Organosilicon Reagents Research Articles

Coherent Solution-phase Synthesis of a Germanium-Graphitic Nanocomposite and Its Evaluation for Lithium-Ion Battery Anodes: Non-innocent Role of the Mashima Reagent.

The organosilicon reagent 1,4-bis-(trimethylsilyl)-1,4-diaza-2,5-cyclohexadiene 2 plays the binary role of the simultaneous reduction of GeCl2 .dioxane 1 dissolved in oleylamine to Ge nanocrystals and the formation of graphitic sheets under hot-injection conditions. This colloidal synthetic route to germanium nanocrystals embedded on N-doped graphitic nanosheets Ge/NG is free of any template or catalyst and involves easy purification techniques. The Ge/NG/C obtained after carbonization has been explored for anode performance in lithium-ion batteries. Both Ge/NG and Ge/NG/C can be obtained on a gram scale and are bottleable under argon for months.

Heteroaromatic N-Oxides in Asymmetric Catalysis: A Review.

An increasing interest in the synthesis and use of optically active pyridine N-oxides as chiral controllers for asymmetric reactions has been observed in the last few years. Chiral heteroaromatic N-oxides can work as powerful electron-pair donors, providing suitable electronic environments in the transition state formed within the reaction. The nucleophilicity of the oxygen atom in N-oxides, coupled with a high affinity of silicon to oxygen, represent ideal properties for the development of synthetic methodology based on nucleophilic activation of organosilicon reagents. The application of chiral N-oxides as efficient organocatalysts in allylation, propargylation, allenylation, and ring-opening of meso-epoxides, as well as chiral ligands for metal complexes catalyzing Michael addition or nitroaldol reaction, can also be found in the literature. This review deals with stereoselective applications of N-oxides, and how the differentiating properties are correlated with their structure. It contains more recent results, covering approximately the last ten years. All the reported examples have been divided into five classes, according to the chirality elements present in their basic molecular frameworks.

Organosilicon-Mediated Organic Synthesis (SiMOS): A Personal Account

The organosilicon-mediated organic synthesis (SiMOS) has attracted much attention over the recent decades. However, the use of organosilicon reagents with novel catalytic strategies remains to be explored. This Account summarizes our group’s progress mainly based on the application of a wide variety of organosilicon reagents, including allylic silanes, trifluoromethyl silane, acylsilanes, chlorosilanes, hydrosilanes, trimethylsilyldiazomethane, trimethylsiloxyfuran, silanols, α-trimethylsilylmethylacetate, and trimethylsilylcyanide, in catalysis and organic reactions. These transformations were proved to be alternative procedures for the construction of structurally diverse compounds.1 Introduction2 The Exploration of New Reactivity of Organosilicon Reagent in Organic Synthesis2.1 Allylic Silanes2.2 Trifluomethylsilane (TMSCF3)2.3 Acylsilanes2.4 Chlorosilanes and Hydrosilanes2.5 Trimethylsilyldiazomethane (TMSD)2.6 Trimethylsiloxyfuran2.7 Silanols2.8 Trimethylsilylcyanide (TMSCN)3 Conclusion and Perspective

Reaction of Nitrogen‐Radicals with Organometallics Under Ni‐Catalysis: N‐Arylations and Amino‐Functionalization Cascades

AbstractHerein, we report a strategy for the generation of nitrogen‐radicals by ground‐state single electron transfer with organyl–NiI species. Depending on the philicity of the N‐radical, two types of processes have been developed. In the case of nucleophilic aminyl radicals direct N‐arylation with aryl organozinc, organoboron, and organosilicon reagents was achieved. In the case of electrophilic amidyl radicals, cascade processes involving intramolecular cyclization, followed by reaction with both aryl and alkyl organometallics have been developed. The N‐cyclization–alkylation cascade introduces a novel retrosynthetic disconnection for the assembly of substituted lactams and pyrrolidines with its potential demonstrated in the short total synthesis of four venom alkaloids.

Reaction of Nitrogen-Radicals with Organometallics Under Ni-Catalysis: N-Arylations and Amino-Functionalization Cascades.

Herein, we report a strategy for the generation of nitrogen‐radicals by ground‐state single electron transfer with organyl–NiI species. Depending on the philicity of the N‐radical, two types of processes have been developed. In the case of nucleophilic aminyl radicals direct N‐arylation with aryl organozinc, organoboron, and organosilicon reagents was achieved. In the case of electrophilic amidyl radicals, cascade processes involving intramolecular cyclization, followed by reaction with both aryl and alkyl organometallics have been developed. The N‐cyclization–alkylation cascade introduces a novel retrosynthetic disconnection for the assembly of substituted lactams and pyrrolidines with its potential demonstrated in the short total synthesis of four venom alkaloids.

Transition metal-catalyzed hydrosilylation of polybutadiene – The effect of substituents at silicon on efficiency of silylfunctionalization process

Herein we present the results of our studies on the hydrosilylation of polybutadiene with alkyl, aryl and alkoxysilanes in the presence of platinum and rhodium complexes. In order to select the most efficient catalytic system, which, under optimal conditions, would smoothly promote incorporation of the above-mentioned organosilicon modifiers into polybutadienes of various structures via hydrosilylation, the real-time in-situ FT-IR spectroscopy was used. The silyl-functionalized polymeric products were characterized by NMR analysis and gel permeation chromatography (GPC). It was demonstrated that the stereo-electronic properties of substituents directly bonded to the HSi moiety play a crucial role in formation of desired products, as well as affect the time required for total conversion of organosilicon reagents. Partially modified polymers containing pendant alkoxy groups can be applied as additives to rubber compounds to enhance dispersion of inorganic particles in the polymer matrix, as well as to promote formation of organic-inorganic hybrid materials.

Activation of O2 by Organosilicon Reagents Yields Quantitative Amounts of H2O2 or (Me3Si)2O2 for Efficient O‐Transfer Reactions

AbstractMolecular oxygen is kinetically inert and rarely used as a primary oxidant for low temperature selective oxygenation reactions. Here, we show that O2 is converted into H2O2 in almost quantitative yields (98 %) at ambient temperature and atmospheric pressure in the presence of bis(trimethylsilyl)‐1,4‐cyclohexadiene 1. Similarly, the reaction of O2 with dihydro‐bis(trimethylsilyl) viologen 2 and pyrazine 3 yields bis(trimethylsilyl) peroxide (BTSP) in excellent yields (up to 99 %) at low temperature. Both processes demonstrate that readily available organosilicon reagents enable chemistry typically observed with mono‐oxygenase co‐enzymes, such as FADH2 and FMNH2, in biological systems, or at higher pressure via the industrial anthraquinone process. This efficient synthesis of H2O2 and BTSP directly from O2 is particularly attractive for the preparation of the corresponding O‐17 and O‐18 labeled reagents without the need of large excess amounts of O2. These are showcased in O‐atom transfer reactions to various organic or inorganic substrates, in a two‐step one‐pot process, making the rapid and on‐demand synthesis of large libraries of O‐labeled compounds readily possible.

Pd-Catalyzed Vinylation of Aryl Halides with Inexpensive Organosilicon Reagents Under Mild Conditions.

Pd-catalyzed Hiyama vinylation reaction of non-activated aryl chlorides and bromides under mild conditions was developed. The use of efficient vinyl donors and electron-rich sterically hindered phosphine ligands was critical for the success of the reaction. The products of this transformation can be used for Am/Cm separation, an important challenge in nuclear fuel reprocessing. The substituent effect on Am/Cm separating selectivity was also achieved, which could contribute to the development of new chromatographic materials for the separation of Am and Cm.

Arylation of hydrocarbons enabled by organosilicon reagents and weakly coordinating anions.

Over the past 80 years, phenyl cation intermediates have been implicated in a variety of C-H arylation reactions. Although these examples have inspired several theoretical and mechanistic studies, aryl cation equivalents have received limited attention in organic methodology. Their high-energy, promiscuous reactivity profiles have hampered applications in selective intermolecular processes. We report a reaction design that overcomes these challenges. Specifically, we found that β-silicon-stabilized aryl cation equivalents, generated via silylium-mediated fluoride activation, undergo insertion into sp3 and sp2 C-H bonds. This reaction manifold provides a framework for the catalytic arylation of hydrocarbons, including simple alkanes such as methane. This process uses low loadings of Earth-abundant initiators (1 to 5 mole percent) and occurs under mild conditions (30° to 100°C).

Rhodium(iii)-catalyzed directed C–H benzylation and allylation of indoles with organosilicon reagents

Rhodium(iii)-catalyzed C2-benzylation and allylation of indoles with organosilicon reagents via chelation-assisted C–H activation has been developed.

Stable Mono- and Dinuclear Organosilver Complexes

A series of mononuclear and dinuclear complexes of silver(I), supported by an N-heterocyclic carbene and bound to sp3-, sp2-, and sp-hybridized carbanions, has been synthesized. Synthetic routes include transmetalation from organozinc, organomagnesium, and organosilicon reagents, as well as the deprotonation of a terminal alkyne. These complexes exhibit greater thermal stability than typical organosilver reagents, permitting spectroscopic and structural characterization. The carbanion-bridged disilver cations feature three-center, two-electron bonding with short Ag···Ag distances. A mononuclear vinylsilver complex releases organic homocoupling products upon thermal decomposition, while mononuclear alkylsilver complexes exhibit nucleophilic behavior, for example, inserting CO2 to form silver carboxylates.

Recent Advances in Transition-Metal-Catalyzed Synthetic Transformations of Organosilicon Reagents

Organosilicon compounds act as a nucleophile upon activation by an appropriate base and behave in a manner similar to main-group organometallic reagents. In the last decades, structurally divergent organosilicon reagents are available and have become more employed for synthetic transformation with the aid of transition-metal complexes, because organosilicon compounds are in general superior to other organometallic compounds in view of stability, solubility, nontoxicity, and easy-handling. Particularly, cross-coupling of organosilicon reagents with organic halides or pseudohalides has been considered to be a useful tool for constructing the carbon frameworks of various target molecules such as pharmaceuticals and π-conjugated functional materials. Perfluoroalkylsilicon compounds such as CF3SiEt3 have found use as reagents for the metal-catalyzed introduction of perfluoroalkyl groups into many substrates. In addition, functionalized organosilicon reagents are readily accessible by catalytic approach startin...

ChemInform Abstract: Copper‐Catalyzed Cross‐Couplings of Organometallic Reagents with and without Assistance from PN Ligands

AbstractReview: [42 refs.

Copper-Catalyzed Cross-Couplings of Organometallic Reagents with and without Assistance from PN Ligands

In this article, recent developments of copper-catalyzed cross-couplings are discussed. Critical results that demonstrate the effectiveness of copper catalysts, ligated by P,N-ligands, for cross-coupling reactions are presented to showcase the potential emergence of copper as an alternative to palladium. The observation that the reaction of heteroaryl coupling partners also proceeds under ‘ligand-free’ conditions holds great promise for developing copper catalysis as a complementary system to palladium catalysis in areas in which palladium either performs unsatisfactorily or requires custom-designed ligands. 1 Introduction 2 Rationale for the Use of Hybrid Bidentate Ligands 3 Coupling with Organosilicon Reagents 4 Coupling with Organoboron Reagents 5 Coupling with Organoindium Reagents 6 General Catalytic Cycle 7 Conclusion and Perspectives

ChemInform Abstract: Palladium‐Catalyzed Direct Arylation of Polyfluoroarenes with Organosilicon Reagents.

The palladium-catalyzed direct arylation of polyfluoroarenes with organosilicon reagents was achieved by establishing general reaction conditions. This protocol was compatible with a broad range of functional groups and offered the desired products in moderate to good yields.

ChemInform Abstract: Mild Rh(III)‐Catalyzed Direct C—H Bond Arylation of (Hetero)Arenes with Arylsilanes in Aqueous Media.

AbstractA rhodium catalyzed regioselective C‐H bond activation of indoles, pyrroles, and benzenes bearing a directing group is demonstrated allowing direct regioselective arylation with different organosilicon reagents.

Palladium‐Catalyzed Direct Arylation of Polyfluoroarenes with Organosilicon Reagents

AbstractThe palladium‐catalyzed direct arylation of polyfluoroarenes with organosilicon reagents was achieved by establishing general reaction conditions. This protocol was compatible with a broad range of functional groups and offered the desired products in moderate to good yields.

Syntheses of Aldol Products and Cyanohydrins from Carboxylic Acids Using Hydrosilanes, Organosilicon Reagents, and Indium Triiodide Catalyst

Abstract Carboxylic acids were applied to an indium triiodide-catalyzed reductive aldol reaction and a reductive cyanation in order to produce aldol adducts and cyanohydrins, respectively, in which the separate addition of two kinds of hydrosilanes was crucial in combination with either ketene silyl acetals or silyl cyanides.

From the chemistry of epoxy-sugar nucleosides to the discovery of anti-HIV agent 4'-ethynylstavudine-Festinavir.

Branched sugar nucleosides have attracted much attention due to their biological activities. We have demonstrated that epoxysugar nucleosides serve as versatile precursor for the stereo-defined synthesis of these nucleoside derivatives on the basis of its ring opening with organoaluminum or organosilicon reagents. In this review article, novel methods for the synthesis of nucleoside analogues branched at the 1' and 4'-position will be described. During this study, we could discover an anti-HIV agent, 4'-ethynylstavudine (Festinavir). Festinavir showed more potent anti-HIV activity than the parent compound stavudine (d4T). Other significant properties of Festinavir are as follows: 1) much less toxic to various cells and also to mitochondorial DNA synthesis than d4T, 2) better substrate for human thymidine kinase than d4T, 3) resistant not only to chemical glycosidic bond cleavage but also to catabolism by thymidine phosphorylase, 4) the activity improves in the presence of a major mutation, K103N, associated with resistance to non-nucleoside reverse transcriptase inhibitors. Detailed profile of the antiviral activities, biology and pharmacology of Festinavir are also described.

Acylsilanes: valuable organosilicon reagents in organic synthesis

Acylsilanes are a fascinating class of compounds that display a number of distinctive chemical and physical properties. The unique reactivity pattern of the acylsilane functional group [R-C(O)Si] makes them an increasingly attractive moiety in modern organic synthesis, and as such, they have been utilised in a diverse range of transformations. This review provides an overview of the recent advances in the synthesis and application of acylsilanes in organic chemistry, with a particular focus on the progress made in the last two decades.