September 18, 2019, 05:32:23 AM
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Topic: Suzuki coupling problem...  (Read 796 times)

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Offline awesomesynthesis

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Suzuki coupling problem...
« on: June 13, 2019, 12:11:56 AM »
I am doing Suzuki coupling reaction like this reaction, but I cannot verify where is my desired product. So Does anyone have  experience with this kind of reaction with the same starting materials? the starting materials are thiophene pinacol ester and dibromo benzothiadiazole
Sorry I am new here so I dont know how to insert picture..

Offline rolnor

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Re: Suzuki coupling problem...
« Reply #1 on: June 13, 2019, 03:37:21 AM »
Can you run TLC? LC-MS?

Offline awesomesynthesis

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Re: Suzuki coupling problem...
« Reply #2 on: June 13, 2019, 05:46:16 AM »
I only run TLC, in solvent system of hexane and ethyl acetate, the Rf of pinacol ~0.7 and Dibromo benzothiadiazole ~ 0.25 and crude product TLC shows 2 strong spot in Rf~ 0.35 and 0.9, the starting materials nearly disappear. I got the spot at 0.35 for NMR but it wasn't my product. And the spot at 0.9 I doubt it is product from homo coupling. So I dont know where my product is.
« Last Edit: June 13, 2019, 07:01:11 AM by awesomesynthesis »

Offline wildfyr

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Re: Suzuki coupling problem...
« Reply #3 on: June 13, 2019, 08:15:50 AM »
Could you be getting bis functionalization? Is the mono coupled perhaps more reactive than the starting material which drives the product all the way to entirely bis?

Offline awesomesynthesis

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Re: Suzuki coupling problem...
« Reply #4 on: June 13, 2019, 08:18:31 PM »
My product doesn't have ability to coupling or forming bis functionalization, the homo-coupling happens with the pinacol ester sometimes (just by reaction), but all of my starting materials seem to disappear.

Offline wildfyr

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Re: Suzuki coupling problem...
« Reply #5 on: June 13, 2019, 10:32:35 PM »
Have you looked at it by any method aside from TLC? Also, uploading a quick picture of the reaction scheme would be helpful.

Offline awesomesynthesis

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Re: Suzuki coupling problem...
« Reply #6 on: June 13, 2019, 11:57:54 PM »
Here is my reaction scheme. I just check for TLC.

Offline phth

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Re: Suzuki coupling problem...
« Reply #7 on: June 14, 2019, 01:32:31 AM »
All other posters gave good ideas. Check by NMR or MS. could be due to catalyst deactivation by oxygen

Offline awesomesynthesis

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Re: Suzuki coupling problem...
« Reply #8 on: June 14, 2019, 02:22:22 AM »
I do experiment in inert condition with nitrogen and color of catalyst seem to be good. But I cannot verify my product by TLC. Could it be on the top with the highest Rf?

Offline wildfyr

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Re: Suzuki coupling problem...
« Reply #9 on: June 14, 2019, 09:22:08 AM »
I do experiment in inert condition with nitrogen and color of catalyst seem to be good. But I cannot verify my product by TLC. Could it be on the top with the highest Rf?

We all try to do reactions under inert conditions, but succeeding is a different story! If a sensitive reaction isn't working, then the first two things to check are always:

1. Starting material purity (USE NMR)
2. Is your reaction really air and water free

Yes, I think this product would run faster than any of the starting materials. It is pretty nonpolar. Why not isolate that 0.9 and see what it is? At worst it may give a hint where your reaction is going wrong.

Also, your catalyst will produce triphenylphosphine oxide when you work it up, that may be one of the spots.

Offline kriggy

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Re: Suzuki coupling problem...
« Reply #10 on: June 14, 2019, 03:21:39 PM »
What about the spot at 0.9 ? Seems like a likely candidate when the molecule has two long nonpolar chains.

Offline awesomesynthesis

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Re: Suzuki coupling problem...
« Reply #11 on: June 14, 2019, 10:53:21 PM »
Thank you for all of your advice. I will isolate the spot on the top. I am a junior in organic synthesis, so many thanks for your supports

Offline Naamari

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Re: Suzuki coupling problem...
« Reply #12 on: June 16, 2019, 03:22:57 PM »
What are the colors of your TLC-spots to the naked eye?

When working with conjugated small molecules, you could be able to identify the structure with the longest conjugation (i.e. the largest molecule) just by their color on TLC-plate.

I have synthesized a very similar compound, and that looked orange to the naked eye on TLC-plate. I bet yours does too.

Offline awesomesynthesis

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Re: Suzuki coupling problem...
« Reply #13 on: June 22, 2019, 09:52:12 PM »
What are the colors of your TLC-spots to the naked eye?

When working with conjugated small molecules, you could be able to identify the structure with the longest conjugation (i.e. the largest molecule) just by their color on TLC-plate.

I have synthesized a very similar compound, and that looked orange to the naked eye on TLC-plate. I bet yours does too.
Yes, I also see some colored spot with the naked eye. Where is your product position on TLC plate, is it in the middle of two starting materials or on the top?

Offline Naamari

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Re: Suzuki coupling problem...
« Reply #14 on: June 24, 2019, 07:50:06 AM »
What are the colors of your TLC-spots to the naked eye?

When working with conjugated small molecules, you could be able to identify the structure with the longest conjugation (i.e. the largest molecule) just by their color on TLC-plate.

I have synthesized a very similar compound, and that looked orange to the naked eye on TLC-plate. I bet yours does too.
Yes, I also see some colored spot with the naked eye. Where is your product position on TLC plate, is it in the middle of two starting materials or on the top?

On the top. My eluent composition was toluene : n-hexane on 1:1 ratio by volume, and the product was the first to elute.

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