Sir ek hi doubt hai...pure mechanism me pd L2 ke sath me dono Ligand cis kab rahenge aur trans kab rahenge. Aur reductive elimination ke liye cis hona jaruri hai??
I will say let's not get into the isomerization part (experiments has shown trans to cis mechanism happens especially on sonoghashira coupling). Because at times, there may or may not be depending on the reaction. Just remember the general mechanism or shall I say Remember this (1) oxidative addition (for which Pd has to be in 0 oxidation state) (2) transmetallation (3) reductive elimination
Palladium also has a relatively low activation barrier between the oxidation states of 0 and +2 corresponding to the stable d10 and d8 configurations. These oxidation states are important for oxidative insertion and reductive elimination. The lower the activation barrier of the transition from 0 to 2+ and back again, the more rapidly these reactions can take place. The faster and more favorable these reactions are the higher the turnover rate for the catalyst. That apart, There are a lot of other metals that can do much of what Pd does, but cost a lot more- Ir and Pt come to mind. In recent times there has been a push to use first row transition metals (especially nickel, since it's in the same family as Pd) for similar reactions, with some success.
