Org Prep Daily

January 15, 2007

[Pd(py)2].(TFA)2

Filed under: procedures — milkshake @ 3:37 am

stoltz.gif

Pd(OAc)2 253mg (1.127mmol) was dissolved in anh. benzene 17mL (10 min stirring with gentle heating) and pyridine 0.180mL (2.226mmol) was added dropwise over 5 min. The mixture color turned light and a precipitate formed. The closed flask was wrapped in aluminum foil and the mixture was stirred overnight (12 hours). The obtained slurry was evaporated to dryness, the flask with the solid residue was flushed with oxygen and neat trifluoroacetic acid 2.1mL (protein-sequencing grade) was added. The obtained yellow solution was diluted with methanol 20mL and the mixture was stirred under cotton-filled drying tube while wrapped in Al foil for 2 hours. The resulting slurry was filtered through a small medium-porosity frit, the precipitate on the frit was dissolved by gradual washing with 1:1 mixture methanol-dichloromethane (10mL). The combined filtrates were slowly evaporated and the residue was dried on highvac. Y=554mg (100%) of a yellow-white heavy powder. 

1H(CDCl3, 400MHz): 8.512(m, 4H), 7.855(app tt, 7.7Hz, 1.5Hz, 2H), 7.405(m, 4H); 13C(CDCl3, 100MHz): 163.09(q, 37.2Hz, 2C), 151.11(4C), 139.83(2C), 125.70(4C), 114.09(q, 289Hz, 2C)

This is a slightly improved, higher-yielding preparation of a catalyst for the oxidative Pd(II)-catalyzed cyclization of phenols, carboxylic acids and alcohols: Stoltz et al, JACS 127 (2005), 17778-88

5 Comments »

  1. Awesome prep.

    Comment by HOMO-LUMO — January 15, 2007 @ 6:36 pm

  2. I fully second Strem as supplier par exelance. Aldrich is crap for all organomatallics, ligands, and catalysts (their tetrakis is atrocious garbage 90% of the time). Buy from Strem and feel confident that that is not your variable!

    Comment by Jose — January 22, 2007 @ 2:51 pm

  3. Original Update: The Pd(OAc)2 used in the above preparation was Aldrich product 520764-5G batch 09030PC. Few days later when repeating the first part of the procedure with a brand new bottle of Aldrich product – 520764-5G batch 06410JE – I noticed that a large fraction of this new “Pd(OAc)2″ was insoluble in anhydrous benzene. (A good-quality material should be fully soluble to a brown clear solution; no glovebox, flame-drying or other precautions are required when making/handling Pd(OAc)2 benzene solution.) Going back to the original Pd(OAc)2 batch took care of the problem.

    It is quite possible that the quality of Pd(OAc)2 was the actual reason why I obtained a better yield in my preparation (over the published yield in the paper).
    Strem is a preferable source of starting materials when making catalysts. [Aldrich is not a reputable source in this field: Over-reducing Lindlar, partially-oxidised tetrakis, decomposed LiN(TMS)2 are just few problems which I run into over the years. The last incident just re-confirms my scepticism about their reliability in catalysis-related products.]

    Update 2: I was accusing Aldrich here, of selling bad Pd(OAc)2. I called their tech support and requested a replacement or refund. I have told things so terrible (about the quality of their organometalics) that the poor lady in Aldrich tech support audibly SHRUNK. So, the next day, I took the Pd(OAc)2 from my good bottle and saw that it was also partialy-insoluble…

    It turns out that the poor solubility was not a batch-related problem, just a cold bottle of benzene in the morning… Pd(OAc)2 is not that soluble in benzene to begin with and the solubility greatly varies with temperature; and with the winter playing on our manic-depressive air-conditioning system here at the institute, our lab ambient temperature oscillated a great deal. So I do apologize to the old Alfred Bader – as well as to all people whom I was warning about my catalyst “problem”.

    Comment by milkshake — January 23, 2007 @ 12:18 am

  4. You mentioned “tetrakis”. What kind of tetrakis species were you referring to? Just a thought, but have you considered PdCl2[COD] as a more soluble form of Pd?

    I have been in the organmetallic business, so I am interested to hear about the experiences people have with different suppliers.

    Comment by gaussling — January 28, 2007 @ 1:09 pm

  5. tetrakis = Pd(PPh3)4 in the lab jargon

    PdCl2(COD) or PdCl2(norbornadiene) are wonderfull precursors for the Pd(amine)Cl2 complexes which are used to catalyze O2- oxidation of alcohols to carbonyl compounds – not quite what I need to do; actualy I have to avoid such kind of side-products.

    One can transform the Pd(amine)Cl2 complexes to Pd(amine)(OCOCF3)2 complexes with 2 eqivs of AgOCOCF3. This detracts a bit from the beauty (using 2 equivs of Ag) but I guess one would go this way for some precious asymmetric catalyst.

    Right now I am trying to decrease the Pd(II) loading for my substrate cyclization – and solubility of the catalyst was definitely a problem, especialy for the reproducibility at lower loadings – but I think I found a decent catalytically-active system alternative for my chemistry and the upshot is that the catalyst is more soluble. But I cannot be more specific at the moment.

    Comment by milkshake — January 29, 2007 @ 12:34 am


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