Chiral Pyrrolidine Bridged Polyhedral Oligomeric Silsesquioxanes as Heterogeneous Catalysts for Asymmetric Michael Additions

Polyhedral Oligosilsesquioxanes in Functional Chiral Nanoassemblies

Incorporation of giant molecular nanoparticles with atomic precision into chiral nanoassemblies facilitates the fabrication of functional ordered phases with supramolecular chirality, which remains mysterious. Reported here is the first example of polyhedral oligosilsesquioxane (POSS) derivatives that self-assemble into well-defined chiral nanoassemblies. POSSs were covalently conjugated to N-terminal aromatic amino acids, which self-assembled into nanohelices and twists with explicit handedness tuned by solvent polarity. Chiral nanoassemblies showed active chiroptical responses including Cotton effects and circularly polarized luminescence. The chiral systems can bind guest molecules by charge-transfer interactions, whereby self-assembled structures, chiroptical activities, and luminescent colors were further modulated. The unique coassembly systems were applied for instant information encryption and storage with multiple luminescent displays. This work offers a new protocol for the design of functional chiral materials of POSS by molecular self-assembly.

Mono-substituted cage-like silsesquioxanes bound by trifunctional acyl chloride as a multi-donor N,O-type ligand in copper(ii) coordination chemistry: synthesis and structural properties

In this paper, we report on the synthesis of novel copper(ii) complexes containing a multi-donor N,O-type ligand based on mono-substituted cage-like silsesquioxanes bound by trifunctional acyl chloride.

POSS nanostructures in catalysis

In this review we highlight the use of appealing POSS-based nanostructures for both homogeneous and heterogeneous catalytic applications.

Chiral hybrid materials based on pyrrolidine building units to perform asymmetric Michael additions with high stereocontrol

A new chiral mesoporous hybrid material was synthesized based on pyrrolidine units included in a siliceous framework, HybPyr, and integrated into the organic-inorganic structure, from a specific bis-silylated precursor. A fluoride sol-gel methodology under soft synthesis conditions and in the absence of sophisticated structural directing agents allowed the generation of a mesoporous architecture with a homogeneous distribution of active chiral moieties along the network. The hybrid material was studied by means of different characterization techniques (TGA, NMR and IR spectroscopy, chemical and elemental analyses, TEM, and textural measurements), verifying the stability and integrity of the asymmetric active sites in the solid. The hybrid material, HybPyr, is an excellent asymmetric heterogeneous and recyclable catalyst for enantioselective Michael addition of linear aldehydes to β-nitrostyrene derivatives with high stereocontrol of the reaction products.

Anion identification using silsesquioxane cages

Anthracene-conjugated octameric silsesquioxane cages thermodynamically display intramolecular excimer formation, which can be used to identify anions through the change of fluorescence.

Anthracene-conjugated octameric silsesquioxane (AnSQ) cages, prepared via Heck coupling between octavinylsilsesquioxane (OVS) and 9-bromoanthracene, thermodynamically display intramolecular excimer emissions. More importantly, these hosts are sensitive to each anionic guest, thereby resulting in change of anthracene excimer formation, displaying the solvent-dependent fluorescence and allowing us to distinguish up to four ions such as F^–, OH^–, CN^– and PO₄^3– by fluorescence spectroscopy. Depending on the solvent polarity, for example, both F^– and CN^– quenched the fluorescence emission intensity in THF, but only F^– could enhance the fluorescence in all other solvents. The presence of PO₄^3– results in fluorescence enhancements in high polarity solvents such as DMSO, DMF, and acetone, while OH^– induces enhancements only in low polarity solvents (e.g. DCM and toluene). A picture of the anion recognizing ability of AnSQ was obtained through principal component analysis (PCA) with NMR and FTIR confirming the presence of host–guest interactions. Computational modeling studies demonstrate the conformation of host–guest complexation and also the change of excimer formation. Detection of F^–, CN^– and OH^– by AnSQ hosts in THF is noticeable with the naked eye, as indicated by strong color changes arising from charge transfer complex formation upon anion addition.