Synthesis, Crystal Structures, and Optical and Magnetic Properties of Samarium, Terbium, and Erbium Coordination Entities Containing Mono-Substituted Imine Silsesquioxane Ligands

Mono-substituted cage-like silsesquioxanes of the T₈-type can play the role of potential ligands in the coordination chemistry. In this paper, we report on imine derivatives as ligands for samarium, terbium, and erbium cations and discuss their efficient synthesis, crystal structures, and magnetic and optical properties. X-ray analysis of the lanthanide coordination entities [MCl₃(POSS)₃]·2THF [M = Er³⁺ (3), Tb³⁺ (4), Sm³⁺ (5)] showed that all three compounds crystallize in the same space group with similar lattice parameters. All compounds contain an octahedrally coordinated metal atom, and additionally, 3 and 5 structures are strictly isomorphous. However, surprisingly, there are two different molecules in the crystal structure of the terbium coordination entity 4, monomer (sof 65%) and dimer (sof 35%), with one and two metal centers. Absorption measurements of the investigated materials recorded at 300 K showed that regardless of the lanthanide involved, their energy band gap equals 2.7 eV. Moreover, the analogues containing Tb³⁺ and Sm³⁺ exhibit luminescence typical of these rare earth ions in the visible and infrared spectral range, while the compound with Er³⁺ does not generate any emission. Direct current variable-temperature magnetic susceptibility measurements on polycrystalline samples of 3-5 were performed between 1.8 and 300 K. The magnetic properties of 3 and 4 are dominated by the crystal field effect on the Er³⁺ and Tb³⁺ ions, respectively, hiding the magnetic influence between the magnetic cations of adjacent molecules. Complex 5 exhibits a nature typical for the paramagnetism of the samarium(III) cation.

Zinc Imine Polyhedral Oligomeric Silsesquioxane as a Quattro-Site Catalyst for the Synthesis of Cyclic Carbonates from Epoxides and Low-Pressure CO2

In the present research, the synthesis, spectroscopic characterization, and structural investigations of a unique Zn^II complex of imine-functionalized polyhedral oligomeric silsesquioxane (POSS) is designed, and hereby described, as a catalyst for the synthesis of cyclic carbonates from epoxides and CO₂. The uncommon features of the designed catalytic system is the elimination of the need for a high pressure of CO₂ and the significant shortening of reaction times commonly associated with such difficult transformations like that of styrene oxide to styrene carbonate. Our studies have shown that imine-POSS is able to chelate metal ions like Zn^II to form a unique coordination complex. The silsesquioxane core and the hindrance of the side arms (their steric effect) influence the construction process of the homoleptic Zn₄@POSS-1 complex. The compound was characterized in solution by NMR (¹H, ¹³C, ²⁹Si), ESI-MS, UV/Vis spectroscopy and in the solid state by thermogravimetric/differential thermal analysis (TG-DTA), elemental analysis, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), cross-polarization magic angle spinning (CP MAS) NMR (¹³C, ²⁹Si) spectroscopy, and X-ray crystallography.

Synthesis and Hydrosilylation of Vinyl-Substituted Open-Cage Silsesquioxanes with Phenylsilanes: Regioselective Synthesis of Trifunctional Silsesquioxanes

Herein, we report an efficient synthesis and functionalization of trifunctional open-cage-type silsesquioxanes. The method proposed has been successfully applied for the synthesis of a library of incompletely condensed silsesquioxanes with vinyldiorganosilyl functional groups, which allows further modification. Detailed studies of hydrosilylation of sterically different open-cage vinylsilsesquioxanes with a wide spectrum of phenylsilanes catalyzed by platinum and rhodium compounds are also reported. The influence of the reaction parameters, types of reagents, and catalysts employed on the efficiency of the process was examined. Optimization of the process based on the above results permitted the design of a very attractive method for the synthesis of multifunctionalized silsesquioxanes with excellent yields and regioselectivity. Moreover, the results allowed the choice of the most efficient catalyst whose application led to the selective formation of substituted open-cage silsesquioxanes. These new compounds have been fully characterized and studied in terms of their thermal properties.

The first example of a fully specified synthetic protocol allowing selective modification of trivinyl-substituted open-cage silsesquioxanes with silanes via platinum-catalyzed hydrosilylation is presented.

N-Heterocyclic carbene-based ruthenium-hydride catalysts for the synthesis of unsymmetrically functionalized double-decker silsesquioxanes

The [RuHCl(CO)(SIDip)(PCy₃)] complex efficiently catalyzes the (E)-selective silylative coupling of divinyl-substituted double-decker silsesquioxanes with two distinctly substituted styrenes.

Highly selective synthesis of substituted (E)-alkenylsilatranes via catalytic trans-silylation and mechanistic implications

A new route for the synthesis of functionalized alkenylsilatranes has been developed based on ruthenium-catalyzed trans-silylation with olefins. This transformation allowed for the synthesis of new (E)-alkenylsilatranes in good yields and excellent selectivity. Experimental studies concerning the reaction mechanism were carried out and the intermediate ruthenium-silatranyl complex was isolated and characterized. Moreover, detailed DFT calculations regarding the mechanism of the silylative coupling catalytic cycle of silatranes catalyzed by [Ru]-H complexes were also performed.

A highly selective synthesis of new alkenylsilsesquioxanes by hydrosilylation of alkynes

In this study a selective synthesis of a series of new di- and trisubstituted ethenes with a POSS moiety was performed.

Synthesis and characterization of functionalized molecular and macromolecular double-decker silsesquioxane systems

Synthesis and characterization of new, molecular and macromolecular DDSQ-based compounds functionalized by substituted styrenes and distyrylarenes (also with heteroatoms) in a stereoselective manner is presented.