Introduction of Boron Functionalities into Silsesquioxanes: Novel Independent Methodologies

Access to thioethers from thiols and alcohols via homogeneous and heterogeneous catalysis

A metal-free dehydrative thioetherification method has been reported, enabling the conversion of various alcohols and thiols into thioethers. By employing triflic acid as a catalyst or utilizing a recyclable NAFION® superacid catalyst, these methods significantly improve the efficiency and practicality of sulfide preparation.

Silane-Bearing Borasilsesquioxanes: Synthetic Protocol and Unsuspected Redistribution Reactions

The presented work is a continuation of research on the reactivity of unsaturated borasilsesquioxanes under the conditions of common organometallic transformations. The catalytic hydrosilylation reaction with silanes, siloxanes and silsesquioxanes in presence of platinum catalyst was explored. The majority of the products were obtained in high yields (>90 %) and their structures were confirmed and characterized by spectroscopy and spectrometry, i. e. NMR and MALDI-TOF-MS. The most significant segment of the work is research on the spontaneous redistribution reaction of the alkoxy group from silane to borane moiety occurring in the obtained products, not being limited to the heterosilsesquioxane chemistry, however. The products were confirmed using GC-MS, ESI-MS methods and B3LYP exchange-correlation, in order to ascertain formation of the silicon-boron hybrid molecule.

Eu3+ and Tb3+ @ PSQ: Dual Luminescent Polyhedral Oligomeric Polysilsesquioxanes

The synthesis and characterization of novel luminescent amorphous POSS-based polysilsesquioxanes (PSQs) with Tb³⁺ and Eu³⁺ ions directly integrated in the polysilsesquioxane matrix is presented. Two different Tb³⁺/Eu³⁺ molar ratios were applied, with the aim of disclosing the relationships between the nature and loading of the ions and the luminescence properties. Particular attention was given to the investigation of site geometry and hydration state of the metal centers in the inorganic framework, and of the effect of the Tb³⁺ → Eu³⁺ energy transfer on the overall optical properties of the co-doped materials. The obtained materials were characterized by high photostability and colors of the emitted light ranging from orange to deep red, as a function of both the Tb³⁺/Eu³⁺ molar ratio and the chosen excitation wavelength. A good energy transfer was observed, with higher efficiency displayed when donor/sensitizer concentration was lower than the acceptor/activator concentration. The easiness of preparation and the possibility to finely tune the photoluminescence properties make these materials valid candidates for several applications, including bioimaging, sensors, ratiometric luminescence-based thermometers, and optical components in inorganic or hybrid light-emitting devices.

Zn-Catalyzed Regioselective and Chemoselective Reduction of Aldehydes, Ketones and Imines

An operationally convenient Zn-catalyzed synthesis of alcohols by the reduction of aldehydes, ketones, and α,β-unsaturated aldehydes/ketones is reported. It is a rare example of using mild and sustainable HBpin as a reductant for catalytic reduction of carbonyl compounds in the absence of acid or base as hydrolysis reagent. The reaction is upscalable and proceeds in high selectivity without the formation of boronate ester by-products, and tolerates sensitive functionalities, such as iodo, bromo, chloro, fluoro, nitro, trifluoromethyl, aminomethyl, alkynyl, and amide. The Zn(OAc)₂/HBpin combination has been also proved to be chemoselective for the C=N reduction of imine analogs.

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.

Novel Silsesquioxane-Derived Boronate Esters-Synthesis and Thermal Properties

The functionalization of mono- and octahydrospherosilicate with vinylboranes and allylboranes via hydrosilylation reaction in the presence of a Karstedt’s platinum (0) catalyst is presented. This is the catalytic route to obtain a new class of silsesquioxanes containing boron atoms in their structure in high yields (>90%) and with satisfactory selectivity. The obtained compounds were fully characterized by spectroscopic (¹H, ¹³C, ²⁹Si NMR) and spectrometric methods (MALDI-TOF-MS), as well as thermal analysis (TGA). The obtained compounds were subjected to thermal tests, characterizing the processes of melting, thermal evaporation, sublimation and thermal decomposition.

B(C6F5)3-Catalyzed Dehydrocoupling of POSS Silanols with Hydrosilanes: A Metal-Free Strategy for Effecting Functionalization of Silsesquioxanes

We report a highly effective metal-free catalytic procedure for the functionalization of silsesquioxanes via dehydrocoupling of various POSS silanols with hydrosilanes in the presence of commercially available tris(pentafluorophenyl)borane B(C₆F₅)₃. This approach enables the unprecedented one-pot synthesis of valuable silsesquioxane derivatives under mild conditions, with no corrosive byproducts formed in the process.

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.

Preparation of Tri(alkenyl)functional Open-Cage Silsesquioxanes as Specific Polymer Modifiers

The scientific reports on polyhedral oligomeric silsesquioxanes are mostly focused on the formation of completely condensed T₈ cubic type structures and recently so-called double-decker derivatives. Herein, we report on efficient synthetic routes leading to trifunctionalized, open-cage silsesquioxanes with alkenyl groups of varying chain lengths from -vinyl to -dec-9-enyl and two types of inert groups (iBu, Ph) at the silsesquioxane core. The presented methodology was focused on hydrolytic condensation reaction and it enabled obtaining titled compounds with high yields and purity. A parallel synthetic methodology that was based on the hydrosilylation reaction was also studied. Additionally, a thorough characterization of the obtained compounds was performed, also in terms of their thermal stability, melting and crystallization temperatures (TGA and DSC) in order to show the changes in the abovementioned parameters dependent on the type of reactive as well as inert groups at Si-O-Si core. The presence of unsaturated alkenyl groups has a profound impact on the application potential of these systems, i.e., as modifiers or comonomers for copolymerization reaction.

Magnesium-catalyzed hydroboration of organic carbonates, carbon dioxide and esters

A magnesium(i) complex was employed as a highly efficient precatalyst for the hydroboration of carbonates and esters under mild conditions.

Green hydroboration of carboxylic acids and mechanism investigation

A catalyst-free and solvent-free method for the hydroboration of a variety of carboxylic acids with pinacolborane was developed. The hydroboration of various aromatic and aliphatic carboxylic acids as well as dicarboxylic acids with HBpin could be completed within 6 h at room temperature or within 1 h at 60 °C to give the products in quantitative yields under neat conditions without the need for any solvent or metal catalyst. The possible reaction mechanism was investigated in detail based on the corresponding DFT calculations and the stoichiometric reaction of acetic acid with different equivalents of HBpin (at room temperature and 0 °C) and it revealed the stepwise nature of the protocol.

Synthesis of structured polysiloxazanes via a Piers-Rubinsztajn reaction

A series of siloxazanes were successfully prepared by a Piers-Rubinsztajn reaction between methoxydisilazanes and the corresponding hydrosilanes. Polysiloxazanes with narrow dispersion were also synthesized from methoxydisilazanes and Si-H terminated oligosiloxanes. The possible interaction mechanism between tris(pentafluorophenyl)borane and the methoxydisilazane was investigated.

Catalytic Hydroboration of Aldehydes, Ketones, and Alkenes Using Potassium Carbonate: A Small Key to Big Transformation

An efficient transition-metal-free protocol for the hydroboration of aldehydes and ketones (reduction) was developed. The hydroboration of a wide range of aldehydes and ketones with pinacolborane (HBpin) under the K₂CO₃ catalyst has been studied. The reaction system is practical and reliable and proceeds under extremely mild and operationally simple conditions. No prior preparation of the complex metal catalyst was required, and hydroboration occurred stoichiometrically. Further, the chemoselective reduction of aldehydes over ketones was carried out. Moreover, we demonstrated the use of K₂CO₃ as an efficient catalyst for the hydroboration of alkenes. The operational simplicity, inexpensive and transition-metal-free catalyst, and the applicability to gram-scale synthesis strengthen its potential applications for hydroboration (reduction) at an industrial scale.

Catalyst-Free and Solvent-Free Facile Hydroboration of Imines

A facile process for the catalyst-free and solvent-free hydroboration of aromatic as well as heteroaromatic imines is reported. This atom-economic methodology is scalable, compatible with sterically and electronically diverse imines, displaying excellent tolerance towards various functional groups, and works efficiently at ambient temperature in most of the cases, affording secondary amines in good to excellent yield after hydrolysis.

A Highly Effective Route to Si-O-Si Moieties through O-Silylation of Silanols and Polyhedral Oligomeric Silsesquioxane Silanols with Disilazanes

A simple and highly practical catalyst-free O-silylation of silanols with commercially available disilazanes has been developed under mild conditions. In the case of polyhedral oligomeric silsesquioxane (POSS) silanols and some other silanols, it was necessary to use catalytic amounts of inexpensive Bi(OTf)₃ as additional catalyst. This efficient chlorine-free protocol involves the synthesis of a wide range of important organosilicon derivatives such as unsymmetrical disiloxanes and functionalized silsesquioxanes.

Synthesis of (E)-1,4-disilsesquioxylsubstituted but-1-en-3-ynes via platinum-catalyzed dimerization of ethynylsiloxysilsesquioxanes

A new platinum complex bearing bulky N-heterocyclic carbene ligand of the general formula [Pt(IPr*Ph)(dvtms)] (where IPr*Ph = 1,3-bis{2,4,6-tris(diphenylmethyl)phenyl}imidazol-2-ylidene, dvtms = divinyltetramethyldisiloxane) exhibits a high catalytic activity towards E-selective dimerization of ethynyl substituted siloxysilsesquioxanes. This process leads to a novel class of functionalized silsesquioxane derivatives, resembling their dumbbell-shaped silsesquioxane analogues.

Copper(ii) triflate-mediated synthesis of functionalized silsesquioxanes via dehydrogenative coupling of POSS silanols with hydrosilanes

In light of the fact that the design of new catalytic routes leading to functionalized silsesquioxanes is currently of high relevance; herein we report a novel, highly effective and convenient catalytic approach for the modification of silsesquioxanes. We present a dehydrogenative coupling reaction of completely as well as incompletely condensed POSS silanols with a wide range of commercially available hydrosilanes mediated by inexpensive copper(ii) trifluoromethanesulfonate. This research also includes mechanistic studies for this process.

A facile approach for the synthesis of novel silsesquioxanes with mixed functional groups

An efficient pathway for the synthesis of novel organofunctional silsesquioxanes with varied functional groups.

Catalyst-free and solvent-free hydroboration of ketones

The hydroboration of a wide range of ketones with HBpin under catalyst-free and solvent-free conditions was reported in high yields.

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.