Hello, based on my reading the NHC (or any other ligand like phosphines) simply donates electrons to and controls the steric environment around the metal. The donation of electrons makes the Pd(0) complex more nucleophilic, speeding up oxidative insertion, and the sterics of the ligands help facilitate reductive elimination rather than beta-hydride elimination (if thats a possible pathway).

So the ligand simply is bound to the metal but based on what I have read it does not interact with the susbstrates (the boronic acid and the halide). It is believed though that the ligands do undergo cis-trans isomerization before the reductive elimination step so you should probably show that in your report.

Thank you. This was helpful.

Dear Chijioke,

Although you can catalyze your C-C coupling reaction using Pd alone. But the catalyst activity alters by the use of NHC ligand either increase or decrease in catalytic activity. So, indirectly the inductive effect, steric crowding created by NHC governs the C-C coupling reaction.

NHC are very good ligands. Easy preparation and steric tunability, inexpensive starting materials and also are very strong sigma electron donors, ideal for chlorides, tosylates, mesilates coupling partners. I would not recomend them for C-N Cross coupling by Ni catalisys.

Cheers

NHC ligands in Pd-NHC catalysts are the good electron donors which enhances the electronic properties of Pd-NHC by induction. This may leads to the increased oxidative insertion activity of the catalyst and thereby promote the C-C/C-hetero atom bond couplings at a faster rate. Also the steric factor due to bulkier groups in NHC ligands plays a major role in the catalytic transformations.