Silicon Compounds Research Articles

Silicon analogues of unsaturated hydrocarbons

The proposed communication demonstrates the efforts of researchers undertaken to prove the existence of fundamental analogies in the chemistry of structurally related compounds of carbon and silicon. Stable silicon analogues of ethylene - silenes or silaethylenes R2C=SiR2 - were obtained in 1979, disilynes R2Si=SiR2 - in 1981, and analogues of ethine or acetylene - disilins RSi≡SiR - only in 2004. Moving towards the intended goals, scientists synthesized a number of unique branched (bulky) organic and organosilicon substituents, attached them to silicon atoms, closed them from the action of oxygen and air moisture, and prevented secondary dimerization (oligomerization) reactions. The created steric protection led to the preparation of kinetically stable unsaturated silicon compounds and made it possible to characterize them by IR, NMR, UV-visible spectroscopy, and X-ray diffraction analysis.

Stereospecific synthesis of silicon-stereogenic optically active silylboranes and general synthesis of chiral silyl Anions

Silicon-stereogenic optically active silylboranes could potentially allow the formation of chiral silyl nucleophiles as well as the synthesis of various chiral silicon compounds. However, the synthesis of such silicon-stereogenic silylboranes has not been achieved so far. Here, we report the synthesis of silicon-stereogenic optically active silylboranes via a stereospecific Pt(PPh3)4-catalyzed Si–H borylation of chiral hydrosilanes, which are synthesized by stoichiometric and catalytic asymmetric synthesis, in high yield and very high or perfect enantiospecificity (99% es in one case, and >99% es in the others) with retention of the configuration. Furthermore, we report a practical approach to generate silicon-stereogenic silyl nucleophiles with high enantiopurity and configurational stability using MeLi activation. This protocol is suitable for the stereospecific and general synthesis of silicon-stereogenic trialkyl-, dialkylbenzyl-, dialkylaryl-, diarylalkyl-, and alkylary benzyloxy-substituted silylboranes and their corresponding silyl nucleophiles with excellent enantiospecificity (>99% es except one case of 99% es). Transition-metal-catalyzed C–Si bond-forming cross-coupling reactions and conjugate-addition reactions are also demonstrated. The mechanisms underlying the stability and reactivity of such chiral silyl anion were investigated by combining NMR spectroscopy and DFT calculations.

Poisoning of automotive methane oxidation catalysts by silicon compounds

Biomethane production offers a viable option to meet the growing demands of renewable energy sources in the transportation sector. However, biomethane contains trace amounts of impurities, such as siloxanes, that can potentially hinder the methane oxidation catalyst performance and lead to excessive greenhouse gas emissions. To investigate this potential problem, the commercial methane oxidation catalysts were poisoned in a laboratory setup with two common siloxanes found in biomethane and with their combustion product, silica. The performances of the clean and poisoned methane oxidation catalysts were measured under realistic lean-burn conditions, after which the catalyst structural changes were determined using XRD, BET and CO chemisorption. The results revealed two different possible poisoning mechanisms. First, both tested siloxanes poisoned the catalysts by migrating selectively on top of the active metal sites and became combusted to form amorphous silica. This caused the methane oxidation performance to drop rapidly with relatively small amounts of siloxane used. In contrast, a significantly higher dose of silica was required to produce a similar poisoning effect because its poisoning mechanism is based on nonselective deposition and physical blocking of the catalyst surface.

Tuning the Lewis Acidity of Neutral Silanes Using Perfluorinated Aryl‐ and Alkoxy Substituents

AbstractThe emerging field of Lewis acidic silanes demonstrates the versability of molecular silicon compounds for catalytic applications. Nevertheless, when compared to the multifunctional boron Lewis acid B(C6F5)3, silicon derivatives still lack in terms of reactivity. In this regard, we demonstrate the installation of perfluorotolyl groups (TolF) on neutral silicon atoms to obtain the respective tetra‐ and trisubstituted silanes Si(TolF)4 and HSi(TolF)3. These compounds were fully characterized including SC‐XRD analysis but unexpectedly showed no significant Lewis acidity. By using strongly electron‐withdrawing perfluorocresolato groups (OTolF) the tetrasubstituted silane Si(OTolF)4 was obtained, bearing an 8 % increased Δδ(31P) shift when applying the Gutmann‐Beckett method, compared to literature‐known Si(OPhF)4. Ultimately the heteroleptic Si(PhF)2pinF was successfully synthesized and fully characterized including SC‐XRD analysis, introducing a highly Lewis acidic silicon atom holding two silicon‐carbon bonds.

Investigations on microstructure and mechanical properties on LM30-B4C nanocomposites fabricated through ultrasonic-squeeze assisted stir-casting

In this work, Aluminium-Silicon grade LM30 nanocomposites were fabricated through ultrasonic squeeze-assisted stir casting. Five formulations were made by varying the weight percentage of Boron Carbide nanoparticles (nB4C) from 0 to 2.0 wt% in steps of 0.5 wt%. The formulation's microstructure, hardness, tensile, compression, and impact strength properties were evaluated. X-ray diffraction technique was used to study the presence of aluminium, silicon, and boron carbide compounds. The fractured surfaces from the tensile tests were investigated using FESEM for fractography analysis. The ultrasonic vibration employed during manufacturing aided homogeneous nanoparticle distribution and helped to refine the microstructure. The results indicated that the LM30 nanocomposite with 1 wt% nB4C enhanced the hardness, tensile strength, and compressive strength. Also, adding nB4C particles provided excellent resilience in absorbing the impact energy.

Hydrothermal alkaline synthesis and release properties of silicon compound fertiliser using high-ash coal slime.

High-ash coal slime is difficult to utilise as a boiler fuel, and its accumulation results in environmental pollution. In this study, we describe a new method for the preparation of high-ash coal slime silica compound fertiliser (HASF) using CaO-KOH mixed hydrothermal method to optimize the utilization of this industrial waste and relieve the pressure on the fertiliser industry. The coal slime (D0) used in this study and its dry basis ash content by 1mol/L and 4mol/L sulfuric acid pre-activation (D1, D4) were greater than 85%. The effective silicon content of D0, D1, and D4 silica compound fertilisers reached 30.24%, 31.24%, and 17.35%, respectively, and the sums of effective silica-calcium-potassium oxides were 57.28%, 58.87%, and 48.16%, respectively, under the optimal reaction conditions of 230°C, 15h, and 1mol/L KOH, which met the market requirements, as determined using single-factor experiments. We used XRD, FTIR, and SEM-EDS analysis techniques to demonstrate that tobermorite and leucite were the main mineral phases of the compound fertiliser, and activated coal slime D4, which contains only quartz single crystals, required more demanding reaction conditions in the synthesis reaction. Subsequently, the cumulative release pattern of HASF silica was well described by the power function equation via repeated extraction and dissolution experiments, with the dissolution rate following D4 > D1 ≈ D0. Furthermore, 4mol/L sulfuric acid pre-activation resulted in the enrichment of HASF combined with organic matter and increased the slow-release rate of HASF silica. Thus, the synthesized HASF could have potential application prospects in soil improvement and fertilisation.

Quaternary Ammonium Salts: Catalysts for Hydrosilylation of Alkynes with Hydrosilanes

AbstractMixing i‐PrI and DABCO in solvent EtCN gave two quaternary ammonium salts (QASs) quantitatively, one of which is monocationic (QAS‐1) and the other is dicationic (QAS‐2). These QASs were found to catalyze hydrosilylation of alkynes with hydrosilanes (HAH) without the aid of metal and metalloid catalysts. This organocatalysis can be applied to a variety of alkynes: terminal/internal aryl and alkyl alkynes with/without a functional group. With dihydrosilanes (H2Si), the HAH occurred with high E‐selectivity through syn addition, which was exclusively observed when using terminal alkyl alkynes, irrespective of a hydrosilane used. A scalable HAH is also feasible. The H−Si unit remaining in alkenylsilanes derived from H2Si is available for dehydrogenative alkynylation and N‐heteroarylation under zinc–pyridine catalysis. This synthetic application delivers unique silicon compounds that have, for instance, alkyl, aryl, alkenyl, and alkynyl groups in a single molecule. Mechanistic studies suggested that alkynes activated by QASs irreversibly react with hydrosilanes that become more nucleophilic by the coordination of EtCN. A radical pathway is unlikely. The QAS catalysts can be recovered and reused at least 5 times.

Thermodynamic Analysis of the Key Reactions in Synthesizing Inorganic Silicon Compounds or Products

Thermodynamic Analysis of the Key Reactions in Synthesizing Inorganic Silicon Compounds or Products

Harnessing antifungal metabolites from macro basidiomycetes against wilt inciting <i>Fusarium</i> spp.

Plant diseases especially wilt disease caused by Fusarium spp. pose a major threat to the cultivation of vegetables. In the present study, experiments were undertaken to explore the potential antifungal metabolites produced by macro basidiomycetes viz., Lentinus edodes, Ganoderma lucidum and Schizophyllum commune against Fusarium oxysporum and F. solani causing wilt disease of cucumber and capsicum. Among these, the ethyl acetate fraction of Cell-Free Culture Filtrate (CFC) of L. edodes exhibited maximum per cent inhibition of the mycelial growth of F. oxysporum and F. solani (61.11 and 57.77 %, respectively) at a concentration of 2000 ppm. Characterization of antifungal metabolites of Cell Free Condensate (CFC) of ethyl acetate fraction of L. edodes observed as prominent bands in Thin Layer Chromatography (TLC) indicated with an RF value of 0.25 and 0.69. Further GC-MS characterization of TLC-eluted compounds from L. edodes indicated the presence of 14 different compounds including 2H-pyran-2-one 6-pentyl-, possessing antifungal activity. The Fouriertransform Infrared Spectroscopy (FTIR) spectrum revealed the functional groups such as alcohol (O-H), amides (C-O), aliphatic polyes (CH2), triazenes (N=N), silicon compounds (Si-O-Si), amines (C-N) and phosphorus (P=S). The comparison of metabolite distribution patterns by Principal Component Analysis (PCA) obtained from L. edodes (PC 1) showed a positive correlation between the compounds. This study infers that L. edodes possess antifungal activity against F. oxysporum and F. solani that can be explored for formulation and application of these antifungal compounds in plant protection.

Synthesis of 2D type A molecular sieves by alkaline removal of natural kaolin

Type A molecular sieves have been extensively employed in various fields. It is noteworthy that the direct synthesis of type A molecular sieves from natural kaolin is a common practice among researchers. Traditional type A molecular sieves are characterized by a three-dimensional cubic lattice structure. In this study, our objective is to facilitate the transformation of type A molecular sieves into a two-dimensional layered configuration by employing a two-dimensional layered material as a templating agent. In this research, natural kaolin serves as the primary source material. To eliminate impurities including quartz, illite, and dolomite, an alkali-based solvent extraction method is employed, yielding amorphous silicon and aluminum compounds. Subsequently, a graphene-based templating agent is introduced, and a hydrothermal synthesis process is employed to fabricate two-dimensional type A molecular sieves. The method described herein yields two-dimensional layered type A molecular sieves with a crystallinity exceeding 90%, thereby resulting in a specific surface area that is approximately 11-fold greater compared to their three-dimensional type A counterparts. The applicability of this methodology can be extended to the valorization of low-grade natural mineral resources, optimizing their utility. Furthermore, the approach presented herein for the synthesis of two-dimensional molecular sieves is of a universal nature, offering valuable insights that can serve as a reference for the synthesis of various other categories of two-dimensional molecular sieves.

Ge-Cu-Complexes Ph(pyO)Ge(μ2-pyO)2CuCl and PhGe(μ2-pyO)4CuCl-Representatives of Cu(I)→Ge(IV) and Cu(II)→Ge(IV) Dative Bond Systems.

Phenylgermaniumpyridine-2-olate PhGe(pyO)3 (compound 1Ge) and CuCl react with the formation of the heteronuclear complex Ph(pyO)Ge(μ2-pyO)2CuCl (2Ge') rather than forming the expected compound PhGe(μ2-pyO)3CuCl (2Ge). Single-point calculations (at the B2T-PLYP level) of the optimized molecular structures confirmed the relative stability of isomer 2Ge' over 2Ge and, for the related silicon congeners, the relative stability of 2Si over 2Si'. Decomposition of a solution of 2Ge' upon access to air provided access to some crystals of the copper(II) compound PhGe(μ2-pyO)4CuCl (3Ge). Compounds 2Ge' and 3Ge were characterized by single-crystal X-ray diffraction analyses, and the Ge-Cu bonds in these compounds were analyzed with the aid of quantum chemical calculations, e.g., Natural Bond Orbital analyses (NBO), Non-Covalent Interactions descriptor (NCI), and topology of the electron density at bond critical point using Quantum Theory of Atoms-In-Molecules (QTAIM) in conjunction with the related silicon compounds PhSi(μ2-pyO)3CuCl (2Si), PhSi(μ2-pyO)4CuCl (3Si), as well as the potential isomers Ph(pyO)Si(μ2-pyO)2CuCl (2Si') and PhGe(μ2-pyO)3CuCl (2Ge). Pronounced Cu→Ge (over Cu→Si) lone pair donation was found for the Cu(I) compounds, whereas in Cu(II) compounds 3Si and 3Ge, this σ-donation is less pronounced and only marginally enhanced in 3Ge over 3Si.

Activation of the Olefinic C–H Bond of NHC and NHO by Perimidine-Based Silicon and Germanium Compounds

Activation of the Olefinic C–H Bond of NHC and NHO by Perimidine-Based Silicon and Germanium Compounds

Composition and thermoelectric properties of structures based on iron silicide grown by pulse laser deposition

Silicon compounds have a wide range of electrical properties. In particular, the possibility of creating thermoelectric converters based on them looks extremely attractive. The use of most silicides as thermoelectrics today is limited by their low efficiency. The development of approaches consisting in the creation of low-dimensional structures using non-equilibrium formation methods is one of the priority directions for improving the properties of thermoelectric generators. Determination of the effect of technological regimes on the structure, phase-chemical composition and thermoelectric properties of metal-silicide structures is a key task, the solution of which will allow creating highly efficient thermoelectric generators based on them. Thin-film structures with a layer thickness of ~50 nm formed at different growth temperatures by pulsed laser deposition on two types of substrates: sapphire and gallium arsenide coated with an Al2O3 nanolayer were studied in this work. On the formed samples, a chemical analysis and a study of the phase composition were performed. Chemical analysis was carried out by X-ray photoelectron spectroscopy with the chemical composition depth profiling. The phase composition was studied by Raman spectroscopy. In addition, analysis of the elements in the films was carried out by X-ray spectral microanalysis based on a scanning electron microscope. To determine the thermoelectric properties of the formed thin-film structures, the temperature dependences of the Seebeck coefficient and the electrical conductivity coefficient were recorded. The dependence of the thermoelectric characteristics of iron silicide films on the phase composition is analyzed. In particular, measurements of the thermoelectric properties of FeSix thin-film structures registered the manifestation of a strong thermoelectric effect in layers with the maximum number of chemical bonds between iron and silicon. The parameters of the growth process at which the most effective formation of iron-silicon chemical bonds is achieved were determined using the method of X-ray photoelectron spectroscopy. Line shifts from the beta phase of iron disilicide were found in the Raman spectra and the reasons for their appearance were proposed

Characterisation of Dendromass Ash Fractions Captured in Power Plant with a View to their Further Utilization

Small and larger dendromass-burning power plants entrust the management of the ash waste to companies which guarantee its ecological disposal. In order to specify the correct disposal or further utilization of the dendromass ash, the various slag and fly ash fractions from a power plant combusting waste wood were analyzed and compared in this work. The plant produces approximately 660 t of ash waste/year. The efficiency of combustion depends on the season, dendromass quality and plant operating conditions. The proportion of carbon residue (incomplete burnt wood-chips) in slag and ash fractions increases in the winter months. Except for the seasonal carbon residue, the crumble slag and fine ashes captured in the flue channel and cyclone are similar in chemical composition and phase (28–44 wt.% CaO; 25–35% SiO2; ~7% Al2O3; ~5% K2O; ~4.5% MgO). The finest ash captured in the fabric filter contains less silicon and alumina compounds (<7% SiO2; ~2% Al2O3) and a significantly higher portion of potassium and sulphur, and chlorine compounds (approx. 13%K2O; 3.5%S; <1.5% Cl) which are well soluble in water. All ash fractions produce strongly alkaline leaches in first contact with water. The differences in the chemical composition of captured ashes provide an impulse for considering the possibility of effective re-utilization of individual fractions.

Microstructural evolution during H2 corrosion of Al2O3–SiO2 based refractory aggregates

Hydrogen-based direct reducing iron production (H-DRI) has caused more and more attention in metallurgical industry owing to the near-zero carbon emission. However, the strong reducibility of H2 at elevated temperature can possibly cause serious corrosion to the lining refractories of furnaces. In this study, four types of Al2O3–SiO2 based aggregates (brown corundum, bauxite, mullite and quartz) with various SiO2/Al2O3 mass ratios were utilized for the H2 corrosion test at 1673 K with a soaking time of 8 h. Based on the analysis of weight-loss ratios, phase-composition variation and reduction thermodynamics, the microstructure evolution during H2 corrosion was investigated in detail. The results indicates that the SiO2 impurity of brown corundum was partly reduced by H2 which led to the formation of rod-like or flaky intergranular grains. For bauxite, a porous structure was produced by the accumulation of rod-like or elongated grains owing to the significant reduction of intergranular silicon compounds. Nevertheless, due to the high sintering activity between the Al2O3 products from the reduction of mullite, a high densification structure was realized to effectively prevent the further H2 penetration, hence, mullite inversely obtained the better H2 corrosion resistance than bauxite in spite of its higher S/A ratio. The accumulation of SiO and H2O gases due to the high reduction rate of SiO2 led to the formation of a great deal of SiO2 fiber on the surface of quartz aggregates. The [O] provided by the phase-transformation from α-quartz to cristobalite could be partially captured by the H2 for the reduction, which caused the deterioration of corrosion. With this study, we aim to provide theoretical assistance for the refractory selection applied in hydrogen metallurgy.

Polysiloxanes and Silanes with Various Functional Groups-New Compounds for Flax Fibers' Modification.

There is an increasing desire to use natural products that will be both effective and biodegradable. The aim of this work is to investigate the effect of modifying flax fibers with silicon compounds (silanes and polysiloxanes), as well as examining the effect of the mercerization process on their properties. Two types of polysiloxanes have been synthesized and confirmed by infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (NMR). Scanning electron microscopy (SEM), FTIR, thermogravimetry analysis (TGA) and pyrolysis-combustion flow calorimetry (PCFC) tests of the fibers were performed. On the SEM pictures, flax fibers purified and covered with silanes were visible after treatment. FTIR analysis showed stable bonds between the fibers and the silicon compounds. Promising results of thermal stability were obtained. It was also found that modification had a positive effect on the flammability. The conducted research showed that the use of such modifications, in the context of using flax fibers for composites, can yield very good results.

Optimization of microwave extraction of biocompounds from black pepper using meat quality assessment

Black pepper (Piper nigrum) is a plant highly valued for its functional aromatic compounds. To increase bioavailability of its phytochemicals, a novel approach to extraction using microwave heating and optimization was investigated. Fixed (microwave power and particle size) and variable (heating time and solvent volume) extraction criteria were applied to obtain aqueous extracts, followed by the optimization of the quality of extracts by subjecting the extracts to meat quality test using the central composite design. Thereafter, quality indices (pH, 2-thiobarbituric acid reactive substance value, refrigeration loss, colour and cooking loss) of meat subjected to storage were determined and the outcomes were analysed using response surface methodology. A total of six optimised solutions were derived but the best extraction criteria (variable) were 87.28 min and 364.26 mL of heating time and solvent volume respectively with a desirability value of 0.624, while microwave power and particle size were kept constant. Afterwards, selected optimised extraction criteria was applied, and black pepper aqueous extract obtained was compositionally analysed using Gas Chromatography Mass Spectrometry. Remarkably, a total of 71 compounds were extracted, comprising element-based compounds such as silicon, nitrogen, sulphur and iodine. Two silicon and nitrogen-based compounds as well as one sulphur and nitrogen-sulphur based compound were obtained while seven iodine-based compounds were discovered alongside other functional compounds. This approach results in green and efficient extraction process with increased bioavailability of functional compounds. However, further modifications of extraction criteria can be applied to upscale the desirability level (score) for increased extraction efficiency.

On ways of conversion of silicon dioxide SiO2 in lithium battery systems: a review

Silicon and silicon oxide compounds SiO, SiO2, SiOx and SiOC are considered as a promising family of materials for high-energy lithium batteries due to their high theoretical capacity, widespread in nature, low cost, environmental safety and ease of synthesis. Silicon oxide compounds have replaced silicon in the hope of improving the discharge characteristics of lithium batteries. Oxides of silicon show excellent stability during cycling after structure optimization. However, they suffer from the problem of low Coulomb efficiency and high voltage hysteresis (difference in charge and discharge voltage), which prevents their practical application. Significant bulk expansion of silicon oxides during cycling and irreversible loss of capacity in the initial cycles are an obstacle to their large-scale practical use. This review pays attention to the peculiarities of the conversion of SiO2 and its hybrid compounds into the redox reaction with lithium and ways to overcome existing problems. Silicon dioxide is more resistant to bulk expansion than silicon. Various structural formats of nanometer SiO2 have been developed and tested for lithium batteries, such as nanotubes, nanorods, nanowires, nanoparticles, thin films. To solve problems in the SiO2/Li system, a number of SiO2 composites with carbon, graphene, active and inactive metals, etc. have also been proposed and studied. Analyzing the results of the studies, we found a significant role of the solid electrolyte interphase film in the efficient conversion of SiO2. In turn, the formation of a film on silicon dioxide depends on the method of synthesis of dioxide, which introduces impurities into the final synthesis product. Impurities contribute to the distortion of the solid electrolyte interphase film during the cycling of the SiO2/Li system, and the loss of discharge capacity. SiO2 dioxide obtained in a dry environment of a ball mill differs favorably from that obtained from solutions. Many efforts have been made to overcome the problems in Si-containing electrode materials, however, they have to go a certain way for large-scale practical application.

Robert C. West (1928–2022): A Giant in Organosilicon Chemistry, Cosmopolitan, Mountain Climber and Pilot

Robert C. West (1928–2022): A Giant in Organosilicon Chemistry, Cosmopolitan, Mountain Climber and Pilot

Crystal structures and Hirshfeld surface analyses of tetra-kis-(4,5-di-hydro-furan-2-yl)silane and tetra-kis-(4,5-di-hydro-furan-2-yl)germane.

The title compounds Si(C4H5O)4 (1) and Ge(C4H5O)4 (2) are di-hydro-furyl compounds of silicon and germanium and are useful building blocks for the functionalization of these elements. Both structures crystallize in space group P21/n in the monoclinic crystal system with two mol-ecules in the asymmetric unit: the Si and Ge atoms adopt slightly distorted tetra-hedral geometries, while the C4H5O moieties exhibit shallow envelope conformations. Through a Hirshfeld surface analysis of the structures, inter-actions within the crystal packing could be elucidated: compound 1 features a polymeric chain in the (101) plane via C-H⋯O hydrogen bonds whereas in 2 C-H⋯O hydrogen bonds create a polymeric chain in the (010) plane.