Organozinc compounds with aromatic halides

The electrochemical preparation of organozinc compounds obtained from the corresponding aromatic halides and with the use of a nickel complex as catalyst is only efficient in dimethylformamide as solvent. Moreover, in most cases and as described previously, the reaction requires the presence of excess 2,2 -bipyridine (five molar equivalents with respect to nickel) to achieve the transmetallation reaction leading to the organozinc compound and to avoid the formation of biaryl, Ar-Ar (equation 53). 

Since transmetalation of organozinc halides in the presence of palladium or nickel compounds easily proceeds, the coupling reaction is carried out by the catalytic reaction via formation reaction of these organometallic compounds. For example, an aromatic /i-ester is prepared in a high yield by a reaction with a palladium catalyst as shown in eq. (5.31) [78]. 

---