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 reactions 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.