[dielsalder33]

Dear colleagues,

I am currently working on a Pd(PPh3)4 catalyzed allyl ester deprotection using morpholine. 

The reaction scale is about 2-10 mg of starting material in 300 µL solvent (DCM or DMF) and because of this I want to purify the product (DMF solution) directly by preparative HPLC and skip an aqueous workup. The reaction itself works out fine and was analysed by analytical HPLC. Unfortunately, the catalyst Pd(PPh3)4 is not as stable as I thought in aqueous slightly acidic acetonitrile/water mixtures. The result is impure product and ugly preparative HPLC spectra. Of course, I also do not want to damage the HPLC column by colloidal palladium, as well.

I ran the catalyst on a TLC in pure EtOAc and the result was surprising. I had a strong UV active spot on the starting position and a quite weak UV-active spot with a retention factor of 1/3.

Does anybody know a nice method to decompose Pd(PPh3)4 for such HPLC purifications?
If I still have to do an aqueous workup what is needed (favoured are slightly acidic or neutral aqueous solutions) to destroy the catalyst and how does the catalyst behave on a silica gel column?

I appreciate suggestions and comments a lot.

Thank you!

[Mitch]

I don't have an answer because Pd(PPh3)4 is the scourge of all analytical columns. There is probably no way to go around doing a work-up. Pd(PPh3)4 is oxygen sensitive, so the dissolved oxygen in the water mixture is probably killing the thing.

[g-bones]

why not trying filtering your crude reaction mixture with either a little HPLC filter (look like little flyling saucers) or simply pass the mixture through a plug of silica (or celite if you fear that your material will not survive on silica or is to streaky to get all of it off)?

[kiwi]

Have you tried a scavenger resin (eg. like these http://www.biotage.com/DynPage.aspx?id=23862 )? Med chem types seem to use them quite a bit for this sort of thing, and they are available with good Pd ligands on them.