RUDN chemists have created a palladium catalyst for the Suzuki-Miyaura reaction for a more economical and safe synthesis of complex molecules for the pharmaceutical and chemical industries. It keeps palladium from unwanted leaching into the final product, allows the reaction to be carried out in a green solvent and achieve 97% of the product yield. The results are published in Molecular Catalysis
Newswise — To synthesise complex molecules for pharmaceuticals and the chemical industry they use cross-coupling reactions in which two carbon atoms from different molecules combines. One of the cross-coupling reactions is the Suzuki-Miyaura reaction. It requires palladium-based catalysts. The noble metal allows the reaction to be carried out effectively, but it can "wash out" and get into the resulting product. This is especially undesirable, for example, in the production of medicines.
"To stop the leaching of metal during the catalytic cycle, we propose to use organometallic compounds. The strong interaction between organic molecules and metals forms highly stable complexes. This effective interaction helps to keep the metal from leaching," said Professor Leonid Voskresensky, Dean of the Faculty of Science at RUDN University.
RUDN chemists have created a palladium nanocatalyst based on N-heterocyclic carbene (NHC). After use, it leaves no traces of palladium in the product. The catalyst proved to be efficient and economical for the Suzuki reaction between phenylboronic acid and aryl chlorides. The reaction took place at 90 ℃ for eight hours. After that, the solid residue was washed in water and ethyl acetate, dried and the reaction was carried out again to check how the structure and effectiveness of the catalyst changed. Chemists also tested different reaction conditions, temperature, solvent and base to find the optimal ones.
After separating the catalyst, chemists performed a spectroscopic analysis of the filtrate and made sure that it did not contain palladium. The maximum yield of the final product was 97% for one of the aryl chlorides. This is comparable to the results of other catalysts, but, unlike analogues, the consumption of the catalyst was less. In addition, a green solvent was used — an aqueous solution of isopropanol. After 10 cycles of use, the efficiency of the catalyst has practically not changed, remaining above 90%. Moreover, after the ninth use, chemists checked the structure of the nanocatalyst using a scanning electron microscope and found out that it remained almost the same as it was before the first use.
"The hybrid nanomaterial act as highly active catalysts for the Suzuki–Miyaura cross-coupling between deactivated aryl chlorides and phenylboronic acid under heterogeneous and aerobic conditions. The supported catalyst exhibited excellent activity and stability and it could be reused at least ten times without any significant loss of activity. We found no traces of palladium in the products, and leaching tests confirmed that the reaction was really heterogeneous," said Rafael Luque, professor at the Center for Molecular Design and Synthesis of Innovative Compounds for Medicine of RUDN.
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