Nickel(O) complexes coordinatively unsaturated with 2,2'-bipyridine (bpy) are more reactive in the oxidative addition to organic halides than the saturated analogs. sigma-Organonickel complexes formed as intermediates of catalytic cycles were prepared in high yields using nickel complexes coordinatively unsaturated with bpy and aromatic halides containing a methyl group in the ortho-position of the ring.