Regioselective Condensation Polymerization of Propargylic Electrophiles Enabled by Catalytic Element-Cupration

Here, we report a set of new polymerization reactions enabled by the 1,2-regioselective hydro- and silylcupration of enyne-type propargylic electrophiles. Highly regioregular head-to-tail poly(2-butyne-1,4-diyl)s (HT-PBD), bearing either methyl or silylmethyl side chains, are synthesized for the first time. A rapid entry into carbon-rich copolymers with adjustable silicon content is developed via in situ monomer bifurcation. Furthermore, a one-pot polymerization/semireduction sequence is developed to access a cis-poly(butadiene)-derived backbone by a ligand swap on copper hydride species. Interestingly, borocupration, typically exhibiting identical regioselectivity with its hydro- and silyl analogues, seems to proceed in a 3,4-selective manner. Computational studies suggest the possible role of the propargylic leaving group in this selectivity switch. This work presents a new class of regioregular sp-carbon-rich polymers and meanwhile a novel approach to organosilicon materials.

Challenges in the Synthesis and Processing of Hydrosilanes as Precursors for Silicon Deposition

Hydrosilanes are highly attractive compounds, which can be processed as liquids with printing technology to amorphous silicon films on nearly any solid substrate. The silicon layers can be processed for electronic devices like transistors or thin-film solar cells. The endothermic character of hydrosilanes with their positive enthalpies of formation results in favorable properties for processing. The larger the molecules, the lower their decomposition temperature and the higher their photoactivity. Cyclic hydrosilanes such as cyclopentasilane and cyclohexasilane can be easily deposited. The branched neopentasilane is more difficult to deposit but yields better-quality films after processing. The key challenge is the complex synthesis of the precursors and the hydrosilanes. The available preparative methods are presented in this review and their advantages and disadvantages are evaluated. The following synthesis methods are presented and discussed in this article: Wurtz coupling and other reductive coupling processes, dehydrogenative coupling of silanes, plasma synthesis of chlorinated polysilanes, amine- or chloride-induced disproportionations, and transformation of monosilane to higher silanes. Plasma synthesis is already carried out today as a continuous industrial process. The most effective synthesis methods in the laboratory are currently amine- and chloride-induced disproportionations. There is a great need to further optimize the syntheses of hydrosilanes and to develop new simple synthesis variants.

Hydroboration of vinylsilanes providing diversity-oriented hydrophobic building blocks for biofunctional molecules

Hydroboration of vinylsilanes with BH3 affords two silylethanol regioisomers. Herein, we investigated the regioisomeric ratio of hydroboration products from various vinylsilanes, focusing on the characteristic reaction profile. All investigated vinylsilanes afforded both regioisomers, and greater bulkiness increased the proportion of the Markovnikov products. The obtained silylethanols were used as hydrophobic building blocks for constructing nuclear progesterone receptor (PR) modulators. Notably, structural conversions from an α-isomer (silylethan-1-oxy derivative) to a β-isomer (2-silylethoxy derivative) caused complete activity-switching from a PR agonist to an antagonist. Our results indicate that silylethanols are useful for structural development, and vinylsilanes are a versatile source of hydrophobic building blocks for obtaining biofunctional molecules.

Recent advances in carbosilylation of alkenes and alkynes

Alkene and alkyne difunctionalization is a flexible process that allows the construction of two functional groups simultaneously in one step. On the other hand, carbosilylation, an ingenious difunctionalization pathway to concurrently incorporate both a silyl group and an organic functional group (alkyl, (hetero)aryl, alkenyl, alkynyl and allenyl) across a carbon-carbon multiple-bond system, is achieving immense interest in recent days. This review article provides a decade's update on the discoveries and developments in the synthesis of carbosilylated products from two very important carbon-carbon unsaturated substrates, alkenes and alkynes.

Research Progress of Elastomer Materials and Application of Elastomers in Drilling Fluid

An elastomer is a material that undergoes large deformation under force and quickly recovers its approximate initial shape and size after withdrawing the external force. Furthermore, an elastomer can heal itself and increase volume when in contact with certain liquids. They have been widely used as sealing elements and packers in different oil drilling and development operations. With the development of drilling fluids, elastomer materials have also been gradually used as drilling fluid additives in drilling engineering practices. According to the material type classification, elastomer materials can be divided into polyurethane elastomer, epoxy elastomer, nanocomposite elastomer, rubber elastomer, etc. According to the function classification, elastomers can be divided into self-healing elastomers, expansion elastomers, etc. This paper systematically introduces the research progress of elastomer materials based on material type classification and functional classification. Combined with the requirements for drilling fluid additives in drilling fluid application practice, the application prospects of elastomer materials in drilling fluid plugging, fluid loss reduction, and lubrication are discussed. Oil-absorbing expansion and water-absorbing expansion elastomer materials, such as polyurethane, can be used as lost circulation materials, and enter the downhole to absorb water or absorb oil to expand, forming an overall high-strength elastomer to plug the leakage channel. When graphene/nano-composite material is used as a fluid loss additive, flexibility and elasticity facilitate the elastomer particles to enter the pores of the filter cake under the action of differential pressure, block a part of the larger pores, and thus, reduce the water loss, while it would not greatly change the rheology of drilling fluid. As a lubricating material, elastic graphite can form a protective film on the borehole wall, smooth the borehole wall, behaving like a scaly film, so that the sliding friction between the metal surface of the drill pipe and the casing becomes the sliding friction between the graphite flakes, thereby reducing the friction of the drilling fluid. Self-healing elastomers can be healed after being damaged by external forces, making drilling fluid technology more intelligent. The research and application of elastomer materials in the field of drilling fluid will promote the ability of drilling fluid to cope with complex formation changes, which is of great significance in the engineering development of oil and gas wells.

Visible-light-mediated metal-free C–Si bond formation reactions

Conserving the environment is one of the most imperative goals in recent days among the chemists throughout the world. Swiftly increasing the environmental awareness also increases the demand to build new approaches for synthesizing the same active molecules with zero-waste and pollution. In this background, visible-light-mediated synthesis and functionalization of diverse organic compounds has been established as a tremendously successful topic and has achieved a remarkable stage of superiority and efficiency in the last 20 years. Alternatively, organosilicon derivatives are gradually aspiring leaves among chemists because of their significant application on synthetic, medicinal, and material chemistry. In this scenario, the addition of Si–H group to carbon−carbon multiple bonds (alkenes, hetero-arenes, alkynes, allenes, carboxylic acids, enynes, and dienes) provides an extremely step- and atom-efficient method to obtain silicon-containing compounds. Several attempts for the development of mild, robust, and efficient green protocol were taken in the last two decades. In spite of substantial advancement/research on C–Si bond formation using transition metal catalysis, a green and metal-free approach is highly essential considering its application in the field of medicine and with respect to environmental aspects as well. In this article, we will summarize the reports considering suitable visible-light-mediated metal-free silylation of C–C multiple bonds that includes alkenes, hetero-arenes, alkynes, allenes, enynes, and dienes.

Visible-light-induced silylation: an update

This review summarizes the recent findings and developments in the emerging area of photocatalytic silylation with literature coverage mainly extending from 2014 to February 2021.

Modification of silicone resins by Si–N cross-dehydrocoupling with perfect thermal stability and mechanical performance

A series of new types of modified hydrosilanes were synthesized, using hydrosilanes and nitrogen heterocycles by Si–N cross-dehydrocoupling catalyzed by Ru3CO12.

Syntheses and Molecular Structures of Liquid Pyrophoric Hydridosilanes

Trisilane, isotetrasilane, neopentasilane, and cyclohexasilane have been prepared in gram scale. In-situ cryo crystallization of these pyrophoric liquids in sealed capillaries on the diffractometer allows access to the single crystal structures of these compounds. Structural parameters are discussed and compared to gas-phase electron diffraction structures from literature and with the results from quantum chemical calculations. Significantly higher packing indices are found for the silanes compared to the corresponding alkanes. Radiation with ultraviolet light (365 nm) and parallel ESR (EPR) measurement shows that cyclohexasilane is easily split into radicals, which subsequently leads to the formation of branched and chain-like oligomers. The other compounds form no radicals under these conditions. NMR spectra of all four compounds have been recorded.

A Polymer with "Locked" Degradability: Superior Backbone Stability and Accessible Degradability Enabled by Mechanophore Installation

Though numerous applications require degradable polymers, there are surprisingly few polymer systems that combine superior stability and controllable degradability. Particularly, the degradability of a conventional degradable polymer is typically enabled by cleavable groups on the backbone, which can be attacked by stimuli in ambient conditions, causing undesirable material deterioration. Here we report a general strategy to overcome this issue: "locking" the degradability during handling and use of the polymers and "unlocking" it when degradation is needed. This strategy is demonstrated with a cyclobutane-fused lactone (CBL) polymer. The cyclobutane keeps polymer backbone intact under conditions that hydrolyze the lactone and allows the ester group to be recovered when undesirable hydrolysis occurs. When backbone degradation is needed, the degradability can be unlocked by mechanochemical activation that converts the polyCBL into a linear polyester. The rare combination of two intrinsically conflicting properties, i.e., backbone stability and accessible degradability, can make this polymer a potential option for new sustainable materials.

Branched Hydrosilane Oligomers as Ideal Precursors for Liquid-Based Silicon-Film Deposition

Herein a convenient synthetic method to obtain 2,2,3,3-tetrasilyltetrasilane 3 and 2,2,3,3,4,4-hexasilylpentasilane 4 on a multigram scale is presented. Proton-coupled ²⁹ Si NMR spectroscopy and single-crystal X-ray crystallography enabled unequivocal structural assignment. Owing to their unique properties, which are reflected in their nonpyrophoric character on contact with air and their enhanced light absorption above 250 nm, 3 and 4 are valuable precursors for liquid-phase deposition (LPD) and the processing of thin silicon films. Amorphous silicon (a-Si:H) films of excellent quality were deposited starting from 3 and characterized by conductivity measurements, ellipsometry, optical microscopy, and Raman spectroscopy.

Synthesis of hydrocarbon-soluble, methyl-substituted highly branched polysilanes via the Wurtz-type reductive coupling of trifunctional trisilanes and their pyrolysis to silicon carbide

(ClMe₂Si)₂SiMeCl was successfully converted into a hydrocarbon-soluble, highly branched polymethylsilane, which is usable as soluble precursor for the pyrolytic preparation of SiC.

σ-π conjugated organosilicon hybrid polymers from copolymerization of a tetrasiladiene and 1,4-diethynylbenzene

A catalyst- and by-product-free protocol for the synthesis of σ-π conjugated organosilicon polymers is reported. The regiospecific [2+2] cycloaddition of C≡C triple bonds to Si=Si double bonds allowed the preparation of air-stable ethynyl-terminated extended monomers from 1,4-bis(ethynyl)benzene and the para-phenylene bridged tetrasiladiene, Tip2 Si=SiTip-pC6H4-SiTip=SiTip2 (Tip = 2,4,6-iPr3C6H2). The polymer obtained from the extended monomer and further tetrasiladiene exhibits pronounced σ-π conjugation, as was evident from the red-shift in the absorption spectrum compared to model systems. We show that the thermal stability of the employed bis(alkyne) co-monomer is translated into this polymer.

Zinc mediated allylations of chlorosilanes promoted by ultrasound: Synthesis of novel constrained sila amino acids

A simple, fast and efficient method for allylation and propargylation of chlorosilanes through zinc mediation and ultrasound promotion is reported. As a direct application of the resulting bis-allylsilanes, three novel, constrained sila amino acids are prepared for the first time.