Out of Pd(PPh3)4 and PdCl2(dppf), which catalyst will be better for the Negishi coupling, in particularly if the bromo-substrate is sterically hindered.
Pd(0) is preferable in these coupling reactions so I would second Vivek Gupta's recommendation. Go with Pd(PPh3)4.
Hi
I have several suggestions and points of view
1- You should first think about the activation of your Pd catalyst that is to have a vacant site i.e. Pd (16 e or 14 e) .. for Pd(PPh3)4 you can activate it at room temperature using THF as a solvent or in toluene but you have to heat at temp more than 60 while for Pd(Cl)2(dppf) two Cl groups should be eleminated and this is done by either the Zn substrate or by adding some base in your mixture like NEt3
2- If the Br is sterically hindered you should search for a catalyst which also doesn't have a big ligand so that you will be able to make the oxidative addition and consequently reductive elimination easily or else what you will observe is the loss of Br group and its replacement by a H. So I don't think that these catalysts are the correct choice but you can try
3- I don't know how do you prepare your Zn organometallic species or whether you buy it, but I strongly suggest you to add some eq of MgCl2 or MgBr2 to your reaction mixture, this will greatly enhance the reactivity. And if you prepare your Zn derivative through transmetallation with a Mg grignard reagent, all what you have to do is to make one pot reaction since the Mg salt will precipitate after the formation of Zn.
Pd(PPh3)4 is better for the reaction, but it is also depends on your other reaction conditions like ligands, reagents, solvents.
The Negishi cross-coupling reaction of aryl (Pd(PPh3)4)is an efficient catalyst.
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