Silylation Reaction Research Articles

Base-Triggered Oxidative Addition to Gold.

The coordination of secondary phosphine oxides (SPO) was shown to efficiently promote the activation of C(sp2 )-I bonds by gold, as long as a base is added (NEt3 , K2 CO3 ). These transformations stand as a new type of chelation-assisted oxidative addition to gold. The role of the base and the influence of the electronic properties of the P-ligand were analyzed computationally. Accordingly, the oxidative addition was found to be dominated by Au→(Ar-I) backdonation. In this case, gold behaves similarly to palladium, suggesting that the inverse electron flow reported previously (with prevailing (Ar-I)→Au donation, resulting in faster reactions of electron-enriched substrates) is a specific feature of electron-deficient cationic gold(I) complexes. The reaction gives straightforward access to (P=O,C)-cyclometallated Au(III) complexes. The possibility to chemically derivatize the SPO moiety at Au(III) was substantiated by protonation and silylation reactions.

Catalytic asymmetric silicon-carbon bond-forming transformations based on Si-H functionalization

In view of the exciting advancement on silicon-carbon bond-forming transformations achieved in the past decade, this review intends to show a unified illustration of the recent findings on enantioselective Si-H bond functionalization aided by asymmetric catalysis. Accordingly, this review describes the enantioselective silicon-carbon bond-forming Si-H bond functionalization, focusing on the reactivity and stereoselectivity in catalytic asymmetric hydrosilylation, carbene Si-H insertion, Si-H silylation, and Si-C bond-forming cross-coupling reactions that were achieved with high enantioselectivity in the presence of transition-metal catalyst systems. This review highlights recent and representative examples of the enantioselective Si-H bond functionalization, discusses the origins of silicon-involving stereoselectivities, and evaluates the substrate scopes and limitations in these catalytic asymmetric Si-H bond functionalization reactions due to the special reactivity of different hydrosilanes.

Tuning lattice strain in Quasi-2D Au-rGO nanohybrid catalysts for dimethylphenylsilane solid state silylation to disiloxane

This study investigates the effect of lattice strain on quasi-2D Au-rGO nanohybrids by growing cubic shape-controlled Au nanocrystals on rGO. To induce the lattice strain, a trisodium citrate capping agent and different concentrations of Au nanoparticles ranging from 0.2 to 1 mM were used. The 0.4 mM Au-rGO was confirmed with a low lattice strain differential of 0.1% between crystallographic planes (111), (200), (220), and (220) (311). The catalytic solid-state activity of 0.4 mM Au-rGO during conversion of dimethylphenylsilane to diphenyltetramethyldisiloxane is highest due to the low lattice strain differential. Following first-order kinetics, more dimethylphenylsilane was converted to diphenyltetramethyldisiloxane at a rate of 5.5 mol. L-1s-1 and 0.75 s-1 rates constant after increasing the solid-state silylation reaction time to 12 h. The findings represent a significant advance towards understanding the synergy of lattice strain in nanomaterials and their activity for the development of quantum catalytic devices.

Covalently Functionalized MXenes for Highly Sensitive Humidity Sensors.

Transition metal carbides and nitrides (MXenes) are an emerging class of 2D materials, which are attracting ever-growing attention due to their remarkable physicochemical properties. The presence of various surface functional groups on MXenes' surface, e.g., F, O, OH, Cl, opens the possibility to tune their properties through chemical functionalization approaches. However, only a few methods have been explored for the covalent functionalization of MXenes and include diazonium salt grafting and silylation reactions. Here, an unprecedented two-step functionalization of Ti3 C2 Tx MXenes is reported, where (3-aminopropyl)triethoxysilane is covalently tethered to Ti3 C2 Tx and serves as an anchoring unit for subsequent attachment of various organic bromides via the formation of CN bonds. Thin films of Ti3 C2 Tx functionalized with linear chains possessing increased hydrophilicity are employed for the fabrication of chemiresistive humidity sensors. The devices exhibit a broad operation range (0-100% relativehumidity),highsensitivity(0.777or3.035), a fast response/recovery time (0.24/0.40 s ΔH-1 , respectively), and high selectivity to water in the presence of saturated vapors of organiccompounds. Importantly, our Ti3 C2 Tx -based sensors display the largest operating range and a sensitivity beyond the state of the art of MXenes-based humidity sensors. Such outstanding performance makes the sensors suitable for real-time monitoring applications.

Effects of Derivatization on the Metabolite Profiling of the Cadmium-Tolerant Mangrove Fungus Trichoderma atroviride Using GC-MS Analysis

The mangrove fungus Trichoderma atroviride was found to be tolerant to the heavy metal cadmium and it is of high interest to profile its metabolites to gain insight into its response to cadmium toxicity. This study aimed to investigate the effect of derivatization agents on the number and types of metabolites present in the cadmium-tolerant T. atroviride, detected using GC-MS analysis. The intracellular and extracellular metabolites of T. atroviride treated with cadmium for ten days were derivatized using silylation and alkylation reactions. The results showed that a higher number of metabolites were identified when the three different derivatization agents were used: BSTFA, TBDMSTFA, and MCF. More types of metabolites were identified by silylation, making it suitable for non-targeted metabolites profiling study. Silylation is efficient for the analysis of sugars and their derivatives while alkylation is suitable for a targeted study involving amino acids and organic acids. Statistical analysis for the data set of identified metabolites was performed using Metaboanalyst 3.0 followed by visualization using Partial Least Square-Discriminant Analysis. The plots showed clear separations of metabolites between the different types of derivatization agents and between control and cadmium-treated samples. A more comprehensive metabolite profile of T. atroviride obtained using different derivatization agents in this study, followed by distinct metabolites detected between control and treated samples, will provide good baseline information for future investigations including the pathways and biomarkers responsible for the fungal tolerance to cadmium toxicity.

Photocatalytic Generations of Secondary and Tertiary Silyl Radicals from Silylboranes Using an Alkoxide Cocatalyst.

Silyl radicals are valuable species to prepare diverse organosilicon compounds. However, unlike stable tertiary silyl radicals, the use of secondary silyl radicals has been problematic in silylation reactions due to their instability. Here, we present photocatalytic in situ generations of both secondary and tertiary silyl radicals by one-electron oxidation of ate complexes, formed from silylboranes and an alkoxide cocatalyst, achieving highly efficient hydrosilylation and deuterosilylation of electron-rich alkenes and dienes as well as electron-deficient alkenes. The theoretical studies show that anionic borate complexes activated with an alkoxide have lower oxidation potentials than neutral borate complexes, allowing the formation of secondary silyl radicals. The calculated reaction pathways reveal that anionic conditions using the conjugate acid-base pair of NaOEt (cocatalyst) and EtOH (solvent) are the key to expanding the scope of silyl radicals and alkenes.

Theoretical study on the interactions between cellulose and different methyltriethoxysilane hydrolysis products

Silylation is an effective means of cellulose modification. However, the condensation reaction process between the hydrolysis products of the silane coupling agent and cellulose, as well as the structure of the coating, which both have a strong influence on the wettability, are still controversial. In this paper, the reactions of different methyltriethoxysilane hydrolysis products with cellulose were simulated via the density functional theory method. The reaction activity centers of the different methyltriethoxysilane hydrolysis products in an ethanol solution were analyzed via the front-line orbital theory and the Fukui function. The silylation reaction of different methyltriethoxysilane hydrolysis products in an ethanol solution on the cellulose surface were investigated via the transition state theory. The results show that although the initial hydrolysis product has the lowest grafting energy barrier, considering the whole process of grafting and condensation on the cellulose surface, the hydrolysis product with two hydroxyl groups is more favorable for the growth of organosilicon on the cellulose surface, so it is desirable to control the reaction where this product is dominant. In addition, the silylation process on the cellulose surface is more inclined to a multilayer coating mechanism.

The Impact of Vinylotrimethoxysilane-Modified Linseed Oil on Selected Properties of Impregnated Wood

This study aimed to examine the effect of organosilicon compounds-modified linseed oil parameters on wood utility properties. Linseed oil silylation with an organosilicon compound containing a vinyl group (vinyltrimethoxysilane) has made it possible to synthesize products characterized by high stability in storage. The impregnation of wood with these resulting products contributed to increased resistance of the protected wood to water exposure when compared to unprotected wood or wood protected by polymerized oil that was not subject to the silylation reaction. The protected wood was characterized by a lower water absorption rate in liquid as well as vapor forms contained in the humid air. This property immediately translated into an increase in the resistance of the wood exposed to Basidiomycota. The loss of mass of Pinus sylvestris L. (pine wood) exposed to the Coniophora puteana was approximately 3%. This parameter did not improve when the wood was subjected to the washing process (mass loss approx. 3.6%). Thus, the resulting products are those demonstrating the highest potential for use in the preparation of wood protection means.

Enhanced effect of phenyl silane-modified hexagonal boron nitride nanosheets on the corrosion protection behavior of poly(arylene ether nitrile) coating

Developing alternative protective coating with long serve life under complicated aggressive condition possesses desperate need in corrosion protection filed. Herein, a high performance functional polymer called poly(arylene ether nitrile) (PEN) was employed as a novel organic corrosion protection coating for preservation of P110 steel in this work. The phenyl silane functionalized hexagonal boron nitride (h-BN-MPDTS) synthesized via silylation reaction was introduced into PEN, forming a more efficient protection coating system with superior corrosion resistance. The obtained EIS experimental consequences confirmed that impedance of h-BN-MPDTS PEN coating (1.036 × 108 Ω cm2) was promoted by two orders of magnitude when compared to the neat coating (2.226 × 106 Ω cm2) with one time constant remained throughout the immersion process of 80 days. Meantime, less rust was seen from the artificial scratches of h-BN-MPDTS sample during the salt spray experiment, further demonstrating better corrosion resistance of h-BN-MPDTS PEN coating. Thus, this study provides a neoteric feasibility of high-performance polymer in anticorrosion coatings field.

Regulation of gut microbiome with redox responsible bacterial cellulose hydrogel for precision chemo-radiotherapy of intestinal cancer

Although various types of radiosensitive nanoplatforms are explored to enhance radiotherapy, digestible and radiosensitive nanofiber hydrogel with sensitive responsiveness to the intestinal environment, greatly amplified radiation-induced intestinal tumor destruction, as well as the ability to regulate gut microbiome is still demanded. Herein, sulfhydryl crosslinked bacterial cellulose hydrogel (SulBC gel) was synthesized through silylation and oxidation reaction. Anticancer drug, cis-dichlorodiamineplatinum (CDDP) is loaded into the hydrogel (CDDP@SulBC gel) for precision radiotherapy of intestinal cancer. The CDDP@SulBC gel selectively degrades and consequently exhibits an accelerated drug release behavior in reductive environments. Meanwhile, the CDDP@SulBC gel can increase X-ray-induced double-strand breaks, induce G2/M phase arrest, and enhance the radio-sensitivity to intestinal tumor cells. Upon intragastric administration of CDDP@SulBC gel, the hydrogel is noninvasively monitored in the gastrointestine by micro-CT imaging contributed to the relative high Z-element of silicon and shows an excellent anti-tumor efficacy under X-ray-irradiation of the human intestinal cancer xenograft nude mice. Additionally, the hydrogel can also elevate the ratio of Bacteroidetes / Firmicutes and reconstruct gut microbiome balance, benefiting to the reduction of colitis induced by irradiation. This work thus presents a digestible nanofiber hydrogel-based radiosensitizer with in vivo micro-CT imaging, intestine-specific decomposition/drug release profiles, and great efficacy in chemo-radiotherapy of cancer.

C18-modified halloysite as a novel sorbent in matrix solid-phase dispersion for the extraction of bisphenol A and diethylstilbestrol from human placenta.

In the current study, the C18-modified halloysite was fabricated via silylation reaction and subsequently used as sorbent in matrix solid-phase dispersion (MSPD) for the extraction of bisphenol A and diethylstilbestrol from human placenta, followed by high-performance liquid chromatography-tandem mass spectrometry analysis. The as-prepared sorbent was characterized by scanning electron microscopy, energy-dispersive spectrometry, Fourier transform infrared spectroscopy, X-ray diffraction, and thermo-gravimetric analysis. Varied parameters such as methanol concentration in wash solvent, pH and salt concentration in elution solvent, elution volume, and mass ratio of sample to sorbent were optimized. The adsorption capacities of bisphenol A and diethylstilbestrol on the developed C18-modified halloysite were 6.3 and 14.2mgg-1, respectively, higher than those on the commercial C18 silica gel. Under the optimal condition, the average recoveries of bisphenol A and diethylstilbestrol by MSPD varied from 91.0 to 106.0%, and the relative standard deviations were less than 10.6% for human placenta samples. The limits of detection in the human placenta were 0.2μgkg-1 for bisphenol A and diethylstilbestrol. The simple C18-modified halloysite-based MSPD method holds great potential for the determination of trace bisphenol A and diethylstilbestrol in the human placenta and other tissues of pregnant women with high sensitivity, accuracy, and reliability.

Multicovalent crosslinked double-network graphene–polyorganosiloxane hybrid aerogels toward efficient thermal insulation and water purification

Macroscopic-scale graphene-based aerogels are attractive candidates for thermal insulation and water purification due to their unique properties. However, both the mechanically brittle and single functionality restrain their practical application. Herein, covalently crosslinked double−network graphene-based aerogels were designed and prepared via co−gelation of graphene oxide and organosilanes, followed by freeze-drying and thermal-annealing processes. The multicovalent interactions including hydrolytic copolycondensation, ring opening, and silylation reactions occurred during the co−gelation process. The optimized aerogel exhibits highly elastic performance, which can maintain 93.7% of the maximum stress after 200 compress-release cycles at 50% strain. The graphene−polyorganosiloxane hybrid aerogel also synchronously satisfies hydrophobic property and low thermal conductivity (23 mW m−1 K−1) at room temperature, demonstrating its great potential as a thermal insulator in humid and hot environments. Moreover, the aerogels show excellent absorption capacity (uptake of >200 g g−1) and efficient separation of three-component water/oil/dye mixtures. This work shows that organosilanes are promising crosslinkers for producing highly compressible and multifunctional graphene-based aerogels for thermal management and environmental remediation.

Recent Advancements in Development of Radical Silylation Reactions

Abstract: Transition metal-free radical hydrosilylation of alkynes and factionalized alkenes to vinylsilanes, organosilanes from alkenes, radical silylative cyclizations for sila heterocycles, aromatic dehydrogenative radical silylation, sila-amino acids, silyl hydroperoxides by using transition metal-free reaction conditions such as peroxides, photocatalyst, hydrogen atom transfer catalyst, radical initiators have become one of the most important and useful methodologies for the construction of C-Si bonds for their synthetic applications. In order to demonstrate the growth in this area, this review highlights the last twenty years of success in the fields of silylation of aromatics, silylative cyclizations of sila heterocycles, synthesis of vinylsilanes by hydrosilylation of alkynes, and functionalized alkenes, organosilanes from alkenes and dehydrogenative approaches for vinylsilanes involving radical mechanisms. We believe that summarizing these methods would be very useful for the chemists who are interested in the synthesis of organosilicon compounds for drug discovery or the development of silicon-based materials for industrial applications.

Synthesis of α-Aminosilanes by 1,2-Metalate Rearrangement Deoxygenative Silylation of Aromatic Amides.

An efficient nickel-catalyzed deoxygenative silylation reaction of aromatic amides with silylboranes in the presence of a Sm/SmI2 system for the construction of α-aminosilanes is described. This strategy provides a direct method for synthesizing α-aminosilanes with high efficiency and good functional group compatibility and includes readily accessible starting materials and valuable products.

Olefin Metathesis in Confinement: Towards Covalent Organic Framework Scaffolds for Increased Macrocyclization Selectivity.

Covalent organic frameworks (COFs) offer vast structural and chemical diversity enabling a wide and growing range of applications. While COFs are well‐established as heterogeneous catalysts, so far, their high and ordered porosity has scarcely been utilized to its full potential when it comes to spatially confined reactions in COF pores to alter the outcome of reactions. Here, we present a highly porous and crystalline, large‐pore COF as catalytic support in α,ω‐diene ring‐closing metathesis reactions, leading to increased macrocyclization selectivity. COF pore‐wall modification by immobilization of a Grubbs‐Hoveyda‐type catalyst via a mild silylation reaction provides a molecularly precise heterogeneous olefin metathesis catalyst. An increased macro(mono)cyclization (MMC) selectivity over oligomerization (O) for the heterogeneous COF‐catalyst (MMC:O=1.35) of up to 51 % compared to the homogeneous catalyst (MMC:O=0.90) was observed along with a substrate‐size dependency in selectivity, pointing to diffusion limitations induced by the pore confinement.

PH-responsive cinnamaldehyde-TiO2 nanotube coating: fabrication and functions in a simulated diabetes condition

Current evidence has suggested that diabetes increases the risk of implanting failure, and therefore, appropriate surface modification of dental implants in patients with diabetes is crucial. TiO2 nanotube (TNT) has an osteogenic nanotopography, and its osteogenic properties can be further improved by loading appropriate drugs. Cinnamaldehyde (CIN) has been proven to have osteogenic, anti-inflammatory, and anti-bacterial effects. We fabricated a pH-responsive cinnamaldehyde-TiO2 nanotube coating (TNT-CIN) and hypothesized that this coating will exert osteogenic, anti-inflammatory, and anti-bacterial functions in a simulated diabetes condition. TNT-CIN was constructed by anodic oxidation, hydroxylation, silylation, and Schiff base reaction to bind CIN, and its surface characteristics were determined. Conditions of diabetes and diabetes with a concurrent infection were simulated using 22-mM glucose without and with 1-μg/mL lipopolysaccharide, respectively. The viability and osteogenic differentiation of bone marrow mesenchymal stem cells, polarization and secretion of macrophages, and resistance to Porphyromonas gingivalis and Streptococcus mutans were evaluated. CIN was bound to the TNT surface successfully and released better in low pH condition. TNT-CIN showed better osteogenic and anti-inflammatory effects and superior bacterial resistance than TNT in a simulated diabetes condition. These findings indicated that TNT-CIN is a promising, multifunctional surface coating for patients with diabetes needing dental implants.Graphical abstract

Recent advances in photo- and electro-enabled radical silylation

This review aims to highlight the recent advances in the area of radical type silylation reactions mediated by photo- and electrocatalysis.

Palladium-Catalyzed ortho-C(sp2)-H Silylation of Aromatic Ketones Using an Aminooxyamide Auxiliary.

A palladium-catalyzed direct and selective ortho-C(sp2)-H silylation of aromatic ketones has been achieved using an aminooxyamide auxiliary. The reaction tolerates various orth-, meta-, and para- substituents on the aromatic ring and can be applied to thiophenyl and vinyl ketones. The ortho-C(sp2)-H bond was monosilylated selectively in comparison with other aromatic C-H bonds, benzyl or allylic C(sp3)-H bonds, and acidic α-C(sp3)-H bonds. The aminooxyamide auxiliary can be easily installed and readily removed after the silylation reaction. The resulting ortho-silyl aromatic ketone derivatives are potentially useful building blocks for organic synthesis.

Hydrophobic modification of lignin for rubber composites

Lignin being the second most abundant natural biopolymer after cellulose constitutes between 18 wt% and 35 wt% of wood. Due to its abundance, sustainability, renewability, and the ability to undergo numerous modifications through chemical reactions, there is a significant interest in lignin valorization for material applications. However, its hydrophilicity, lack of melt processability, and poor dispersibility have hindered its wide scale application. Structural modifications have been reported to counter its detrimental properties effectively. Thus, in the present work, a novel silylation reaction was employed to successfully modify kraft lignin and enhance its hydrophobicity. The modification was verified by using nuclear magnetic resonance and infrared spectroscopies. The change in the wettability and dispersibility in various solvent systems indicated the increase in hydrophobicity due to the modifications. This enabled it to better disperse in natural rubber composites. Lignin being the hard moiety imparted mechanical strength, while, NR being the soft moiety, provided it with elastomeric characteristics in the composites. The incorporation of 5 wt% modified lignin in the hydrophobic NR matrix led to a 44.4% increase in the tensile strength. With higher loadings of filler in composites, an increase in elastic moduli and intensity of Payne effect were recorded. The hypothesized dispersibility improvement of the modified lignin in NR compared to its unmodified counterparts was also evident from the morphological analysis.

Recent Advances in Organophosphorus‐Catalyzed Borylation and Silylation Reactions

AbstractOver the past few decades, organophosphorus catalysis has emerged as a robust platform for the preparation of highly functionalized molecules with excellent control of reactivity and selectivity. Organophosphorus catalysis has the advantages of mild and metal‐free reaction conditions. The easy‐to‐tune electronic and steric properties of phosphorus provide an easy handle for developing efficient synthetic methodologies with high stereochemical fidelity. This review describes the efforts to introduce boron and silicon functionalities into organic substrates catalyzed by organophosphorus compounds. These catalysts are categorized into nucleophilic, electrophilic, and biphilic phosphorus catalysts. Phosphorus compounds efficiently catalyze hydroboration of various unsaturated systems, carbonyl compounds, imines, etc.; hydro‐/cyano‐silylation of carbonyls; and silylation of alcohols. The present review emphasizes the scope of nucleophilic, electrophilic, and biphilic phosphorus‐based catalysis to introduce boron and silicon functionalities into organic compounds, mainly from the recent decade.magnified image