Synthesis and Characterization of Unsymmetrical Double-Decker Siloxane (Basket Cage)

Synthesis of Novel Luminescent Double-Decker Silsesquioxanes Based on Partially Condensed TetraSilanolPhenyl POSS and Tb3+/Eu3+ Lanthanide Ions

In this study, novel lanthanide-containing double-decker polyhedral oligomeric silsesquioxanes (POSS) were prepared by combining the partially condensed TetraSilanolPhenyl POSS with terbium (Tb3+) and europium (Eu3+) ions. This open-cage POSS possesses four diametrically opposite silanol groups that are able to coordinate, under mild conditions, different luminescent ions through a simple corner-capping method. The two metal-containing POSS functionalized with Tb3+ and with an equimolar combination of Tb3+ and Eu3+ show a completely condensed structure with different luminescent properties. Their emission features depend on the chemical nature of the metal ions incorporated in the framework. An improved stokes shift was detected in the bimetallic compound containing both the Tb3+ and Eu3+ ions, promoted by the occurrence of a Tb3+→Eu3+ energy transfer mechanism. These characteristics identify this metal-functionalized silica platform as a potential candidate for the development of novel luminescent devices.

Unexpected and frustrating transformations of double-decker silsesquioxanes

This paper outlines an unexpected type of intramolecular transformation of DDSQ during hydrolytic condensation and surprising catalytic reactivity in silylative coupling.

The Influence of HCl Concentration on the Rate of the Hydrolysis-Condensation Reaction of Phenyltrichlorosilane and the Yield of (Tetrahydroxy)(Tetraphenyl)Cyclotetrasiloxanes, Synthesis of All Its Geometrical Isomers and Thermal Self-Condensation of Them under "Pseudo"-Equilibrium Conditions

The rate of hydrolysis–condensation reaction of phenyltrichlorosilane in water-acetone solutions and the product yields were shown to significantly depend on the concentration of HCl (C_HCl) in the solutions. The main product of the reaction was all-cis-(tetrahydroxy)(tetraphenyl)cyclotetrasiloxane. This was different from the earlier published results of analogous reactions of m-tolylSiCl₃, m-ClPhSiCl₃, and α-naphtylSiCl, in which some products of other types were formed. For example, trans-1,1,3,3-tetrahydroxy-1,3-di-α-naphtyldisiloxane was obtained in the case of α-naphtylSiCl₃. All-cis-(tetrahydroxy)(tetraphenyl)cyclotetrasiloxane was treated in acetone with HCl to give the other three geometric isomers (cis-cis-trans-, cis-trans-, and all-trans-). The thermal self-condensation of these four isomers under “pseudo”-equilibrium conditions (under atmospheric pressure) was investigated in different solvents, in quartz or molybdenum glass flasks. The compositions of the products were monitored by APCI-MS and ²⁹Si NMR spectroscopy. It was shown that all-cis- and cis-cis-trans-isomers in toluene or anisole mostly gave the cage-like Ph-T_8,10,12,14 and uncompleted cage-like Ph-T_10,12OSi(HO)Ph compounds. In contrast to these two isomers, the cis-trans–isomer in toluene mainly formed dimers with the loss of one or two molecules of water. However, in acetonitrile, significant amounts of Ph-T_10,12 and Ph-T_10,12OSi(HO)Ph species were formed along with the dimers. All-trans-isomer did not enter into the reaction at all.

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.

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.

Silylation of silanols with hydrosilanes via main-group catalysis: the synthesis of unsymmetrical siloxanes and hydrosiloxanes

Apart from some specific synthetic solutions, a dehydrogenative coupling of silanols with hydrosilanes seems to be the most atom-economical and practical method for the formation of unsymmetrical siloxanes.