Synthesis,Characterization,Functionalization And Catalytic Performance Of Chiral Norbornane-Bridged Periodic Mesoporous Organosilicas

Constructed by rationally designed bis-alkoxysilane precursors with a bridging organic group, i.e., (R'O)3Si-R-Si(OR')3, periodic mesoporous organosilica materials (PMOs) have been receiving much research interest since their discovery in 1999 by three independent groups. Due to the combined advantages of ordered mesoporous structure and unique pore-wall functionality, this new class of organic-inorganic hybrid materials is of potential importance in adsorption, chromatography, catalysis, optical application, and host-guest chemistry. One of the main aspects in this area is, therefore, to synthesize desired chiral PMOs which are potentially applicable in heterogeneous asymmetric catalysis. It is, however, difficult to prepare PMO materials from pure and undiluted bis-alkoxysilane precursors, especially from those in lack of molecular rigidity. Few examples have been reported for successful construction of chiral PMO materials from 100% chiral building blocks.In Charpterâ…¢, we report the synthesis and characterization of novel norbornane-bridged chiral PMO material which possesses the following advantages:i) The four-chiral-center Precursor 1, (1R,2S,4R,5S)-exo,exo-2,5-bis(trimethoxysilyl)bicycle [2,2,1]heptane, could be facilely synthesized in 91% yield and 99% ee, involving only two-step chemical transformation from norbornadiene. ii) The highly-ordered chiral PMO material with P6mm mesostructure was successfully prepared from the self-condensation of chiral Precursor 1. Moreover, the PMO chirality was confirmed via the eluting method. The PMO material obtained was characterized by powder X-ray diffraction (XRD), N2 adsorption-desorption measurement, scanning electron microscope, transmission electron microscope, thermogravimetric analysis and solid-state NMR spectroscopy.In Chapterâ…£, morphology control of norbornane-bridged chiral PMOs was conducted by adding co-surfactant, co-solvent, inorganic salts, and organic salts, respectively.In Chapterâ…¤, the synthesis, characterization and catalytic performance of heteroatm-functionalized chiral PMOs were investigated. Al or B atoms can be successfully incorporated into the chiral PMO framework.27Al and 11B solid-state NMR spectroscopy were applied to characterize these heteroatom-functionalized materials. The catalytic performance of norbornane-bridged chiral PMO and Al-PMOs was examined in asymmetric catalysis under heterogeneous conditions.