Hi !
I am trying to couple a dibromoanthracene derivative with bishexyloxy benzene boronic acid using Suzuki coupling. [Please see to the attachment] The anthracene derivative is highly insoluble even in Chloroform and Toluene at reflux temperature and slightly soluble in DMF.
I used Sodium carbonate, potassium carbonate and Potassium phosphate for the reactions in toluene, THF and DMF using Pd(PPh3)4 as the catalyst.
The reaction either doesn't proceed (most of the time) or methyl esters convert to the acid.
Which is the ideal Pd catalyst to carry out Suzuki reaction of reactants with poor solubility? What are other alternatives for this coupling?
You can do Suzuki reaction even in methanol. Please check solubility in methanol and even in acetonitrile/water mix. If it is getting soluble you can try different bases.
The problem of reagent incompatibility can be overcome by using surfactant aggregates... Coupling reactions like suzuki etc have been efficiently done in water using self-assembled systems..Pls see the works of Bruce H. Lipshutz and others on coupling reactions in micellar media..
Chlorinated aromatics (like chlorobenzene or 1,2 dichlorobenzene) often solubilize anthracene derivatives. Since the reactivities of chlorines can be well controlled with temperature, it should not pose a problem.
Besides the already mentioned suggestions, please be aware of another issue: The boronic acid is better soluble than your starting material and I bet that most of the time you will see deborylation. It essentially means that the boronic moiety slowly degrades over time and cross coupling cannot take place anymore. Improving the catalyst will unfortunately also speed up deborylation (since it is present in a large excess over your starting material). The issue you need to talke first is solubility, maybe functionalize the anthracene (replace the methyl esters with tertButly or hexyl for instance should enhance solubilities greatly). Switching from Bromines to iodines can also help tremendously. The cleavage of esters can be prevented by using KF as base, but unfortunately often the reaction rates are diminished. In general, cleavage of acids is mediated in aqueous media (which unfortunately is also the best cosolvent in Suzuki reactions), switching to DMF can help.
Dear Arun Naibi Lakshminarayana
You check solubility in water. Please check the attachments. In some case Suzuki reactions possible in water depending upon the your ligands.
Reactants are highly insoluble in water. Anyways, I will go through the links. Thanks a load Md. Subarkhan n Xi Chen !
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