The Negishi cross-coupling reaction involves the union of an organic (pseudo)halide electrophile and an organozinc nucleophile in the presence of a transition metal catalyst. The mild nature of organozinc reagents and the extremely broad scope of both the nucleophile and the electrophile are attractive features of this reaction. Although palladium catalysts are most commonly employed, recent work has highlighted the utility of chiral nickel catalysts for asymmetric reactions. Examples of Negishi couplings catalyzed by first-row transition metal complexes are also known.
The generally accepted mechanism of Negishi coupling catalyzed by palladium complexes is similar to the mechanisms of other palladium-catalyzed cross-coupling reactions, such as the Suzuki and Stille reactions. Oxidative addition of the organo(pseudo)halide to a Pd(0) species affords an organopalladium(II) complex. Transmetallation of the organozinc reagent to this complex, accompanied by loss of a zinc salt, is followed by reductive elimination to establish a carbon–carbon bond and regenerate the Pd(0) species.