Designable Synthesis of Layered Silicates and Tunable Interlayer Expanded to Zeolites.

Layered zeolitic silicates and corresponding interlayer-expanded porous materials exhibit attractive application potential in wide fields. Nonetheless, designable synthesis and structure analysis of layered silicates remain challenging. Herein, two kinds of layered silicates are synthesized using different di-quaternary ammonium-type organic structure-directing agents (OSDAs). Their crystal structures are analyzed and verified by 3D electron diffraction (3D ED) and high-resolution TEM imaging. The suitable configurations of OSDA can lead to desirable interlayer states. Additionally, two new zeolite structures both with 12-membered ring (MR) channels intersected by 8 MR channels and larger interlayer spaces are constructed from layered silicate precursors by interlayer silylation. The new zeolitic material exhibits potential application in adsorption of organic pollution and catalytic reaction. This study is expected to develop versatile ways for the design and synthesis of layered silicates even zeolites and provide references in characterizing layered materials and zeolites as well.

Mexican Coccoloba uvifera L. Leaf and Fruit Extracts: Identification of Pentacyclic Triterpenes and Volatile Profile by GC-MS.

Mexican Coccoloba uvifera fruit contains polyphenols, flavonoids, and anthocyanins, while in the leaves, lupeol, α- and ß-amyrin have been previously identified by HPLC. However, the low resolution by HPLC of pentacyclic triterpenes (PTs) is a limitation. Moreover, the volatile profile of C. uvifera fruit is still unknown. Therefore, this study aimed to identify PTs in C. uvifera leaf and fruit extracts by CG-MS analysis and to determine the volatile profile of C. uvifera pulp by headspace solid-phase microextraction. The results showed trimethylsilylated compounds of standards lupeol, α- and ß-amyrin, indicating that the silylation reaction was suitable. These trimethylsilylated compounds were identified in leaf and fruit extracts. The fruit volatile profile revealed the presence of 278 esters, 20 terpenes, 9 aldehydes, 5 alcohols, and 4 ketones. The fruit showed a high content of esters and terpenes. Due to their flavour properties, esters are essential for the food, cosmetics, and pharmaceutics industries. Moreover, terpenes in the fruit, such as menthone, ß-elemene, junipene, and ß-caryophyllene have the potential as anticancer and phytopathogen agents. The results indicated that GC-MS is an alternative to HPLC approaches for identifying PTs. Besides, identifying volatile compounds in the fruit will increase the value of this plant and expand its application. Identifying PTs and volatile compounds in Mexican C. uvifera leads to a better understanding of the potential benefits of this plant. This would increase the consumption of Mexican C. uvifera fresh or as functional ingredients in nutraceutical or pharmaceutical products.

Anti-Selective Carbosilylation: Nickel-Catalyzed Multicomponent Reaction of Solid Me3SiZnI.

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.

Iron-Catalyzed Allylic C(sp3)-H Silylation: Spin-Crossover-Efficiency-Determined Chemoselectivity.

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.

Enantioselective and Regiodivergent Synthesis of Propargyl- and Allenylsilanes through Catalytic Propargylic C-H Deprotonation.

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.

Nickel-Catalyzed Reductive Coupling of Chlorosilanes.

Organosilanes play essential roles in many important research areas. The use of readily available chlorosilanes to catalytically access these compounds is synthetically appealing but remains a long-standing challenge. Nickel-catalyzed reductive cross-coupling reaction has recently emerged as a promising protocol to arrive at this goal. This strategy allows the chlorosilanes to be coupled with various carbon electrophiles under mild conditions. These reactions afford organosilanes with improved molecular diversity, structural complexity, and functional group compatibility. This Concept article summarizes the recent advance on nickel-catalyzed reductive C-Si couplings of chlorosilanes.

Recent Progress in the Synthesis of Silaspiranes.

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.

Photocatalytic and Electrochemical Borylation and Silylation Reactions.

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.

Mechanism of Silylation of Vinyl Arenes by Hydrodisiloxanes Driven by Stoichiometric Amounts of Sodium Triethylborohydride-A Combined DFT and Experimental Study.

The reactions of vinyl arenes with hydrodisiloxanes in the presence of sodium triethylborohydride were studied using experimental and computational methods. The expected hydrosilylation products were not detected because triethylborohydrides did not exhibit the catalytic activity observed in previous studies; instead, the product of formal silylation with dimethylsilane was identified, and triethylborohydride was consumed in stoichiometric amounts. In this article, the mechanism of the reaction is described in detail, with due consideration given to the conformational freedom of important intermediates and the two-dimensional curvature of the potential energy hypersurface cross sections. A simple way to reestablish the catalytic character of the transformation was identified and explained with reference to its mechanism. The reaction presented here is an example of the application of a simple transition-metal-free catalyst in the synthesis of silylation products, with flammable gaseous reagents replaced by a more convenient silane surrogate.

New Insights in the Synthesis of High-Molecular-Weight Aromatic Polyamides-Improved Synthesis of Rod-like PPTA.

By employing a variation of the polyamidation method using in situ silylated diamines and acid chlorides, it was possible to obtain a rod-type polyamide: poly(p-phenylene terephthalamide) (PPTA, a polymer used in the high-value-added material Kevlar), with a molecular weight much higher than that obtained with the classical and industrial polyamidation method. The optimization of the method has consisted of using, together with the silylating agent, a mixture of pyridine and a high-pKa tertiary amine. The research was complemented by a combination of nuclear magnetic resonance and molecular simulation studies, which determined that the improvements in molecular weight derive mainly from the formation of silylamide groups in the growing polymer.

Access to Enantiomerically Pure P-Chiral 1-Phosphanorbornane Silyl Ethers.

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.

Ruthenium-Catalyzed Dehydrogenative Intermolecular O-H/Si-H/C-H Silylation: Synthesis of (E)-Alkenyl Silyl-Ether and Silyl-Ether Heterocycle.

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.

Rhodium-Catalyzed Trans-Bis-Silylation Reactions of 2-Ethynyl-3-pentamethyldisilanylpyridines.

Rhodium-catalyzed reactions of 2-ethynyl-3-pentamethyldisilanylpyridine derivatives (1 and 2) are reported. The reactions of compounds 1 and 2 in the presence of catalytic amounts of rhodium complexes at 110 °C gave the corresponding pyridine-fused siloles (3) and (4) through intramolecular trans-bis-silylation cyclization. The reaction of 2-bromo-3-(1,1,2,2,2-pentamethyldisilanyl)pyridine with 3-phenyl-1-propyne in the presence of PdCl2(PPh3)2-CuI catalysts afforded 1:2 bis-silylation adduct 6. DFT calculations were also performed to understand the reaction mechanism for the production of compound 3 from compound 1.

Organopotassium-Catalyzed Silylation of Benzylic C(sp3 )-H Bonds.

Benzylsilanes have found increasing applications in organic synthesis as bench-stable synthetic intermediates, yet are mostly produced by stoichiometric procedures. Catalytic alternatives based on the atom-economical silylation of benzylic C(sp3 )-H bonds remain scarcely available as specialized directing groups and catalytic systems are needed to outcompete the kinetically-favored silylation of C(sp2 )-H bonds. Herein, we describe the first general and catalytic-in-metal undirected silylation of benzylic C(sp3 )-H bonds under ambient, transition metal-free conditions using stable tert-butyl-substituted silyldiazenes (tBu-N=N-SiR3 ) as silicon source. The high activity and selectivity of the catalytic system, exemplified by the preparation of various mono- or gem-bis benzyl(di)silanes, originates from the facile generation of organopotassium reagents, including tert-butylpotassium.

Thioethers as Dichotomous Electrophiles for Site-Selective Silylation via C-S Bond Cleavage.

The development of aryl alkyl sulfides as dichotomous electrophiles for site-selective silylation via C-S bond cleavage has been achieved. Iron-catalyzed selective cleavage of C(aryl)-S bonds can occur in the presence of ß-diketimine ligands, and the cleavage of C(alkyl)-S bonds can be achieved by t-BuONa without the use of transition metals, resulting in the corresponding silylated products in moderate to excellent yields. Mechanistic studies suggest that Fe-Si species may undergo metathesis reactions during the cleavage of C(aryl)-S bonds, while silyl radicals are involved during the cleavage of C(alkyl)-S bonds.

Chiral PSiSi-Ligand Enabled Iridium-Catalyzed Atroposelective Intermolecular C-H Silylation.

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.

Nickel-Catalyzed Cross-Electrophile 1,2-Silyl-Arylation of 1,3-Dienes with Chlorosilanes and Aryl Bromides.

Catalytic, three-component, cross-electrophile reactions have recently emerged as a promising tool for molecular diversification, but studies have focused mainly on the alkyl-carbonations of alkenes. Herein, the scope of this method has been extended to conjugated dienes and silicon chemistry through silylative difunctionalization of 1,3-dienes with chlorosilanes and aryl bromides. The reaction proceeds under mild conditions to afford 1,2-linear-silylated products, a selectivity that is different to those obtained from conventional methods via an intermediary of H(C)-η3 -π-allylmetal species. Preliminary mechanistic studies reveal that chlorosilane reacts with 1,3-diene first and then couples with aryl bromide.

Cobalt-Catalyzed Dehydrogenative C-H Silylation of Alkynylsilanes.

Herein, we report that a cobalt catalyst permits the general synthesis of substituted alkynylsilanes through dehydrogenative coupling of alkynylsilanes and hydrosilanes. Several silylated alkynes, including di- and trisubstituted ones, were prepared in a one-step procedure. Thirty-seven compounds were synthesized for the first time by applying our catalyst system. The alkynylsilanes bearing hydrosilyl moieties provide an opportunity for further functionalization (e. g., hydrosilylation). The use of primary silanes as substrates and precatalyst activators permits the use of inexpensive and easily accessible 3d metal precatalysts, and avoids the presence of additional activators.

Strain Sensing Behavior of 3D Printable and Wearable Conductive Polymer Composites Filled with Silane-Modified MWCNTs.

3D printing of conductive polymers is an attractive technique for achieving high flexibility, wearability, and sensing characteristics without geometrical limitations. However, there is an urgent need to integrate printability, conductivity, and sensing capability. Herein, a conductive polymer ink for 3D printing that combines the desirable features of high electrical conductivity, flexible stretchability, and strain-sensing monitoring is prepared. The ink matrix is polydimethylsiloxane and synergistically enhanced by acetylene carbon black (ACB) and multi-walled carbon nanotubes (MWCNTs) (silane or un-silane-modified). The inks are screened step-by-step to explore their printability, rheology, mechanical properties, and electrical performance upon loading. The formation of an electrically conductive network, electrical properties upon tensile load, and strain sensing stability under cyclic stretching are investigated intensively. It is demonstrated that conductive polymers filled by ACB and silane-modified, MWCNTs (MWCNTs-MTES) possess superior printability, stretchability, conductivity, and strain sensing behaviors. Finally, a flexible wearable strain-sensing skin patch is printed, and it successfully records joint motion signals on human fingers, wrists, and elbows with good stability and repeatability. Those results show the extent of potential applications in healthcare and motion monitoring fields. This work provides an efficient and simple route to achieve comfortably wearable and high-performance strain sensors.

Nanocellulose-based membrane as a potential material for high performance biodegradable aerosol respirators for SARS-CoV-2 prevention: a review.

The controversy surrounding the transmission of COVID-19 in 2020 has revealed the need to better understand the airborne transmission route of respiratory viruses to establish appropriate strategies to limit their transmission. The effectiveness in protecting against COVID-19 has led to a high demand for face masks. This includes the single-use of non-degradable masks and Filtering Facepiece Respirators by a large proportion of the public, leading to environmental concerns related to waste management. Thus, nanocellulose-based membranes are a promising environmental solution for aerosol filtration due to their biodegradability, renewability, biocompatibility, high specific surface area, non-toxicity, ease of functionalization and worldwide availability. Although the technology for producing high-performance aerosol filter membranes from cellulose-based materials is still in its initial stage, several promising results show the prospects of the use of this kind of materials. This review focuses on the overview of nanocellulose-based filter media, including its processing, desirable characteristics and recent developments regarding filtration, functionalization, biodegradability, and mechanical behavior. The porosity control, surface wettability and surface functional groups resulting from the silylation treatment to improve the filtration capacity of the nanocellulose-based membrane is discussed. Future research trends in this area are planned to develop the air filter media by reinforcing the filter membrane structure of CNF with CNCs. In addition, the integration of sol-gel technology into the production of an air filter can tailor the pore size of the membrane for a viable physical screening solution in future studies.