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Topic: multiple cross-coupling  (Read 5888 times)

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Offline mahirtz

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multiple cross-coupling
« on: August 27, 2007, 03:09:13 PM »
I have an aromatic substrate which has multiple chlorines substituted on its outer rim. I could cross couple alkyl grignard reagents in Kumada coupling manner. But cannot finish suzuki coupling. Though itsso popular its not working. I cannot make chlorines into Bromine or Iodine. The cross-coupling has to work with chlorine.
I take Base 10 equiv and Boronic acid 4 equiv for each chlorine together with Pd/NHC in nolan et al method. Still didn't work. I wonder why. somebody reported 50% yield with the same substrate but when i see his supporting info the final product NMR was to low (compound might be very low). i doubt the yield. thanks any suggestion.
Thanks guys
Mahender
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Offline movies

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Re: multiple cross-coupling
« Reply #1 on: August 27, 2007, 05:02:41 PM »
Did you try Pd(Pt-Bu3)2 - the Fu method?
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Offline alphahydroxy

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Re: multiple cross-coupling
« Reply #2 on: August 28, 2007, 08:23:17 AM »
Yeah, there are a few systems out there for performing suzuki coupling reactions, you may want to try a couple of others...

Just to be clear, could you draw up a scheme of the reaction you are actually attempting?
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Offline kiwi

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Re: multiple cross-coupling
« Reply #3 on: August 29, 2007, 06:45:50 AM »
aryl chlorides can be challenging substrates afaik, but i haven't done much coupling stuff. what about a biphenylphosphine-type ligand? (such as this one: Aldrich cat# 638080; CAS# 564483-19-8). apparently the intermediate PdL complex (formed from Pd2(dba)3 in situ) with these sorts of ligands is very nucleophilic, which sounds like what you need.
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Offline CEDLIN

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Re: multiple cross-coupling
« Reply #4 on: September 07, 2007, 03:44:20 AM »
We've found the POPd ligands developed by Li to be extremely good catalyst systems for aryl chlorides.

You can buy them from CombiPhos (http://www.combiphos.com/home.htm) who also have excellent preps and leading references on their website.  Also they are much easier to clean up than PdCl2dppf etc.

Have you tried encapsulated palladium? The PdEncat with BINAP may work for you?
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Offline mahirtz

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Re: multiple cross-coupling
« Reply #5 on: September 11, 2007, 01:00:05 AM »
I tried the Fu and Ackerman method. Those work only for limited aromatic substrate. Functionalized aromatics are really hard to couple. The subtrate is Corannulene penta chloride, which is bowl shaped PAH. Suzuki coupling is the only reaction. I modified the reaction procedure by applying pressure externally (like putting the reaction in pressure vessel and lowering the temp to -78oC under N2 and heating it 150oC for 5-10 days.) still no use.. Any suggestion in Experimental procedures?
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