Catalytic silylation of O–nucleophiles via Si–H or Si–C bond cleavage: A route to silyl ethers, silanols and siloxanes

Interfacial hydrogen evolution reaction from Ouzo-effect-generated bulk nano/micro droplets of liquid organic hydrogen carriers

HYPOTHESIS

Organosilanes as liquid organic hydrogen carriers (LOHCs) offer a promising solution for the safe storage and transport of hydrogen gas as a clean energy source. However, the dehydrogenation reaction of organosilanes in the presence of water faces the challenge of sluggish kinetics in conventional bulk reactions. Dispersing organosilanes as stable nanodroplets in basic water offers a potential strategy to increase the interfacial area, thereby enhancing H2 production efficiency.

EXPERIMENTS

Organosilane nanodroplets were generated through spontaneous emulsification via the Ouzo effect in a ternary organosilane-water-acetone system. The reaction between the organosilane nano/microdroplets and the alkaline aqueous phase led to H2 generation. This study investigates how the composition and size distribution of these droplets influence H2 production yield. To gain deeper insight into the reaction mechanisms, single reacting microdroplets were analyzed using side-view imaging and confocal microscopy.

FINDINGS

Organosilane nano/microdroplets formed from the Ouzo effect in the presence of a co-solvent. H2 formation yields from interfacial reactions of these droplets reached up to 25%, whereas single reacting microdroplets achieved a maximum yield of 3.5%. This study demonstrates that spontaneous emulsification in ternary mixture using the Ouzo effect can enhance reaction kinetics and product yields. Furthermore, detailed insights into the behavior of H2 bubbles, from their nucleation within a microdroplet to their growth and eventual detachment, were obtained through the analysis of single reacting microdroplets.

Surfactant-Mediated Interfacial Hydrogen Evolution Reaction

Hydrogen is a highly promising clean energy source without greenhouse gas emissions. Liquid organic hydrogen carriers (LOHCs) offer a promising alternative for convenient storage and transportation. This study investigates the interfacial hydrogen evolution reaction between polymethylhydrosiloxane (PMH), a representative LOHC, and water, focusing on controlling reaction kinetics by modifying interfacial properties with surfactants. The hydrogen production rate at a planar interface between PMH and water catalyzed by sodium hydroxide revealed that surfactants such as Tween 20 and sodium dodecyl sulfate (SDS) can slow down the hydrogen formation by 5 to 20 times, possibly due to an overcrowded interface effect. In contrast, cationic surfactants, such as hexadecyltrimethylammonium bromide (CTAB) and other quaternary ammonium surfactants, act as pseudo phase-transfer catalysts and accelerate the hydrogen formation rate up to 3-fold at a concentration of 0.05 times their critical micelle concentration. As the PMH microdroplets were dispersed in the surfactant aqueous solution, the conversion yields of hydrogen with cationic surfactants reached up to 45%, which is significantly higher than the yields achieved with Tween 20 or SDS. The effects of the surfactant type were further confirmed by following hydrogen bubble growth in a single PMH droplet. Overall, our findings demonstrate that selecting an appropriate surfactant can provide an effective control over the interfacial reaction rate of dehydrogenation of LOHCs. This offers strategies for manipulating liquid-liquid interfaces and controlling in-demand hydrogen production.

Rising Opportunities in Catalytic Dehydrogenative Polymerization

This article gives a perspective on various types of catalytic dehydrogenative polymerization reactions (including organic and main group polymers) while introducing "hydrogen-borrowing polymerization" and "acceptorless dehydrogenative polymerization" to this class. Limitations and future opportunities of each method have been discussed.

Enantioselective Deoxygenative Amino-Cyanation of Carboxylic Acids via Ti-Multicatalysis

Carboxylic acids are valued synthetic building blocks that offer shelf life stability, structural diversity, and wide commercial availability. Despite the remarkable synthetic utility of carboxylic acids, a direct enantioselective deoxygenative functionalization of carboxylic acids remains rare. We present enantioselective deoxygenative amino-cyanation of carboxylic acids using a novel TiIV-multicatalytic system that catalytically modified each C-O bond of carboxylic acid to C-C, C-N, and C-H bonds, generating enantio-enriched chiral α-amino nitriles (up to 98:2 er).

Frustrated Lewis Pair-Promoted Organocatalytic Transformation of Hydrosilanes into Silanols with Water Oxidant

Owing to their unique properties, the silanols have attracted intense attention but remain challenging to prepare from the organocatalytic oxidation of hydrosilanes using H2O as a green oxidant. Herein, we employ a frustrated Lewis pair (FLP) to successfully suppress the formation of undesired siloxanes and produce silanols in high to excellent yields in the presence of H2O. Mechanistic studies suggest that the reaction is initiated with the activation of FLP by H2O rather than by silanes and goes through a concerted SN2 mechanism. More importantly, the combination of the FLP-catalyzed oxidation of hydrosilanes with B(C6F5)3-catalyzed dehydrogenation enables us to realize the precise synthesis of sequence-controlled oligosiloxanes. This method exhibits a broad substrate scope and can be easily scaled up, thus exhibiting promising application potentials in the precision synthesis of silicon-containing polymer materials.

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.

Facile Synthesis of Ultra-Small Silver Nanoparticles Stabilized on Carbon Nanospheres for the Etherification of Silanes

The dehydrocoupling reaction between alcohols and hydrosilanes is considered to be one of the most atom-economical ways to produce Si-O coupling compounds because its byproduct is only hydrogen (H2), which make it extremely environmentally friendly. In past decades, various kinds of homogeneous catalysts for the dehydrocoupling of alcohols and hydrosilanes, such as transition metal complexes, alkaline earth metals, alkali metals, and noble metal complexes, have been reported for their good activity and selectivity. Nevertheless, the practical applications of these catalysts still remain unsatisfactory, which is mainly restricted by environmental impact and non-reusability. A facile and recyclable heterogeneous catalyst, ultra-small Ag nanoparticles supported on porous carbon (Ag/C) for the etherification of silanes, has been developed. It has high catalytic activity for the Si-O coupling reaction, and the apparent activation energy of the reaction is about 30 kJ/mol. The ultra-small Ag nanoparticles dispersed in the catalyst through the carrier C have an enrichment effect on all reactants, which makes the reactants reach the adsorption saturation state on the surface of Ag nanoparticles, thus accelerating the coupling reaction process and verifying that the kinetics of the reaction of the catalyst indicate a zero-grade reaction.

Advances in disilylation reactions to access cis/trans-1,2-disilylated and gem-disilylated alkenes

Organosilane compounds are widely used in both organic synthesis and materials science. Particularly, 1,2-disilylated and gem-disilylated alkenes, characterized by a carbon-carbon double bond and multiple silyl groups, exhibit significant potential for subsequently diverse transformations. The versatility of these compounds renders them highly promising for applications in materials, enabling them to be valuable and versatile building blocks in organic synthesis. This review provides a comprehensive summary of methods for the preparation of cis/trans-1,2-disilylated and gem-disilylated alkenes. Despite notable advancements in this field, certain limitations persist, including challenges related to regioselectivity in the incorporation and chemoselectivity in the transformation of two nearly identical silyl groups. The primary objective of this review is to outline synthetic methodologies for the generation of these alkenes through disilylation reactions, employing silicon reagents, specifically disilanes, hydrosilanes, and silylborane reagents. The review places particular emphasis on investigating the practical applications of the C-Si bond of disilylalkenes and delves into an in-depth discussion of reaction mechanisms, particularly those reactions involving the activation of Si-Si, Si-H, and Si-B bonds, as well as the C-Si bond formation.

Single-Walled Cluster Nanotubes for Single-Atom Catalysts with Precise Structures

Spatially confining isolated atomic sites in low-dimensional nanostructures is a promising strategy for preparing high-performance single-atom catalysts (SACs). Herein, fascinating polyoxometalate cluster-based single-walled nanotubes (POM-SWNTs) with atomically precise structures, uniform diameter, and single-cluster wall thickness are constructed by lacunary POM clusters (PW11 and P2W17 clusters). Isolated metal centers are accurately incorporated into the PW11-SWNTs and P2W17-SWNTs supports. The structures of the resulting MPW11-SWNTs and MP2W17-SWNTs are well established (M = Cu, Pt). Molecular dynamics simulations demonstrate the stability of POM-SWNTs. Furthermore, the turnover frequency of PtP2W17-SWNTs is 20 times higher than that of PtP2W17 cluster units and 140 times higher than that of Pt nanoparticles in the alcoholysis of dimethylphenylsilane. Theoretical studies indicate that incorporating a Pt atom into the P2W17 support induces straightforward electron transfer between them, combining the nanoconfined environment to enhance the catalytic activity of PtP2W17-SWNTs. This work shows the feasibility of using subnanometric POM clusters to assemble single-walled cluster nanotubes, highlighting their potential to prepare superior SACs with precise structures.

Catalytic Synthesis of Silanols by Hydroxylation of Hydrosilanes: From Chemoselectivity to Enantioselectivity

As a crucial class of functional molecules in organosilicon chemistry, silanols are found valuable applications in the fields of modern science and will be a potentially powerful framework for biologically active compounds or functional materials. It has witnessed an increasing demand for non-natural organosilanols, as well as the progress in the synthesis of these structural features. From the classic preparative methods to the catalytic selective oxidation of hydrosilanes, electrochemical hydrolysis of hydrosilanes, and then the construction of the most challenging silicon-stereogenic silanols. This review summarized the progress in the catalyzed synthesis of silanols via hydroxylation of hydrosilanes in the last decade, with a particular emphasis on the latest elegant developments in the desymmetrization strategy for the enantioselective synthesis of silicon-stereogenic silanols from dihydrosilanes.

Rhodium-Catalyzed Hydrolytic Cleavage of the Silicon-Carbon Bond of Silacyclobutanes to Access Silanols

Herein, we report the first rhodium-catalyzed hydrolytic cleavage of the silicon-carbon bond in silacyclobutanes using water as the reactant. A series of silacyclobutanes could be employed in this reaction in the presence of the Rh/BINAP complex, resulting in the corresponding silanols in good yields. Additionally, a chiral 1,1,4,4-tetraaryl-2,3-O-isopropylidene-l-threitol-derived phosphoramidite ligand could be used in this reaction to yield Si-stereogenic silanol with promising enantioselectivity.

Facile Preparation of Polysiloxane-Modified Asphalt Binder Exhibiting Enhanced Performance

The development of polymer-modified asphalt (asphalt = asphalt binder) is significant because the polymer modifier can improve the performance of asphalt mixture and meet the requirements of the modern asphalt pavement. Herein, we present a novel polysiloxane-modified asphalt with enhanced performance, formed by simply mixing hydroxy-terminated polysiloxane (HO-PDMS) into base asphalt at 140 °C. The interaction mechanism of HO-PDMS in base asphalt was characterized by FT-IR, GPC, and DSC. It reveals that HO-PDMS polymers have been chemically bonded into the asphalt, and, thus, the resultant asphalt exhibits optimal compatibility and storage stability. The results based on fluorescence microscopy and a segregation test prove that HO-PDMS has good compatibility with base asphalt. Moreover, by virtue of the intriguing properties of polysiloxane, the present asphalt possesses improved low- and high-temperature properties, higher thermal stability, and enhanced hydrophobicity compared to conventional asphalt when using an appropriate dosage of HO-PDMS. DSC indicated that the Tg of modified asphalt (-12.8 °C) was obviously lower than that of base asphalt (-7.1 °C). DSR shows that the rutting parameter of modified asphalt was obviously higher than that of base asphalt. BBR shows that modified asphalt exhibited the lowest stiffness modulus and the highest creep rate with an HO-PDMS dosage of 6% and 4%, respectively. These results demonstrate that polysiloxane-modified asphalt can be promisingly utilized in realistic asphalt pavement with specific requirements, particularly high-/low-temperature resistance.

Access to germasiloxanes and alkynylgermanes mediated by earth-abundant species

The reactions between silanols or terminal acetylenes with alkynylgermanes have been accomplished using potassium bis(trimethylsilyl)amide as the catalyst. This strategy has provided an entry point into various organogermanes including germasiloxanes and alkynylgermanes. Remarkably, not only KHMDS but also simple bases such as KOH can serve as efficient catalysts in this process.

An unusual autocatalysis with an air-stable Pd complex to promote enantioselective synthesis of Si-stereogenic enynes

Given the powerful potential of chiral-at-silicon chemistry, enantioselective synthesis of Si-stereogenic centers has attracted substantial research interest in recent years. However, the catalytic asymmetric synthesis of Si-stereogenic organosilicon compounds remains an appealing venture and is a challenging subject because of the difficulty in achieving high reactivity and stereoselectivity for "silicon-center" transformations. Herein, we disclose a highly enantioselective palladium-catalyzed hydrosilylation of 1,3-diynes with dihydrosilanes, which enables the facile preparation of Si-stereogenic enynes and an enyne-linked chiral polymer (polyenyne) in good yields and excellent ees (up to >99%) by desymmetrization. The unusual stereoselectivity in this reaction is achieved by precisely controlling the steric hindrance and electronic effect of the newly developed chiral ligands, resulting in a wide range of chiral silanes and a Si-containing polymer bearing a Si-stereogenic center which is otherwise difficult to access. The key to the high enantioselectivity relies on catalyst aggregation-induced non-covalent interaction, which exerts a remarkably positive influence on the Si-H bond activation and enhancement of enantioselectivity, in which the palladium/P-ligand complex was proved to be air-stable and moisture-insensitive in this reaction.

A Fusion of Molecular Imprinting Technology and Siloxane Chemistry: A Way to Advanced Hybrid Nanomaterials

Molecular imprinting technology is a well-known strategy to synthesize materials with a predetermined specificity. For fifty years, the "classical" approach assumed the creation of "memory sites" in the organic polymer matrix by a template molecule that interacts with the functional monomer prior to the polymerization and template removal. However, the phenomenon of a material's "memory" provided by the "footprint" of the chemical entity was first observed on silica-based materials nearly a century ago. Through the years, molecular imprinting technology has attracted the attention of many scientists. Different forms of molecularly imprinted materials, even on the nanoscale, were elaborated, predominantly using organic polymers to induce the "memory". This field has expanded quickly in recent years, providing versatile tools for the separation or detection of numerous chemical compounds or even macromolecules. In this review, we would like to emphasize the role of the molecular imprinting process in the formation of highly specific siloxane-based nanomaterials. The distinct chemistry of siloxanes provides an opportunity for the facile functionalization of the surfaces of nanomaterials, enabling us to introduce additional properties and providing a way for vast applications such as detectors or separators. It also allows for catalyzing chemical reactions providing microreactors to facilitate organic synthesis. Finally, it determines the properties of siloxanes such as biocompatibility, which opens the way to applications in drug delivery and nanomedicine. Thus, a brief outlook on the chemistry of siloxanes prior to the discussion of the current state of the art of siloxane-based imprinted nanomaterials will be provided. Those aspects will be presented in the context of practical applications in various areas of chemistry and medicine. Finally, a brief outlook of future perspectives for the field will be pointed out.

Rhodium-Catalyzed Dynamic Kinetic Asymmetric Hydrosilylation to Access Silicon-Stereogenic Center

Strategies on the construction of enantiomerically pure silicon-stereogenic silanes generally relies on desymmetrization of prochiral and symmetric substrates. However, dynamic kinetic asymmetric transformations of organosilicon compounds have remained underdeveloped and unforeseen owing to a lack of an effective method for deracemization of the static silicon stereocenters. Here we report the first Rh-catalyzed dynamic kinetic asymmetric intramolecular hydrosilylation (DyKAH) with "silicon-centered" racemic hydrosilanes that enables the facile preparation of silicon-stereogenic benzosiloles in good yields and excellent enantioselectivities. The special rhodium catalyst controlled by non-diastereopure-type mixed phosphine-phosphoramidite ligand with axial chirality and multiple stereocenters can induce enantioselectivity efficiently in this novel DyKAH reaction. Density functional theory (DFT) calculations suggest that the amide moiety in chiral ligand plays important role in facilitating the S_N 2 substitution of chloride ion to realize the chiral inversion of silicon center.

Dehydrocoupling Polymerization: Poly(silylether) Synthesis by Using an Iron β-Diketiminate Catalyst

We describe the iron-catalyzed polymerizations of diol and silane monomers to obtain fourteen different poly(silylether) products with number average molecular weights (Mn ) up to 36.3 kDa. The polymerization reactions developed in this study are operationally simple and applicable to 1° and 2° silane monomer substrates and a range of benzylic and aliphatic diol substrates as well as one polyol example. The polymers were characterized by IR spectroscopy, DSC and TGA and, where solubility allowed, 1 H, 13 C{1 H}, 29 Si{1 H} NMR spectroscopies, GPC and MALDI-TOF were also employed. The materials obtained displayed low Tg values (-70.6 to 19.1 °C) and were stable upon heating up to T-5%,Ar 421.6 °C. A trend in T-5%,Ar was observed whereby use of a 2° silane leads to higher T-5%,Ar compared to those obtained using a 1° silane. Reaction monitoring was undertaken by in situ gas evolution studies coupled with GPC analysis to follow the progression of chain-length growth which confirmed a condensation polymerization-type mechanism.

Silicon-nitrogen bond formation via dealkynative coupling of amines with bis(trimethylsilyl)acetylene mediated by KHMDS

The catalytic synthesis of silylamines mediated by s- and p-block catalysts is largely underdeveloped. Herein, commercially available potassium bis(trimethylsilyl)amide serves as an efficient alternative to transition metal complexes. N-H/Si-C dealkynative coupling was achieved by means of user-friendly main-group catalysis with ample substrate scope and high chemoselectivity.

Formation of nanostructured silicas through the fluoride catalysed self-polymerization of Q-type functional silica cages

Octa(dimethylsiloxy)silica cages (Q₈M₈^H) undergo rapid self-polymerization in the presence of a fluoride catalyst to form complex 3D porous structural network materials with specific surface areas up to 650 m² g^-1. This establishes a new method to form bio-derived high inorganic content soft silicas with potential applications in filtration, carbon capture, catalysis, or hydrogen source.

Reduction of N2O with hydrosilanes catalysed by RuSNS nanoparticles

A series of RuSNS nanoparticles, prepared by decomposition of Ru(COD)(COT) with H₂ in the presence of an SNS ligand, have been found to catalyse the reduction of the greenhouse gas N₂O to N₂ employing different hydrosilanes.

Silane promoted glycosylation and its applications for synthesis of sugar compounds and active pharmaceutical ingredients (APIs)

Silane promoted glycosylation and its applications for preparation of active pharmaceutical ingredients.

Siloxane-containing derivatives of benzoic acid: chemical transformation of the carboxyl group

This research presents a scalable method for chemical transformation of Si-containing derivatives of benzoic acid to a wide range of corresponding esters, thioesters, amides, etc. Some of them form HOF-like structures in the crystalline state.