The Negishi coupling reaction is an important transition-metal-catalysed cross-coupling reaction used in Organic Chemistry for the formation of carbon–carbon bonds. It involves the coupling of an organic halide or pseudohalide with an organozinc compound in the presence of a transition-metal catalyst, generally palladium or nickel. The reaction was developed by Ei-ichi Negishi and has become a valuable method for the synthesis of biaryls, substituted alkenes, alkylated aromatic compounds and other structurally complex organic molecules. The general reaction can be represented as: [ R-X + R'-ZnX' \xrightarrow[\text{ligand}]{Pd\ or\ Ni} R-R' ] Here, (R-X) represents an aryl, vinyl or alkyl halide, while (R'-ZnX') represents an organozinc reagent. (X) is generally Cl, Br or I. The organozinc reagent may contain alkyl, alkenyl, aryl or other carbon groups. The important feature of the Negishi reaction is that the carbon group attached to zinc is transferred to the organic halide through the action of a palladium or nickel catalyst. For example, ethylbenzene can be prepared by coupling bromobenzene with ethylzinc chloride: [ C_6H_5Br + C_2H_5ZnCl \xrightarrow{Pd(PPh_3)_4} C_6H_5C_2H_5 + ZnBrCl ] In this reaction, bromobenzene acts as the organic halide and ethylzinc chloride acts as the organozinc reagent. Tetrakis(triphenylphosphine)palladium(0), (Pd(PPh_3)_4), may be used as the catalyst. The phenyl group originally bonded to bromine becomes bonded to the