Homo-coupling reactions of aryl halides to biaryls catalysed by nickel complexes

Homo-coupling reactions of aryl halides to biaryls catalysed by nickel complexes 

Semmelhack and coworkers [1,2] described homo-coupling of aryl halides to biaryls mediated by stoichiometric amount of Ni(COD)2 in DMF as solvent at 30-60 °C in good to high yields. 4-Bromoacetophenone (73) was converted to 4,4 -diacetylbiphenyl (74) by this method in 93% yield [1], Sheme 6. 

Two equivalents of aryl halide require one equivalent of Ni(COD)2 for the coupling reaction. This method proved to be efficient in a number of examples. Table 1. 

Aryl halide Reaction conditions temp. (°C) / time (h) Yield (%) 

The last disadvantage is typical for all nickel-based processes. The reactivity of the aryl halides is aproximately in the order I Br Cl, while tosylates are completely unreactive under these reaction conditions. 

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