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Topic: Removing Pd(PPh3)4 from Reaction  (Read 3092 times)

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Offline AlphaScent

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Removing Pd(PPh3)4 from Reaction
« on: August 26, 2019, 10:27:09 PM »
Hey all!

Does any one have a trick to removing Pd(PPh3)4 from a cross-coupling reaction?  In my case I did a Negishi coupling.

VinylMgCl was cooled to 0C and THF soln of ZnBr2 is added and stirred for 15 min.  My vinyl iodide was dissolved in THF and 0.03 eq Pd(PPh3)4 was added.  The homogeneous soln was added to the organozinc reagent.  Let stir at RT 2.5 hr.

Quench with 3 aliquots of sat. ammonium chloride and then add 1/2 aliquot of hexanes.  Extract aqueous. Wash aqueous with ammonium chloride, water, brine, dry.  NMR looks great except the Pd(PPh3)4. 

The problem is the complex is soluable in hexane/THF so celite is a no go.  Any help would be great.  I know removing these types of catalysts can be a pain.  I am trying to do a reaction on scale and a column is just not practical.

Thank you in advance!

Cheers!
If you're not part of the solution, then you're part of the precipitate

Offline AlphaScent

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Re: Removing Pd(PPh3)4 from Reaction
« Reply #1 on: August 26, 2019, 10:28:05 PM »
sorry, wash organics...im tired and didnt proof read...

Prost!
If you're not part of the solution, then you're part of the precipitate

Offline OrganicDan96

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Re: Removing Pd(PPh3)4 from Reaction
« Reply #2 on: August 27, 2019, 08:20:24 AM »
maybe try to precipitate it by addition of a bad solvent for Pd(PPh3)4 to your hexane solution, make sure your compound is soluble obviously.

Offline AlphaScent

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Re: Removing Pd(PPh3)4 from Reaction
« Reply #3 on: August 27, 2019, 12:45:21 PM »
I am trying to optimize the procedure.  It seems that a scavenger is maybe the best way to go.  Specifically TMT.  There is a polymer bound Pd scavenger made by biotage.
If you're not part of the solution, then you're part of the precipitate

Offline wildfyr

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Re: Removing Pd(PPh3)4 from Reaction
« Reply #4 on: August 27, 2019, 12:46:38 PM »
The pph3 part can be removed by letting it convert to the oxide then using zinc chloride. It will make an adduct that can be filtered out.

Offline AlphaScent

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Re: Removing Pd(PPh3)4 from Reaction
« Reply #5 on: August 30, 2019, 10:18:19 AM »
@wildfyr

When you say let it convert to the oxide do you mean to atmospheric oxygen?

I have bought some TMT and it is on its way.  I am interested to see how well it works.  It seems it is used in industry as a Pd scavenger a lot.  I have also found that simple activated charcoal works to soak up some Pd, and then a simple Si plug works to purify the material to about 95% purity.
If you're not part of the solution, then you're part of the precipitate

Offline TheUnassuming

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Re: Removing Pd(PPh3)4 from Reaction
« Reply #6 on: August 30, 2019, 10:49:56 AM »
Are you sure its the Pd(PPh3)4 complex?  In theory at least two PPh3 have to dissociate from the Pd in order for the reaction to proceed and I think you get other PdX2/4 species on workup, so you might just have the triphenylphosphine problem... which is in some ways worse.  I've heard PPh3 referred to as the herpes of reagents, and not without cause.

If it is tetrakis, you could probably oxidize the PPh3 and force the Pd to complex a less soluble ligand like wildfyr suggested.

Take it you don't want to run a column?
When in doubt, avoid the Stille coupling.

Offline wildfyr

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Re: Removing Pd(PPh3)4 from Reaction
« Reply #7 on: August 30, 2019, 05:20:54 PM »
Yes, though I guess some weak inorganic (i.e. easily aqueous seperable) oxidizing agent could do it too.

My suggestion was to oxidize the PPh3 and complex that to the zinc to make an insoluble salt. I'm not sure what exactly to do with the Pd. Maybe if you can make it into some insoluble Pd salt like palladium oxide it can just be removed with celite filtration.
« Last Edit: August 30, 2019, 10:02:49 PM by wildfyr »

Offline rolnor

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Re: Removing Pd(PPh3)4 from Reaction
« Reply #8 on: August 31, 2019, 01:14:17 AM »
Why not chromatography?

Offline wildfyr

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Re: Removing Pd(PPh3)4 from Reaction
« Reply #9 on: August 31, 2019, 02:12:18 PM »
  I am trying to do a reaction on scale and a column is just not practical.

Thank you in advance!

Cheers!

@rolnor

Offline rolnor

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Re: Removing Pd(PPh3)4 from Reaction
« Reply #10 on: September 01, 2019, 04:13:24 AM »
Sorry, missed that!

Offline kriggy

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Re: Removing Pd(PPh3)4 from Reaction
« Reply #11 on: September 01, 2019, 06:46:20 PM »
I think you might be able to oxidize PPh3 to OPPh3 and precipitate it with ZnCl2 and then maybe chelate the palladium with EDTA and wash it away? I recall talking to a industry guy at a conference that mentioned having problems removing residual palladium after hydrogenation so they had to change the pathway completely but AFAIK he mentioned its possible to remove with edta.

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