Organozincs biaryl formation

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). 

Aryl-aryl coupling by reaction of halides with organozinc reagents is a useful and mild route for the formation of some mixed biaryls. Such a process has been used in the reaction of pyridylzinc reagents with various iodoaromatic compounds giving good yields of coupled products (equation 65)484 87. 

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