Structure–Reactivity Relationships in Negishi Cross‐Coupling Reactions

Competition experiments have been performed to determine the relative reactivities of substituted bromobenzenes and of different arylzinc reagents in the [Pd(PPh 3 ) 4 ]‐catalyzed Negishi cross‐coupling reaction in THF at 25 °C. The cross‐coupling reactions are accelerated by electron acceptors in the bromobenzenes, the effect of which increases in the order ortho < meta < para . On the other hand, electron acceptors in the arylzinc halides diminish the reaction rates. Hammett correlations show that substituent variations in the bromobenzenes ( ρ =+2.5) have a larger effect than substituent variations in the arylzinc halides ( ρ =−0.98).