Evidence of Fast Activation of Unreactive Aryl Chlorides in Cross-Coupling Reactions

It has been demonstrated that aryl chlorides traditionally showing low reactivity in cross-coupling reactions are able to compete successfully with more reactive aryl bromides for the formation of the products of Suzuki-Miyaura and Mizoroki-Heck reactions. The results of competing experiments indicate that the true reason for low reactivity of aryl chlorides in these reactions cannot be a low rate of their oxidative addition to Pd(0) complexes that has been stated in literature as a default. The data obtained suggest that the determining factor in the reactivity of aryl chlorides in the Suzuki-Miyaura and Mizoroki-Heck reactions is a sharp reduction in the fraction of active palladium catalyst due to changes in its formation-deactivation processes on passing from more reactive aryl iodides and aryl bromides to aryl chlorides.