Kletskov Alexey «Mixed 1,2-azole heterocycles in homogeneous and heterogeneous catalysis in aqueous media»
As a result of joint researches, methods for the synthesis of mixed heterocyclic ligands containing heterocycles completely different in electronic properties (for example, 1,2-azole-1,2,3-triazole, 1,2-azole-pyridine, 1,2-azole-pyrimidine) and their complexes with palladium and nickel were obtained. Palladium isoxazole-1,2,3-triazole complexes are such active catalysts for cross-coupling and reduction reactions in aqueous media that they can be used in trace amounts (1–10 ppm). For the first time, a promising and very active in catalysis of cross-coupling and reduction reactions hybrid bimetallic material based on Pd-Ni-B-L doped with palladium and modified with azole ligands [L - isoxazole-1,2,3-triazole(pyrimide) ligands] was developed.
The ability of Pd-Ni-B-L, as well as Co and Fe analogues, to form stable colloidal solutions in methanol made it possible to develop a method of their simple deposition on mesoporous supports (Al2O3, SiO2, styrene-divinylbenzene copolymer - DIAION HP20) and to create on their basis active heterogeneous catalysts. The following bimetallic composites were obtained: Pd-M-L/Al2O3(SiO2), Pd-M-L/HP20 (M = Ni, Co, Fe; Pd: M = 1: 100). In the presence of new catalysts, reactions proceed in practically quantitative yields, which make it possible to simplify the isolation procedure of target compounds as much as possible. Developed catalytic materials are readily recovered from the reaction mixture and can be reused up to 5-10 times without loss of activity. The synthetic potential of new catalysts has been studied in several types of cross-coupling reactions on a wide range of aryl halides, arylboronic acids, olefins and terminal acetylenes, as well as their heterocyclic analogs. Examples of practically significant compounds synthesized by the Suzuki, Heck and Sonogashira reactions in the presence of reusable bimetallic catalysts (0.01 mol% Pd) are presented at the scheme.