[faust]

Hello!

I'm working in michael addition of Ar-X on methyl vinyl ketone by using a cobalt(I) catalyst.

It works fine in DMF/Pyridine (9/1) with Co(Bipyridine)2Br2. The complexe is reduced to [Co(I)(Bypiridine)Br2]- then the Co(I) goes to an oxidative insertion in ArX --> Ar-Co(III)Ligand-X and may be the methyl vinyl ketone is also coordinated.

But how can you explain the following fact : when I use 2,2'-bisimidazole, only the dimere Ar-Ar is observed, and no addition on the MVK. Idem with orthophenanthroline!

I know I need a pi acceptor ligand, but I don't understand why the bipyridine is the only ligand that works...

Do you have any suggestion for other ligands?

Thanks a lot

[rkaminski]

I would have to thing about it more, and I don't have time now (maybe later) but the formation of Ar-Ar in my opinion is caused by radical mechanism. I don't know the mechanism of that reaction of yours but I think that here you have something like double bond in vinyl ketone activation and also the C-Co bond in probably very polarizable so you have different mechanism than in Ar-Ar coupling. You have changed the ligand. Those ligands that you mentioned are totally different from steric and electronic point of view. Maybe think about the possibility of coordination (it means activation) of ketone by metal centre when you're changing the ligand and so on... I hope my thoughts can help a little...