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I am conducting Buchwald-Hartwig amination. I use $\ce{Pd_2(dba)3}$ and $\ce{P(o-tol)_3}$ as catalyst and toluene as solvent. Temperature is 100 ℃ and reaction time is 24 hours. During the reaction, formation of dark precipitate is observed. So I filter the reaction mixture through Celite pad when I do work-up.

Celite filtration

The dark precipitate is observed. Is this dark material $\ce{Pd}$ metal formed by degradation of $\ce{Pd_2(dba)3}$? Reactant is aza-crown and bromothiophene, base is $\ce{Et_3N}$. Initially I thought that this would be the insoluble salt, $\ce{Et_3NHBr}$, but Pubchem says that its color is white. I searched several papers using keywords 'Buchwald-Hartwig amination byproducts', 'Buchwald-Hartwig amination degradation of catalyst', etc, but couldn't find satisfying answers. If this is really $\ce{Pd}$ metal, is the degradation due to too high temperature?

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    $\begingroup$ Assuming you are past the stage of reaction (which solvent? what scale? how many mol% of catalyst?) and completion of the workup, up and including the isolation of the product; is your yield of isolation substantially lower than the one reported in the literature for this reaction/for reactions with similar substrates/products to yours? Only in this run «low» (yields are a measurement, thus have a standard deviation, too)? Or do you worry, the smudge on the frit may pollute subsequent batches of synthesis (i.e., the metal residues to create additional trap states for organic electronics)? $\endgroup$
    – Buttonwood
    Sep 29, 2021 at 17:14

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