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Topic: several question about palladium cross coupling  (Read 1868 times)

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Offline Alcor

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several question about palladium cross coupling
« on: May 27, 2017, 03:07:44 PM »


Hi, everyone. I'm a master's student in first year, and doing research in Nation Sun Yat-sen University which is located in Taiwan.

 I have some questions about palladium cross coupling, but I have no one to discuss with,  neither my professor and my classmates, so I decided to post this article, hope someone can help me...

I'd read several review about palladium cross coupling, and what I really curious is about Heck reaction, I know that Heck reaction is about unsaturated halides or pseudohalides with an alkene to form a substituted alkene, but I had saw some example doing palladium cross coupling without halides or pseudohalides, like the paper publish in ChemComm in 2010 《Oxindole synthesis by palladium-catalysed aromatic C–H alkenylation》(DOI:10.1039/b926560k), and I don't know how to explain it.

The second question is, although the paper I read is not so much, but seems that the case
 about palladium cross coupling work with the compound which have carboxylic acid  functional group but not remove or break the carboxylic acid is uncommon to see, but Decarboxylative cross-coupling is common.

This question I'd ask my friend before (he is a PhD from Texas A&M-Chemistry),and he give me a several reason:

1. the carboxylic acid (COOH or COO-) is probably to coordination with metal to form kappa-1 or kappa-2 complex to decrease the reactivity of metal.
 
2. carboxylic acid is and acid , it may quench with base.

3. the selectivity, metal may react with C=C double bone to hydrogenation the alkene to alkane, or just to reductive the C=O doubling bond to alcohol.

4. it may go decarboxylation to make RCOOH to R-H, or go decarbonylation to form the OC-Metal complex to kill the metal, even the metal is still alive, but the RCOOH is no longer exist.

But I'm not sure is that right or not, like the first reason, as we know Pd(OAc)2 is exist with RCOO- and it still have reactivity, and the second reason maybe can add more than 1 eq base to solve this question?

Hope someone  can help me, even just tell me which paper I should study to find the answer is okay, too.

And sorry about my poor english.



Offline phth

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Re: several question about palladium cross coupling
« Reply #1 on: May 28, 2017, 03:22:30 AM »
It works because it is an intramolecular reaction.  Palladium reacts selectively with the alkene over the carbonyl: 95%+. read the back references.  Coordingation of a carboxylate to the metal center will only slow down the reaction, and it could decarboxylate, but it is a limited number of substrates that will...

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