Is oxidative addition indeed the rate-determining step of the Suzuki-Miyaura reaction with less-reactive aryl chlorides under ligand-free conditions?

The retarded oxidative addition of aryl chloride to Pd(0) is believed, by most scientists, to be the main hindrance in achieving effective conversion in the Suzuki-Miyaura reaction and other cross-coupling reac-tions of aryl chlorides. Herein, we have demonstrated by competing experiments, using two aryl chlorides under ligand-free catalytic conditions (absence of strong ligands; high ratio of substrate to catalyst), that the elementary step of oxidative addition is substantially reversible. This implies that the hypothesis on the rate-determining character of the oxidative addition step is incorrect, and the existing problems with aryl chloride conversion in the Suzuki-Miyaura reaction are caused by some other reasons that need to be investigated. (C) 2020 Elsevier B.V. All rights reserved.