Homogeneous and Heterogeneous Catalysts with 1,2-Azole Ligands for Cross-Coupling Reactions in Aqueous Media
Convenient methods for synthesis of functionally substituted 1,2-azoles were developed, and highly active homogeneous and heterogeneous palladium catalysts based on them were developed for cross-coupling reactions in aqueous media. Distinctive features of the new catalysts are the highest catalytic activity, reusability without loss of activity and ability to work effectively in aqueous media. There have been developed methods for the synthesis of isoxazole ligands and their complexes with Pd(II), methods of non-covalent functionalization of mesoporous oxide and carbon supports with azoles, methods of Pd(II) and Pd(0) (Pd nanoparticles) deposition on the resulting hybrid materials. It has been shown that the application water or aqueous methanol as reaction media leads to a significant intensification of catalytic process compared to conventional organic solvents - catalytic reactions carried out with almost quantitative yields, their duration is reduced by an order or more. It was found that in 50% aqueous methanol, the effectiveness of new heterogeneous catalysts is so high that the reactions are completed in 20-30 minutes, even at room temperature with high yields. The quantity of introduced Pd catalyst does not exceed 0.1 mol%, i.e. 1000 times less than the quantity of reagents. The absence of by-products makes it possible to exclude from the process laborious and expensive chromatographic methods of isolation and purification of target compounds.