the calcium and barium salts of aliphatic acids leads to ketones, e.g. 

When certain salts of organic acids with heavy B-elements decarboxylate, however, metal-carbon bonds are formed. It is generally necessary for the organic acid to contain electron-withdrawing groups. Most examples come from Cu, Hg, Tl, Sn or Pb chemistry, e.g. 

Contrast the effect of heat on mercury(II) benzoate, when substitution of the aromatic ring ortho to the carboxyl group occurs. Mercury(II) trichloroacetate decarboxylates so rapidly that it has not yet been isolated. Bis(trichloromethyl)mercury was obtained in good yield by the reaction of sodium trichloroacetate and mercuric halides in 1,2-dimethoxyethane  

---