debate, with critical mechanistic questions unanswered. It was proven in 2018 by Košmrlj et al. that the reaction proceeds along the two interconnected Pd0/PdII catalytic cycles. Similar to the original mechanism, the Pd0 cycle begins with the oxidative addition of the aryl halide or triflate to the Pd0 catalyst, forming complex B and activating aryl halide substrate for the reaction. Acetylene is activated in the second, PdII mediated cycle. Phenylacetylene was proven to form Pd monoacetylide complex D as well as Pd bisacetylide complex F under mild reaction conditions. Both activated species, namely complexes B and F, are involved in the transmetallation step, forming complex C and regenerating D. The resulting products of reductive elimination, disubstituted alkyne product as well as regenerated Pd0 catalytic species, complete the Pd0 catalytic cycle. It was demonstrated that amines are competitive to the phosphines and can also participate as ligands L in the described reaction species. Depending on the rate of the competition between amine and phosphines, a dynamic and complex interplay is expected when using different coordinative bases. Reaction conditions The Sonogashira reaction is typically run under mild conditions. The cross-coupling is carried out at room temperature with a base, typically an amine, such as diethylamine, that also acts as the solvent. The reaction medium must be basic to neutralize the hydrogen halide produced as the byproduct of this coupling reaction, so alkylamine compounds such as triethylamine and diethylamine are sometimes used as solvents, but also DMF or ether can be used as solvent. Other bases such as potassium carbonate or cesium carbonate are occasionally used. In addition, deaerated conditions are formally needed for Sonogashira coupling reactions because the palladium(0) complexes are unstable in the air, and oxygen promotes the formation of homocoupled acetylenes. Recently, development of air-stable organopalladium catalysts enable this reaction to be conducted in the ambient atmosphere. In addition, R.M Al-Zoubi and co-workers successfully developed a method with high regioselectivity for 1,2,3-trihaloarene derivatives in good to high yields under ambient conditions. Catalysts Typically, two catalysts are needed for this reaction: a zerovalent palladium complex and a copper(I) halide salt. Common examples of palladium catalysts include those containing phosphine ligands such as . Another commonly used palladium source is [, but complexes containing bidentate phosphine ligands, such as , , and have also been used. The drawback to such catalysts is the need for high loadings of palladium (up to 5