 Nickel(II) chloride is first reduced to nickel(0) with 2 equivalents of chromium(II) chloride (as sacrificial catalyst) leaving chromium(III) chloride.The next step is oxidative addition of nickel into the carbon to halide bond forming an alkenylnickel R–Ni(II)–X intermediate followed by a transmetallation step exchanging NiX with a Cr(III) group to an alkenylchromium R–Cr(III)–X intermediate and regenerating Ni(II).This species reacts with the carbonyl group in a nucleophilic addition.