Study On Hydrosilylation Of Alkene Catalyzed By Rhodium Complex/Ionic Liquid System

In this paper, issues dealing with hydrosilylation of different olefins , such as activity of catalyst, selectivity of adduct, reuse of noble metal catalyst, were focused. It was founded the relation of the catalyst structure and activity or circulation by rhodium complex/ionic liquid （molten salt） as a catalytic system for the hydrosilylation of different olefins with trialkoxysilane （trialkylsiane）.Rh（PPh₃）₃Cl/ionic liquid （molten salt） as a thermoregulated and recyclable catalytic system for the hydrosilylation of different olefins with trialkoxysilane （trialkylsiane） have been investigated. N, N-dialkylimidazolium salts or N-alkylpyridinium salts can specifically vary their physical and chemical properties by altering the attached substituents, and it was found that both activity and selectivity of catalyst system could be influenced by the alkyl chains attached to the pyridinium or imidazolium cations. The ratio of theβ-adduct to the -adduct （β/ ） is clearly increased with increasing length of alkyl chain attached to the pyridinium or imidazolium cations. And hydrosilylation reaction of styrene with triethoxysilane was conducted by Rh（PPh₃）₃Cl/Bn₂ImPF₆. The Rh（PPh₃）₃Cl/Bn₂ImPF₆ showed the highest conversion of styrene, 95.7%。Along with research to minimize the amount of ionic liquid and noble metal catalyst in hydrosilylation processes, this paper reported in the present study that ionic liquid （IL）-functionalized SiO₂ can be prepared by a one-step procedure. The Rh（PPh₃）₃Cl was then supported on the IL-functionalized SiO₂ to obtain the Rh（PPh₃）₃Cl/IL-functionalized SiO₂ catalyst. Subsequently, the hydrosilylation of styrene and -olefins with triethoxysilane catalyzed with this supported catalyst was investigated. Furthermore, the catalyst system could be recovered easily. For example, the Rh（PPh₃）₃Cl/SiO₂-（CH₂CH₂CH₂）MimPF6 catalyst system could be recovered easily and reused more than 10 times without any notable loss of catalytic activity or selectivity.A series of rhodium complexes employing 2-imidazolium phosphines as ligands synthesized exhibited greater catalytic activity and selectivity for hydrosilylation of different olefins with trialkoxysilane （trialkylsiane）. The electron-rich heterocycle provides a suitable framework that stabilizes the Rh-phosphine center located between the two nitrogen atoms. It is possible that close proximity of the positive charge to the phosphorus atom greatly enhances the catalytic activity and can afford highly efficient catalytic activity. When amounts of rhodium complexes employing 2-imidazolium phosphines as ligands were 0.02mol% of styrene, the conversion of styrene were >90.4%,the selectivity ofβ-adduct were >89.8%.The hydrosilylation of alkenes in a supercritical CO₂ （scCO₂） /ionic liquid system was first investigated. scCO₂ can be used to extract high boiling point organic substances from ILs without cross-contamination. During hydrosilylation in the scCO₂/IL system, the reactants were possibly transferred into the IL phase by scCO₂, in which the catalyst was dissolved. The products can be flushed with scCO₂ after the reaction and the catalyst/IL system reused. During a new hydrosilylation process in a scCO₂/IL system with a rhodium complex as the catalyst process, rhodium complexes of NHC were formed by direct carboxylation of 1,3-dialkylimidazolium hexafluorophosphate with CO₂ in situ. Herein, It was found that both the catalytic activity and selectivity of the rhodium complexes bearing NHC ligands were influenced by the attached substituents of the imidazolium cation, and no hydrogenation by-product （alkane） was detected.