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Author: Subject: Trying out a stille coupling reaction
Okaris
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[*] posted on 9-11-2018 at 23:47
Trying out a stille coupling reaction


I was trying out a stille coupling reaction with the following set of procedures:

1. To a refluxing solution of 1-bromo-4-nitrobenzene (1.88 g, 9.3 mmol) in toluene (110
mL) was added tetrakis(triphenylphosphine)palladium(0) (0.04 g, 0.03 mmol).

2. After 20 min,
2-(trimethylstannyl)bithiophene (3.5 g, 10 mmol) was added via a syringue.

3. After complete
addition, the mixture was refluxed for 15h. After cooling, the mixture was filtered and then
S1
subjected to rotary evaporation to give a solid. Filtration using hot hexane gave pure 1-(2-
thienyl)-4-nitrobenzene in 65% yield.

Instead of 2-(trimethylstannyl)bithiophene (CAS: 133144-35-1), I used 5,5′-Bis(trimethylstannyl)-2,2′-bithiophene instead (CAS: 143367-56-0), which has an extra trimethylstannyl group on the second thiophene. What would be the possible product and other side-products of this reaction?

EDIT: Changed the reaction name from suzuki to stille, thanks for pointing it out.

[Edited on 11-11-2018 by Okaris]
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VSEPR_VOID
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[*] posted on 10-11-2018 at 04:51


It would help if your had a diagram of your reaction, intended product, more information about your reagents, and pictures. Its less work for us that way. It looks very interesting!



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myr
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[*] posted on 10-11-2018 at 08:50


I do not believe any diagrams are needed here. All the reactants are very clearly defined in a well-studied reaction.

A small problem- this is the Stille, not Suzuki reaction.

Stille reactions can give dimerization of the stannane partner, which for you would make some thiophene oligiomer I guess.
Per (doi.org/10.1002/0471264180.or050.01) another possible side product is exchange of the (in your reaction) nitrophenyl with a phenyl in the intermediate Pd-complex. see pg 47-ish. I would also guess the stannane is a lot more water-sensitive than phenylstannane (more electron rich)- so to keep side products at a minimum, run the reaction cold and dry.
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Okaris
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[*] posted on 10-11-2018 at 17:15


Should not be an issue, as either thiophene derivatives are both phenylstannanes. I'm not sure what you meant by running the reaction cold though.
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[*] posted on 11-11-2018 at 00:20


I think the issue is less the complexity of the reaction but more just whether we believe that you did in fact perform this reaction and achieve these yields.
Something ive been thinking about alot lately, ive also been guilty of lack of characterization as well.
Its very easy for someone to do enough research on a reaction to understand how to fabricate a result for whatever reason and this can be detrimental for future researchers, as they can go and make assumption based on your work that you may not have actually performed.

The major issue with your write up is that you haven't in anyway characterized your final product and so how do you know that you reaction has actually worked?
If you cant know and have made little effort to know, then how can we know.
VSEPR_VOID has also pointed out how necessary it is to also characterize your reagents, this is necessary so that your results are reproducible and if someone is attempting to reproduce your results and are having problems then they can compare your reagents with their reagents.
These kind of writes up as simple as they are also have a habit of missing out rather important details such as other products that came over during distillation, some problems controlling temperature or bumping issues etc.

Tis an unfortunate problem for us amateurs (although its not just secluded to amateur chemistry, it also appears in alot of professional write ups).
A good place to look for what a clear and concise write up should look like, would probably be some of magpies work in the publications section.




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DJF90
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[*] posted on 11-11-2018 at 02:27


Try these conditions: https://www.organic-chemistry.org/abstracts/literature/681.s...
...but using Pd2(dba)3 and tris(2-furyl)phosphine as your catalyst/ligand system

[Edited on 12-11-2018 by DJF90]
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Okaris
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[*] posted on 11-11-2018 at 03:52


I understand your point of fabricating the results, Assured Fish. I would like to point out that this procedure is actually taken from the supplementary section of this paper (DOI: 10.1021/ja068143u) with the yield of 65% reported there. I have tried to replicate the results with little success.


This is the thiophene derivative originally mentioned in this paper. Based on what they wrote, the eventual product should be:




Instead, I bought this reactant by accident with an extra trimethylstannyl group instead (I blame myself for not being able to properly differentiate the nomenclature):




As such, I believe one of the possible products may be this instead:


I am unable to properly determine if this was the compound by a preliminary NMR, as some of the starting material may still be present. I am slightly confused by step 3 which suggests that gravity filtration using hot hexane is sufficient (instead of column chromatography) to purify it for the next step of reducing the nitro group to an amino group, while my own TLC shows that more than one final product is present, possibly due to the change of one of my reactants.
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[*] posted on 11-11-2018 at 13:10


Oh i see, your op put me into thinking it was your write up not a procedure you were following, i missed that part.



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Okaris
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[*] posted on 12-11-2018 at 17:44


No worries. Based on this procedure, would you think filtering the product with hot hexane using gravity filtration is sufficient, or column chromatography with hexane as eluent is needed?
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[*] posted on 13-11-2018 at 00:01


It looks like you've neglected to adjust your stoichiometry to account for your change in stannane. I suspect you'll have a mixture of bis(tributyltin), (tributyltin)/(nitrophenyl) and bis(nitrophenyl) bithiopenes.

I'd suggest column chromatography using 1:9 K2CO3:silica. You won't see any tin pass through, but you'll still have to separate your desired product from any unreacted bromonitrobenzene, protodestannylation/protodebromination products and Ph3P/Ph3PO.
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