Search

We studied the reaction of N‐alkyl(aryl)pyrazoles with silylformamidine 1 that exists in an equilibrium with its carbene form via migration of the trimethylsilyl group from the carbon to nitrogen atom. The carbene insertion proceeded at the C−H group in 5th position. N‐alkyl(aryl)pyrazoles featuring substituents such as Br, CN and NO2 group reacted readily affording the corresponding aminals. This approach allowed us to synthesize pyrazole dialdehyde and phosphine featuring a vicinal aldehyde group. The reaction does not require any catalyst. The insertion position was unambiguously confirmed by X‐ray analysis of an aminal and a set of derivatives. Aminals hydrolysis afforded the corresponding pyrazole carbaldehydes. Methanolysis of the aminals gave N‐methylimines of the pyrazolecarbaldehydes. Highly acidic nitro pyrazole instead of the insertion underwent silylation in 5th position. [ABSTRACT FROM AUTHOR]

We describe a method for the synthesis of various 2‐silyloxy‐2‐norbornen‐7‐ones by exploiting the specific reactivity of the 1,4‐bis(silyloxy)‐1,3‐cyclopentadiene framework, which is generated by the silylation of a 2,2‐disubstituted‐1,3‐cyclopentanedione bearing a picolinoyloxy group at the 2′ position of its C‐2 side chain. The release of the acyloxy group during the reaction generates carbocations that are then attacked by silyloxy‐substituted carbons in the 1,4‐bis(silyloxy)‐1,3‐cyclopentadiene moiety skeleton, forming a 4,5‐cis‐fused ring skeleton. Skeletal rearrangement of the bicyclic core results in the formation of the corresponding 2‐silyloxy‐2‐norbornen‐7‐one. This novel transformation of 1,3‐cyclopentanedione moieties can be used to synthesise other cyclopentenone‐fused bicyclic frameworks. [ABSTRACT FROM AUTHOR]

Chiral guanidine-catalyzed acylative and silylative dynamic kinetic resolutions of 6-hydroxy-2 H -pyran-3(6 H)-one were achieved. We succeeded in developing a non-enzymatic acylative dynamic kinetic resolution of 6-hydroxy-2 H -pyran-3(6 H)-one with high enantioselectivity, which could be improved by recrystallization. In contrast, the non-enzymatic silylative dynamic kinetic resolution of 6-hydroxy-2 H -pyran-3(6 H)-one was accomplished with a moderate selectivity for the first time. [ABSTRACT FROM AUTHOR]

After the use of chemical weapons, there is a gradual spontaneous decomposition of chemical warfare agents (CWAs), and only degradation products can be present at the time of sample collection. Depending on the type of parent compound, these are most often acids, alcohols, or thiols. This article deals with the development and optimization of methods for the trimethylsilylation of controlled alcohols that outperforms the currently widely used method with N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) prior to gas chromatographic identification. Thiodiglycol (TDG) was chosen as a model alcohol for the development and optimization of methods. Nine trimethylsilylating agents were tested as derivatization agents. For each reagent, the method was optimized in terms of reaction medium (seven tested solvents), reaction time, and temperature. The temporal stability of the resulting derivatives and the effect of the addition of the reaction catalyst were also monitored. Subsequently, optimal methods were applied in the derivatization of N-ethyldiethanolamine, N-methyldiethanolamine, triethanolamine, 2-diisopropylaminoethanol (DIAE), and 3-quinuclidinol. The developed methods were compared in all monitored properties with the standard BSTFA-method (in acetonitrile for 30 min at 60 °C). From the developed methods, three were selected that showed similar or better sensitivity parameters than BSTFA, and at the same time were less demanding to perform. Trimethylsilylation via trimethylsilyl cyanide (TMSCN) appears to be the most successful method. In conclusion, the selected methods were applied in the analysis of contaminated environmental and urban samples – sand, acrylic paint, asphalt-aluminum paint, and concrete. The samples were measured on both a benchtop and a field gas chromatograph. [ABSTRACT FROM AUTHOR]

Here we report stepwise methylation of end-on bridging dinitrogen to a hydrazido ligand to a pentamethylhydrazinium salt, which is mediated by a titanium system with a tripodal aryloxide supporting ligand. The results constitute a synthetic cycle for pentamethylhydrazinium formation from dinitrogen and methyl iodide. We also describe silylation of the dinitrogen complex and carboxylation of the hydrazido complex. [ABSTRACT FROM AUTHOR]

We present herein an approach for the enantioselective C3-functionalization of 2,1-benzothiazine 2,2-dioxides using N-heterocyclic carbene (NHC) catalysis. Our method involves a sequence of [3+3] cycloaddition and ring-opening reactions with different N- and O-nucleophiles, followed by silylation. Overcoming the challenge of selectivity targeting the C3 position, this protocol demonstrates a broad substrate scope and high enantioselectivity. This marks a significant advancement in the field of NHC-catalyzed transformations. [ABSTRACT FROM AUTHOR]

Ethoxylation is one of the common industrial process in which ethylene oxide (EO) is added to compounds containing active hydrogen atom (OH, COOH, SH, NH, etc.) to form surfactants. Alcohol ethoxylates are a major class of non‐ionic surfactants composed of an alkyl chain combined with few EO units. They are widely used in homecare products, personal care products, textiles, oilfield, construction, lubricants, food, paper, leather. The analysis of these ethoxylates possess several challenges since they contain 'n' number of EO units (n > 1). With increase in "n," the product becomes more and more viscous and the boiling point increases making it difficult to analyze by normal gas chromatography (GC) technique. This paper describes a method of derivatizing these ethoxylates so that they can be eluted on a high temperature GC. BSTFA (N, O‐bis (trimethylsilyl) trifluoroacetamide) is used as the derivatizing agent (silylating agent). The ethoxylate combines with BSTFA to form the corresponding trimethylsilylated (TMS) product, which have comparatively lower boiling point. Thus, we detect trimethyl silyl product, which is the resemblance for the ethoxylated product. In this paper, we present a quantitative GC method for the ethoxylates of a few simple alcohols (2‐ethyl hexanol, glycerin), and complex vegetable oils (castor oil). The products formed during the reaction have also been identified on a gas chromatograph coupled with mass spectrometer (GCMS). GCMS shows the mass corresponding to the TMS derivatized product. The derivatization technique not only helps in increasing the volatility of these compounds but also improves the chromatographic efficiency, selectivity, and enhances the detectability. [ABSTRACT FROM AUTHOR]

Silylation of aryl and alkenyl triflates is found to occur readily with silylboronic esters as a silicon source under copper catalysis. The silyl moieties are exclusively installed into the organic frameworks through the preferential generation of a silylcopper species, wherein base-mediated direct borylation is totally suppressed. The combined use of tri-n-butylphosphine and 4,4′-diphenyl-2,2′-bipyridine as a ligand combination turned out to be indispensable for achieving the high catalytic activity. [ABSTRACT FROM AUTHOR]

The stereodefined and highly substituted vinylsilanes are essential building blocks for constructing complex organic molecules. Transition metal‐mediated silylmetalation of alkynes was developed to overcome the limitations of conventional hydrosilylations; however, a very limited study was carried out to utilize transient vinylmetal species in cross‐coupling reactions. Moreover, they produce syn‐adduct, and the anti‐selective cross‐coupling is still unknown and highly desired. Silylzinc reagents are highly functional group tolerant, however, their synthesis from pyrophoric silyllithium and dissolved lithium salts hampers cross‐coupling reactions. Our novel solid silylzinc reagents circumvent these constraints are employed in the anti‐selective synthesis of vinylsilanes via a multi‐component reaction involving Me3SiZnI, terminal alkynes, and activated alkyl halides. An intensive computational and experimental investigation of the mechanism reveals an equilibrium between the intermediate syn‐ and anti‐adducts; the greater barrier at the single electron reduction of alkyl halides and the thermodynamic stability of the Ni(III) adduct determine the anti‐selectivity. [ABSTRACT FROM AUTHOR]

The nuanced role of spin effects remains a critical gap in designing proficient open‐shell catalysts. This study elucidates an iron‐catalyzed allylic C(sp3)−H silylation/alkyne hydrosilylation reaction, in which the spin state of the open‐shell iron catalyst dictates the reaction kinetics and pathway. Specifically, spin crossover led to alkyne hydrosilylation, whereas spin conservation resulted in a novel allylic C(sp3)−H silylation reaction. This chemoselectivity, governed by the spin‐crossover efficiency, reveals an unexpected dimension in spin effects and a first in the realm of transition‐metal‐catalyzed in situ silylation of allylic C(sp3)−H bonds, which had been previously inhibited by the heightened reactivity of alkenes in hydrosilylation reactions. Furthermore, this spin crossover can either accelerate or hinder the reaction at different stages within a single catalytic reaction, a phenomenon scarcely documented. Moreover, we identify a substrate‐assisted C−H activation mechanism, a departure from known ligand‐assisted processes, offering a fresh perspective on C−H activation strategies. [ABSTRACT FROM AUTHOR]

PGPR is an emulsifier (E476) widely used in the food industry. In this study, a gas chromatography–flame ionisation detection (GC-FID) method was developed for the quantitative characterisation of the polyglycerol composition of PGPR. The method was validated to analyse quantitatively the polyglycerol species in neat PGPR products and in PGPR samples present in a lipid matrix. This method consists of saponification, acidification and petroleum ether extraction to remove interfering fatty acids, neutralisation, silylation and finally GC-FID analysis. Phenyl β-D-glucopyranoside was used as internal standard as sorbitol proved unsuitable due to its susceptibility to interference from Na/K chloride during silylation. The response factors of glycerol and diglycerol towards phenyl β-D-glucopyranoside were determined using pure standards, while response factors of polyglycerols with a degree of polymerisation of at least 3 could be reliably estimated according to an effective carbon number (ECN) approach. The validity of the method applied to PGPR samples was further supported on the basis of a mass balance considering the experimentally determined polyglycerol and fatty acid content. Moreover, recoveries of di-, tri-, tetra- and pentaglycerol were more than 95% for various PGPR samples added to two different lipid matrices at 2 wt% and 5 wt% concentrations. Furthermore, the method proved to be very repeatable (with relative standard deviation values below 2.2%). On the other hand, the inevitable presence of glycerol in the lipid samples caused fouling of the detector and column overloading, requiring frequent cleaning of the detector and trimming off part of the column. [ABSTRACT FROM AUTHOR]

Three silyl [PSiP] pincer cobalt(II) chlorides 1–3 [(2-Ph2PC6H4)2MeSiCo(Cl)(PMe3)] (1), [(2-iPr2PC6H4)2MeSiCo(Cl)(PMe3)] (2) and [(2-Ph2PC6H4)2MeSiCo(Cl)(LSi:)] (LSi: = {PhC(NtBu)2}SiCl) (3) were synthesized and used as catalysts and their catalytic activity for dinitrogen silylation was studied. Among the three complexes complex 3 was new and was synthesized via the reaction of [PSiP] pincer preligand L1 with CoCl2 in the presence of chlorosilylene via Si–H bond cleavage. The molecular structure of 3 was determined by single crystal X-ray diffraction analysis. Compared to complex 1, complex 2 is the more effective catalyst for dinitrogen silylation and 363 equiv. of N(SiMe3)3 could be reached per Co atom. Further study indicates that using the silylene ligand in complex 3 instead of the PMe3 ligand in complex 1, the catalytic activity of 3 is lower than that of 1. The catalytic mechanism for this catalytic system is proposed with the support of experimental evidence. The [PSiP] pincer cobalt(I) dinitrogen complex was proposed as the active catalyst for dinitrogen silylation. [ABSTRACT FROM AUTHOR]

The direct conversion of specific C−H bonds to C−Si bonds in alkanes or aromatics via catalytic methods has attracted growing research interest. Herein, we report the preparation of a new iridium catalyst supported on a naphthyridine‐based porous organic polymer and its successful application in the dehydrogenative silylation of 2‐arylphenols or alcohol and hydrosilanes to access ring‐fused oxasilacycles. The synthetic method exhibits broad substrate scope and good functional group compatibility while avoiding the use of hydrogen acceptors. In addition, this organic polymer supported iridium catalyst could be easily recovered from the reaction system and reused for at least seven times without apparent deactivation. This research provides new insights for the further design of heterogeneous nanocatalysts and contributes to the synthesis of silicon‐substituted functional molecules. [ABSTRACT FROM AUTHOR]

A novel silyl radical-induced cascade silylation/cyclization of 1,7-dienes has been realized employing readily available hydrosilanes as a silicon source and Cu(I) salt as a catalyst. This protocol introduces diverse silicon fragments into a challenging 7-membered ring structure and provides an efficient approach to a wide array of biologically important silyl-substituted benzo[b]azepin-2-ones. Several control experiments suggest that the reaction undergoes a free radical process. The gram-scale synthesis and late-stage transformations further demonstrate the scalability and applicability of the reaction in organic synthesis. [ABSTRACT FROM AUTHOR]

We report a highly enantioselective intermolecular C−H bond silylation catalyzed by a phosphoramidite‐ligated iridium catalyst. Under reagent‐controlled protocols, propargylsilanes resulting from C(sp3)−H functionalization, as well the regioisomeric and synthetically versatile allenylsilanes, could be obtained with excellent levels of enantioselectivity and good to excellent control of propargyl/allenyl selectivity. In the case of unsymmetrical dialkyl acetylenes, good to excellent selectivity for functionalization at the less‐hindered site was also observed. A variety of electrophilic silyl sources (R3SiOTf and R3SiNTf2), either commercial or in situ‐generated, were used as the silylation reagents, and a broad range of simple and functionalized alkynes, including aryl alkyl acetylenes, dialkyl acetylenes, 1,3‐enynes, and drug derivatives were successfully employed as substrates. Detailed mechanistic experiments and DFT calculations suggest that an η3‐propargyl/allenyl Ir intermediate is generated upon π‐complexation‐assisted deprotonation and undergoes outer‐sphere attack by the electrophilic silylating reagent to give propargylic silanes, with the latter step identified as the enantiodetermining step. [ABSTRACT FROM AUTHOR]

The inadvertent release of crude oil and its derivatives into aquatic ecosystems has emerged as a significant and concerning environmental issue, often leading to catastrophic accidents. Ongoing research efforts are diligently working toward devising effective remedies to curtail and alleviate the adverse impacts of these incidents on the delicate balance of aquatic life. Amidst these endeavors, cellulose, an eco-friendly and cost-effective material, has garnered attention for its potential in addressing this formidable challenge. In this pioneering study, we delve into a novel approach by harnessing waste-derived cellulose to combat oil spills within aquatic environments. Specifically, cellulose was extracted from post-consumer waste cloths (PCWCs) and subjected to a transformative treatment involving strategically chosen silanating agents. This treatment facilitated the creation of a three-dimensional, water-repelling matrix, characterized by a remarkable hydrophobic nature, exemplified by a substantial contact angle of 126.2°. The resultant matrix exhibited exceptional reusability, demonstrating consistent performance over five successive cycles, and showcased an impressive oil absorption capacity of up to 24.36 g/g. Notably, the engineered polyester sponge exhibited a remarkable buoyancy, being approximately 28.5 times lighter than water, and boasted a density ranging from 0.026 to 0.040 g/cm3. This innovative approach not only presents a tangible solution for oil–water separation during scenarios of marine or environmental oil spills, but it also offers a sustainable and valuable application for well-processed PCWCs. By effectively harnessing the intrinsic properties of cellulose and employing meticulous design, this study represents a significant stride toward mitigating the ecological impact of accidental oil discharges in aquatic ecosystems. [ABSTRACT FROM AUTHOR]

The reaction of chlorosilanes with organometallic reagents is an old and well‐developed approach to organosilicon compounds, however, its application was limited due to the sensitivity of organometallic reagents to air, water. Here we display a mechanochemical access to arylsilanes via Barbier‐type reaction of chlorosilanes with aryl halide with magnesium. By treatment of the two halides with Mg powder under electromagnetic milling, a series of arylsilanes are obtained within 15 minutes. Taking the advantages of the electromagnetic milling, this protocol features transition‐metal free, good functional group tolerance, air stable and mild conditions. [ABSTRACT FROM AUTHOR]

Silylzinc reagents are desirable for the synthesis of organosilanes due to their compatibility with functional groups; however, the use of pyrophoric silyllithium and dissolved lithium salts in their production hinders their development. Our solid Me3SiZnI circumvents these limitations, and herein, we demonstrate its significance in the synthesis of aryl and alkyl trimethylsilanes via cross‐coupling of aryl and alkyl bromides. The milder reaction condition tolerates functional groups such as MOM, Boc, Bpin, and aldehydes. [ABSTRACT FROM AUTHOR]

The primary objective of the study was to develop a method for enhancing the oil adsorption capacity of cellulose nanofibers (CNFs) by modifying their surface. To achieve this goal, aerogels were first dried in a freeze dryer, followed by surface hydrophobization of CNFs using hexadecyltrimethoxysilane (HDTMS) as the modifier. The optimal concentration of the HDTMS for enhancing the nanofiber's surface was determined by testing different concentrations ranging from 0 to 3 mL. The efficacy of the modifier was confirmed by FTIR, which showed the presence of functional groups and hydrogen bonding between CNFs and HDTMS. BET analysis revealed that high concentrations of HDTMS modifier increased the density and reduced the porosity of the aerogels. Moreover, the high concentration of the modifier improved the pressure resistance of the aerogels, with the highest pressure resistance observed for the sample modified with 2 mL of HDTMS. The oil adsorption capacity of the modified samples was also evaluated, and it was found that the highest oil adsorption capacity was observed for the adsorbent with 0.5 mL of the modifier. Conversely, the lowest adsorption rate was observed for the adsorbent with 3 mL of the modifier. Interestingly, it was observed that higher-viscosity oil was absorbed less effectively than lower-viscosity oil. SEM micrographs showed that increasing the amount of HDTMS modifier in the samples resulted in smaller existing pores, thicker pore walls, and a transition from hydrophilic to hydrophobic aerogels. Overall, the results suggest that the optimal concentration of HDTMS for enhancing the surface of the nanofibers is 2 mL, as this concentration provides the highest pressure resistance while still maintaining good oil adsorption capacity. [ABSTRACT FROM AUTHOR]

Rhodium-catalyzed reactions of 3-ethynyl-2-pentamethyldisilanylthiophene derivatives (1a–1c) have been reported. At 110 °C, compounds 1a–1c reacted in the presence of a rhodium complex catalyst, yielding thiophene-fused siloles (2a–2c) through intramolecular trans-bis-silylation. To understand the production of 2a from 1a, the mechanism was investigated using density functional theory (DFT) calculations. [ABSTRACT FROM AUTHOR]

This article discusses a method for incorporating gem-difluoroalkene moieties into organic molecules, which have important applications in drug discovery and compound production. The authors propose a photoredox defluorosilylation reaction using silacarboxylic acids as silyl radical precursors. They demonstrate the feasibility of this method using model substrates and optimize the reaction conditions. The results show that this approach allows for the rapid synthesis of structurally diverse gem-difluoroalkenes under mild conditions. Additionally, the authors propose a radical pathway for the reaction based on their experimental results. Overall, this method provides a convenient strategy for accessing structurally diverse gem-difluoroalkenes. [Extracted from the article]

Herein a Pd(II)‐catalyzed C−H silylation of o‐alkynylanilines with hexamethyldisilane for the synthesis of disilylated 2‐phenyl‐1H‐indoles is reported. In this reaction, o‐alkynylanilines undergo an aminopalladation, C−H activation, and dealkylation sequence to form five‐membered C,C‐palladacycles, which then couple with hexamethyldisilane to construct one C−N bond and two C−Si bonds. This method provides an alternative strategy for C−H silylation. [ABSTRACT FROM AUTHOR]

We found that gold nanoparticles function as single‐electron transfer catalysts to promote decarboxylative cross‐coupling between N‐hydroxy phthalimide esters and disilanes or diborons. A variety of disilanes coupled with alkyl radicals could be generated from N‐hydroxy phthalimide esters via single‐electron reduction by active carbon‐supported gold nanoparticle catalysts to afford diverse alkylsilanes without the need for external bases. Furthermore, the present gold catalytic system was also effective for decarboxylative carbon‐boron coupling to afford alkyl boronates. A detailed mechanistic investigation revealed that single‐electron transfer mediated by supported gold nanoparticles enabled the generation of alkyl radical and silyl radical, thereby enabling radical cross‐coupling. The reusability and environmentally‐friendly nature of supported gold catalyst as well as the scalability of the reaction system enable the practical transformation of carboxylic acid derivatives into value‐added organosilicon and organoboron compounds. [ABSTRACT FROM AUTHOR]

We prepared polysaccharide films from silylated chitosan cross-linked with starch using six kinds of carboxylic acids (oxalic, maleic, citric, succinic, azelaic and sebacic acids) to explore the effects of molecular structures of cross-linkers on the mechanical, hydrophobic and water vapor permeability properties of these hydrophobicity-enhanced films. The films were analyzed by FT-IR, SEM, mechanical tests (stress versus strain, tensile strength and elongation at break curves) as well as the measurements of water contact angle, water solubility and water vapor permeability rate. We observed that the cross-linkers with a long chain provide a large mechanical strength; the tensile strength increases from 6 to 27 MPa with the chain length of dicarboxylates. The hydrophobicity, evaluated by the contact angle (ranging 80° ∼ 120°), increased with the chain length of the cross-linkers and was correlated well with the decreases of the solubility (94 ∼ 17%) and vapor permeability rate of water (14.5 ∼ 1.5 × 10−12 g s−1 m−1 Pa−1). We demonstrate that these mechanical, hydrophobic and water permeability properties are varied considerably only by the choice of the cross-linking acid also in the hydrophobicity-enhanced film by pre-silylation, which may widen the range of potential applications of polysaccharide film such as food packaging.

Transamination reactions of two different aminosilanes (trimethyl(tert-butylamino)silane and dimethyl(diamino)silane) with amines (diethylamine, pyrrolidine, tert-butylamine, iso-propylamine, and n-propylamine) are studied. For trimethyl(organoamino)silanes, the reaction of trimethyl(iso-propylamino)- or trimethyl(diethylamino)silane as aminosilanes and aniline or pyrrolidine are good starting materials to produce trimethyl(anilino)- and trimethyl(pyrrolidino)silane. The investigated equilibrium constants of the reactions of monoaminosilanes show a good correlation with quantum chemically calculated values. The reaction of two different diaminosilanes Me2Si(NR1R2)2 and Me2Si(NR3R4)2 containing different amino moieties leads to the formation of mixed diaminosilanes Me2Si(NR1R2)(NR3R4) in most cases.

Aromatic, short-chain fatty and dicarboxylic acids are low-molecular-weight microbial and mitochondrial metabolites; therefore, their simultaneous screening in biological samples, including cerebrospinal fluid, is a promising solution to an important problem – the timely differential diagnosis of various diseases and pathologies, in particular, those associated with the disruption of the central nervous system. There is a need in developing a sensitive method for the simultaneous determination of these compounds, because they are most often present in biological samples in trace amounts. Blood serum and cerebrospinal fluid are complex matrices including various compounds. Aromatic, short-chain fatty and dicarboxylic acids were isolated and preconcentrated in the present study by traditional liquid–liquid extraction modified at the derivatization stage: the organic extractant was not evaporated and derivatization was carried out directly in the volume of diethyl ether. The different volatilities and polarities of the compounds was taken into account; therefore, derivatization was carried out with moderate heating (60°C) using various silylating reagents. Depending on the type of silyl derivatives, we set the analysis mode of gas chromatography–mass spectrometry method in order to achieve an acceptable analysis time, increase sensitivity to target compounds, and carry out a complete gas chromatographic separation of all analytes. To assess the applicability of the developed conditions, analytical characteristics were determined in model solutions and in the blood serum of healthy donors. For all the developed analysis conditions, linearity was observed in a clinically significant range; the lower limits of quantitation were in the range from 0.06 to 0.9 μmol L–1, which made it possible to analyze samples of the cerebrospinal fluid of neurosurgical patients (n = 6). [ABSTRACT FROM AUTHOR]

Silaspiranes bearing a spiro‐silicon center are promising ring frameworks for the synthesis of novel spirocyclic molecules possessing unique properties. Development of efficient methods towards these ring structures has therefore attracted considerable attentions of synthetic chemists. This minireview highlights the representative advances in the field, and is categorized into four parts according to the ring formation strategies: cyclization, annulation, ring expansion and cycloaddition. [ABSTRACT FROM AUTHOR]

Flavonoids are a class of secondary plant metabolites with low molecular weights. Most flavonoids are highly polar and unsuitable for gas chromatographic analyses. Derivatization is commonly used to make them amenable to gas chromatography by altering their physicochemical properties. Although highly effective, derivatization techniques introduce extra preparation steps and often use hazardous chemicals. The aim of this study was to automate derivatization (specifically, silylation) by developing 3D printed microfluidic devices in which derivatization of flavonoids can occur. A microfluidic device was designed and 3D printed using clear polypropylene. Quercetin and other flavonoids (TED 13 and ZTF 1016) isolated from plant extracts were silylated with N-tert-butyldimethylsilyl-N-methyltrifluoroacetamide (MTBSTFA) at room temperature both in batch and in continuous flow. All the samples were analyzed using Fourier transform infrared (FTIR) spectroscopy, gas chromatography combined with mass spectrometry (GC–MS), and high-resolution accurate mass spectrometry (HR-MS). Interestingly, the HR-MS results showed that the flow method was about 25 times more efficient than the batch method for quercetin samples. The TED 13 flavonoid was completely derivatized in the flow method compared to the batch method where the reaction was incomplete. Similar results were observed for ZTF 1016, where the flow method resulted in a four times derivatized compound, while the compound was only derivatized once in batch. In conclusion, 3D printed microfluidic devices have been developed and used to demonstrate a semi-automated, inexpensive, and more efficient natural product derivatization method based on continuous flow chemistry as an alternative to the traditional batch method. [ABSTRACT FROM AUTHOR]

New 2-(4-(fluorosulfonyloxy)phenyl)benzoxazole (2) was synthesized through the SuFEx click reaction in a two-chamber reactor. The effect of silylation on the yield of the target compound was investigated. The fluorescent properties of compound 2 were determined using experimental and computational methods. [ABSTRACT FROM AUTHOR]

Environmental context: Wildland fire smoke and its impacts on air quality and human health are increasing globally. However, uncertainties in organic emissions from these fires hinder our understanding of downwind atmospheric photochemical processes driving the formation of hazardous air pollutants. In this study, we investigated the impact of fuel moisture content on organic species emission during the combustion of ponderosa pine needles, an important fuel source in the western United States. Rationale: Pine needles represent an important fuel source in coniferous forest systems in the western United States. During forest fires, they can be easily ignited and help sustain flame on the ground. Methodology: In this study, a comprehensive chemical analysis was conducted to examine oxygenated organic compounds (OOCs) present in PM2.5 (particles ≤ 2.5 µm in aerodynamic diameter) formed from burning dry and moist ponderosa pine (Pinus ponderosa) needles (PPN) in the presence and absence of fine woody debris (FWD). The effect of fuel moisture content (FMC), a key parameter that influences smoke formation, has not received much attention. Therefore, we also investigated the effect of FMC on PM2.5 formation and its composition. Thirty three experiments were conducted at the US Forest Service Fire Science Laboratory. PM2.5 was collected onto 47-mm Teflon filters, and silylated extracts were analysed by gas chromatography-mass spectrometry. Results: More than 50 OOCs were identified, including levoglucosan and mannosan; n-dodecanoic acid and n-hexadecanoic acid; dihydroabietic acid, and dehydroabietic acid; and a series of intermediate volatile and semivolatile organic compounds. Mass spectra of a wide variety of compounds in electron and chemical ionisation mode are provided. Most of these OOCs were identified in this study for the first time in PPN aerosol, although some were previously reported in pine wood and other biomass burning aerosol. Our results show significant changes in the composition and abundance of particles depending on the amount and type of PPN burned. When compared with dry PPN, moist PPN showed decreased emissions of PM2.5 and OOCs, due likely to the presence of water in the system that partially suppressed the production of OOCs. Discussion: Incorporating pine needles in atmospheric models as a contributor to smoke particles generated during forest fires is an essential step towards reducing the current uncertainties regarding the influence of these aerosols on chemical/air mass characteristics, regional meteorology, and the climate. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: A photoelectrochemical approach for the C—H silylation of heteroarenes through dehydrogenation cross‐coupling with H2 evolution has been developed. The photoelectrochemical C—H silylation depends on hydrogen atom transfer (HAT) from silanes to Cl‐radical generated through the light‐induced homolytic cleavage of Cl2, in which Cl2 was produced by electrochemical oxidation of chloride. A large number of silylated heterocyclic molecules are rapidly constructed in satisfactory yields without relying on oxidants and metal reagents. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: A photoelectrochemical approach for the C—H silylation of heteroarenes through dehydrogenation cross‐coupling with H2 evolution has been developed. The photoelectrochemical C—H silylation depends on hydrogen atom transfer (HAT) from silanes to Cl‐radical generated through the light‐induced homolytic cleavage of Cl2, in which Cl2 was produced by electrochemical oxidation of chloride. A large number of silylated heterocyclic molecules are rapidly constructed in satisfactory yields without relying on oxidants and metal reagents. [ABSTRACT FROM AUTHOR]

Acetoacetanilide reacts with trimethylchlorosilane (reagent ratio 1:1) in a hexane medium at room temperature to form N-phenyl-3-[(trimethylsilyl)oxy]but-2-enamide as a mixture of E and Z isomers in the ratio 11 : 0.1. Multinuclear NMR monitoring showed that at room temperature the ratio of isomers E : Z gradually changes in a CDCl3 solution, reaching 3.1 : 9.6 after 14 days. A possible mechanism of the isomerization is discussed. [ABSTRACT FROM AUTHOR]

Due to their high versatility borylated and silylated compounds are inevitable synthons for organic chemists. To escape the classical hydroboration/hydrosilylation paradigm, chemists turned their attention to more modern and green methods such as photoredox chemistry and electrosynthesis. This account focuses on novel methods for the generation of boryl and silyl radicals to forge C−B and C−Si bonds from our group. [ABSTRACT FROM AUTHOR]

Structural control of siloxane-based materials at multiple length scales is important for various applications. In this study, we report the controlled assembly of cage oligosiloxane building blocks by both intermolecular hydrogen bonding and hydrophobic interactions. A cage siloxane molecule modified with seven dimethylsilanol groups and an octadecyldimethylsilyl group was synthesized by stepwise silylation of double-four-ring (D4R) cage octasilicate anions. This molecule self-assembled to form a molecularly and mesoscopically ordered structure by solvent evaporation. Furthermore, the silanol groups in the assembled solids were cross-linked by silylation with dichlorodimethylsilane. This approach will allow for the creation of various hierarchically ordered siloxane-based materials by molecular design. Highlights: A cage siloxane molecule containing seven dimethylsilanol groups and an octadecyldimethylsilyl group was synthesized. The cage siloxane molecules formed an ordered solid with both molecular and mesoscale periodicities by self-assembly. The silanol groups in the ordered solid were cross-linked by dichlorodimethylsilane to form siloxane networks. [ABSTRACT FROM AUTHOR]

Selective dehydrogenative silylation is one of the most valuable tools for synthesizing organosilicon compounds. In this study, a regio- and stereoselective ruthenium-catalyzed dehydrogenative intermolecular silylation was firstly developed to access (E)-alkenyl silyl-ether derivatives and silyl-ether heterocycles with good functional group tolerance. Furthermore, two pathways for RuH2(CO)(PPh3)3/NBE-catalyzed dehydrogenative intermolecular silylation of alcohols and alkenes as well as intermolecular silylation of naphthol derivatives were investigated with H2SiEt2 as the hydrosilane reagent. [ABSTRACT FROM AUTHOR]

Although a diverse of different superhydrophobic biomaterials have been developed, facile preparation of recyclable bulk superhydrophobic biomaterials is still a great challenge. In this paper, one-step preparation of superhydrophobic rod-shaped corn straw (RCS) can be achieved by utilizing the hydroxyl-driven silylation process of growing polysiloxane nanofilaments on the surface of the RCS. The water contact angle of the prepared RCS is as high as 159°, showing excellent water repellency. The prepared RCS can selectively absorb organic solvents and oils from water and shows strong oil retention capacity. The absorption capacity of the prepared RCS is not affected by the length and diameter of the straw itself, which makes the utilization of the pristine straw more convenient. The prepared RCS can be used continuously for at least 10 times, showing a good recycling ability. This work provides a new simple and effective idea for the synthesis of bulk straw-based superhydrophobic materials. [ABSTRACT FROM AUTHOR]

Detector response of carboxylic acids (C2-C12, straight and branched chain) were investigated using a flame ionization detector (FID) in a capillary gas chromatographic system. The response of the FID for hydrocarbons is almost directly proportional to the carbon quantity introduced into the flame. Heteroatoms in the molecule reduce signal magnitude, depending on their quality and on the bond they are involved in. We expressed this reduced response with the effective carbon number (ECN). We determined the ECN contribution (ΔECN) of the carboxyl group on the alkyl skeleton. We examined how the responses of carboxylic acids change if trimethylsilyl derivatives are evaluated and we compared the ECN of the neat and derivatized form. [ABSTRACT FROM AUTHOR]

Deep saline aquifers are often favorable for underground CO2 sequestration due to their large capacity and relatively low likelihood for resource conflicts. However, many possible issues can arise during CO2 injection. Often these aquifers have a significant salinity level (as these often present minimal resource conflict issues) and as such salt precipitation near the injection wellbore can be problematic. Furthermore, when water blockage occurs, salt precipitation can be exacerbated since large amounts of water remain near the wellbore. Altering the rock wettability towards less water-wet can alleviate water blockage and in turn reduce the likelihood or severity of salt precipitation. Previous lab experiments have shown that supercritical CO2 (sc-CO2)-based silylation can effectively functionalize rock surfaces with hydrophobic silanes. In this study, numerical models were constructed to evaluate the combined effects of multi-phase fluid flow, water evaporation and salt precipitation assuming a change in wettability (thus impacting the relative permeability characteristics of the reservoir) resulting from the silylation process. The aim of this study is to evaluate the efficacy of this chemical treatment to address near wellbore salt precipitation induced by CO2 injection. According to the simulation results, a decrease in injectivity due to salt precipitation is more significant when water blockage is also present. Injectivity is deteriorated prominently in high salinity reservoirs with water blockage since evaporation into the injected CO2 phase will cause significant salt precipitation. In a representative formation, the injectivity decline is worse (up to 68.6% relative injectivity change (RIC)) when both salt precipitation and water blockage are considered since the latter provides more trapped brine inducing more salt accumulation around the wellbore. With hydrophobic silylation, the combined effects of salt precipitation and water blockage on RIC are decreased on an absolute basis by up to 7%. Depending on techno-economic considerations, this method is encouraged to be implemented as early as possible during a CO2 injection program to minimize salt accumulation from the outset. [ABSTRACT FROM AUTHOR]

Enantioselective reactions that install functional groups at the positions of unactivated C-H bonds can be envisioned to produce intermediates for the synthesis of the active ingredients in pharmaceuticals and agrochemicals directly from simple feedstocks. Among these C-H bond functionalization reactions, those that form carbon-silicon (C-Si) and carbon-boron (C-B) bonds have been pursued because the products of these reactions can be converted to those containing a wide range of functional groups and because compounds containing silicon and boron possess unique properties that can be valuable for medicinal and materials chemistry. Although the silylation and borylation of C-H bonds have undergone extensive development during the past two decades, enantioselective versions of these reactions were not known until a few years ago. In this Minireview, we present the rapid development of enantioselective silylation and borylation of C-H bonds, with an emphasis on the design and development of the types of chiral ligands needed to achieve these reactions and an intention to inspire an expansion of these types of transformations.

Dual Ni and Ir catalysis enables the preparation of arylsilanes having a (TMS)3Si substituent from the corresponding aryl bromides and (TMS)3SiH at 30 °C using visible-light irradiation. This protocol avoids strong bases, high temperature and air and moisture sensitive silyl reagents, providing the expected arylsilanes in moderate to good yields. The reaction was shown to proceed through a silyl radical, likely generated by hydrogen atom abstraction from (TMS)3SiH by a bromide radical. [ABSTRACT FROM AUTHOR]

A new homogenous silylation method of cellulose is developed by mixing it with monohydrosilane in an ionic liquid. In this concise reaction with high atom economy, the ionic liquid acts as both the solvent and catalyst, and the only formal by-product generated is the clean fuel of molecular hydrogen. [ABSTRACT FROM AUTHOR]

Catalytic enantioselective intermolecular C−H silylation offers an efficient approach for the rapid construction of chiral organosilicon compounds, but remains a significant challenge. Herein, a new type of chiral silyl ligand is developed, which enables the first iridium‐catalyzed atroposelective intermolecular C−H silylation reaction of 2‐arylisoquinolines. This protocol features mild reaction conditions, high atom economy, and remarkable yield with excellent stereoselectivity (up to 99 % yield, 99 % ee), delivering enantioenriched axially chiral silane platform molecules with facile convertibility. Key to the success of this unprecedented transformation relies on a novel chiral PSiSi‐ligand, which facilitates the intermolecular C−H silylation process with perfect chem‐, regio‐ and stereo‐control via a multi‐coordinated silyl iridium complex. [ABSTRACT FROM AUTHOR]

This paper presents the effect of drying control agents on the physicochemical and thermal properties of hydrophobic silica aerogels derived via the ambient pressure drying (APD) method by a surface silylation using a TMCS/n-hexane mixture. The structural and physicochemical properties of synthesized DMF-modified and unmodified hydrophobic silica aerogels were characterized using Brunauer–Emmett–Teller (BET) analysis, thermo-gravimetric analysis, FT-IR, and Raman spectroscopic techniques. Based on the obtained results, the differences in structure between samples before and after a surface silylation and the effect of drying control agents were documented. The structural measurements confirmed the efficient silylation process (TMCS/n-hexane), as well as the presence of DMF residues of hydrogen bonded with unreacted Si-OH silanol groups within the silica backbone after surface modification. Based on TG analysis, it was found that DMF addition improves thermal resistance (up to 320 °C) and hydrophobic character of prepared aerogel. Modification of the silica aerogel synthesis process by DMF also resulted in a significant increase in BET—the specific surface area, for the unmodified aerogel was ~828 m2/g, and for the DMF-modified aerogel more than 1200 m2/g—much higher than the value of silica aerogels available on the market. [ABSTRACT FROM AUTHOR]

Imidazole‐2‐thiones have attracted considerable interest in the past as materials for potential applications in the pharmaceutical and chemical industries. Herein, the synthesis of a series of backbone silylated 1,3‐dialkylimidazol‐2‐thiones is reported. The developed synthesis protocol involves the silylation of N,N‐dimethylimidazol‐2‐thione 1 followed by the addition of organochlorosilanes RnSiCl4–n (R=Me, Ph; n=0–4) and enabled the synthesis of the C‐silylated derivatives with monocyclic, silyl‐bridged or fused tricyclic structures. Reactivity studies performed with N,N‐dimethyl‐4,5‐bistrimethylsilylimidazole‐2‐thione as a model substance showed surprisingly stable silicon‐vinyl bonds and reactivity patterns closely related to those observed for the unsilylated species 1. Combined UV‐spectroscopic and computational studies revealed only minor impact of the silyl substituents on the electronic structure of the imidazol‐2‐thione ring. [ABSTRACT FROM AUTHOR]

Sulfur-protected enantiopure P-chiral 1-phosphanorbornane silyl ethers 5a,b are obtained in high yields via the reaction of the hydroxy group of P-chiral 1-phosphanorbornane alcohol 4 with tert-butyldimethylsilyl chloride (TBDMSCl) and triphenylsilyl chloride (TPSCl). The corresponding optically pure silyl ethers 5a,b are purified via crystallization and fully structurally characterized. Desulfurization with excess Raney nickel gives access to bulky monodentate enantiopure phosphorus(III) 1-phosphanorbornane silyl ethers 6a,b which are subsequently applied as ligands in iridium-catalyzed asymmetric hydrogenation of a prochiral ketone and enamide. Better activity and selectivity were observed in the latter case. [ABSTRACT FROM AUTHOR]

Bent (hetero)allenes such as carbodicarbenes and carbodiphosphoranes can act as neutral C‐donor ligands, and diverse applications in coordination chemistry have been reported. N‐Heterocyclic diazoolefins are heterocumulenes, which can function in a similar fashion as L‐type ligands. Herein, we describe the synthesis and the reactivity of an anionic diazoolefin. This compound displays distinct reactivity compared to neutral diazoolefins, as evidenced by the preparation of diazo compounds via protonation, alkylation, or silylation. The anionic diazoolefin can be employed as an ambidentate, X‐type ligand in salt metathesis reactions with metal halide complexes. Extrusion of dinitrogen was observed in a reaction with PCl(NiPr2)2, resulting in a stable phosphinocarbene. [ABSTRACT FROM AUTHOR]