Mesoporous silica supported catalysts for carbon-carbon bond forming reactions

摘要

The synthesis and characterisation of well-ordered mesoporous silicas, MCM-41, MCM-48, SBA-1, and SBA-2 has been carried out successfully. All of the synthesised materials possess the expected characteristic ordering as confirmed by powder X-ray diffraction. Moreover, surface modification of these mesoporous silicas had also been achieved through the incorporation of alkylamine groups and attachment of an asymmetric organometallic nickel-salen complex. The catalytic activity of the amino and nickel complex-modified mesoporous silica materials was examined for carbon-carbon bond forming reactions; Knoevenagel condensation of benzaldehyde and ethylcyanoacetate, and Kumada-Corriu coupling reaction between an organobromide and Grignard reagent, respectively. All the NH2-mesoporous silica catalysts result in high conversion (>95%) and can easily be reused by washing with water. Furthermore, the catalytic performances of the asymmetric nickel-salen complex bound to mesoporous silicas were found to be greater than 60% which is comparable to the homogenous nickel complex catalyst (62% conversion) but are more easily recycled. The further modification of catalysts to capture the remaining surface silanol groups in the modified-mesoporous silicas has been carried out by using chlorotrimethylsilane to obtain the surface functionalised with trimethyl groups instead of silanols. The methylated catalysts with MCM-41 and MCM-48 as support demonstrate better recyclability, while this was not observed in the cage-like SBA-1 and SBA-2 supports catalyst as the presence of additional trimethylsilyl groups could cause more pore blocking.