Tunable Porosity of Cross-Linked-Polyhedral Oligomeric Silsesquioxane Supports for Palladium-Catalyzed Aerobic Alcohol Oxidation in Water

Cage-rearranged and cage-intact syntheses of azido-functionalized larger T10 and T12 POSSs

Herein, we investigate the product type and distribution during the synthesis of azido-functionalized larger polyhedral oligomeric silsesquioxanes (POSSs) using 3-chloropropyl- and chloromethyldimethylsilylethyl-functionalized T8, T10, and T12 POSSs as precursors. Our findings indicate that cage rearrangement occurs for the 3-chloropropyl-functionalized POSS cages with a stability order of T12 > T10 > T8, while the chloromethyldimethylsilylethyl-functionalized POSS cages remain structurally intact after the nucleophilic substitution.

Oil foams stabilized by POSS/organosilica particle assemblies: application for aerobic oxidation of aromatic alcohols

A novel amphiphilic polyhedral oligomeric silsesquioxane (POSS) with surfactant-like behavior was synthesized. By combining this new POSS, used as a frother, with surface-active catalytic organosilica particles, used as a stabilizer, we designed a dual particle system able to generate foams in pure organic solvents. Tunable foamability and foam stability were achieved in a variety of organic solvents by simply adjusting the POSS concentration. As a result, the catalytic activity was drastically boosted in the aerobic oxidation of pure aromatic alcohols under 1 bar O₂ pressure. Particles were conveniently recycled with high foamability and the catalytic efficiency was maintained for at least 7 consecutive runs.

Vinyl-Functionalized Janus Ring Siloxane: Potential Precursors to Hybrid Functional Materials

A vinyl-functionalized all-cis-tetrasiloxycyclotetrasiloxane [ViSi(OSiMe2H)O]4 (Vi = vinyl group) Janus precursor was prepared from potassium cyclotetrasiloxane silanolate. The Janus precursor was selectively modified at its dimethylhydrosilyl groups [-SiMe2H] via the Piers-Rubinsztajn reaction to obtain a family of new tetravinyl-substituted Janus rings [ViSi(OR')O]4 containing various functional groups in moderate yields. Remarkably, the tetravinyl groups on the structure remained intact after modification by the Piers-Rubinsztajn reaction. Since these synthesized compounds possess multiple functional groups (up to eight per molecule), they are potential precursors for advanced hybrid organic-inorganic functional materials.

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.

Synthesis of Tricyclic Laddersiloxane with Various Ring Sizes (Bat Siloxane)

A new synthetic method for tricyclic laddersiloxanes, ladder-type silsesquioxanes with defined structures, is developed based on intramolecular cyclization of hydrosilyl-functionalized cyclic siloxanes. This method enables the construction of unprecedented laddersiloxanes with various ring sizes. Herein, the preparation of tricyclic laddersiloxanes containing 6-8-6-, 8-8-8-, or 12-8-12-membered-ring systems is reported. These products can be considered as bat-shape siloxanes, owing to their rigid inorganic siloxane body with flexible oligosiloxane "wings" as side rings. The synthesized compounds are potential building blocks for well-defined nanomaterials, porous materials, and host molecules.

Janus ring siloxane: a versatile precursor of the extended Janus ring and tricyclic laddersiloxanes

All-cis-tetrasiloxycyclotetrasiloxanes (Janus ring siloxanes) were facilely prepared from all-cis-cyclotetrasiloxanetetraol or sodium cyclotetrasiloxane silanolates. Moreover, we demonstrated the synthesis of extended Janus rings, [RSi(OR')O]4, containing various functional groups, via the Piers-Rubinsztajn reaction using a Janus ring siloxane as a precursor. Remarkably, we discovered the formation of an unexpected all-cis tricyclic laddersiloxane as a by-product. These synthesized compounds can be potential monomers of well-defined cage silsesquioxanes, Janus-type nanomaterials, and porous materials.

R-Silsesquioxane-Based Network Polymers by Fluoride Catalyzed Synthesis: An Investigation of Cross-Linker Structure and Its Influence on Porosity

Silsesquioxane-based networks are an important class of materials that have many applications where high thermal/oxidative stability and porosity are needed simultaneously. However, there is a great desire to be able to design these materials for specialized applications in environmental remediation and medicine. To do so requires a simple synthesis method to make materials with expanded functionalities. In this article, we explore the synthesis of R-silsesquioxane-based porous networks by fluoride catalysis containing methyl, phenyl and vinyl corners (R-Si(OEt)₃) combined with four different bis-triethoxysilyl cross-linkers (ethyl, ethylene, acetylene and hexyl). Synthesized materials were then analyzed for their porosity, surface area, thermal stability and general structure. We found that when a specified cage corner (i.e., methyl) is compared across all cross-linkers in two different solvent systems (dichloromethane and acetonitrile), pore size distributions are consistent with cross-linker length, pore sizes tended to be larger and π-bond-containing cross-linkers reduced overall microporosity. Changing to larger cage corners for each of the cross-linkers tended to show decreases in overall surface area, except when both corners and cross-linkers contained π-bonds. These studies will enable further understanding of post-synthesis modifiable silsesquioxane networks.

Cage-like silsesquioxanes-based hybrid materials

Cage-like silsesquioxanes are considered to be ideal and versatile building blocks of hybrid materials due to their unique structures and excellent performance. This Perspective highlights recent advances in the field of cage-like silsesquioxane-based hybrid materials, ranging from monomer functionalization and materials preparation to application. The existing issues are reviewed and the challenges and prospects in this field are also discussed for further development and exploitation.

Aerobic Oxidation of Alcohols Catalyzed by in Situ Generated Gold Nanoparticles inside the Channels of Periodic Mesoporous Organosilica with Ionic Liquid Framework

In situ generated gold nanoparticles inside the nanospaces of periodic mesoporous organosilica with an imidazolium framework (Au@PMO-IL) were found to be highly active, selective, and reusable catalysts for the aerobic oxidation of activated and nonactivated alcohols under mild reaction conditions. The catalyst was characterized by nitrogen adsorption-desorption measurement, thermogravimetric analysis (TGA), transmission electron microscopy (TEM), elemental analysis (EA), diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma atomic emission spectroscopy (ICP-AES). The catalyst exhibited excellent catalytic activity in the presence of either Cs₂CO₃ (35 °C) or K₂CO₃ (60 °C) as reaction bases in toluene as a reaction solvent. Under both reaction conditions, various types of alcohols (up to 35 examples) including activated benzylic, primary and secondary aliphatic, heterocyclic, and challenging cyclic aliphatic alcohols converted to the expected carbonyl compounds in good to excellent yields and selectivity. The catalyst was also recovered and reused for at least seven reaction cycles. Data from three independent leaching tests indicated that amounts of leached gold particles were negligible (<0.2 ppm). It is believed that the combination of bridged imidazolium groups and confined nanospaces of PMO-IL might be a major reason explaining the remarkable stabilization and homogeneous distribution of in situ generated gold nanoparticles, thus resulting in the highly active and recyclable catalyst system.

POSS nanostructures in catalysis

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

Quaternized POSS modified rGO-supported Pd nanoparticles as a highly efficient catalyst for reduction and Suzuki coupling reactions

Hydrophilic QPOSS modified rGO nanosheets are fabricated as a robust catalyst support of PdNPs for reduction and Suzuki coupling reactions.

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.

Porous Silsesquioxane-Imine Frameworks as Highly Efficient Adsorbents for Cooperative Iodine Capture

The efficient capture and storage of radioactive iodine (¹²⁹I or ¹³¹I), which can be formed during nuclear energy generation or nuclear waste storage, is of paramount importance. Herein, we present highly efficient aerogels for reversible iodine capture, namely, porous silsesquioxane-imine frameworks (PSIFs), constructed by condensation of octa(3-aminopropyl)silsesquioxane cage compound and selected multitopic aldehydes. The resulting PSIFs are permanently porous (Brunauer-Emmet-Teller surface areas up to 574 m²/g), thermally stable, and present a combination of micro-, meso-, and macropores in their structures. The presence of a large number of imine functional groups in combination with silsesquioxane cores results in extremely high I₂ affinity with uptake capacities up to 485 wt %, which is the highest reported to date. Porous properties can be controlled by the strut length and rigidity of linkers. In addition, PSIF-1a could be recycled at least four times while maintaining 94% I₂ uptake capacity. Kinetic studies of I₂ desorption show two strong binding sites with apparent activation energies of 77.0 and 89.0 kJ/mol. These energies are considerably higher than the enthalpy of sublimation of bulk I₂.

Silsesquioxane cages as fluoride sensors

Pyrene functionalized silsesquioxane cages (PySQ) not only provide significant fluorescence from pyrene-pyrene excimers with a very large Stokes shift (Δλ = 143 nm, 69 930 cm^-1) in DMSO but also exhibit fluoride capture results coincidentally with a π-π* fluorescence enhancement. On the other hand, PySQ-F^- in THF significantly exhibits π-π* fluorescence quenching and a color change can be observed with the naked eye from light yellow to deep orange by forming a charge-transfer (CT) complex among the pyrenyl rings. Moreover, PySQ selectively captures F^- with a response time of <2 min and with a very low detection limit (1.61 ppb), while ¹⁹F NMR is used to confirm encapsulation of F^- with Δδ = 19 ppm.

Polyhedral Oligomeric Silsesquioxane (POSS) Bearing Glyoxylic Aldehyde as Clickable Platform Towards Multivalent Conjugates

The straightforward access to octafunctional "cubic" silsesquioxane platform grafter with pendant glyoxylic aldehydes is described. This clickable hybrid platform readily reacts with oxyamine or hydrazide compounds to provide, respectively, oxime and acylhydrazone conjugates, thereby offering a new and effective access from which one can elaborate multivalent systems for the targeting of biomolecules of interest.

Development of the optical sensor for discriminating isomers of fatty acids based on emissive network polymers composed of polyhedral oligomeric silsesquioxane

It was shown that water-soluble network polymers composed of polyhedral oligomeric silsesquioxane (POSS) had hydrophobic spaces inside the network because of strong hydrophobicity of the cubic silica cage. In this study, the water-soluble POSS network polymers connected with triphenylamine derivatives (TPA-POSS) were synthesized, and their functions as a sensor for discriminating the geometric isomers of fatty acids were investigated. Accordingly, in the photoluminescence spectra, different time-courses of intensity and peak wavelengths of the emission bands were detected from the TPA-POSS-containing solution in the presence of cis- or trans-fatty acids during incubation. Furthermore, variable time-dependent changes were obtained by changing coexisting ratios between two geometric isomers. From the mechanistic investigation, it was implied that these changes could be originated from the difference in the degree of interaction between the POSS networks and each fatty acid. Our data could be applicable for constructing a sensing material for generation and proportion of trans-fatty acids in the oil.