Preparation Of Co-Salen Type Heterogeneous Catalyst Supported On SiO₂ On The Basis Of A Ring Opening Reaction Of Dihydrochromone And Its Application In Organic Transformations

Salen ligands have been considered as one of the most important ligands in organic chemistry,which can coordinate with metal ions in various oxidation states.Traditional methods of immobilizing M-Salen complexes include impregnation method,ion exchange method,ship-in-bottle,chemical grafting method,sol-gel method and organic polymerization method.Immobilized M-Salen is widely used in heterogeneous catalysis,CO₂ capture,chemical sensors and electrochemistry.Although there are many reports on the application in the field of heterogeneous catalysis,due to the complicated preparation process of immobilized catalyst,its practical application in chemical synthesis still faces many problems,such as high catalyst cost,poor stability and so on.In this paper,by means of the Michael addition reaction between the ring-opening product of 2,3-dihydrobenzopyran-4-one and sulfhydryl group,M-Salen was grafted onto the surface of solid material using cheap and easily available sulfhydryl functionalized silica（HMS-SH）as the support,and then the organic/inorganic hybrid material HMS-Co-Salen catalyst was obtained.By Fourier transform infrared spectroscopy,ultraviolet spectroscopy,X-ray photoelectron spectroscopy,field emission scanning electron microscopy,transmission electron microscopy and other analysis and characterization methods,it was proved that the material was successfully synthesized,with the expected M-Salen structural fragments.Using HMS-Co-Salen as catalyst,the ring opening reaction between N-methylaniline and epoxy styrene was realized to prepare 1,3-oxazolidine.Under the optimum conditions,the yield of the target product could reach 70%.The material can also efficiently catalyze the oxidative condensation reaction between o-phenylenediamine and benzaldehyde to prepare 2-phenylbenzimidazole,which the TOF value and reaction conditions of the catalyst were better than those reported in the literature.HMS-Co-Salen can also catalyze the oxidative cyclization of o-aminophenol and tert-butyl isocyanate.HMS-Co-Salen catalyst can be reused for 5 times in the model reaction and the catalytic activity does not decrease significantly.