[jayana]

Hello All,

I have been performing a Suzuki reaction between an electron-rich aryl bromide and an aryl-BF3K with EWG, and have noticed the reaction mixture going from orange to black within 30 to 60 minutes of reflux (solvent used was PhH/EtOH, base 2M Na2CO3 and catalyst-Pd(PPh3)4). The reaction either gets halted or half of the SM gets converted to the corresponding protodehalogenated material.

Could someone shed light on the mechanism for the formation of Pd-black (references/articles) & what tricks are there for avoiding it?  Do other Pd catalysts help?  What about additives/solvents?  Also, should you use a large excess of ArBF3K to avoid the reductive side reaction you are seeing?  (How is this usually avoided?).

Thank you.
Jayana

[discodermolide]

Try using a different base.
I though this was not such a problem with the BF3 salts. According to Molander they seem to be better.

[OC pro]

Suzukis are usually very fast. If the setup is good you will have a nice conversion. Almost no dehalogenation is observed.
Did you degas well? After dissolving everything, you should thoroughly evac and backfill with N2 or argon several times. Then add Tetrakis Pd.
How old is your Tetrakis? Still yellow-orangish crystals?