Silyl Ethers Research Articles

Streamlining Si-O bond formation through cobalt-catalyzed dehydrocoupling.

Herein we report a strategy for the synthesis of organosilicons, including siloxanes, silyl ethers, and aminosilanes, via Co-catalyzed dehydrogenative coupling between hydrosilanes and nucleophiles. This discovery represents an expansion of the synthetic toolkit for organosilicon synthesis, forging Si-O and Si-N bonds in the presence of cobalt complexes with salen-type ligands.

Iron-catalyzed aerobic oxidation of silyl ethers to carboxylic acids.

Direct aerobic oxidation of silyl ethers to carboxylic acids has been developed. The mild reaction conditions lead to a broad range of functional group compatibility. Different types of silyl groups have been investigated and selective deprotective oxidation has been realized. The reaction could be conducted under air.

Visible-light-promoted desulfonylative radical difluoroalkylation between difluoroenol silyl ethers and difluoroalkyl sulfones to construct functionalized aryltetrafluoroethane derivatives

A visible-light-promoted desulfonylative radical difluoroalkylation between difluoroenol silyl ethers and difluoroalkyl sulfones has been developed.

Magic Effect of Diphenylprolinol Silyl Ethers for the Enantioselective Allenation of 2-Alkynals

The diphenylprolinol silyl ethers have been successfully identified as the efficient chiral amines in enantioselective allenation reaction of terminal alkynes and 2-alkynals. This reaction provides a diverse set of chiral...

Organocatalyst-mediated asymmetric one-pot/two domino/three-component coupling reactions for the synthesis of trans-hydrindanes.

Highly substituted trans-hydrindanes were synthesized by the three-component coupling reactions of 1,3-diethyl 2-(2-oxopropylidene)propanedioate and two different α,β-unsaturated aldehydes catalyzed by diphenylprolinol silyl ether. The reaction proceeds via two successive independent catalytic domino reactions in a one-pot reaction by a single chiral catalyst. Domino reactions involve Michael/Michael and Michael/aldol reactions to afford trans-hydrindanes with excellent diastereoselectivity and nearly optically pure form.

Nickel-Catalyzed C(sp3)-Sb Coupling of Chlorostibines with Unactivated Alkyl Chlorides and In Vitro Anticancer Activity of Products.

In this study, we present a nickel-catalyzed reductive C(sp3)-Sb coupling of unactivated alkyl chlorides with chlorostibines. This approach is highly versatile, tolerating various functional groups such as acetal, alkene, nitrile, amine, ester, silyl ether, thioether, and various heterocyclic compounds. Notably, the late-stage modification of bioactive molecules and the satisfactory anticancer activity against cancerous MDA-MB-231 also demonstrate the potential application.

Polyhydroxyurethane and Poly(ethylene oxide) Multiblock Copolymer Networks: Crosslinking with Polysilsesquioxane, Reprocessing and Solid Polyelectrolyte Properties.

This contribution reports the synthesis of polyhydroxyurethane (PHU)-poly(ethylene oxide) (PEO) multiblock copolymer networks crosslinked with polysilsesquioxane (PSSQ). First, the linear PHU-PEO multiblock copolymers were synthesized via the step-growth polymerization of bis(6-membered cyclic carbonate) (B6CC) with α,ω-diamino-terminated PEOs with variable molecular weights. Thereafter, the PHU-PEO copolymers were allowed to react with 3-isocyanatopropyltriethoxysilane (IPTS) to afford the derivatives bearing triethoxysilane moieties, the hydrolysis and condensation of which afforded the PHU-PEO networks crosslinked with PSSQ. It was found that the PHU-PEO networks displayed excellent reprocessing properties in the presence of trifluoromethanesulfonate [Zn(OTf)2]. Compared to the PHU networks crosslinked via the reaction of difunctional cyclic carbonate with multifunctional amines, the organic-inorganic PHU networks displayed the decreased reprocessing temperature. The metathesis of silyl ether bonds is responsible for the improved reprocessing behavior. By adding lithium trifluoromethanesulfonate (LiOTf), the PHU-PEO networks were further transformed into the solid polymer electrolytes. It was found that the crystallization of PEO chains in the crosslinked networks was significantly suppressed. The solid polymer electrolytes had the ionic conductivity as high as 7.64 × 10-5 S × cm-1 at 300 K. More importantly, the solid polymer electrolytes were recyclable; the reprocessing did not affect the ionic conductivity.

Rhodium-Catalyzed Enantioselective Formal [4+1] Cyclization of Benzyl Alcohols and Benzaldimines: Facile Access to Silicon-Stereogenic Heterocycles.

The carbon-to-silicon switch in formation of bioactive sila-heterocycles with a silicon-stereogenic center has garnered significant interest in drug discovery. However, metal-catalyzed synthesis of such scaffolds is still in its infancy. Herein, a rhodium-catalyzed enantioselective formal [4+1] cyclization of benzyl alcohols and benzaldimines has been realized by enantioselective difunctionalization of a secondary silane reagent, affording chiral-at-silicon cyclic silyl ethers and sila-isoindolines, respectively. Mechanistic studies reveal a dual role of the rhodium-hydride catalyst. The coupling system proceeds via rhodium-catalyzed enantio-determining dehydrogenative OH silylation of the benzyl alcohol or hydrosilylation of the imine to give an enantioenriched silyl ether or silazane intermediate, respectively. The same rhodium catalyst also enables subsequent intramolecular cyclative C-H silylation directed by the pendent Si-H group. Experimental and DFT studies have been conducted to explore the mechanism of the OH bond silylation of benzyl alcohol, where the Si-O reductive elimination from a Rh(III) hydride intermediate has been established as the enantiodetermining step.

Rhodium‐Catalyzed Enantioselective Formal [4+1] Cyclization of Benzyl Alcohols and Benzaldimines: Facile Access to Silicon‐Stereogenic Heterocycles

AbstractThe carbon‐to‐silicon switch in formation of bioactive sila‐heterocycles with a silicon‐stereogenic center has garnered significant interest in drug discovery. However, metal‐catalyzed synthesis of such scaffolds is still in its infancy. Herein, a rhodium‐catalyzed enantioselective formal [4+1] cyclization of benzyl alcohols and benzaldimines has been realized by enantioselective difunctionalization of a secondary silane reagent, affording chiral‐at‐silicon cyclic silyl ethers and sila‐isoindolines, respectively. Mechanistic studies reveal a dual role of the rhodium‐hydride catalyst. The coupling system proceeds via rhodium‐catalyzed enantio‐determining dehydrogenative OH silylation of the benzyl alcohol or hydrosilylation of the imine to give an enantioenriched silyl ether or silazane intermediate, respectively. The same rhodium catalyst also enables subsequent intramolecular cyclative C−H silylation directed by the pendent Si‐H group. Experimental and DFT studies have been conducted to explore the mechanism of the OH bond silylation of benzyl alcohol, where the Si‐O reductive elimination from a Rh(III) hydride intermediate has been established as the enantiodetermining step.

1,6‐Addition Reactions of Difluoroenol Silyl Ethers with Benzoquinones and Quinonediimines To Access Difluorooxymethyl and Difluoroaminomethyl Compounds

AbstractThe etherification and amination of difluoroenol silyl ethers with benzoquinones and quinonediimines were achieved by using hexafluoroisopropanol (HFIP) as the solvent. This 1,6‐addition reaction could construct difluorooxymethyl and difluoroaminomethyl compounds under metal‐free conditions. It is preliminarily speculated that the reaction took place through a single electron transfer (SET) process.

Organocatalytic Asymmetric Vinylogous Michael Addition of Electron-Deficient Aryl Alkane Nucleophiles to Enals.

We report herein a protocol for an organocatalyzed asymmetric vinylogous Michael addition of aryl alkane nucleophiles with enals under base- and additive-free conditions. A series of allylic building blocks were obtained in 60%-93% yield and 88-99% ee with 20 mol % diphenylprolinol silyl ether as catalyst. This protocol has advantages such as excellent chemoselectivity and regioselectivity, good tolerance of functionalities, and simple reaction conditions.

Deconstructable and Chemically Recyclable High-Density Polyethylene (HDPE)-Like Materials Based on Si-O Bonds.

Polyethylene (PE) is the most widely produced synthetic polymer. By installing chemically cleavable bonds into the backbone of PE, it is possible to produce chemically deconstructable PE derivatives; to date, however, such designs have primarily relied on carbonyl- and olefin-related functional groups. Bifunctional silyl ethers (BSEs; SiR2(OR'2)) could expand the functional scope of PE mimics as they possess strong Si-O bonds, excellent oxidative stabilities, and facile chemical tunability. Here, we report BSE-containing high-density polyethylene (HDPE)-like materials synthesized through a one-pot catalytic ring-opening metathesis polymerization (ROMP) and hydrogenation sequence. The crystallinity of these materials can be adjusted by varying the BSE concentration or the steric bulk of the Si-substituents, providing handles to control thermomechanical properties while maintaining the high thermal stability of HDPE. Two methods for chemical recycling of HDPE mimics are introduced, including a circular approach that leverages acid-catalyzed Si-O bond exchange with 1-propanol. Additionally, despite the fact that the starting HDPE mimics were synthesized by chain-growth polymerization (ROMP), we show that it is possible to recover the molar mass and dispersity of recycled HDPE products using step-growth Si-O bond formation or exchange, generating high molecular weight recycled HDPE products with mechanical properties similar to commercial HDPE.

Photoredox Synthesis of Silyl Ethers via Radical Coupling of Ketones with Hydrosilanes and [1, 2]‐Brook Rearrangement

AbstractAn expedient synthesis of silyl ethers is reported via photocatalytic free radical coupling of ketones with hydrosilanes and subsequent [1, 2]‐Brook rearrangement. This strategy features the advantages of 100 % atom economy, environmental friendliness, easily available starting materials as well as late‐stage functionalization of complex molecules.

Thermally Robust yet Deconstructable and Chemically Recyclable High‐Density Polyethylene (HDPE)‐Like Materials Based on Si−O Bonds

AbstractPolyethylene (PE) is the most widely produced synthetic polymer. By installing chemically cleavable bonds into the backbone of PE, it is possible to produce chemically deconstructable PE derivatives; to date, however, such designs have primarily relied on carbonyl‐ and olefin‐related functional groups. Bifunctional silyl ethers (BSEs; SiR2(OR′2)) could expand the functional scope of PE mimics as they possess strong Si−O bonds and facile chemical tunability. Here, we report BSE‐containing high‐density polyethylene (HDPE)‐like materials synthesized through a one‐pot catalytic ring‐opening metathesis polymerization (ROMP) and hydrogenation sequence. The crystallinity of these materials can be adjusted by varying the BSE concentration or the steric bulk of the Si‐substituents, providing handles to control thermomechanical properties. Two methods for chemical recycling of HDPE mimics are introduced, including a circular approach that leverages acid‐catalyzed Si−O bond exchange with 1‐propanol. Additionally, despite the fact that the starting HDPE mimics were synthesized by chain‐growth polymerization (ROMP), we show that it is possible to recover the molar mass and dispersity of recycled HDPE products using step‐growth Si−O bond formation or exchange, generating high molecular weight recycled HDPE products with mechanical properties similar to commercial HDPE.

Bis(2-ethylhexyl)amine as an Effective Organocatalyst for the Racemic Reactions of α,β-Unsaturated Aldehydes Involving an Iminium Ion

AbstractBis(2-ethylhexyl)amine is shown to be a suitable organocatalyst to prepare racemic compounds in the reactions of α,β-unsaturated aldehydes involving an iminium ion, whereas diphenylprolinol silyl ether is a well-known chiral organocatalyst for the asymmetric versions of the same reactions. The generality and limitations of bis(2-ethylhexyl)amine are disclosed.

Combining Ligand Deuteration with Ligand Bulkiness in Non‐Heme Iron Oxidation Catalysis: Enhancing Catalyst Lifetime and Site‐Selectivity

AbstractBulky tri‐isopropyl silyl (TIPS) substituents and deuterium atoms in the ligand design have been shown to enhance the site‐selective oxidation of aliphatic C−H bonds and the epoxidation of C=C bonds in non‐heme iron oxidation catalysis. In this work, a series of non‐heme iron complexes were developed by combining TIPS groups and deuterium atoms in the ligand. These bulky deuterated complexes show a significant increase in catalytic performance compared to their counterparts containing only TIPS groups or deuterium atoms. A broad range of substrates was oxidized with excellent yields, particularly, using [Fe(OTf)2((S,S)‐TIPSBPBP‐D4)] (1‐TIPS‐D4) (0.1 mol % to 1 mol %) via a fast or slow oxidant addition protocol, resulting in an overall improvement in catalytic performance. Notably, in the oxidation of the complex substrate trans‐androsterone acetate, the use of a slow addition protocol and a lower catalyst loading of 1‐TIPS‐D4 resulted in significant increases in reaction efficiency. In addition, kinetic and catalytic studies showed that deuteration does not affect the catalytic activity and the secondary C−H site‐selectivity but increases the catalysts’ lifetime resulting in higher conversion/yield. Accordingly, the yield of selectively oxidized secondary C−H products also increases with the overall yield by using the bulky deuterated iron complexes as catalysts. These catalytic improvements of the bulky deuterated complexes exemplify the enhanced design of ligands for homogeneous oxidation catalysis.

Iron(II)-Catalyzed Activation of Si-N and Si-O Bonds Using Hydroboranes.

We report the activation and functionalization of Si-N bonds with pinacol borane catalyzed by a three-coordinate iron(II) β-diketiminate complex. The reactions proceed via the mild activation of silazanes to yield useful hydrosilanes and aminoboranes. The reaction is studied by kinetic analysis, along with a detailed investigation of decomposition pathways using catecholborane as an analogue of the pinacol borane used in catalysis. We have extended the methodology to develop a polycarbosilazane depolymerization strategy, which generates hydrosilane quantitatively along with complete conversion to the Bpin-protected diamine. The analogous Si-O bond cleavage can also be achieved with heating, using silyl ether starting materials to generate hydrosilane and alkoxyborane products. Depolymerization of poly(silyl ether)s using our strategy successfully converts the polymer to 90% Bpin-protected alcohols.

Photocatalytic dehydrogenative coupling of silanes with alcohols triggered by light-induced sulfur vacancies on CdS nanosheets

Photocatalytic organosilicon transformation is a green and emerging synthetic strategy toward silyl ethers production. This approach takes advantage of the highly reactive photogenerated electron-hole pairs to trigger redox reactions for chemical transformations under mild conditions. However, the development of heterogenous photocatalysts for silyl ethers synthesis is greatly hampered by the lack of sufficient reactive sites on the catalyst surface for the adsorption and activation of silanes. Herein, we demonstrate that the light-induced sulfur vacancies (SVs) in-situ generated on ultrathin CdS nanosheet (CdS-NS) can function as typical Lewis acid sites to adsorb and activate silanes via the formation of SiH···Cd coordination species. In addition, these electron-deficient SVs can also trap the photogenerated electrons to promote charge separation. The CdS-NS with SVs exhibits an excellent photocatalytic performance toward silyl ethers synthesis while producing H2 simultaneously. This synthetic strategy based on in-situ creation of abundant Lewis acid sites on photocatalyst surface to activate silanes will have broad implications in the development of high-performance photocatalysts for organosilicon transformations.

TIPS group-assisted isomerization of benzyl protected d-manno- and d-glucopyranose to d-fructofuranose derivatives

Base-promoted (MeONa in MeOH or imidazole in DMF) isomerization of a series of 3,4,6-tri-O-benzyl-d-gluco- and d-mannopyranose derivatives with triisopropylsilyl (TIPS) substituents was studied. The presence of a bulky TIPS group at O-1 or O-2 was shown to be favorable for the isomerization of benzyl protected d-gluco- and d-mannopyranose derivatives to d-fructofuranose derivatives, in which the bulky silyl group occupies less sterically hindered primary position. The highest yield (33%) of the fructofuranose derivative was achieved when 3,4,6-tri-O-benzyl-2-O-triisopropylsilyl-d-mannopyranose was treated with MeONa in MeON at 50 °C.

A Model Ensemble Approach Enables Data-Driven Property Prediction for Chemically Deconstructable Thermosets in the Low-Data Regime.

Thermosets present sustainability challenges that could potentially be addressed through the design of deconstructable variants with tunable properties; however, the combinatorial space of possible thermoset molecular building blocks (e.g., monomers, cross-linkers, and additives) and manufacturing conditions is vast, and predictive knowledge for how combinations of these molecular components translate to bulk thermoset properties is lacking. Data science could overcome these problems, but computational methods are difficult to apply to multicomponent, amorphous, statistical copolymer materials for which little data exist. Here, leveraging a data set with 101 examples, we introduce a closed-loop experimental, machine learning (ML), and virtual screening strategy to enable predictions of the glass transition temperature (Tg) of polydicyclopentadiene (pDCPD) thermosets containing cleavable bifunctional silyl ether (BSE) comonomers and/or cross-linkers with varied compositions and loadings. Molecular features and formulation variables are used as model inputs, and uncertainty is quantified through model ensembling, which together with heavy regularization helps to avoid overfitting and ultimately achieves predictions within <15 °C for thermosets with compositionally diverse BSEs. This work offers a path to predicting the properties of thermosets based on their molecular building blocks, which may accelerate the discovery of promising plastics, rubbers, and composites with improved functionality and controlled deconstructability.