_P.-Powell-auth.-Principles-of-Organometallic-Chemistry-Springer-Netherlands-1988

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 ofthe metal
halide with the diazonium salt are first isolated and then decomposed by a metal
such as copper or zinc, e.g.
NaN0 2 llgCI 1 L'u/Cu' +
ArNH, -----> ArN, +CI- -----> ArN; HgCI; --'---------> ArHgCI
HCI
In this way an aromatic amine is converted regiospecifically into the corresponding
mercurial. An alternative method ofpreparation, electrophilic mercuration of
an arene, however, leads to a mixture of position isomers (p. 62).
2. 7 Decarboxylation of heavy 8-metal salts
The decarboxylation of the calcium and barium salts of aliphatic acids leads to
ketones, e.g.
[ro +Coca,
[ CHz·<~- ++ 6
0 - Ca -------
/
CHz·C~
~o
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, TI. Sn or Pb chemistry, e.g.
heat
(
--
R = c 6 F 5 , c 6 CL5 , CF 3 , CCL3 ,
2, 4,6-trinitrophenyl)
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:
2Cl,CCO,Na + HgCI, ---> (Cl,C),Hg + 2:\faCI + 2CO,
Similarly certain triphenyllead salts of organic acids with electron-withdrawing
substituents decarboxylate on heating at about 160°C under reduced pressure,
e.g.
Ph,PbOCOCII,COOEt ---> Ph,PbCH,CO,Et + CO,
A rather unusual reaction of this type is the decomposition of tributyltin formate,
in which tributyltin hydride is produced:
170 c
Bu,SnOCHO ------+ Bu,SnH + CO,
IOmm
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