Search

Heteroarylsilyl cations elaborated from a quinoline skeleton have been prepared from the corresponding silanes, and their structures were studied by 1H, 29Si, and 15N NMR. DOSY experiments and DFT calculations were also carried out which showed that the silyl cation center is stabilized intramolecularly by the quinoline nitrogen atom (N1), forming a highly strained and quasi planar 4‐membered ring. Oxygenated and nitrogenated substituents at the C4 position on the quinoline ring were shown to reinforce the Si−N1 interaction through a p‐π conjugation. The Lewis acidity of this class of silylium was finally determined using Müller's nitrilium method. [ABSTRACT FROM AUTHOR]

Main observation and conclusion: A general synthesis of chiral 1,3‐disubstituted allylsilanes is established through copper(I)‐catalyzed asymmetric 1,4‐conjugate silylation of α,β‐unsaturated sulfones and subsequent Julia‐Kocienski olefination. By modification of McQuade's NHC ligand, the catalytic asymmetric conjugate silylation with a broad substrate scope is achieved in high enantioselectivity. The following Julia‐Kocienski olefination proceeds smoothly at room temperature to deliver an array of chiral allylsilanes in moderate yields. More interestingly, a one‐pot asymmetric synthesis with high synthetic efficiency is successfully realized. Utility of the prepared chiral 1,3‐disubsituted allylsilanes is demonstrated in the asymmetric allylation of both aldehyde and aldimine. Finally, an interesting "match and mismatch" phenomenon is observed in the asymmetric allylation of chiral aldehydes. [ABSTRACT FROM AUTHOR]

Using a pyrazolate‐bridged dinucleating ligand that provides two proximate pincer‐type PNN binding sites ("two‐in‐one pincer"), different synthetic routes have been developed towards its dicobalt(I) complex 2 that features a twice deprotonated ligand backbone and two weakly activated terminal N2 substrate ligands directed into the bimetallic pocket. Protonation of 2 is shown to occur at the ligand scaffold and to trigger conversion to a tetracobalt(I) complex 4 with two end‐on μ1,2‐bridging N2; in THF 4 is labile and undergoes temperature‐dependent N2/triflate ligand exchange. These pyrazolate‐based systems combine the potential of exhibiting both metal–metal and metal–ligand cooperativity, viz. two concepts that have emerged as promising design motifs for molecular N2 fixation catalysts. Complex 2 serves as an efficient (pre)catalyst for the reductive silylation of N2 into N(SiMe3)3 (using KC8 and Me3SiCl), yielding up to 240 equiv N(SiMe3)3 per catalyst. [ABSTRACT FROM AUTHOR]

Using a pyrazolate‐bridged dinucleating ligand that provides two proximate pincer‐type PNN binding sites ("two‐in‐one pincer"), different synthetic routes have been developed towards its dicobalt(I) complex 2 that features a twice deprotonated ligand backbone and two weakly activated terminal N2 substrate ligands directed into the bimetallic pocket. Protonation of 2 is shown to occur at the ligand scaffold and to trigger conversion to a tetracobalt(I) complex 4 with two end‐on μ1,2‐bridging N2; in THF 4 is labile and undergoes temperature‐dependent N2/triflate ligand exchange. These pyrazolate‐based systems combine the potential of exhibiting both metal–metal and metal–ligand cooperativity, viz. two concepts that have emerged as promising design motifs for molecular N2 fixation catalysts. Complex 2 serves as an efficient (pre)catalyst for the reductive silylation of N2 into N(SiMe3)3 (using KC8 and Me3SiCl), yielding up to 240 equiv N(SiMe3)3 per catalyst. [ABSTRACT FROM AUTHOR]

Using a pyrazolate‐bridged dinucleating ligand that provides two proximate pincer‐type PNN binding sites ("two‐in‐one pincer"), different synthetic routes have been developed towards its dicobalt(I) complex 2 that features a twice deprotonated ligand backbone and two weakly activated terminal N2 substrate ligands directed into the bimetallic pocket. Protonation of 2 is shown to occur at the ligand scaffold and to trigger conversion to a tetracobalt(I) complex 4 with two end‐on μ1,2‐bridging N2; in THF 4 is labile and undergoes temperature‐dependent N2/triflate ligand exchange. These pyrazolate‐based systems combine the potential of exhibiting both metal–metal and metal–ligand cooperativity, viz. two concepts that have emerged as promising design motifs for molecular N2 fixation catalysts. Complex 2 serves as an efficient (pre)catalyst for the reductive silylation of N2 into N(SiMe3)3 (using KC8 and Me3SiCl), yielding up to 240 equiv N(SiMe3)3 per catalyst. [ABSTRACT FROM AUTHOR]

Using a pyrazolate‐bridged dinucleating ligand that provides two proximate pincer‐type PNN binding sites ("two‐in‐one pincer"), different synthetic routes have been developed towards its dicobalt(I) complex 2 that features a twice deprotonated ligand backbone and two weakly activated terminal N2 substrate ligands directed into the bimetallic pocket. Protonation of 2 is shown to occur at the ligand scaffold and to trigger conversion to a tetracobalt(I) complex 4 with two end‐on μ1,2‐bridging N2; in THF 4 is labile and undergoes temperature‐dependent N2/triflate ligand exchange. These pyrazolate‐based systems combine the potential of exhibiting both metal–metal and metal–ligand cooperativity, viz. two concepts that have emerged as promising design motifs for molecular N2 fixation catalysts. Complex 2 serves as an efficient (pre)catalyst for the reductive silylation of N2 into N(SiMe3)3 (using KC8 and Me3SiCl), yielding up to 240 equiv N(SiMe3)3 per catalyst. [ABSTRACT FROM AUTHOR]

We have developed a C2-selective mono-silylation of a variety of pyridines using a Rh–Al complex. Both the site- and mono-selectivity are controlled via the pyridine coordination to the Lewis-acidic Al center prior to the activation of the pyridine C(2)–H bond at the proximal Rh center. A reaction mechanism is proposed based on several mechanistic studies, including the isolation of a (2-pyridyl)silylrhodium intermediate. [ABSTRACT FROM AUTHOR]

The chemistry of silylated sulfuric acid, O2S(OSiMe3)2 (T2SO4, T=Me3Si; also known as bis(trimethylsilyl) sulfate), has been studied in detail with the aim of synthesizing the formal autosilylation products of silylated sulfuric acid, [T3SO4]+ and [TSO4]−, in analogy to the known protonated species, [H3SO4]+ and [HSO4]−. The synthesis of the [TSO4]− ion only succeeds when a base, such as OPMe3 that forms a weakly coordinating cation upon silylation, is reacted with T2SO4, resulting in the formation of [Me3POT]+[TSO4]−. [T3SO4]+ salts could be isolated starting from T2SO4 in the reaction with [T−H−T]+[B(C6F5)4]− or T+[CHB11Br6H5]− when a weakly coordinating anion is used as counterion. All silylated compounds could be crystallized and structurally characterized. [ABSTRACT FROM AUTHOR]

A Rh‐catalyzed asymmetric synthesis of silicon‐stereogenic dihydrodibenzosilines featuring axially chiral 6‐membered bridged biaryls is demonstrated. In the presence of a RhI catalyst with a chiral diphosphine ligand, a wide range of dihydrodibenzosilines containing both silicon‐central and axial chiralities are conveniently constructed in excellent enantioselectivities via dehydrogenative C(sp3)−H silylation. Absolute configuration analysis by single‐crystal X‐ray structures revealed a novel silicon central‐to‐axial chirality relay phenomenon, which we believe will inspire further research in the field of asymmetric catalysis and chiroptical materials. [ABSTRACT FROM AUTHOR]

Rationale: Due to the ubiquity of fluorides and the small gap between a safe dose and a harmful one, it is necessary to develop a robust analytical method for determination of fluoride ions in various water samples with complex matrices. Methods: Silylation of the fluoride ion was carried out by treatment with hydrochloric acid and phenyldimethylchlorosilane at room temperature. The formed phenyldimethylfluorosilane was detected by gas chromatography/mass spectrometry (GC/MS). Results: Under the optimized conditions, linearity in the analytical method ranged from 0.050 to 5.0 μg/mL for the fluoride ion with R2 >0.9999. Reasonable reproducibility was obtained with the intraday relative standard deviation (RSD) (N = 5) of 2.04% and interday RSD (N = 5) of 3.75% at the concentration of 0.10 μg/mL. The developed method has been successfully applied to determine the fluoride ion in real water samples, including waste water samples, with the recovery between 81.12% and 113.04%. Conclusions: A robust method for the determination of the fluoride ion has been developed by silylation with phenyldimethylchlorosilane and GC/MS analysis. The established method showed good anti‐interference and precision, and it has been applied for determination of the fluoride ion in various water samples. [ABSTRACT FROM AUTHOR]

Herein we report a versatile concept for the synthesis of fourfold functionalized, soluble pyrenes, peropyrenes, terropyrenes, and quarterropyrenes. They were obtained by a modular stepwise approach towards the rylene scaffold via Suzuki–Miyaura cross coupling, oxidative cyclodehydrogenation in the presence of caesium hydroxide under air, and finally zinc‐mediated reductive silylation. The silylated reaction products were characterized by X‐ray crystallography. The first example of a synthesized and crystallized quarterropyrene is presented and its oxidation reaction investigated. The functionalized ropyrenes were systematically characterized by means of UV/Vis–NIR and photoluminescence spectroscopy showing a bathochromic shift of 80 nm per naphthalene unit and a nearly linear increase of the extinction coefficients. Cyclic voltammograms and DFT calculations identify them as electron‐rich dyes and show a narrowing of the electrochemically determined HOMO–LUMO gap and lower oxidation potentials for the higher homologues. [ABSTRACT FROM AUTHOR]

An iridium-catalyzed intermolecular dehydrogenative C--H/Si--H cross-coupling reaction for the synthesis of arylbenzyl bis (silanes) is developed. This hydrosilyl group steered intermolecular C--H silylation process features high chemo- and regioselectivity, giving access to a wide range of multi-functionalized organosilanes in good yields from readily available starting materials with atom economy, efficiency, and environmental benignity. [ABSTRACT FROM AUTHOR]

A metal‐free and effective method for the preparation of silyl ether is described. The protocol employed commercially available and easy to handle 4‐NH2‐TEMPO as catalyst to enable the dehydrogenative coupling of silanes with alcohols by releasing H2 gas as by‐product. The scope of the coupling partners is wide and delivers the desired products in good to excellent yields. [ABSTRACT FROM AUTHOR]

• Preparation and characterization of a set of C-stereogenic P, S ligands is reported. • Corresponding S, S and S, Se ligands can be obtained by oxidation of the phosphanes. • Au(I) coordination occurs exclusively at the phosphane or phosphorane units. • Aurophilic interactions are observed with the selenophosphorane ligand exclusively. This study focuses on synthesis and investigation of coordination modes of phosphorus and sulfur-containing C-stereogenic compounds, prepared from thioanisole. Isolation of the C-stereogenic organolithium compound [RR'CHLi · 2THF] 2 (R = C 6 H 5 S, R' = (CH 3) 3 Si, THF = tetrahydrofuran) instead of in situ usage turned out to be mandatory for controlled reactivity. Variation of the steric and electronic properties of the substituents at phosphorus furnished three different phosphane substituted P, S ligands RR'CHPPh 2 , RR'CHP(N(C 2 H 5) 2) 2, and RR'CHP(t- C 4 H 9) 2. Furthermore, the corresponding chalcogenphosphoranes were synthesized by oxidation with elemental sulfur and selenium. Preliminary investigation of the coordination behavior of RR'CHP(t- C 4 H 9) 2 , RR'CHP(S)(t- C 4 H 9) 2 and RR'CHP(Se)(t- C 4 H 9) 2 towards coinage metals was explored with Au(tht)Cl, both for the phosphanes and the corresponding phosphoranes. Intermolecular aurophilic interactions have been observed for the selenophosphorane exclusively. Sequential lithiation and silylation of thioanisole leads to a C-stereogenic organolithium compound which has been employed to construct a set of C-stereogenic heteroditopic P, S ligands. Their coordination behavior towards Au(I) was explored as well as their reactivity with respect to chalcogens. [Display omitted] [ABSTRACT FROM AUTHOR]

A transition metal-free direct C–H silylation of pharmaceutically relevant pyrrolo[2,3- d ]pyrimidine (7-DAPs) derivatives with hydrosilanes has been developed via a radical reaction. This protocol provides the divergent silylated 7-DAPs in moderate to good yields with good regioselectivity. The protocol features operational simplicity, broad substrate scope and the use of safe and readily available LPO (Lauroyl peroxide) as the radical initiators. Preliminary mechanistic studies suggest that the induced silyl radical is involved in this transformation. [Display omitted] [ABSTRACT FROM AUTHOR]

Since stationary phase is the key to chromatographic separations, it is worth pursuing simpler and more efficient methods for preparing chromatographic stationary phases. In this work, co-condensation and pseudomorphic transformation were combined to prepare a functionalized shell on the surface of the silica core in one step, and different kinds of silylation reagents were used to investigate the self-assembly mechanism. 3-Mercaptopropyltriethoxysilane facilitated the formation of the shell during pseudomorphic transformation, and sulfhydryl groups were distributed in the shell uniformly. These core-shell particle were applied in hydrophilic chromatography and ion-exchange chromatography successfully after the oxidation of the sulfhydryl groups to sulfonic acid groups. Pseudomorphic transformation with silylated reagents has the advantage of rapid preparation of chromatographic stationary phases with good reproducibility. [Display omitted] • Co-condensation and pseudomorphic transformation methods were combined to prepare the core-shell particles. • Functionalized mesopores were formed on the surface of solid silica cores in one step. • Self-assembly mechanism was explored to explain the different impacts of silylation reagents. • Core-shell particles can be served as stationary phases for chromatography. [ABSTRACT FROM AUTHOR]

Nanoreactors encapsulating homogeneous catalysts behave as heterogeneous catalysts at the macroscopic scale, enabling the homogeneous catalyst to be easily recovered. One way to synthesize such nanoreactors is by inserting the homogeneous catalyst (or synthesizing it in situ) in the porosity of an inorganic oxide material, followed by a silylation reaction to narrow the pore entrance, preventing the outwards diffusion of the jailed homogeneous catalyst during the reaction. This way, the often-superior activity of homogeneous catalysts is combined with the robustness and the easy recovery of heterogeneous ones. Hereunder, we report for the first time the implementation of such a strategy towards the synthesis of a deoxydehydration (DODH) catalyst, namely a bis-amino phenol Re-complex. 1,2-hexanediol was used as the DODH vicinal diol model substrate. The encapsulation of the homogeneous catalyst in SBA-1 was demonstrated. It proved active in the DODH test reaction although not sustainably; the deactivation mechanism was therefore elucidated. [Display omitted] ● Encapsulation of a DODH precatalyst in silylated SBA-1. ● Stability of the encapsulated catalyst is assessed in the DODH of 1,2-hexanediol. ● The deactivation mechanism of the encapsulated catalyst is pointed out. [ABSTRACT FROM AUTHOR]

In this work, the synthesis and characterization of a new magnetically supported Mo6+ complex have been reported as a catalyst for epoxidation of olefins. For this purpose, a new silylating compound containing a birhodanine moiety, i.e. [(E)-5-(3-(3-(trimethoxysilyl)propyl)-4-oxo-2-thioxothiazolidin-5-ylidene)-3-phenethyl-2-thioxothiazolidin-4-one] (TMOS-BIRD) has been synthesized and used for silylation of magnetite nanoparticles (MNPs). The magnetically supported catalyst was then prepared by deposition of dioxomolybdenum(VI) adduct, dichlorobis(dimethylformamide)dioxomolybdenum (MoO2Cl2(dmf)2), on MNP@BIRD. The prepared supported magnetic catalyst was characterized in detail by FT-IR, transmission electron microscopy (TEM), thermogravimetric analysis (TGA), X-ray diffraction (XRD), vibrating sample magnetometry (VSM) and energy-dispersive X-ray (EDX) analyses. Cyclooctene was used as a model substrate to optimize the epoxidation reaction conditions, and the prepared magnetically retrievable catalyst was then used for epoxidation of cyclohexene, cyclooctene, styrene, indene, trans-trans-cis-1,5,9-cyclododecatrien, 1-octene, 1-heptene, α-pinene, 1-dodecene and trans-stilbene using tert-butyl hydroperoxide (TBHP) as oxidant under solvent-free conditions. The catalyst showed excellent conversion, good turn over frequency, and a short reaction time at 95 °C for epoxidation of cyclooctene.

Polyphenols are present in many plants and herbs, and the scientific community and consumers are aware of their health-promoting effects. Plants of Greek origin were studied for their polyphenol content and their antioxidant and antimicrobial activities. Gas chromatography–mass spectrometry (GC–MS) and high-performance liquid chromatography coupled to a diode array detector (HPLC–DAD) were used for the identification and characterization of plant polyphenols. For GC–MS, a silylation procedure was employed. Ferulic acid, quercetin, and catechin were the most abundant polyphenols. The Rancimat test, FRAP (Ferric-reducing Antioxidant power) assay, and DPPH (2,2-Diphenyl-1-picrylhydrazyl) assay were used to study the antioxidant capacity, which was proven for all studied plants. The antimicrobial activity was studied against specific pathogenic microorganisms. Pelargonium purpureum and Sideritis scardica plant extracts inhibited most microorganisms such as L. monocytogenes and E. coli. Extracts of studied plants showed both antioxidant and antimicrobial activities; hence, they can be considered to be used by the food industry.

The relations of crystallite sizes over Silicalite-1 zeolite with the silanols distribution and catalytic performance in methanol to propene (MTP) reaction were determined. The catalytic lifetime and the formation of ethene was independent of the crystallite size, but was attributed to the silanols distribution. The internal isolated silanol groups (I) affects the diffusion restrictions of intermediate species. The external isolated silanols (E) determined the tolerance for coke capacity on the external surface. Propene and the initial catalytic activity was dominated by the amount of Brønsted acid sites.

Interlayer silylation of layered sodium octosilicate (Na-Oct) with various organoalkoxysilanes was conducted using hexadecyltrimethylammonium ion-exchanged layered octosilicate (C16TMA-Oct) as an intermediate in the presence or absence of tetrabutylammonium fluoride (TBAF). The degree of silylation was increased by adding TBAF. It is suggested that F- ions perform a nucleophilic attack on the alkoxysilanes, which promotes the silylation reaction. C16TMA-Oct was silylated with octyltriethoxysilane (C8TES) or 3-mercaptopropyltriethoxysilane (MPTES) to compare the reactivity of the two organoalkoxysilanes in the presence or absence of TBAF. A higher degree of silylation of C16TMA-Oct was observed with MPTES, suggesting the higher accessibility of this silylating agent into the interlayer polar region of C16TMA-Oct. Overall TBAF appears as a relevant catalyst for the covalent interlayer surface modification of layered silicates with organic functional groups. [ABSTRACT FROM AUTHOR]

This paper describes a novel conjugate biodegradable sponge based on the tree gum kondagogu with excellent selective oil/organic solvent absorption ability. The conjugate sponge is made hydrophobic (water contact angle 133°) by post-process vapor phase silylation, has porosity of ≈94% with very low density (18.4 mg cm-3). The sponge can absorb selectively up to 19-43 times its weight of oils and organic solvents. Meanwhile, good reusability is also observed in up to at least 10 cycles. The biodegradation behavior is studied from BOD (biological oxygen demand) analysis, where the non-silylated and silylated sponges degraded over 28 days by 92% and 76%, respectively, in waste-water sludge. The novel conjugate bio-based and biodegradable sponge used in this study is a promising sustainable material for clearing oil spills and for water treatment. [ABSTRACT FROM AUTHOR]

The first iron‐catalyzed defluorosilylation of unactivated gem‐difluoroalkenes was developed, delivering gem‐disilylated alkenes and (E)‐silylated alkenes with excellent efficiency. This protocol features good functional group compatibility and excellent regio‐ and stereoselectivity, enabling the late‐stage silylation of biologically relevant compounds, thus providing good opportunities for applications in medicinal chemistry. Preliminary mechanistic studies and DFT calculations reveal that a nucleophilic addition and elimination of the second C−F bond might be involved in the disilylation catalytic system, demonstrating unusual reactivity characteristics of iron catalysis. [ABSTRACT FROM AUTHOR]

Utility of a thermally stable divalent silicon species (silylene) toward the dehydroaromatization of a dihydropentacene is demonstrated. The reaction of a cyclic (alkyl)(amino)silylene with 6,13-dipropyl-5,14-dihydropentacene afforded the corresponding pentacene-silylene adducts. The reaction likely proceeds through a combination of 1,4-dehydrogenation and (1+ 4) cycloaddition of the silylene towards the dihydropentacene. [ABSTRACT FROM AUTHOR]

Metal-catalyzed activations of inert sp2C–H and sp3C–H bonds have recently brought about a revolution in the synthesis of useful molecules and molecular materials. Among them, the catalytic silylation of sp3C–H bonds has been developed due to the interest in the formed sp3C–SiR3 silanes, a stable organometallic species, for carrying out further functionalizations that cannot be directly achieved using sp3C–H bonds. Besides many examples of sp2C–H bond catalytic silylations, metal-catalyzed silylations of sp3C–H bonds have been mostly discovered during the last decade in spite of the high reactivity of the sp3C–SiR3 group. This review will present all the methods of metal-catalyzed silylations of sp3C–H bonds into sp3C–SiR3 functions, discuss the catalytic mechanisms according to various metal-catalysts, and illustrate their applications in synthesis. The review describes successively the intermolecular sp3C–H bond silylations directed first by N-containing heterocycles with silanes using various Ru, Rh, and Ir catalysts and then directed by an amide type function using a Pd(II) catalyst and R3Si–SiR3 reagent. The catalytic intramolecular silylations of sp3C–H bonds can be performed after the catalytic formation of CH–OSiR2H or CH–N(R)SiR2H groups from alcohols, ketones, esters, or amine NH bonds by catalytic hydrosilylation with R2SiH2. Both catalytic processes can be performed using Ir(I) and Rh(I) catalysts with an alkene to capture the formed H2. This reaction with Rh(I) and Ir(I) catalysts can be applied to the formation of 5-membered cyclic silanes from aryl silanes and from alkyl silanes arising from hydrosilylated terminal C＝C bonds of alkenes. Oxidation of the cyclic silane derivatives easily leads to 1,3- and 1,4-diols, from alcohol or ketone precursors and to 1,2-amino alcohols from amines. Several methods show how to transform various heteroatom–methyl groups X–CH3: B–CH3, O–CH3, Si–CH3, N–CH3, Ge–CH3 and S–CH3 into their reactive functionalized X–CH2SiR3 group, using various Ru(0), Ir(I), pincer-Ru(II), or Y catalysts. Examples are shown of catalytic transformations of the allylic moiety CH3–C(R)＝CH2 into its silylated CH2＝C(R)–CH2SiR′3 form via (i) Pd(II) allyl activation, (ii) silyl radical generation with photocatalyst and (iii) dual Ir(I) and Fe(II) catalysts for hydrosilylation of alkanes, via alkene formation, isomerization and hydrosilylation. Finally, a Ru(II)-catalyzed sp3C–H silylation of a methyl group of arylphosphine, directed by a P(III) atom, will be presented. [ABSTRACT FROM AUTHOR]

Tris(pentafluorophenyl)borane has been found to catalyze the two‐fold C(sp3)−H silylation of various trialkylamine derivatives with dihydrosilanes, furnishing the corresponding 4‐silapiperidines in decent yields. The multi‐step reaction cascade involves amine‐to‐enamine dehydrogenation at two alkyl residues and two electrophilic silylation reactions of those enamines, one inter‐ and one intramolecular. [ABSTRACT FROM AUTHOR]

Tris(pentafluorophenyl)borane has been found to catalyze the two‐fold C(sp3)−H silylation of various trialkylamine derivatives with dihydrosilanes, furnishing the corresponding 4‐silapiperidines in decent yields. The multi‐step reaction cascade involves amine‐to‐enamine dehydrogenation at two alkyl residues and two electrophilic silylation reactions of those enamines, one inter‐ and one intramolecular. [ABSTRACT FROM AUTHOR]

The objective was to investigate the mechanical properties, fluoride release and apatite formation of resin based dental composites based on a fluoride containing Bioactive Glass (BG) with and without a silylating agent. A SiO 2 –P 2 O 5 –CaO–SrO–Na 2 O–CaF 2 BG was synthesized by the melt quench route. This glass and a commercially available inert glass (IG) were incorporated into a light cured BisGMA-TEGMA resin. The composite resins were then evaluated in terms of their ability to form apatite by Fourier Transform Infrared spectroscopy (FTIR) and by scanning electron microscopy (SEM) following immersion in artificial saliva at pH 4 (AS4) and pH 7 (AS7). The experiments were performed with and without silylation of the BG. The compressive strength and flexural strength were determined after 1, 28 and 84 days of immersion in the AS4 and AS7 immersion media. The FTIR spectra of the BG composites exhibited split bands at approximately 560 and 600 cm−1 corresponding to a apatite formation in the surface or on the surface under all immersion conditions. SEM showed the presence of a reacted layer of glass particles in the composite surface and the presence of a surface layer of apatite in AS7. The compressive strength and flexural strength were significantly higher for the silylated BG composites. The strengths of both silylated and non silylated BG composites and IG composites decreased upon immersion. BG composites exhibit reduced strengths upon immersion but still exhibit strengths comparable to existing composites after 84 days of immersion. [ABSTRACT FROM AUTHOR]

The signature reactivity of silacyclobutane (SCB) is their cycloaddition reactions with various π bonds. Recently, the first cases were disclosed where SCBs reacted with both Csp2−H and Csp3−H σ bonds in an intramolecular fashion. Herein, it is reported that SCB is also an efficient reagent for Csp−H bond silylation. Thus, rhodium‐catalyzed intermolecular reactions between SCBs and terminal alkynes produced a series of symmetrical and unsymmetrical tetraorganosilicons bearing a Csp−Si functionality. Preliminary studies suggested that the reaction did not involve a cycloaddition pathway, but instead a direct activation of Csp−H bonds. [ABSTRACT FROM AUTHOR]

The use of an operationally convenient and stable silicon reagent (octamethyl‐1,4‐dioxacyclohexasilane, ODCS) for the selective silacyclization of (hetero)arenes via twofold C−H activation is reported. This method is compatible with N‐containing heteroarenes such as indoles and carbazoles of varying complexity. The ODCS reagent can also be utilized for silacyclization of other types of substrates, including tertiary phosphines and aryl halides. A series of mechanistic experiments and density functional theory (DFT) calculations were used to investigate the preferred pathway for this twofold C−H activation process. [ABSTRACT FROM AUTHOR]

Olefinic C–H functionalization represents an atom- and step economic approach to valuable olefin derivatives from simpler ones, but controlling the selectivity remains a challenge. Remarkable progress has been made in the site-selective C–H functionalization of arenes and alkanes, but there are still limited examples of selective C–H functionalization of olefins presumably due to the lability and easy decomposition of the alkenyl moiety. Chelation-assisted C–H activation represents an efficient protocol for site- and stereo-selective construction of carbon–carbon and carbon–heteroatom bonds. This review highlights recent advances in vicinal- and geminal-group-directed olefinic C–H functionalization, including alkenylation, arylation, alkynylation, alkylation, halogenation, silylation, cyanation and annulation by the formation of exo-/endo-metallocycles. In particular, geminal-group-directed C–H functionalization is covered for the first time, as well as distal-selective alkenyl C–H functionalization under palladium/norbornene cooperative catalysis, which provides novel disconnections in retrosynthetic analysis and represents the future trend in green chemistry. [ABSTRACT FROM AUTHOR]

The development of catalytic silylation of alcohols under ambient reaction conditions plays an important role in organic synthesis. New silyl groups and methods for their introduction and removal are constantly being developed and offer chemists a wider range of options. In recent years, silyl protecting groups have been given expanded roles beyond their traditional use of temporarily rendering inactive alcohols. As silyl ether can be further converted to the parent alcohols in acidic conditions, silylation of alcohols can be regarded as an alternative method for hydroxyl protection under ambient reaction conditions. Merging the silyl protection/deprotection of alcohols with such modern methodologies, as green chemistry and nanoscience, has added additional value to these temporary components of synthetic intermediates. This review describes the historical background of the trimethylsilyl ethers preparation from alcohols using catalytic complexes and also the transformation of trimethylsilyl ethers into alcohol‐containing compounds via deprecation techniques. [ABSTRACT FROM AUTHOR]

Isotopic analyses of plant samples are now of considerable importance for food certification and plant physiology. In fact, the natural nitrogen isotope composition (δ15N) is extremely useful to examine metabolic pathways of N nutrition involving isotope fractionations. However, δ15N analysis of amino acids is not straightforward and involves specific derivatization procedures to yield volatile derivatives that can be analysed by gas chromatography coupled to isotope ratio mass spectrometry (GC-C-IRMS). Derivatizations other than trimethylsilylation are commonly used since they are believed to be more reliable and accurate. Their major drawback is that they are not associated with metabolite databases allowing identification of derivatives and by-products. Here, we revisit the potential of trimethylsilylated derivatives via concurrent analysis of δ15N and exact mass GC-MS of plant seed protein samples, allowing facile identification of derivatives using a database used for metabolomics. When multiple silylated derivatives of several amino acids are accounted for, there is a good agreement between theoretical and observed N mole fractions, and δ15N values are satisfactory, with little fractionation during derivatization. Overall, this technique may be suitable for compound-specific δ15N analysis, with pros and cons.

The exploitation of chirality at silicon in asymmetric catalysis is one of the most intriguing and challenging tasks in synthetic chemistry. In particular, construction of enantioenriched mediem-sized silicon-stereogenic heterocycles is highly attractive, given the increasing demand for the synthesis of novel functional-materials-oriented silicon-bridged compounds. Here, we report a rhodium-catalyzed enantioselective construction of six- and seven-membered triorgano-substituted silicon-stereogenic heterocycles. This process undergoes a direct dehydrogenative C−H silylation, giving access to a wide range of triorgano-substituted silicon-stereogenic heterocycles in good to excellent yields and enantioselectivities, that significantly enlarge the chemical space of the silicon-centered chiral molecules. Further elaboration of the chiral monohydrosilane product delivers various corresponding tetraorgano-substituted silicon-stereogenic heterocycles without the loss of enantiopurity. These silicon-bridged heterocycles exhibit bright blue fluorescence, which would have potential application prospects in organic optoelectronic materials. Enantioenriched medium-sized silicon-stereogenic heterocycles are in high demand due to the potential use in functional materials. Here, the authors show a rhodium-catalyzed enantioselective synthesis of six- and seven-membered tri-organosubstituted silicon-stereogenic heterocycles. [ABSTRACT FROM AUTHOR]

ortho-Silylaryl triflate precursors (oSATs) have been responsible for many recent advances in aryne chemistry and are most commonly accessed from the corresponding 2-bromophenol. A retro-Brook O- to C-silyl transfer is a key step in this synthesis but not all aromatic species are amenable to the transformation, with no functionalized bisbenzyne oSATs reported. Simple Hückel models are presented which show that the calculated aromaticity at the brominated position is an accurate predictor of successful retro-Brook reaction, validated synthetically by a new success and a predicted failure. From this, the synthesis of a novel difunctionalized bisaryne precursor has been tested, requiring different approaches to install the two C-silyl groups. The first successful use of a disubstituted o-silylaryl sulfonate bisbenzyne precursor in Diels–Alder reactions is then shown. [ABSTRACT FROM AUTHOR]

A method for introducing dimethylphenylsilyl at the 4‐position in carbohydrates has been developed. Two C‐silylated glycosyl donors were prepared via levoglucosenone, starting from cellulose. The glycosylation properties were studied using three glucoside acceptors, a 3‐OH, 4‐OH, and 6‐OH. Compared with the 4‐deoxy variant, it was found that the anomeric selectivity was influenced more by the C‐2 substituents orientation than the silyl in the 4‐position. In general, the reactivity of these donors was higher than the corresponding 4‐deoxy‐analogue, albeit a competition experiment showed that the introduction of a C−Si increases the relative reactivity by a modest factor of around two. [ABSTRACT FROM AUTHOR]

Reaction of 6-amino-2-methylthio-3-methyluracil with ethyl ethoxymethyleneoxaloacetate or methyl(Z)-2-acetylamino-3-dimethylaminopropenoates afforded diethyl 2-(1,6-dihydro-1-methyl-2-(methylthio)-6-oxopyrimidin-4-yl-amino)methylene malonate or (2E)-methyl 3-(1,6-dihydro-1-methyl-2-(methylthio)-6-oxopyrimidin-4-yl-amino)-2-acetamidoacrylate, respectively. Cyclization of each of the latter products by sodium ethoxide afforded new pyrido [2,3-d]pyrimidines, which were ribosylated with 1-O-acetyl-2,3,5-O-benzoyl-β-D-ribofuranose by the silylation method yielded the protected nucleosides. The protected nucleosides were debenzoylated by sodium methoxide to afford novel pyrido[2,3-d]pyrimidine nucleosides. The structural assignmentsv for the new compounds were based on their elemental analysis and spectroscopic data. [ABSTRACT FROM AUTHOR]

2,2-Dimethyl-3-[(4-methylphenyl)sulfonyl]-2,3-dihydro-1,3,2-benzoxazasilole was synthesized by the reaction of N-(2-hydroxyphenyl)-4-methylbenzenesulfonamide with dimethyl-dichlorosilane or N, N-bis(dimethylamino)dimethylsilane in 68 and 96% yield, respectively. The structure of the new compound was assigned using NMR and IR spectroscopy and confirmed by X-ray diffraction. In the crystal, the silole molecules are linked to each other by short O⋯H-C contacts (∼2.6 Å) between the oxygen atoms of the bicyclic moiety and the methyl hydrogen atoms of adjacent molecules. [ABSTRACT FROM AUTHOR]

Silicon‐containing molecules are of great interest with widespread applications in several research areas such as polymer chemistry, materials science, medicinal chemistry, and complex molecule synthesis. Transition‐metal‐free C−H silylation is an essential process because this process is useful in fabricating carbon‐silicon bonds which can be further transformed into a number of other compounds. Since transition‐metal‐catalyzed C−H bond silylation is a developed field, therefore this context only contains transition‐metal‐free pathways for transforming C−H bond to C−Si (Si=SiR3) bond. This review has been further categorized and subcategorized based on intermediates involved and catalysts used during this transformation. This synopsis summarizes recent developments in the area of silicon chemistry with a focus of innovative transition‐metal‐free catalytic silylation using different strategies such as free radical, base promoted, Brønsted acid, Lewis acid, and frustrated Lewis pair. [ABSTRACT FROM AUTHOR]

An interlayer expanded zeolite, IEZ-PLS-3(Si–O–Si), was post-synthesized by the simple interlayer silylation of layered ECNU-9(P), which was derived from a lamellar precursor (PLS-3) using dichlorotetramethyldisiloxane (DCTMS) as the silylation reagent. The IEZ-PLS-3(Si–O–Si) was composed of ferrierite sheets and an intersected 14 × 12-ring (R) extra-large pore system. The results revealed that the IEZ-PLS-3(Si–O–Si) was composed of nanosized crystals, indicating that it is favorable for catalysis. Ti active sites were introduced into the framework of the IEZ-PLS-3(Si–O–Si) by solid-phase stirring in H2TiF6 aqueous solution at room temperature. The catalytic properties of the resulting material (Ti-IEZ-PLS-3(Si–O–Si)) were tested by carrying out the epoxidation of propene and allyl chloride, both of which have industrial application value. The Ti-IEZ-PLS-3(Si–O–Si) showed a higher catalytic activity compared to the typical well-known titanosilicate zeolites, including titanium silicalite-1 (TS-1) and Ti-MWW, which are currently used in industries. We also conducted the epoxidation of cyclohexene using bulk tert-butyl peroxide (TBHP) in decane as the oxidant to explore the pore properties of the Ti-IEZ-PLS-3(Si–O–Si). The Ti-IEZ-PLS-3(Si–O–Si) exhibited better catalytic performance than the TS-1 and Ti-MWW for cyclohexene due to its larger pore aperture. [ABSTRACT FROM AUTHOR]

Heteroarenes containing carbon-silicon (C-Si) bonds are important building blocks that play an important role in the construction of natural products, pharmaceuticals, and organic materials. In this context, the C-H silylation of heteroarenes is a topic of intense interest. Indole C-H silylation can preferentially occur at the nucleophilic C3 and C2 position (pyrrole core), while accessing the C4-C7 positions (benzene core) of the indole remains highly challenging. Here, we show a general strategy for the regioselective C7-H silylation of indole derivatives. Mainly, the regioselectivity is determined by strong coordination of the palladium catalyst with phosphorus (III) directing group. Using this expedient synthetic strategy, the diverse C7-silylated indoles are synthesized effectively which exhibits the broad functional group compatibility. Moreover, this protocol also been extended to other heteroarenes such as carbazoles. The obtained silylated indoles have been employed in various transformations to enable the corresponding differently functionalized indole derivatives. Significantly, a cyclopalladated intermediate is successfully synthesized to test the hypothesis about the P (III)-directed C-H metalation event. A series of mechanistic experiments and density functional theory (M06-2X) calculations has shown the preferred pathway of this directed C-H silylation process. [ABSTRACT FROM AUTHOR]

Direct activation of inert C(sp3)−H bonds by main group element species is yet a formidable challenge. Herein, the dehydrogenation of cyclohexene and 1,2,3,4‐tetrahydronaphthalene through the allylic/benzylic and homoallylic/homobenzylic C−H bond activation by cyclic (alkyl)(amino)silylene 1 in neat conditions is reported to yield the corresponding aromatic compounds. As for the reaction of cyclohexene, allylsilane 3 and 7‐silanorbornene 4 were also observed, which could be interpreted as a direct dehydrogenative silylation reaction of monoalkenes at the allylic positions. Experimental and computational studies suggest that the dehydrogenation of cyclohexene at the homoallylic position was accomplished by a combination of silylene 1 and radical intermediates such as hydrosilyl radical INT1 or cyclohexenyl radical H, which are generated in the initial step of the reaction. [ABSTRACT FROM AUTHOR]

Direct C–H silylation of quinoxalinones was achieved by the combination of organic photoredox catalysis and hydrogen atom transfer (HAT) under ambient air conditions. Transition metal- and external oxidant-free conditions were the major features of this protocol. A series of silylated quinoxalinones with broad functional groups had been synthesized in moderate to high yields. This methodology was also applicable for the C–H silylation of some electron-deficient heteroarenes. [ABSTRACT FROM AUTHOR]

A nonenzymatic dynamic kinetic resolution of acyclic and cyclic benzylic alcohols is reported. The approach merges rapid transition‐metal‐catalyzed alcohol racemization and enantioselective Cu‐H‐catalyzed dehydrogenative Si‐O coupling of alcohols and hydrosilanes. The catalytic processes are orthogonal, and the racemization catalyst does not promote any background reactions such as the racemization of the silyl ether and its unselective formation. Often‐used ruthenium half‐sandwich complexes are not suitable but a bifunctional ruthenium pincer complex perfectly fulfills this purpose. By this, enantioselective silylation of racemic alcohol mixtures is achieved in high yields and with good levels of enantioselection. [ABSTRACT FROM AUTHOR]

The influence of 3-(triethoxy silyl) propyl amine (TESPA) concentration on Multi Wall Carbon Nanotubes (MWCNTs) modification, is experimentally investigated. The MWCNTs modification were performed by 150, 75 and 25 weight percent (wt.%) of TESPA with respect to MWCNTs weight and the properties of the prepared samples were compared with each other and pristine MWCNTs. The MWCNTs silylation has been confirmed by Fourier Transformation Infrared Spectroscopy due to O-H stretching absorption peak disappearing. The 75 wt.% silyl grafted MWCNTs with increasing at about 26.7% in mean value diameters size owns more uniform morphology among the samples based on Scanning Electron Microscopy images. Also, Thermo Gravimetric Analysis shows that this sample has higher thermal stability because of lower weight loss (9.97%) in coupling agent decomposition temperature range at about 119.5–480 °C. Furthermore, X-Ray Diffraction indicates that the mentioned sample has higher level of amorphous structure with 39% reduction in crystallite size in comparison with the pristine MWCNTs. So, the 75 wt.% of TESPA introduced as the optimal concentration for this type of MWCNTs modification. Introduction of silyl compounds as a proper coupling agent to modify the carbon nanotube surfaces Determination of optimal silyl compounds concentration to modify the carbon nanotube surface Cristallinity in XRD pattern can determine the success of CNTs grafted with silyl compounds [ABSTRACT FROM AUTHOR]

In this study, we report the synthesis and characterization of novel nanocomposite namely doubly functionalized chloromethyl-calix[4]arene-methoxy grafted silylated clay (SC-C[4]). The silylation of nanoclay (thickness of the sheets ≈ 1 nm) was performed using (3-aminopropyl)trimethoxysilane (APTMS) (height ≈ 4.55 Å) coupling agent. The resulting organoclay was characterized by various techniques such as X-ray diffraction (XRD), infrared spectroscopy (IR), thermal gravimetric analysis (TGA), and 29Si and 13C solid-state NMR. The XRD results suggested the presence of a double layer of silanes molecules into the clay galleries of nanoclay minerals by increasing in the basal spacing. While the IR, 29Si and 13C solid-state NMR, and TGA analysis demonstrated the successful silylation of clay by the appearance of novel absorption bands, the changes in the chemical environment and the peaks degradation in the range 200 to 500 ° C related to aminosilane molecules, respectively. The calix[4]arenes derivatives were synthesized and characterized by IR spectroscopy and 1HNMR. The results showed that calix[4]arene was functionalized at the lower and upper rim. The grafting of the doubly functionalized calix[4]arene onto clay surfaces was performed through nucleophilic reaction. Structure, thermal properties of the nanocomposite SC-C[4] were also investigated. All data approved the successful grafting of para-chloromethyl-calix[4]arene-OMe onto clay surfaces. [ABSTRACT FROM AUTHOR]

Electrophilic functionalisation of [Cp*Fe(η5‐P5)] (1) yields the first transition‐metal complexes of pentaphospholes (cyclo‐P5R). Silylation of 1 with [(Et3Si)2(μ‐H)][B(C6F5)4] leads to the ionic species [Cp*Fe(η5‐P5SiEt3)][B(C6F5)4] (2), whose subsequent reaction with H2O yields the parent compound [Cp*Fe(η5‐P5H)][B(C6F5)4] (3). The synthesis of a carbon‐substituted derivative [Cp*Fe(η5‐P5Me)][X] ([X]−=[FB(C6F5)3]− (4 a), [B(C6F5)4]− (4 b)) is achieved by methylation of 1 employing [Me3O][BF4] and B(C6F5)3 or a combination of MeOTf and [Li(OEt2)2][B(C6F5)4]. The structural characterisation of these compounds reveals a slight envelope structure for the cyclo‐P5R ligand. Detailed NMR‐spectroscopic studies suggest a highly dynamic behaviour and thus a distinct lability for 2 and 3 in solution. DFT calculations shed light on the electronic structure and bonding situation of this unprecedented class of compounds. [ABSTRACT FROM AUTHOR]

Nano fibrillated cellulose (NFC) has turned into a material widely studied due to its desirable performance for numerous organic systems. Nevertheless, its surface is not very compatible with most organic systems; hence, chemical functionalization methods offer a path to solve this problem. In this study, NFC is successfully functionalized with two silane coupling agents: 3-glycidyloxypropyl trimethoxysilane (GPS) and 3-glycidyloxypropyl dimethylethoxysilane (GPMES) by a simple, direct, and environmentally friendly method. Different analyses have been carried out in order to confirm the chemical modification of NFC. ATR-IR, XPS, and 29Si NMR spectroscopies confirmed the chemical modification that allowed the understanding of the structure and the conformation onto the modified NFC surface. SEM and AFM microscopies were performed to study possible alterations in morphology; a slight change was observed. Thermal properties were also analyzed by TGA analysis. It remains stable after chemical functionalization. Grafted NFC showed good performance compared to the pristine one. It allows a better dispersion into organic systems improving their properties. [ABSTRACT FROM AUTHOR]

A rhodium(I)‐catalyzed enantioselective silylation of aliphatic C−H bonds for the synthesis of silicon‐stereogenic dihydrobenzosiloles is demonstrated. This reaction involves a highly enantioselective intramolecular C(sp3)−H silylation of dihydrosilanes, followed by a stereospecific intermolecular alkene hydrosilylation leading to the asymmetrically tetrasubstituted silanes. A wide range of dihydrosilanes and alkenes displaying various functional groups are compatible with this process, giving access to a variety of highly functionalized silicon‐stereogenic dihydrobenzosiloles in good to excellent yields and enantioselectivities. [ABSTRACT FROM AUTHOR]