Chlorosilanes Research Articles

Nickel-Catalyzed Reductive Cross-Coupling of Propargylic Acetates with Chloro(vinyl)silanes: Access to Silylallenes.

Because of their various reactivities, propargyl acetates are refined chemical intermediates that are extensively applied in pharmaceutical synthesis. Currently, reactions between propargyl acetates and chlorosilanes may be the most effective method for synthesizing silylallenes. Nevertheless, owing to the adaptability and selectivity of substrates, transition metal catalysis is difficult to achieve. Herein, nickel-catalyzed reductive cross-coupling reactions between propargyl acetates and substituted vinyl chlorosilanes for the synthesis of tetrasubstituted silylallenes are described. Therein, metallic zinc is a crucial reductant that effectively enables two electrophilic reagents to selectively construct C(sp2)-Si bonds. Additionally, a Ni-catalyzed reductive mechanism involving a radical process is proposed on the basis of deuteration-labeled experiments.

Rapid access to diverse indoles by addition/SNAr with Grignard reagents and 2-fluorophenyl acetonitriles

Indoles are essential heterocycles in natural products, biological chemistry, and medicinal chemistry. Efficient approaches to their synthesis, therefore, remain in demand. Herein is reported a novel and scalable method to produce a wide variety of indoles by combining Grignard reagents and 2-fluorobenzyl cyanides (59 examples, 45%–95% yields). The Grignard reagent adds to the nitrile to give a metalated imine that undergoes SNAr with unactivated C–F bonds. This strategy installs the R group of RMgX at the indole 2-position, and it is noteworthy that a diverse array of Grignard reagents (aryl, alkyl, vinyl, and cyclopropyl) provide the desired heterocyclic products. The resulting N-magnesiated indole can be in situ functionalized at the 3-position with alkyl halides or functionalized on the nitrogen with silyl chlorides. This method enables the synthesis of indoles with functional groups at each position of the indole backbone (C4–C7), providing handles for further functionalization.

Organocatalytic Asymmetric Synthesis of Si-Stereogenic Siloxanols.

We report the organocatalytic synthesis of Si-stereogenic compounds via desymmetrization of a prochiral silanediol with a chiral imidazole-containing catalyst. This metal-free silylation method affords high yields with enantioselectivity up to 98:2 for various silanediol and silyl chloride substrate combinations (including secondary alkyl, vinyl, and H groups), accessing products with potential for further elaboration. NMR and X-ray studies reveal insight into the H-bonding interactions between the imidazole organocatalyst and the silanediol and the dual activating role of the Lewis basic imidazole to account for the high enantioselectivity.

Cobalt-Promoted Electroreductive Cross-Coupling of Prop-2-yn-1-yl Acetates with Chloro(vinyl)silanes.

An electroreductive cross-coupling of prop-2-yn-1-yl acetates with chloro(vinyl)silanes for producing tetrasubstituted silylallenes is developed. The method enables the formation of a new C─Si bond through the cathodic reduction formation of the silyl radical, radical addition across the C≡C bond, the alkenyl anion intermediate formation, and deacetoxylation and represents a mild, practical route to the synthesis of silylallenes. Mechanistic studies reveal that CoCl2 acts as the mediator to promote the formation of the alkenyl anion intermediate via electron transfer.

Metal-free Catalytic Hydrogenolysis of Chlorosilanes into Hydrosilanes with "Inverse" Frustrated Lewis Pairs.

The challenging metal-free catalytic hydrogenolysis of silyl chlorides to hydrosilanes is unlocked by using an inverse frustrated Lewis pair (FLP), combining a mild Lewis acid (Cy2BCl) and a strong phosphazene base (BTPP) in mild conditions (10bar of H2, r.t.). In the presence of a stoichiometric amount of the base, the hydrosilanes R3SiH (R=Me, Et, Ph) are generated in moderate to high yields (up to 95%) from their chlorinated counterparts. A selective formation of the valuable difunctional monohydride Me2SiHCl is also obtained from Me2SiCl2. A mechanism is proposed based on stoichiometric experiments and DFT calculations; it highlights the critical role of borohydride species generated by the heterolytic splitting of H2.

One-pot synthesis of (2,4,6-Trimethylbenzoyl)diphenylphosphine oxide from triphenylphosphine oxide

A simple one-pot preparation of (2,4,6-Trimethylbenzoyl)diphenylphosphine oxide (TPO) by employing the low-cost triphenylphosphine oxide (Ph3PO) as the starting material was described. Reaction with trimethylsilyl chloride (TMSCl) that transforms the intermediate sodium diphenylphosphonite (Ph2PONa) into (trimethylsilyl)oxy)diphenylphosphine (Ph2POTMS) is the key for the high yield of TPO. The reactions of Ph2PONa with other silyl chlorides are discussed.

Iterative Synthesis of Oligosilanes Using Methoxyphenyl- or Hydrogen-Substituted Silylboronates as Building Blocks: A General Synthetic Method for Complex Oligosilanes.

Organosilanes have attracted the attention of researchers for more than 150 years due to their unique properties, and they have become indispensable industrial assets. However, many synthesized oligosilanes with multiple Si-Si bonds are relatively simple, i.e., they often only contain a single repeating unit. More laborious customized synthetic routes can lead to more complex oligosilanes, but compared to carbon-based molecules, their structural diversity remains limited. The development of effective and practical synthetic routes to complex oligosilanes that contain mixed substituents constitutes a long-standing challenge. Here, we describe an iterative synthesis of oligosilanes using methoxyphenyl- or hydrogen-substituted silylboronates, which were obtained via transition-metal-catalyzed Si-H borylation reactions. The first key reaction is a cross-Si-Si bond-forming reaction between chloro(oligo)silanes and silylboronates activated by MeLi. The second key reaction is the selective chlorination of the methoxyphenyl group or the hydrogen atom at the terminal of the oligosilanes. Iteration of these two key reactions enables the synthesis of various oligosilanes that are otherwise difficult to access. As a demonstration of the synthetic utility of this iterative synthetic approach, oligosilanes with different sequences were prepared by simply changing the order of the reaction of four different silicon units. Furthermore, a bespoke tree-shaped oligosilane is easily obtained via the present iterative synthesis. The solid-state structures of several of these oligosilanes were unequivocally determined using single-crystal X-ray diffraction analysis.

Benzoyldiisopropylchlorosilane: a visible light photocleavable alcohol protecting group.

Silyl chlorides are highly valuable and popular reagents for the protection of alcohols. In this edge article we introduce a photocleavable alcohol protecting group on the basis of acyl silanes. To achieve this, acylchlorosilanes that represent a new class of acylsilanes were developed. They can be easily synthesized in a concise sequence of three steps in high overall yield. Alcohol silyl protection takes place under established mild conditions, akin to those associated with classical silicon-based protecting groups. The removal of the Si-group is achieved at room temperature through exposure to visible light (456 nm) in methanol. We demonstrate a broad spectrum of substrates with remarkable tolerance toward diverse functional groups, highlighting a substantial level of orthogonality with respect to other protecting groups. Furthermore, we showcase the robustness of this approach against various transformations.

Anionic Magnesium and Calcium Hydrides: Transforming CO into Unsaturated Disilyl Ethers

AbstractThe synthesis, characterisation and reactivity of two isostructural anionic magnesium and calcium complexes is reported. By X‐ray and neutron diffraction techniques, the anionic hydrides are shown to exist as dimers, held together by a range of interactions between the two anions and two bridging potassium cations. Unlike the vast proportion of previously reported dimeric group 2 hydrides, which have hydrides that bridge two group 2 centres, here the hydrides are shown to be “terminal”, but stabilised by interactions with the potassium cations. Both anionic hydrides were found to insert and couple CO under mild reaction conditions to give the corresponding group 2 cis‐ethenediolate complexes. These cis‐ethenediolate complexes were found to undergo salt elimination reactions with silyl chlorides, allowing access to small unsaturated disilyl ethers with a high percentage of their mass originating from the C1 source CO.

Anionic Magnesium and Calcium Hydrides: Transforming CO into Unsaturated Disilyl Ethers.

The synthesis, characterisation and reactivity of two isostructural anionic magnesium and calcium complexes is reported. By X-ray and neutron diffraction techniques, the anionic hydrides are shown to exist as dimers, held together by a range of interactions between the two anions and two bridging potassium cations. Unlike the vast proportion of previously reported dimeric group 2 hydrides, which have hydrides that bridge two group 2 centres, here the hydrides are shown to be "terminal", but stabilised by interactions with the potassium cations. Both anionic hydrides were found to insert and couple CO under mild reaction conditions to give the corresponding group 2 cis-ethenediolate complexes. These cis-ethenediolate complexes were found to undergo salt elimination reactions with silyl chlorides, allowing access to small unsaturated disilyl ethers with a high percentage of their mass originating from the C1 source CO.

Two Complementary Approaches to Silicon-Supported Soluble [FeFe]-Hydrogenase Mimics

Two series of silicon-supported [(μ-SCH2)2NRFe2(CO)6] (R = p-OHC6H4, 3, and (CH2)2OH, 4a, and (CH2)5OH, 4b) hydrogenase mimics, as well as octamethylsilsesquioxane (POSS)-based nanostructures containing eight [(μ-SCH2)2NRFe2(CO)6] moieties, have been prepared either by reaction of the corresponding silyl and silyloxy chlorides and compounds 3 and 4 or by CuAAC between propargyl derivatives of silyl and silyloxy chlorides and azide 14. Cycloaddition between POSS-derived azide 23b and [(μ-SCH2)2NRFe2(CO)6] (R = alkyne) complexes 24 and 26 is efficient, leading to POSS-based nanostructures containing eight [(μ-SCH2)2NRFe2(CO)6] units. All of the complexes prepared through this work were soluble in organic solvents and hence fully characterizable by spectroscopic media. The electrochemistry of the linear siloxanes 6a and 10 is similar, with a reduction wave around −1.7 V, which is characteristic of these [(μ-SCH2)2NRFe2(CO)6] entities. Complexes 6a and 6b lacking 1,2,3-triazole moieties were electrochemically stable in the presence of AcOH, showing a strong electrocatalytic wave at −2.2 V, while complexes 16 and 18 having the 1,2,3-triazole ring decomposed but were electrocatalytically active in the wave at −2.2 V. POSS-[(μ-SCH2)2NRFe2(CO)6] derivatives 25 and 27 show a strong irreversible reduction event and are deposited in the electrode either when adding AcOH or over time (successive voltammograms). 29Si NMR shows that the integrity of the silicon cage is not affected by time or AcOH addition. These synthetic protocols and electrochemical studies will be applied in the design of silicon-supported [(μ-SCH2)2NRFe2(CO)6] mimics.

Hydrophobization of Monolithic Resorcinol-Formaldehyde Xerogels by Means of Silylation.

In materials research, the control of wettability is important for many applications. Since they are typically based on phenolics, organic aerogels, and xerogels are intrinsically hydrophilic in nature, and examples of the chemical functionalization of such gels are scarce and often limited to powders. This study reports on the silylation of monolithic resorcinol-formaldehyde (RF) xerogels using solutions of silyl chlorides and triflates, respectively, in combination with an amine base. The resulting gels are structurally characterized by means of elemental analysis, X-ray photoelectron spectroscopy, pycnometry, sorption analysis, and scanning electron microscopy with electron-dispersive X-ray spectroscopy. The wetting behavior of the silylated gels was studied by the determination of the contact angle to water after exposure of the gels to ambient air. Additionally, the uptake of liquid water and aqueous acids and bases was investigated. As a result, processes for the functionalization of RF xerogels with sterically demanding silyl moieties have been established. Although the analyses indicate that silylation occurred to a rather small extent, highly hydrophobic gels resulted which retained the wetting behavior over the course of several months with contact angles of >130°. Monoliths bearing sterically demanding silyl groups showed higher stability towards aqueous acid than trimethylsilylated RF gels.

Renewable Reagent for Nucleophilic Fluorination.

Herein, we report a study on the reactivity of three 1,3-diarylimidazolium-based fluoride reagents, with a general formula of [IPrH][F(HF)n] (n = 0, 1, or 2), that tackle the challenges of limited solubility, hygroscopicity, instability, and laborious preparation procedures of nucleophilic fluoride reagents. Fluorination of 4-tert-butylbenzyl bromide reveals that trifluoride [IPrH][F(HF)2] is the most selective reagent. Microwave-assisted activation coupled with the addition of sterically hindered amine DIPEA or alkali metal fluorides increases the rate of fluorination with [IPrH][F(HF)2], making it an excellent reagent for the fluorination of various organic substrates. The scope of substrates includes benzyl bromides, iodides, chlorides, aliphatic halides, tosylates, mesylates, α-haloketones, a silyl chloride, acyl and sulfuryl chlorides, and a nitroarene. The exceptional stability of the air-stable and nonhygroscopic [IPrH][F(HF)2] reagent is illustrated by its convenient synthesis and detailed experimental regeneration protocol using hydrofluoric acid without organic solvents.

Practical method for hydroxyl-group protection using strontium metal and readily available silyl chlorides.

We have found that the etherification of silyl-protected secondary alcohols proceeds smoothly in the presence of strontium metal using silyl chloride instead of the expensive, yet more reactive, and commonly used silyl triflate. The reaction occurred almost completely with various alcohols.

Surface Properties and Biological Activity of the Synthesized Polymeric Surfactant and its Complexes

Poly (4-vinyl pyridine) (P4-VP) was quaternized and complexed with salt chloride to obtain polymeric surfactant complexes having to improve surface properties and microbial activity. P4-VP was quarternized by trimethyl chloro silane to give (QP4-VP) (I) and then complexed by using stannous chloride and cobalt chloride to give polymeric surfactant complexes. The quaternized P4-VP and its complexes were characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Also, the surface properties of this polymeric surfactant and its complexes were studied. The influence of metal chlorides on the antibacterial activity of this polymeric surfactant was estimated and screened through the length of the field of hindrance versus various microorganisms. It shows an enhancement in the surface characteristics and fine germicidal action for quaternized P4-VP when complexed with metal chlorides. The designed cationic polymeric surfactant and its complexes have a good biological action against all such microorganisms.

Mechanistic investigations of alcohol silylation with isothiourea catalysts.

The mechanism of the asymmetric silylation of alcohols with isothiourea catalysts was studied by employing reaction progress kinetic analysis. These reactions were developed by the Wiskur group, and use triphenyl silyl chloride and chiral isothiourea catalysts to silylate the alcohols. While the order of most reaction components was as expected (catalyst, amine base, alcohol), the silyl chloride was determined to be a higher order. This suggested a multistep mechanism between the catalyst and silyl chloride, with the second equivalent of silyl chloride assisting in the formation of the reactive intermediate leading to the rate-determining step. Through the addition of additives and investigating changes in the silyl chloride, an understanding of the catalyst equilibrium emerged for this reaction and provided pathways for further reaction development.

Polymer compositions on kinetic resolution of secondary alcohols using polymer-supported silyl chlorides

Modulating the polarity of the polymer backbone affects the selectivity of asymmetric silylation.

Application of Mathematical Modeling in Optimization of Synthesis Process Parameters of Methylchlorosilane

Methylchlorosilane is an important chemical raw material. It has been matured since the direct synthesis technology has been applied for many years. However, due to the characteristics of gas-solid two-phase catalytic reaction, it still faces many problems in industrial production. The use of systems engineering methods to solve production problems has become an important task for organic chlorosilane monomer manufacturers. This paper introduces the application of mathematical modeling in the optimization of methylchlorosilane synthesis process parameters as an example to illustrate the important role of system engineering ideas in the production practice process, to achieve digitization of the fluidized bed reactor control process, parameter optimization. Through the research and analysis of the production control process, the mathematical model of superficial gas velocity and catalyst feed coefficient control was established to optimize the methylchlorosilane synthesis process. The results show that the apparent gas velocity should be controlled in stages during the direct synthesis of methylchlorosilane. The induction period is 0.10~0.12 m/s, and the stable period is 0.25~0.28 m/s. After the catalyst is added to the reactor, it will undergo three stages of induction period, stable period and aging period. After the catalyst reaction performance, the catalyst will gradually lose its catalytic ability due to various physical and chemical factors. Catalyst stability and life-span in industrial production are related to its own performance and mixing ratio, the ternary copper catalyst life-span is generally 50-60 hours, the suitable mixing ratio is 2.0-2.5%.

Synthesis and Anticholinesterase Activity of [(4Z)-2-Aryl-4-(arylmethylidene)-5-oxo-4,5-dihydro-1H-imidazol-1-yl]alkanoic Acids

ω-[(4Z)-2-Aryl-4-arylmethylidene-5-oxo-4,5-dihydro-1H-imidazol-1-yl]alkanoic acids were synthesized by reaction of N-substituted α,β-dehydropeptides with chloro(trimethyl)silane or 1,1,1,3,3,3-hexamethyldisilazane. Both initial peptides and (4H)-imidazol-5-one derivatives based thereon were tested for anticholinesterase activity.

Size-dependent rate acceleration in the silylation of secondary alcohols: the bigger the faster.

Relative rates for the reaction of secondary alcohols carrying large aromatic moieties with silyl chlorides carrying equally large substituents have been determined in organic solvents. Introducing thoroughly matching pairs of big dispersion energy donor (DED) groups enhanced rate constants up to four times, notably depending on the hydrogen bond donor ability of the solvent. A linear correlation between computed dispersion energy contributions to the stability of the silyl ether products and experimental relative rate constants was found. These results indicate a cooperation between solvophobic effects and DED-groups in the kinetic control of silylation reactions.