Reductive elimination can be seen as one of the last steps within a typical cross-coupling reaction. Within this step, we have the R₁ group, which was originally part of our carbon halide, and the R₂ group, which is originally part of our coupling agent, finally leaving our transition metal complex and forming a sigma or single bond with one another. Now, this step can be seen as the opposite of oxidative addition. Remember, in oxidative addition, we have ligands bonding to our transition metal complex in order to get that transition metal closer to the 18 or 16 electron rule. Within this step, we have the exact opposite. We have those same ligands finally leaving our transition metal complex, and we're turning it back to a count that's not 18 or 16 under normal cases.

Now we're going to say that elimination usually signifies the formation of a pi bond, but reductive elimination doesn't always do that with every cross-coupling reaction. Now, the way it works is we're going to have our R₁ group leaving our transition metal M and bonding to our R₂ group. At the same time, we have the bond between R₂ and M breaking, and the electrons going to M. This creates R₁ single bonding to R₂. Then we're going to have the regeneration of our transition metal complex or transition metal catalyst. Now, this is a good thing because remember, the catalyst is not consumed within the reaction so it had to return to its original form. Also, this gives extra motivation for the catalyst to undergo another cycle of cross-coupling reactions because, remember, it's no longer following the 18 or 16 electron rule, so it desperately wants to undergo oxidative addition again so that its transition metal can get closer to the 18 or 16 electron rules. So that's how we can keep this reaction going and going. Also, by going through the reaction again, we have a chance to make more conjugated products later on. So those two driving forces can help this reaction go through another cycle.

Now, this step also follows stereochemical rules. So, with stereochemistry, we're going to say the reductive elimination generally results in the retention of stereochemistry when it comes to double bonds. So if your alkene has E or Z configurations, it tries to retain that as much as possible in terms of this last step. So remember, with a typical cross-coupling reaction, we have 3 steps. We have oxidative addition, usually somewhere in the beginning, transmetalation near the middle, and at the end we have our reductive elimination step. Now these three steps will be found in some way within these cross-coupling reactions. Some may contain additional steps, but these three steps here of oxidative addition, transmetalation, and reductive elimination form the foundation for a lot of the reactions we'll see later on. So just keep them in mind and keep in mind some of the rules that we covered in terms of how they operate.