Organosilicon Research Articles

Construction of Si‐Stereogenic Silanes through C−H Activation Approach

AbstractThe asymmetric synthesis of Si‐stereogenic silanes has attracted great attention due to the increasing values of Si‐containing functional molecules in synthetic chemistry, medicinal chemistry, and material chemistry. Merging organosilicon chemistry with transition‐metal‐catalyzed C−H approach has led to rich sets of new reactions holding great synthetic values. This Minireview aims to summarize the advances in the construction of Si‐stereogenic silanes through the transition‐metal‐catalyzed C−H activation approach.

Simple Approach for Reliable Prediction of the Flash Point of Organosilicon Compounds as Compared to the Best Available Methods

Simple Approach for Reliable Prediction of the Flash Point of Organosilicon Compounds as Compared to the Best Available Methods

Asymmetric Disilylation of Spirocyclic Palladacyclopentanes via Tandem Heck/C−H Activation of Aryl Iodides

AbstractThe synthesis of chiral organosilicon compounds is highly appealing due to their wide and important applications in synthetic chemistry and medicinal science. However, catalytic asymmetric disilylation are surprisingly underrepresented because of the lack of enantioselective methods in the stereoselective control of silyl group transformations. Herein, an asymmetric palladium‐catalyzed disilylation of ether‐tethered aryl iodide contained a styrene moiety through Heck/C−H activation sequence was explored for the first time. Upon high‐throughput screening of TADDOL‐derived phosphoramidites, it was found that L18 is a good match in combination with Pd(dtbpf)Cl2 in the tandem Heck/C−H activation of aryl iodide with hexamethyldisilane to afford disilylated 2.3‐dihydrobenzofunan derivatives in good yields with moderate enantioselectivity.

Flow-Assisted Synthesis of Alkyl Citrate Natural Products.

The development of a flow-assisted synthesis of alkyl citrate natural products is described. The flow route harnesses a number of steps including the generation of ketene silyl acetal, a formal [2 + 2] cycloaddition, and a methanolysis cascade to efficiently generate a highly substituted, and stereodefined tetrahydrofuran intermediate. A heterogeneous pseudo-Finkelstein reaction and zinc-mediated elimination furnish a key alkene alkyl citrate fragment in high yield over a multistep sequence that provides direct entry to compounds such as (-)-CJ-13982 (1), (-)-CJ-13,981 (2), L-731,120 (3), and related natural products. The flow methodology developed in this study enables a new machine-assisted approach toward the efficient and scalable synthesis of the alkyl citrate family of natural products.

Novel Porous Rhodium Metal-Organic Aerogel for Efficient Removal of Organic Dyes and Catalysis of Si-H Insertion Reactions.

Metal–organic gels (MOGs) are attracting increasing attention for removal of organic dyes from aqueous solution and for catalysis of Si–H insertion reactions. Herein, we report that a reaction of porphyrin derivative 1 with Rh2(OAc)4 generates stable metal–organic gels and subsequent subcritical carbon dioxide drying affords metal–organic aerogels. Owing to their micro- and mesoporosity, the aerogels adsorbed dyes. Moreover, aerogel I catalyzed Si–H insertion reactions to give organosilicon compounds in high yields.

EPA maps cyclic siloxane risk evaluation

The US Environmental Protection Agency plans to examine potential hazards and exposures to a cyclic organosilicon compound, octamethylcyclotetrasiloxane (D4), throughout the chemical’s life cycle, the agency announced Sept. 8 in a draft scoping document . The agency will evaluate the risks of manufacturing, processing, distribution, use, and disposal of D4, including repackaging and recycling. D4 is primarily used to make other silicone chemicals and as an ingredient in some consumer products. The EPA will evaluate potential risks of D4 in some plastic and rubber products, adhesives, sealants, automotive products, paints, coatings, and cleaners. It will not, however, evaluate the use of D4 in personal care products, food packaging, dental bonding agents, breast implants, or over-the-counter drugs, because those uses fall under the jurisdiction of the Food and Drug Administration. A coalition of chemical manufacturers, represented by the Silicones Environmental, Health, and Safety Center of the American Chemistry Council, evaluated D4

Reliable predictions of the net heat of combustion and the condensed phase heat of formation of organosilicon compounds

Two general correlations are introduced for reliable predicting the net heat of combustion and the condensed phase heat of formation of organosilicon compounds, which are essential for assessment of thermodynamic stability and risk assessment for loss prevention. The experimental values of the net heat of combustion of 145 of different types of organosilicon compounds are used to derive and test the new correlation, which is based on the contribution of some of the elemental composition and the number of –SiH3 group. The outputs of the net heat of combustion have also been used to calculate their condensed phase heat of formation. The high reliability of the two new models has been proved in comparison with several of the best quantitative structure–property relationships (QSPR) where they require complex descriptors. For 42 organosilicon compounds where the reported net heats of combustion by four recent complex QSPR models were available, the values of root-mean-square error (RMSE) of the new model and the best comparative model are 127.9 and 218.4 kJ mol−1, respectively. Moreover, the values of RMSE for the condensed phase heat of formation of the new model and the best complex QSPR model are 117.1 and 240.1 kJ mol−1, respectively.

Dyedauxiliary Group Strategy for the α-Functionalization of Ketones and Esters.

The synthesis of α-arylketones and α-arylazo esters has been achieved in mixed organic-aqueous media under photocatalyst- and metal-free conditions via visible light activation of arylazo sulfones in the presence of enol silyl ethers and ketene silyl acetals, respectively. The process took place efficiently and exhibits an excellent tolerance for a broad variety of functional groups.

Surface functionalization with nonalternant aromatic compounds: a computational study of azulene and naphthalene on Si(001)

Nonalternant aromatic π-electron systems show promises for surface functionalization due to their unusual electronic structure. Based on our previous experiences for metal surfaces, we investigate the adsorption structures, adsorption dynamics and bonding characteristics of azulene and its alternant aromatic isomer naphthalene on the Si(001) surface. Using a combination of density functional theory, ab initio molecular dynamics, reaction path sampling and bonding analysis with the energy decomposition analysis for extended systems, we show that azulene shows direct adsorption paths into several, strongly bonded chemisorbed final structures with up to four covalent carbon–silicon bonds which can be described in a donor–acceptor and a shared-electron bonding picture nearly equivalently. Naphthalene also shows these tetra-σ-type bonding structures in accordance with an earlier study. But the adsorption path is pseudo-direct here with a precursor intermediate bonded via one aromatic ring and strong indications for a narrow adsorption funnel. The four surface-adsorbate bonds formed lead for both adsorbates to a strong corrugation and a loss of aromaticity.

A quick microwave preparation of isatin hydrazone schiff base conjugated organosilicon compounds: Exploration of their antibacterial, antifungal, and antioxidative potentials

In the current study, five isatin hydrazone schiff base linked acetylinic scaffolds have been synthesized via condensation reaction of isatin hydrazone with aldehydic groups. In order to identify the structure characteristics of the prepared hydrazone derivatives, IR, 1H and 13C NMR spectroscopy, elemental analysis and X- ray crystallography were carried out. The antibacterial and antifungal activity of the derivatives against six bacterial strains (S. aureus, S. Pyogenes, E.coli, V. cholera, L. monocytogens and H.influenza) and seven fungal strains (C. glabrata,C. parapsilosis, C. krusei, C. albicans, C. tropicalis, C. keyfer, and C. neoformans) have been evaluated. All the compounds showed potent antibacterial activity with IC50 ≈ 7.81 µM against H. influenza while the activity against fungal strains was less. Compounds a and c also had IC50 ≈ 7.81 µM against S. Pyogens. Furthermore, the results of total antioxidant activity of hydrazone derivatives, expressed in terms of the ascorbic acid (mM) equivalents per mg of sample, indicates their superior bioactivity. These studies suggested that the istain hydrazone functionalized acetylenic derivatives could be an ideal biomaterial for antibacterial, antifungal and antioxidant applications. Besides this, these derivatives were transformed into isatin hydrazone appended 1,2,3 triazole based organotriethoxysilanes and their reaction conditions were optimised

Effects of Imidacloprid Applied Alone or in Combination With Organosilicone Surfactants on Biological Traits and Predatory Feeding of Chrysoperla nipponensis (Neuroptera: Chrysopidae).

Organosilicone adjuvants are widely used to increase insecticide application on targeted surfaces. In this work, our aim was to investigate side effects of imidacloprid treatment, either applied alone or in combination with organosilicone compounds, against Chrysoperla nipponensis, an important predator of aphids. Four types of organosilicones were mixed with imidacloprid at different concentrations. The toxicity of the mixture to C. nipponensis was measured under laboratory conditions. The LC50 and LC30 of imidacloprid applied alone and in combination with 0.05% organosilicone were determined. Imidacloprid (LC30) applied alone or in combination with 0.05% organosilicone was used to treat second instar larvae of C. nipponensis; thereafter, its effects on the growth, development, longevity, reproduction, and predatory ability of C. nipponensis were evaluated The results demonstrated that the organosilicone Silwet L-77 reduced the LC50 and LC30 of imidacloprid to 6.09 (95% CI: 2.31-9.42) and 10.95 mg/L (95% CI: 8.16-13.63), respectively, and enhanced imidacloprid toxicity to C. nipponensis, as reflected by the resulting extension of the growth and developmental period, reduction in female longevity, and inhibition of reproduction. When applied alone or in combination with an organosilicone, imidacloprid reduced the consumption of Corcyra cephalonica eggs by C. nipponensis. The functional response of C. nipponensis treated with imidacloprid alone or in combination with organosilicone was type II. Concomitantly, the attack rate was reduced and the handling time of prey increased.

Synthesis of Silicon-Stereogenic Silanols Involving Iridium-Catalyzed Enantioselective C–H Silylation Leading to a New Ligand Scaffold

Despite a growing focus on the construction of highly enantioenriched silicon-stereogenic organosilicon compounds, the enantioselective synthesis of silicon-stereogenic silanols through asymmetric catalysis remains a considerable challenge. Herein, we realized enantioselective construction of silicon-stereogenic diarylsilanols via an Ir-catalyzed C–H silylation of diarylsilanols along with stereospecific substitution or Tamao–Fleming oxidation. This strategy gives rise to a class of chiral diol catalyst cores (PSiOLs). Transformation of PSiOLs led to the ligand possessing both Si and P-stereocenters, which is capable of inducing excellent enantioselectivity in the rhodium(I)-catalyzed conjugate 1,4-addition of aryl boronic acids to cyclohexenone.

Palladium-Catalyzed Enantioselective Carbene Insertion into Carbon-Silicon Bonds of Silacyclobutanes.

We report herein a highly efficient palladium-catalyzed carbene insertion into strained Si-C bonds with excellent enantioselectivity, which provides a rapid and distinct method to access silacyclopentanes with a three- or four-substituted stereocenter asymmetrically. Mechanistic studies using hybrid density functional theory suggest a catalytic cycle involving oxidative addition, carbene migratory insertion, and reductive elimination. In addition, roles of the chiral ligands in controlling the reaction enantioselectivity are also elucidated.

Enantioselective Vinylogous Mannich Reaction of Acyclic Vinylketene Silyl Acetals with Acyclic Ketimines

AbstractThe first enantioselective vinylogous Mannich reaction of acyclic vinylketene silyl acetals with acyclic ketimines derived from alkynyl ketoesters was developed. Excellent yields and enantioselectivities were obtained from the reaction using bis(imidazoline)‐Zn(II) catalyst. Based on experiments and MO calculation, a plausible transition state was proposed to explain the stereoselectivity of the reaction. The obtained products were converted into various amines and a lactam. This process provides an efficient route for the synthesis of acyclic δ‐amino‐α,β‐unsaturated carbonyl compounds and their derivatives.magnified image

Kinetics of Plasmon-Driven Hydrosilylation of Silicon Surfaces: Photogenerated Charges Drive Silicon–Carbon Bond Formation

Kinetics of Plasmon-Driven Hydrosilylation of Silicon Surfaces: Photogenerated Charges Drive Silicon–Carbon Bond Formation

Diamine Synthesis via the Nitrogen-Directed Azidation of σ- and π-C-C Bonds.

Diamines are essential building blocks for the synthesis of agrochemicals, drugs, and organic materials, yet their synthesis remains challenging, as both nitrogens need to be differentiated and diverse substitution patterns (1,2, 1,3, or 1,4) are required. We report herein a new strategy giving access to 1,2, 1,3, and 1,4 amido azides as orthogonally protected diamines based on the nitrogen-directed diazidation of alkenes, cyclopropanes, and cyclobutanes. Commercially available copper thiophene-2-carboxylate (CuTc, 2 mol %) as catalyst promoted the diazidation of both π and σ C-C bonds within 10 min in the presence of readily available oxidants and trimethylsilyl azide. Selective substitution of the formed α-amino azide by carbon nucleophiles (electron-rich aromatic, malonate, organosilicon, organoboron, organozinc, and organomagnesium compounds) was then achieved in a one-pot fashion, leading to the formation of 1,2-, 1,3-, and 1,4-diamines with the amino groups protected orthogonally as an amide/carbamate and an azide.

The effect of the electrolyte concentration on the charge transfer at the electrolyte/silicon-carbon interface: Electrochemical impedance spectrometry study

Silicon-carbon films were synthesized by electrochemical deposition from methanol/ethanol and hexamethyldisilazane solution. SEM studies have shown that samples with manganese and those obtained from the methanol-based electrolyte are distinguished by the presence of three-dimensional agglomerates on the surface, while the morphology of films obtained from ethanol-based solution is more uniform. Raman studies confirm the formation of silicon-carbon bonds and the effect of manganese addition on the film structure. Electrochemical behavior was studied using the Mott-Schottky analysis. The plots of all samples contain linear sections with both positive and negative slopes, which indicates n-type and p-type semiconductor behavior The highest charge carrier density was found in the “pure” silicon-carbon films obtained from the methanol-based solution. The Bode plots showed a mix of resistive and capacitive behavior and they do not change much with the type of the sample and electrolyte concentration.

Electrophilic and Nucleophilic Modifiers as a Factor of Formation of Lipophilic Properties of Surface-Modified Materials

Stabilization of the functional properties of dispersed and compact solid metals, as well as regulation of their reactivity, improvement of water-repellent, antifriction and anti-corrosion properties by creating the protective films on the surface is an urgent problem of obtaining resource-saving materials. Previously, the research conducted at REC "Nanotechnology" of Mining University proved that chemisorption of ethylhydridesiloxane vapors together with cationic surfactants based on quaternary ammonium compounds has a beneficial effect on the water-repellent properties of metals. In order to obtain the physicochemical substantiation of the effect of hydrophobization of the surface of modified dispersed metals for the first time, the study of the electrophilic-nucleophilic properties of the active substances of the surface modifiers of dispersed and compact metals was carried out using the methods of quantum-chemical modeling in HyperChem software package. The dipole moment, energy of the highest occupied and the lowest unoccupied molecular orbitals, electrophilic-nucleophilic properties were determined. The series of enhancement of nucleophilic/electrophilic properties and dipole moment for modifiers were obtained. The donor-acceptor properties, the differences in the characteristics of the molecules of alkamone (A), triamone (T) and hydrophobic silicone organic liquid were quantitatively and qualitatively established. The patterns of the formation of hydrophobic properties of the surface during the layering of molecules of ammonium and organosilicon compounds with different electrophilic-nucleophilic properties on dispersed metals have been established. Recommendations for the use of modifiers for the production of high - and superhydrophobic materials are proposed.

Rigid Polyurethane Foams Containing Modified Ammonium Polyphosphate Having Outstanding Charring Ability and Increased Flame Retardancy

Ammonium polyphosphate (APP) with different polymerization degrees were modified by a novel phosphorus-containing organosilicon compound (PCOC), and the products obtained were coded as MAPP-30 and MAPP-1000. Then they were applied to prepare flame-retardant rigid polyurethane foam (RPUF) separately. The impact of modified APP (MAPP) on the flame-retardant properties of RPUF was investigated by the limited oxygen index (LOI) test, horizontal burning test, and cone calorimeter test. The morphologies of the char residues were observed by SEM. Furthermore, the mechanical properties of RPUF composites were measured by the compressive strength test. The results showed that whether the degree of polymerization of MAPP is 30 or 1000, they both had greater charring ability and better flame-retardant properties than unmodified APP. The residual char yield of RPUF/MAPP-30 (37.3%) and RPUF/MAPP-1000 (36.5%) were both significantly higher than RPUF/APP-30 (22.8%) and RPUF/APP-1000 (24.9%). The peak heat release rate value of RPUF/MAPP-30 was 29.9% lower than that of RPUF/APP-30, and the drop of RPUF/MAPP-1000 was 50.9% compared to RPUF/APP-1000. Moreover, the total heat release of RPUF/MAPP-1000 (9.7 MJ/m2) was much lower than that of RPUF/MAPP-30 (11.3 MJ/m2). In summary, MAPP-1000 has the best flame-retardant properties among all RPUF composites. In addition, the results also showed that flame-retardant performance and the mechanical properties dramatically decreased with the increase in the addition of MAPP-1000, and the RPUF composite had the best comprehensive performance with 20% content of MAPP-1000.

Influence of organosilicon admixtures on the hydration of Portland cement

AbstractThe impact of three different organosilicon compounds: poly(dimethylsiloxane) (PDMS), potassium methylsiliconate (MESI) and triethoxyoctylsilane (OTES), used as integral admixtures, on Portland cement hydration has been investigated by isothermal calorimetry and DTA-TG analysis. The silicon-based compounds are widely used as internal hydrophobic agents added into batch water; therefore, their effectiveness was investigated by means of capillary water absorption test. The isothermal calorimetry was used to measure the rate and amount of heat released during ordinary Portland cement hydration with integral organosilicon admixtures at 20 °C, 30 °C, 40 °C and 50 °C. It allowed to determine the activation energy as well. The results indicate that used admixtures (except MESI admixture) decrease in the rate and amount of heat release during cement hydration. In addition, it is noticeable that the addition of MESI admixture significantly prolongs the induction period and delays hydration. In contrast to MESI and OTES admixtures, PDMS-based admixture does not affect significant on the activation energy. DTA-TG analysis had shown differences between reference sample and samples containing organosilicon admixtures during thermal decomposition, in terms of the amount of moisture and bound water, as well as Ca(OH)2or carbonates. The results presented in this paper enable a better understanding of the interactions between the organosilicon integral admixtures and the cement matrix. The study shows the effect of integral admixtures on cement hydration and thus the potential effect on the final properties of the cement-based material.