Immobilization of chiral cationic diphosphine rhodium complexes in nanopores of mesoporous silica and application in asymmetric hydrogenation

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• 作者：Reine Sayah ; Marie Le Floch ; Eric Framery ; Vé ; ronique Dufaud
• 关键词：Asymmetric hydrogenation ; Chiral cationic rhodium complex ; DIOP ligand ; Mesoporous hybrid material ; Covalent immobilization
• 刊名：Journal of Molecular Catalysis A: Chemical
• 出版年：2010
• 出版时间：2 January 2010
• 年：2010
• 卷：315
• 期：1
• 页码：51-59
• 全文大小：900 K

文摘

Heterogeneous chiral cationic rhodium complexes bearing bidentate phosphine derived from (−)-2,2-dimethyl-4,5-bis(diphenylphosphino)methyl)-1,3-dioxolane (DIOP) were prepared by covalent immobilization onto SBA type silica. In order to introduce the tether to the surface, it was necessary to modify chemically the DIOP ligand through a reaction sequence consisting of hydrolysis and condensation with organosiloxane precursor. Two types of cationic rhodium hybrid materials based on SBA-15 and partially capped SBA-3 type silica were prepared under classical grafting procedures. The catalytic solids were fully characterized using a wide variety of molecular and solid-state techniques to determine their structural and textural properties. The performances of these latter were then evaluated in the hydrogenation of methyl (Z)-2-N-acetylaminocinnamate under various reaction conditions (pressure and temperature). Generally, the activity of supported catalysts was high as full conversions were obtained but immobilization of the system leads to significant loss of enantioselectivity. The best ee (20 % ) was observed in the case of the catalyst whose surface had been passivated prior to the grafting but the enantiomeric excesses were fairly below the values of the homogeneous catalysis.