Synthesis of n,n ′‐biquinolines by a coupling reaction of bromoquinolines using organonickel(0) complexes

Tris(triphenylphosphine)nickel(0) (A) and a zerovalent pyridine–nickel complex (B) have been used as reagents for the coupling reaction of 3‐, 6‐ and 8‐bromoquinolines: 3,3′‐, 6‐6′‐ and 8,8′‐ Biquinolines were obtained in quantitative yields when A was used as the coupling reagent. B gave always a mixture of the n,n ′ ‐biquinoline and substitution products. A mechanism can be outlined to explain the coupling reaction of bromoquinolines using zerovalent nickel complexes.