“…[65][66][67] Despite this well-accepted general mechanism, the Heck catalytic reaction can involve different types of Pd(0) and Pd(II) intermediates, whose structure and reactivity vary depending on the experimental conditions, the catalytic precursors (e.g., whether they are Pd(0) complexes, Pd(OAc) 2 , or palladacycles), the types of ligands (e.g., mono-or bisphosphines, carbenes, and bulky monophosphines), and any possible additives (e.g., halides and acetates) used in the reaction. 65 Furthermore, although there is agreement on the general mechanism of the Heck reaction, there is also still some ambiguity about the mechanism of the Heck reactions catalyzed by heterogeneous catalysts. Nonetheless, mechanistic studies of the Heck reactions catalyzed by supported Pd-based heterogeneous catalysts have led to the conclusion that (1) soluble and catalytic-active palladium species form by leaching from the supported-Pd catalysts and (2) these soluble palladium species then involve in the reactions, and their catalytic activities and readsorption on the solid material play major roles in the overall rates of the catalytic reaction.…”