Generation of catalytically active Pd(0) species from Pd(OAc)₂ has been examined, in the context of Suzuki–Miyaura reactions involving substitution of aryl bromides under aerobic and ambient conditions. Using a combination of spectroscopic, microscopic and kinetic measurements, the role of each reaction component is delineated in the speciation of the palladium species. Among the key findings are the effects of O₂, H₂O and inorganic base, and implications for catalytic activity.