Diving into the chiral pool: enantiopure microporous polysilsesquioxane spheres from both enantiomers with an oxazolidinone motif
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Organosilica hybrid materials from bridged silsesquioxanes combine attractive properties of a silica backbone with flexible organic compounds. This class of materials is of interest for different applications. Enantiopure chiral polysilsesquioxanes play a role in fields like the enantioselective catalysis or chromatography. Different applications have been used for their synthesis already. Here, l-valine, representative of the chiral pool, and the respective enantiomer d-valine were used to design two enantiomers of oxazolidinone derivates in a multistep synthesis path. The oxazolidinones were bis-silylated in a double Heck cross-coupling. Formation of micropores was realized by self-assembly of the precursors under suitable conditions, leading to polysilsesquioxanes with high surface areas as could be investigated by argon physisorption. The materials were profoundly characterized using solid-state NMR. The retention of the stereogenic information could be proven by circular dichroism measurements of the precursors as well as the respective hybrid materials. Furthermore, the materials were obtained in spherical morphology.
Nanoporous enantiopure chiral polysilsesquioxanes synthesized from enantiomeric bis-silylated organosilica precursors.
These precursors were synthesized from natural products from the chiral pool—an enantiomeric pair of amino acids. With this approach we got to synthesize both precursor enantiomers purely—a rarely gained aim as in most approaches one enantiomer is inaccessible.
The respective hybrid materials were received exclusively from each of the very precursors without co-condensation with other silica sources, which enables maximal density of the chiral information and benefits the formation of micropores under suitable conditions without templating.
This is accompanied by high apparent surface areas and therewith good accessibility of the functional sides and offers great potential for the utilization of the material in the before named applications.
KeywordsChiral organosilica Polysilsesquioxanes Microporous Spherical morphology
We thank Renate Walter for SEM images and Theresa Nuguid for support with the CD measurements.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
We assure that this manuscript complies to the Ethical Rules applicable for this journal.
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