Hoveyda-Grubbs Catalysts Encapsulated Within Mesoporous Materials For Olefin Metathesis

Olefin metathesis has attracted much attention as a powerful tool to form C-C bonds in organic synthesis. The second generation Hoveyda-Grubbs catalyst is currently the most widely used olefin metathesis catalyst because it is stable in air, versatile to tolerate a variety of functional groups, and compatible with a wide range of solvents. And it has been commercialized now. Despite of these advantages, the separation of this expensive catalyst from the product and any reaction solvent remains difficult. In view of "green" chemistry, simple catalyst separation, high recyclability and low catalyst cost are key factors for practical application in organic synthesis. Along these lines, much effort has been made to immobilize the Ru complex catalysts on solid matrices and polymers. However, the preparation of these heterogeneous catalysts often consists of multiple steps of synthesis and modification of the parent Ru complexes, consequently making them less accessible for general use. Moreover, many catalysts barely survive several recycles and only a few systems have high recyclability.In order to address the above problems, we herein develop a solid catalyst for olefin metathesis by a simple adsorption of the second generation Hoveyda-Grubbs catalyst on different mesoporous materials including MCM-41, SBA-15, SBA-16, FDU-1, SBA-1and commercial silica(H-G/&,&represents different materials). Compared with this complex immobilized on other mesoporous materials and silica, the SBA-1supported solid catalyst has the highest stability and shows the most significantly enhanced recyclability. After it was used the ninth reaction cycle, as high as69%conversion was still afforded. And this solid catalyst not only has a wide range of substrate applicability in ring closing metathesis, but also exhibites excellent activity in cross metathesis.We further improve the solid catalyst preparation method. The mesoporous materials MCM-41, SBA-16, FDU-1and SBA-1are still used as supports. The second generation Hoveyda-Grubbs catalyst was successfully confined in the cavities of mesoporous materials by narrowing the window sizes with diphenyldichlorosilane. The resultant solid catalysts can be stable even in polar solvents such as CH2C12(Ru/&,&represents different materials). These four mesoporous materials-supperted catalysts have different encapsulation efficiency. The encapsulation efficiency of SB A-1over was up to70%, much higher than other mesoporous materials. Ru/SBA-1catalyst showed good activity in both olefin ring-closing metathesis and cross metathesis. Its recyclability was found to be dependant on the reaction temperatures. At25℃the conversion was46%after being used six times, while at40℃the conversion was57%after the seventh reaction cycle.