Organosilicon Research Articles

Enantioselective Synthesis of Chiral Organosilicon Compounds by Organocatalytic Asymmetric Conjugate Addition of Boronic Acids to β-Silyl-α,β-Unsaturated Ketones.

Herein, we report (R)-3,3'-(3,5-(CF3)2-C6H3)2-BINOL-catalyzed enantioselective conjugate addition of organic boronic acids to β-silyl-α,β-unsaturated ketones, furnishing moderate to excellent yields of the corresponding β-silyl carbonyl compounds with stereogenic centers in excellent enantioselectivities (up to 98% ee). Moreover, the catalytic system features mild reaction conditions, high efficiency, broad substrate scope, and easy scale-up.

Diverse Alkyl-Silyl Cross-Coupling via Homolysis of Unactivated C(sp3)-O Bonds with the Cooperation of Gold Nanoparticles and Amphoteric Zirconium Oxides.

Since C(sp3)-O bonds are a ubiquitous chemical motif in both natural and artificial organic molecules, the universal transformation of C(sp3)-O bonds will be a key technology for achieving carbon neutrality. We report herein that gold nanoparticles supported on amphoteric metal oxides, namely, ZrO2, efficiently generated alkyl radicals via homolysis of unactivated C(sp3)-O bonds, which consequently promoted C(sp3)-Si bond formation to give diverse organosilicon compounds. A wide array of esters and ethers, which are either commercially available or easily synthesized from alcohols participated in the heterogeneous gold-catalyzed silylation by disilanes to give diverse alkyl-, allyl-, benzyl-, and allenyl silanes in high yields. In addition, this novel reaction technology for C(sp3)-O bond transformation could be applied to the upcycling of polyesters, i.e., the degradation of polyesters and the synthesis of organosilanes were realized concurrently by the unique catalysis of supported gold nanoparticles. Mechanistic studies corroborated the notion that the generation of alkyl radicals is involved in C(sp3)-Si coupling and the cooperation of gold and an acid-base pair on ZrO2 is responsible for the homolysis of stable C(sp3)-O bonds. The high reusability and air tolerance of the heterogeneous gold catalysts as well as a simple, scalable, and green reaction system enabled the practical synthesis of diverse organosilicon compounds.

Direct Synthesis of Silicon Compounds—From the Beginning to Green Chemistry Revolution

This paper discusses the historical beginnings and the current state of knowledge of the synthesis of organosilicon compounds and chlorine derivatives of silicon. The key importance of these compounds for modern industry, including the semiconductor industry (photovoltaic cells, microprocessors, memory chips and many other electronic elements) is highlighted. Significant environmental threats related to the production of these compounds and the research challenges aimed at their elimination are discussed. The complexity of the catalytic mechanism of direct reaction of silicon with CH3Cl and alcohols is presented in an accessible way. In the last part of the work, the directions of the development of direct synthesis technology in line with the principles of green chemistry are indicated.

Improving the Dispersibility of TiO2 in the Colloidal System Using Trifunctional Spherosilicates

Titanium dioxide is a commonly used ingredient in cosmetics acting as a thickening agent and inorganic UV filter. However, TiO2 is difficult to disperse, which causes problems in spreading the formulations. The solution to this problem is to modify the titanium dioxide surface to change its properties by creation of the new type of hybrid inorganic-organic UV filter. Therefore, this study aimed to functionalize titanium dioxide with organosilicon compounds and determine how this modification will affect the dispersibility of TiO2 in the colloidal system and the stability of emulsions. First, the functionalized octaspherosilicates were obtained and characterized. Next, the synthesized compounds were applied as modifiers for titanium dioxide and were analyzed by FT-IR, UV-Vis, and laser diffraction. Furthermore, the hydrophilic-hydrophobic character was assessed by measuring the contact angle. The new materials were introduced into emulsions and the formulations were analyzed in terms of particle size distribution and stability by multiple light scattering. It was found that the modification of titanium dioxide with spherosilicates significantly improved both the stability of emulsion and the dispersibility of novel materials in the colloidal system compared to nonmodified TiO2. The covalent binding of the modifier with the titanium dioxide had an impact on the stability of the emulsion.

Dearomative triple elementalization of quinolines driven by visible light

Organoboron and organosilicon compounds are used not only as synthetic building blocks but also as functional materials and pharmaceuticals, and compounds with multiple boryl and silyl groups are beginning to be used for these purposes. Especially in drug discovery, methodology providing easy stereoselective access to aliphatic nitrogen heterocycles bearing multiple boryl or silyl groups from readily available aromatic nitrogen heterocycles would be attractive. However, such transformations remain challenging, and available reactions have been mostly limited to dearomative hydroboration or hydrosilylation reactions. Here, we report the dearomative triple elementalization (carbo-sila-boration) of quinolines via the addition of organolithium followed by photo-boosted silaboration, affording the desired products with complete chemo-, regio-, and stereoselectivity. The reaction proceeds via the formation of silyl radicals instead of silyl anions. We also present preliminary studies to illustrate the potential of silaboration products as synthetic platforms.

Metal-catalyst- and fluoride-free oxidative desilylation of arylsilanes and its application

A general and practical approach has been developed to construct aryloxy acrylates, esters, sulfonates, and ethers. This strategy performs smoothly to form the phenol intermediate through metal-catalyst- and fluoride-free oxidative desilylation of arylsilane, followed by Michael addition and nucleophilic substitution. This cascade reaction is characterized by its simple setup and broad functional group compatibility. Further transformation of the formed aryloxy acrylate demonstrated the rich chemistry of oxidative desilylation of organosilicon compounds.

Copper-Catalyzed Electrophilic Amination: An Umpolung Strategy for New C–N Bond Formations

Abstract The nitrogen atom is ubiquitous in bioactive molecules and functional materials, and the development of new C–N bond forming strategies is thus one of the long-standing research subjects in the synthetic community. This account describes the nitrogen-umpolung-enabled copper-catalyzed highly chemo- and stereoselective amination protocols developed by the author’s research group. Starting from the C–H amination, electrophilic amination of stable organoboron and organosilicon compounds, aminoboration/hydroamination of alkenes, and their applications to the synthesis of functionality-rich alkylamines are shown. The reaction design, concept, and substrate scope are briefly summarized.

Malcolm E. Kenney

Malcolm E. Kenney, 94, died Nov. 28, 2022, in Cleveland Heights, Ohio. “Malcolm’s extensive research career focused on phthalocyanines for applications as photodynamic therapy cancer treatments, organosilicon compounds for new materials, and silicates as sulfur dioxide adsorbents for coal gas emissions remediation. He received the R. Patrick Linstead Award in Phthalocyanine Chemistry in 2000. Malcolm published 30 patents and 200 papers and mentored numerous PhD students. He was an avid traveler, especially to Europe to visit sites of scientific interest. In addition to his scientific achievements, Kenney was a generous benefactor to the Cleveland Museum of Art and the Cleveland Orchestra, as well as the Open Doors Academy.”—John Protasiewicz, colleague and friend Most recent title: Hurlbut Professor Emeritus of Chemistry, Case Western Reserve University Education: BS, chemistry, University of Redlands, 1950; PhD, inorganic chemistry, Cornell University, 1953 To recognize your late loved one or colleague, submit obituary information at cenm.ag/obits

Characterization of spherical silica–titania mixed oxide particles synthesized by using a dry process

Silica–titania mixed oxides have excellent properties, such as a low thermal expansion coefficient and a refractive index that can be adjusted by changing the Ti content. However, when the Ti content increases, silica and titania phases in silica–titania mixed oxides can separate. This phase separation leads to the precipitation of the titania component as rutile or anatase crystals. When silica–titania mixed oxides undergo phase separation, their properties become unstable; for example, the refractive index of the particles becomes non-uniform. Therefore, it is preferable to synthesize silica–titania mixed oxides in an amorphous state without causing phase separation. Based on our previous studies on particle size control in silica synthesis, we employed a dry process using organosilicon compounds to synthesize silica–titania mixed oxides. In this study, spherical amorphous silica–titania mixed oxide particles were obtained via flame synthesis using organosilicon and organotitanium compounds. The purpose of this study was to characterize the obtained powder and explore the possibility of controlling particle size during synthesis. By studying the dry process synthesis of spherical silica–titania mixed oxide particles, we confirmed the relationships: between the Si/Ti molar ratio and the obtained crystal structure and between the adiabatic flame temperature and the particle size.

Hydro- and Icephobic Properties and Durability of Epoxy Gelcoat Modified with Double-Functionalized Polysiloxanes.

Anti-icing coatings have provided a very good alternative to current, uneconomic, active deicing methods, and their use would bring a number of significant benefits to many industries, such as aviation and energy. Some of the most promising icephobic surfaces are those with hydrophobic properties. However, the relationship between hydrophobicity and low ice adhesion is not yet clearly defined. In this work, chemical modification of an epoxy gelcoat with chemical modifiers from the group of double organofunctionalized polysiloxanes (generally called multifunctionalized organosilicon compounds (MFSCs)) was applied. The anti-icing properties of manufactured coatings were determined by means of measurements of shear strength between the ice layer and the modified surface, conducted using a tensile machine. In the work, tests were also performed on the roughness, wettability, and durability of the properties in an aging chamber. It was found that the performed modifications of the coating's chemical composition by the addition of polysiloxanes enabled us to reduce ice adhesion by 51% and to increase the water contact angle by 14% in comparison to the neat gelcoat. A reduction in ice adhesion was also observed with the increasing water contact angle and with decreasing surface roughness. In addition, only one modification recorded an increase in ice adhesion after exposure in the aging chamber.

Synthesis of 2,3-Dihydrosiloles via Palladium-Catalyzed Heck-type Arylation of Silacyclopentenes with Aryl Iodides

AbstractThe transition-metal-catalyzed synthesis of chiral silacycles is a challenging processes in organosilicon chemistry. Herein, we report a facile and regioselective synthesis of a novel class of 2,3-dihydrosilole derivatives with good yields via the palladium-catalyzed Heck-type reaction of silacyclopentenes (SCPs) with aryl iodides. Preliminary investigations on the enantioselective version of this palladium-catalyzed Heck-type process reveal that the presence of N-Boc-l-proline allows the diastereo- and enantioselective formation of chiral 2,3-dihydrosilole derivatives bearing both carbon and silicon-stereogenic centers.

Organosilicon Fluorescent Materials.

In the past few decades, organosilicon fluorescent materials have attracted great attention in the field of fluorescent materials not only due to their abundant and flexible structures, but also because of their intriguing fluorescence properties, distinct from silicon-free fluorescent materials. Considering their unique properties, they have found broad application prospects in the fields of chemosensor, bioimaging, light-emitting diodes, etc. However, a comprehensive review focusing on this field, from the perspective of their catalogs and applications, is still absent. In this review, organosilicon fluorescent materials are classified into two main types, organosilicon small molecules and polymers. The former includes fluorescent aryl silanes and siloxanes, and the latter are mainly fluorescent polysiloxanes. Their synthesis and applications are summarized. In particular, the function of silicon atoms in fluorescent materials is introduced. Finally, the development trend of organosilicon fluorescent materials is prospected.

Durability of model degraded wood treated with organosilicon compounds against fungal decay

Conservation agents used to preserve heavily degraded wooden artefacts typically act as consolidants that restore the structural integrity of an object. However, treatments that can provide both dimensional stability and improved resistance to wood-decaying organisms are desirable because even degraded wood is still susceptible to further biodegradation. Some organosilicon compounds proved effective at stabilising waterlogged wood dimensions and could serve as potential multi-purpose conservation agents. To assess whether these chemicals can also impart decay and resistance to filamentous fungi, degraded model Scots pine wood was impregnated with three different organosilicon compounds: Methyltrimethoxysilane – MTMS, (3-Mercaptopropyl) trimethoxysilane – MPTMS, and Bis(diethylamino)-3-propoxypropanol)-1,1,3,3-tetramethyldisiloxane – DEAPTMDS), and moisture properties and durability of the treated wood were measured. All three organosilicons reduced treated pine hygroscopicity and provided various degrees of protection against brown-rot and white-rot fungi. However, only DEAPTMDS completely inhibited the growth of filamentous fungi after four weeks of incubation. The results show that tested organosilicons are suitable multi-purpose conservation agents for degraded wooden objects such as waterlogged archaeological wood because they can both consolidate and protect degraded wood from further biodeterioration.

Reversible C-H bond silylation with a neutral silicon Lewis acid.

The silicon-carbon bond is a valuable linchpin for synthetic transformations. However, installing Si-C functionalities requires metalated C-nucleophiles, activated silicon reagents (silylium ions, silyl radicals, and silyl anions), or transition metal catalysis, and it occurs irreversibly. In contrast, spontaneous C-H silylations with neutral silanes leading to anionic silicates, and their reversible deconstruction, are elusive. Herein, the CH-bond silylation of heterocycles or a terminal alkyne is achieved by reaction with bis(perfluoro(N-phenyl-ortho-amidophenolato))silane and 1,2,2,6,6-pentamethylpiperidine. Computational and experimental insights reveal a frustrated Lewis pair (FLP) mechanism. Adding a silaphilic donor to the ammonium silicate products induces the reformation of the C-H bond, thus complementing previously known irreversible C-H bond silylation protocols. Interestingly, the FLP "activated" N-methylpyrrole exhibits "deactivated" features against electrophiles, while a catalytic functionalization is found to be effective only in the absence of a base.

Disilane-bridged architectures: an emerging class of molecular materials.

Disilanes are organosilicon compounds that contain saturated Si-Si bonds. The structural characteristics of Si-Si single bonds resemble those of C-C single bonds, but their electronic structure is more similar to that of C[double bond, length as m-dash]C double bonds, as Si-Si bonds have a higher HOMO energy level. These organosilicon compounds feature unique intramolecular σ electron delocalization, low ionization potentials, polarizable electronic structure, and σ-π interaction. It has been demonstrated that the employment of disilane units (Si-Si) is a versatile and effective approach for finely adjusting the photophysical properties of organic materials in both solution and solid states. In this review, we present and discuss the structure, properties, and relationships of novel σ-π-conjugated hybrid architectures with saturated Si-Si σ bonds. The application of disilane-bridged σ-conjugated compounds as optoelectronic materials, multifunctional solid-state emitters, CPL, and non-linear optical and stimuli-responsive materials is also reviewed.

Electrifying synthesis of organosilicon compounds – from electrosynthesis to electrocatalysis

Organosilicon compoundsviaelectrosynthesis – the recent developments and further challenges.

Sequential hydrothiolation–hydrosilylation: a route to the creation of new organosilicon compounds with preset structures

An efficient approach to the preparation of functional organosilicon compounds by sequential hydrothiolation (Ht) and hydrosilylation (Hs) reactions using commercially available catalysts and activators is presented.

Adsorption properties of silica aerogel-based materials.

Silica aerogels have piqued the interest of both scientists and industry in recent decades due to their unusual properties such as low density, high porosity, low thermal and acoustic conductivity, high optical transparency, and strong sorption activity. Aerogels may be created via two-step sol-gel synthesis from different organosilicon compounds known as precursors. Various drying processes are employed to remove the solvent from the gel pores, the most common of which is the supracritical drying method. This paper highlights the potential of silica aerogels and their modifications as adsorbents for environmental cleanup based on recent researches. Following an introduction of the characteristics of aerogels, production techniques, and different categorization possibilities, the study is organized around their potential use as adsorbents.

Recent progress in reductive carboxylation of C-O bonds with CO2.

Transformation of carbon dioxide (CO2) into value-added organic compounds has attracted increasing interest of scientific community in the last few decades, not only because CO2 is the primary greenhouse gas that drives global climate change and ocean acidification, but also because it has been regarded as a plentiful, nontoxic, nonflammable and renewable one-carbon (C1) feedstock. Among the various CO2-conversion processes, carboxylation reactions represent one of the most beautiful and attractive research topics in the field, since it offers the possibility for the construction of synthetically and biologically important carboxylic acids from various easily accessible (pseudo)halides, organosilicon, and organoboron compounds. The purpose of this review is to summarize the available literature on deoxygenative carboxylation of alcohols and their derivatives utilizing CO2 as a carboxylative reagent. Depending on the C-O compounds employed, the paper is divided into five major sections. The direct dehydroxylative carboxylation of free alcohols is discussed first. This is followed by reductive carboxylation of carboxylates, triflates, and tosylates. In the final section, the only reported example on catalytic carboxylation of fluorosulfates will be covered. Notably, special attention has been paid on the mechanistic aspects of the reactions that may provide new insights into catalyst improvement and development, which currently mainly relies on the use of transition metal catalysts.

Palladium-catalyzed synthesis of 2,3-disubstituted indoles via arylation of ortho-alkynylanilines with arylsiloxanes.

In this study, we report the electrophilic cyclization of N,N-dimethyl-o-alkynylanilines with arylsiloxanes in the presence of [Pd(OAc)2] and Ag2O catalytic system, which leads to the efficient synthesis of indoles, similar to the one that is obtained through Larock indole synthesis. A range of aryl(trimethoxy)silanes with EDGs and EWGs were successfully utilized for the synthesis of a diverse variety of substituted indoles via the cleavage of the C-Si bond. This protocol exhibits good functional group tolerance and wide substrate scope to provide 2,3-diaryl-N-methylindoles in 26-88% yields.