# Purification of Buchwald-Hartwig amination

I am conducting a synthesis involving Buchwald-Hartwig amination. I use $$\ce{Pd2(dba)3}$$, $$\ce{P(o-tol)3}$$, and $$\ce{Et3N}$$ as base. In many proposed mechanisms, they often omit the precatalyst. I wondered how $$\ce{Pd2(dba)3}$$ and $$\ce{P(o-tol)3}$$ are converted to catalyst. I couldn't find exact mechanism, but I found one for $$\ce{dppf}$$.

In this mechanism, $$\ce{dba}$$ is replaced by $$\ce{dppf}$$. Assuming that this mechanism applies equally for my case, $$\ce{P(o-tol)3}$$, we can assume $$\ce{Pd[P(o-tol)3]}$$ or something is formed. I did MS analysis for my reaction mixture, and it had a major peak at $$m/z=714$$, which can be thought to be $$\ce{Pd[P(o-tol)3]2}$$. If this assumption is correct, then is $$\ce{dba}$$ mixed in my reaction mixture? Should I consider additional purification for $$\ce{dba}$$?

• There will be free dba in your reaction mixture. What percentage catalyst loading are you using and what purification are you doing? If you are doing column chromatography it will run close to the solvent front in most systems Jul 23, 2021 at 6:40
• @Waylander I use toluene as solvent, 3 mol% Pd2(dba)3, 6 mol% P(o-tol)3 (relative to main reagent). I filtrated the reaction mixture through Celite pad, concentrated by rotary evaporator, and dried in vacuum oven at 130 ℃, ~11 Torr. According to Wikipedia, b.p. of dba is 130 ℃. Is dba evaporated? Column chromatography is not performed yet. I have trouble selecting solvent system when I test the TLC. Jul 23, 2021 at 6:53
• The dba may have been removed with the Toluene but you still have residues from the phosphine - most likely the oxide. Jul 23, 2021 at 7:09
• @KrangLee Please consider using appropriate formatting (mhchem) for chemical formulas (e.g. use your previous edited question as an example). Also, "MS analysis" in general doesn't provide sufficient information. Ideally you need to provide supplementary data regarding type of mass-spectrometer, ion source, positive/negative mode, mass analyzer, type of scanning etc. This might not be crucial for this question, but this is a good practice. Jul 23, 2021 at 8:18
• @andselisk Thank you for comment. Actually I am a new graduate school student, still I lack knowledge and experiences about spectroscopy and practical synthesis procedures. Your advice is of help. Jul 28, 2021 at 5:49