* Palladium precatalyst species are activated under reaction conditions to form a reactive Pd compound, A. The exact identity of the catalytic species depends strongly upon reaction conditions. With simple phosphines, such as PPh (n=2), and in case of bulky phosphines (i.e., ) it was demonstrated that monoligated species (n=1) are formed. Furthermore, some results point to the formation of anionic palladium species, [LPdCl] , which could be the real catalysts in the presence of anions and halides.
* The active Pd catalyst is involved in the oxidative addition step with the aryl or vinyl halide substrate to produce Pd species B. Similar to the above discussion, its structure depends on the employed ligands. This step is believed to be the rate-limiting step of the reaction.
* Complex B reacts with copper acetylide, complex F, in a transmetallation step, yielding complex C and regenerating the copper catalyst.
* The structure of complex C depends on the properties of the ligands. For the facile reductive elimination to occur, the substrate motifs need to be in close vicinity, i.e. cis-orientation, so there can be trans-cis isomerisation involved. In reductive elimination the product tolane is expelled from the complex and the active Pd catalytic species is regenerated.