# Degradation of Pd catalyst in Buchwald-Hartwig amination

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.

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?

• 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)? Sep 29, 2021 at 17:14