From J. March, Advanced Organic Chemistry, 4th edition, pp. 716-718, §4-19
Global reaction:
Z-C=C-H + Ar-N2+Cl- =(CuCl2)=> Z-C=C-Ar
Olefins activated by an electron-withdrawing group (Z may be C=C, halogen, C=O, Ar, CN, etc...) can be arylated by tretment with diazonium salt and a cupric chloride(1) catalyst. This is called Meerwein arylation reaction(2). Addition of ArCl to the double bond (to give Z-C(Cl)-C(H)-Ar) is a side reaction(3). In an improved procedure, an arylamine is treated with an alkyl nitrite (generating Ar-N2+ in situ) and a copper(II) halide in the presence of the olefin(4). The mechanism is probably of the free-radical type, with Ar. forming as in Sandmeyer reaction(5) and then(6):
Ar. + H-C=C => Ar-CH-C. =(CuCl2)=> Ar-C=C + CuCl (Principal)
Ar. + H-C=C => Ar-CH-C. =(CuCl2)=> Ar-CH-CCl =(-HCl)=> Ar-C=C (side rxn)
The radical Ar-CH-C. can react with cupric chloride by two pathways, one of which leads to addition and other to substitution. Even when the addition pathway is taken, however, the substitutionn product may still be formed by subsequent elimination of HCl.
(1) FeCl2 is also effective: JOC USSR, 17:765(1981)
(2) for reviews see: Russ. Chem. Rev., 53:943-55(1984); Org. React, 24:225-59(1976)
(3) J. March, pp. 820-1: ArX can be added across double bonds, in a free-radical process, by treatment of olefins with diazonium salts, although Meerwein arylation (substitution) competes.
(4) JOC, 42:2431(1977)
(5) J. March, p. 723:
Ar-N2+X- + CuX => Ar. + N2 + CuX2
Ar. + CuX2 => ArX + CuX
(6) JACS, 84:4150(1962) and 84:4152(1962)