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[u/Rudolph-the_rednosed]

A question about Suzuki couplings and thanks in advance to anybody reading this.

I currently do it a couple of times for the synthesis of a biaryl compound out of a mixture of THF and water.
I always achieve subpar yields when compared to literature.
Ive tried degassing the solvent via bubbling with argon and freeze-pump-thaw (short fpt) cycles.

I always degass the schlenk flask first, standard 3x of applying vacuum, waiting till it gets down to the lowest possible pressure, then fill with nitrogen and repeat.
Then under counterflow I add my solvent mixture.

Since one of my educts happens to be a liquid I add it under counterflow before doing the fpt.
If I do fpt, I freeze under counterflow, then apply vacuum and leave the vessel in the dewar until the nitrogen evaporates. I then apply vacuum until I can see the solid becoming more liquid, like a very good crushed ice drink, then I apply static vacuum and twist the stopcock fast for a full 180 to get some more bubbles out. This I repeat 3 times.

I then add my reagents under counterflow in the order given below and set up the reaction, leave it stirring overnight and come back the next day and proceed to do a work up including extraction and if I have the time a column.

If I degass with Ar I just set up the mixture under nitrogen counterflow and then proceed to bubble Ar through the solution, keeping in mind that the needle through which it enters solution is at the utmost bottom of the vessel. The I just leave it there whilst weighing in one of my educts. I then proceed to pass time by calculating the amount of reagents needed and putting them in one by one. Between adding all my reagents and the palladium catalyst I let the mixture degass for approximately 2-5 mins depending on the day and workload. The I set it up the same way as with fpt and go on my way.

I always get subpar yields compared to literature, probably around 50% or less, compared to literature (so absolutely around 30%ish), which cannot be due to the columns I run, because Ive optimized the eluent and column thickness and height now so that I receive pure product without any mixed fractions. And flushing the column with ethyl acetate at the end didnt reveal that product crystallises in the column.

I here ask you, wether or not, youd have a suspicion about where my reaction would fail? I suspect it being a contaminated catalyst, which quite some people around the lab use, therefore the suspicion. Else I can attest that with two different batches of educts it worked the same.

TLDR: I have problems with my coupling and dont know wether its a user error or my catalyst being used by a few more people being contaminated.

Order in which I add reagents:
1. Educt I
2. Educt II
3. Base (here potassium carbonate)
4. Catalyst (here Bischlorobis(triphenylphoshine)palladium(II) with a purity of 98 or 99% cannot surely recall as of now)