Negishi Coupling Reaction

in this video, we're going to take a look at the Negishi coupling reaction. Now the Negishi reaction involves the coupling between a carbon Halide and an organic zinc Halide with a palladium or nickel catalyst. Now the reaction uses a palladium or nickel catalyst in the formation of mainly by a real or buy vinyl products. Now we're going to say here that the Negishi coupling reaction can mirror the generic setup for a cross coupling reaction. So in our generic cross coupling reaction we have our one X. Which represents our carbon Halide. We have our two C. Which represents our coupling agent. Through the use of a transition metal catalyst, we have the combining of R one and R two to give us our coupling product, C. X. Would just be our our by product. Now, if we take a look at the Negishi coupling reaction, we're gonna say we still have our one X. So we still have a carbon Hallett and we're gonna say here that the R one group of the carbon halid is represented by a vinyl or real. Um Al kiel, Benzel or an illegal group are too represents my coupling agent, but more specifically in terms of the Negishi coupling reaction, it represents my organic zinc khallad. So here are two can represent and our kill group, it could represent a Benzel group or an Alka Neil group. Now here, we're gonna say in terms of this coupling reaction, R C. Is represented by Z and X. Or X. Is either a chlorine or a broom mean, and we're gonna say here that the X group of the carbon khallad, as usual, is represented by good leaving groups of chlorine, bromine iodine or our trifle eight. Now R one and R two combined together to give us our coupling product here and then we have our byproduct being created so fundamentally what's happening looking at it in a simple way, we can say that we have the loss of this X from the carbon khallad and the loss of ZN X for my organic zinc Halide. And then what's left is R. One and R two, which coupled together, combined together to give us our product. So that's the simple way of looking at this reaction. Before we even talk about the mechanism. So based on this pattern, look and see if you can do the example that's below, click on the next video and see how I answer that same example question.

So here we need to determine the product from the following Negishi coupling reaction. So remember what's the simplest way of looking at this? Well we have our halogen here, so this must be our carbon Hallett Therefore this whole benzene ring with the two methyl groups must represent our one here we have ZN connected to X. Which in this case is booming. So this must be our organic no zinc Halide. So the all keen portion must be R. two. So remember the X. Group of our carbon khallad and the C. Group of organic zinc Halide are lost in the process so that my R. One and R. Two groups can combine together. So we draw out our our one group. Then we have this our two group being attached so that would represent the product that I just formed. So basically the R. One group is replacing wherever the Z. And X group was. In order to maintain the same type of stereo chemistry around the AL keen double bond and what we just made is a product that's more conjugated and therefore more stable. Okay, so now that we've gone over the simple way of looking at this coupling reaction, click on the next video and see how exactly does the mechanism work to give us our more conjugated product

So the Negishi coupling reaction follows the traditional steps. In terms of a coupling reaction and a catalytic cycle, we have our oxidative addition step followed by a transmit elation step ending with our reductive elimination step. So in the oxidative addition step we have the carbon halid basically um combining with the transition metal complex. Now remember the transition metal has a lone pair which gets from its d orbital electrons. It uses them to connect to the halogen. And then that causes this bond here to break and attach to that same palladium. So we wind up getting is our palladium with its two legans still attached Now being connected to our one and X. So that is our new transition metal complex. Now we're going to say that the R two group of the organic zinc compound or zinc khalid um transfers from zinc to the palladium complex. Alright, so what's going to happen here is this bond here breaks so that our two can attach to the palladium at the same time, the X. Leaves and attaches to the sink. So we wind up getting our palladium still connected to the same two Liggins now connected to R. One and our two. And then as a by product we have our zinc connected to to allergens. Then finally we have reductive elimination. So this stuff helps to form the coupling product that we want at the end and it also helps to regenerate our transition metal catalyst to help the whole process begin again. So we're going to have this structure here, we're going to bring it down. So are ones going to attach to our two And then R2 is gonna let go of the electrons in the bond and give them to the palladium to help regenerate our catalyst. Right now. We're going to have R one Connected to our two plus The regeneration of our catalyst. Remember the two main driving forces in terms of these types of coupling reactions is to help make a more conjugated, more stable product. But also um we want the transition metal to follow the 18 or 16 electron rule by reforming to its original state. It's no longer following the 18 or 16 electron rule. So I don't want to begin the process again and thereby retaining either 18 or 16 electrons and also helping to make more coupling product at the end. So remember when it comes to this Negishi type reaction, what's happening fundamentally is that we have a carbon Halide, it loses its X group, and then we have an organic zinc Halide which loses its Z and X group, R one and R two combined together to give us our coupling product at the end