Modular approach to silicon-bridged biaryls: palladium-catalyzed intramolecular coupling of 2-(arylsilyl)aryl triflates

Novel thiomaleimide-based fluorescent probe with aggregation-induced emission for detecting H2S

It has been well established that Hydrogen sulfide (H2S) is involved in various pathophysiological processes. Therefore, accurate monitoring H2S levels in vitro or vivo is of great significance in biological systems. Herein, we firstly developed a thiomaleimide-based compound MAL-1 bearing aggregation-induced emission characteristic for selective response toward H2S due to its nucleophilicity. The proposed sensor presented prominent sensitivity and selectivity with low detection limit of 75 nM and pseudo-first-order reaction rate constant of 9.65 × 10-2 s-1, as well as low cytotoxicity which works well in recognizing H2S in real samples and visualizing H2S in living cells. Thus, it could be concluded that the novel thiomaleimide-based probe would be a promising tool for assessing intracellular H2S levels.

Palladium-Catalyzed Synthesis of Substituted Phenanthrenes via a C-H Annulation of 2-Biaryl Triflates with Alkynes

A new palladium-catalyzed efficient method for the synthesis of substituted 9,10-phenanthrenes from 2-biaryl triflates with alkynes has been developed. This method provides a great opportunity to prepare various symmetrical and unsymmetrical phenanthrene derivatives in good yields. This reaction proceeds via C-OTf bond cleavage and alkyne insertion followed by C-H annulation.

Solid-State Emissive Pillar[6]arene Derivative Having Alternate Methylene and Nitrogen Bridges

Macrocyclic arenes show conformational adaptability, which allows host-guest complexations with the size-matched guest molecules. However, their emission properties are often poor in the solid states due to the self-absorption. Herein, we newly synthesized pillar[6]arene derivatives having alternate methylene and nitrogen bridging structures. Solvatochromic study reveals that the nitrogen-embedding into the cyclic structures can strengthen the intramolecular charge transfer (CT) nature compared to that of the linear nitrogen-bridged precursor. Owing to the large Stokes shift in the solid state, one of the nitrogen-embedded pillar[6]arenes shows high absolute photoluminescence quantum yield (ΦPL=0.36). Furthermore, it displays a turn-off sensing ability toward nitrobenzene (NB) vapor; a fluorescence quenching is observed when exposed to the NB vapor. From the structural analysis before and after the exposure of NB vapor, the amorphous nitrogen-embedded pillar[6]arene efficiently co-crystallize with NB and formed non-emissive intermolecular CT complexes with NB.

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.

Dehydrogenative Annulation of Silylated 1H-Indoles with Alkynes via Silyl Migration

We investigated the dehydrogenative annulation of silylated 1H-indole derivatives with alkynes to synthesize a silole-fused indole. The addition of the in situ generated silylium ion to alkynes was followed by the sila-Friedel-Crafts reaction via silyl migration, realizing regioselective dehydrogenative annulation controlled by the steric bulkiness of a base. The optical properties of the obtained siloloindoles indicated fluorescence of which the intensity depends on the location of the fused silole.

1,2-Palladasilacyclobutene: The Missing Link in the Pd-Catalyzed Annulation of Alkynes for the Silirene-to-Silole Transformation

The palladium-catalyzed annulation reaction of alkynes enables an attractive approach to siloles. Their access from silirenes and terminal alkynes proved rather general, involving reactive intermediates that have remained elusive to date. Starting from 1,2-bis(3-thienyl)silirene as a source of photochromic siloles, the mechanism of the annulation reaction has been revisited, and palladasilacyclobutenes resulting from the activation of the silirene could be isolated and thoroughly characterized (NMR, X-ray, and DFT). Their role as reactive intermediates and their fate in the course of the reaction were also studied in situ. In combination with in-depth DFT calculations, a clearer picture of the mechanism and the reactive key species is disclosed.

A theoretical study of the ligand-controlled palladium-catalysed regiodivergent synthesis of dibenzosilepin derivatives

Palladium-catalysed ligand-controlled 1,n-palladium migration of silicon-tethering substrates provides a regiodivergent synthesis strategy for constructing silicon-bridged π-conjugated compounds possessing a 6,6-fused or a 5,7-fused scaffold. Density functional theory (DFT) calculations were carried out to elucidate the detailed mechanism of this 1,n-palladium migration involving syn- or anti-carbopalladation. The computational results suggest that alkyne insertion is the regioselectivity-determining step. Upon catalysis without the BINAP ligand, the 1,2-insertion of an alkyne into the Pd-aryl bond leads to the formation of 6,6-fused benzophenanthrosiline, which is more favorable than the 2,1-insertion of alkyne by 4.2 kcal mol^-1. The selective formation of 5,7-fused benzofluorenosilepins via the 2,1-alkyne insertion is facilitated by the BINAP ligand. The 1,2-alkyne insertion with the BINAP ligand is disfavoured due to the steric repulsion between the phenyl group of the substrate and the naphthalene group of the BINAP ligand. The 2,1-alkyne insertion with the BINAP ligand orients the ligand away from the phenyl group of the substrate, which can avoid steric repulsion.

Enantioselective C–H Functionalization toward Silicon-Stereogenic Silanes

In recent years, transition-metal-catalyzed enantioselective C–H bond functionalization has emerged as a powerful and attractive synthetic approach to access silicon-stereogenic centers, which provides impetus for the innovation of chiral organosilicon chemistry. This short review summarizes recent advances in the construction of silicon-stereogenic silanes via transition-metal-catalyzed enantioselective C–H functionalization. We endeavor to highlight the great potential of this methodology and hope that this review will shed light on new perspectives and inspire further research in this emerging area.

1 Introduction

2 Enantioselective C–H Functionalization Induced by Oxidative Addition­ of an Aryl-OTf Bond

3 Enantioselective C–H Functionalization Induced by Oxidative Addition­ of a Silacyclobutane

4 Directing-Group-Assisted Enantioselective C–H Functionalization

5 Enantioselective Dehydrogenative C–H/Si–H Coupling

5.1 Enantioselective C(sp2)–H Silylation

5.2 Enantioselective C(sp3)–H Silylation

6 Summary and Outlook

Synthesis of Ring-Locked Tetracyclic Dithienocyclopentapyrans and Dibenzocyclopentapyran via 1,5-Hydride Shift and Copper-Catalyzed C-O Bond Formation for Nonfullerene Acceptors

We discovered a unique synthetic route to construct 2H-pyran-containing tetracyclic dithienocyclopentapyran (DTCP) and dibenzocyclopentapyran (DBCP) architectures. The synthesis involves an acid-induced dehydration cyclization followed by a [1,5] hydride-shift isomerization to form a cyclopentanone moiety which was converted to the pyran-embedded tetracyclic products by a CuI-catalyzed intramolecular C-O bond formation in good yield. DTCP was used as a building block to prepare an acceptor-donor-acceptor (A-D-A) type n-type material DTCP-BC leading to a solar cell efficiency of 9.32%.

Enantioselective construction of six- and seven-membered triorgano-substituted silicon-stereogenic heterocycles

The exploitation of chirality at silicon in asymmetric catalysis is one of the most intriguing and challenging tasks in synthetic chemistry. In particular, construction of enantioenriched mediem-sized silicon-stereogenic heterocycles is highly attractive, given the increasing demand for the synthesis of novel functional-materials-oriented silicon-bridged compounds. Here, we report a rhodium-catalyzed enantioselective construction of six- and seven-membered triorgano-substituted silicon-stereogenic heterocycles. This process undergoes a direct dehydrogenative C-H silylation, giving access to a wide range of triorgano-substituted silicon-stereogenic heterocycles in good to excellent yields and enantioselectivities, that significantly enlarge the chemical space of the silicon-centered chiral molecules. Further elaboration of the chiral monohydrosilane product delivers various corresponding tetraorgano-substituted silicon-stereogenic heterocycles without the loss of enantiopurity. These silicon-bridged heterocycles exhibit bright blue fluorescence, which would have potential application prospects in organic optoelectronic materials.

Catalytic Asymmetric trans-Selective Hydrosilylation of Bisalkynes to Access AIE and CPL-Active Silicon-Stereogenic Benzosiloles

Chirality widely exists in a diverse array of biologically active molecules and life forms, and the catalytic constructions of chiral molecules have triggered a heightened interest in the fields of chemistry and materials and pharmaceutical sciences. However, the synthesis of silicon-stereogenic organosilicon compounds is generally recognized as a much more difficult task than that of carbon-stereogenic centers because of no abundant organosilicon-based chiral sources in nature. Herein, we reported a highly enantioselective rhodium-catalyzed trans-selective hydrosilylation of silicon-tethered bisalkynes to access chiral benzosiloles bearing a silicon-stereogenic center. This protocol featured with chiral Ar-BINMOL-Phos bearing hydrogen-bond donors as a privileged P-ligand for catalytic asymmetric hydrosilylation that is operationally simple and has 100% atom-economy with good functional group tolerability as well as high enantioselectivity (up to >99:1 er). Benefiting from the trans-selective hydrosilylation with the aid of Rh/Ar-BINMOL-Phos-based asymmetric catalysis, the Si-stereogenic benzosiloles exhibited pronounced aggregation-induced emission (AIE) and circularly polarized luminescence (CPL) activity.

Palladium-Catalyzed Synthesis of Benzophenanthrosilines by C-H/C-H Coupling through 1,4-Palladium Migration/Alkene Stereoisomerization

A new and efficient synthesis of 8H-benzo[e]phenanthro[1,10-bc]silines from 2-((2-(arylethynyl)aryl)silyl)aryl triflates under palladium catalysis has been developed. The reaction mechanism was experimentally investigated and a catalytic cycle involving C-H/C-H coupling through a new mode of 1,4-palladium migration with concomitant alkene stereoisomerization is proposed.

Advances in Synthesis of π-Extended Benzosilole Derivatives and Their Analogs

Benzosiloles and their π-extended derivatives are present in many important advanced materials due to their excellent physical properties. Especially, they have found many potential applications in the development of novel electronic materials such as OLEDs, semiconductors and solar cells. In this review, we have summarized several main approaches to construct (di)benzosilole derivatives and (benzo)siloles fused to aromatic five- and six-membered heterocycles.

Preparation of Polyfunctional Biaryl Derivatives by Cyclolanthanation of 2-Bromobiaryls and Heterocyclic Analogues Using nBu2 LaCl⋅4 LiCl

Various aryl- and heteroaryl-substituted 2-bromobiaryls are converted to cyclometalated lanthanum intermediates by reaction with nBu2 LaCl⋅4 LiCl. These resulting lanthanum heterocycles are key intermediates for the facile preparation of functionalized 2,2'-diiodobiaryls, silafluorenes, fluoren-9-ones, phenanthrenes, and their related heterocyclic analogues. X-ray absorption fine structure (XAFS) spectroscopy was used to rationalize the proposed structures of the involved organolanthanum species.

Regioselective Functionalization of 9,9-Dimethyl-9-silafluorenes by Borylation, Bromination, and Nitration

Despite the utility of 9-silafluorenes as functional materials and as building blocks, methods for efficient functionalization of their backbone are rare, probably because of the presence of easily cleavable C-Si bonds. Although controlling the regioselectivity of iridium-catalyzed direct borylation of C-H bonds is difficult, we found that bromination and nitration of 2-methoxy-9-silafluorene under mild conditions occurred predominantly at the electron-rich position. The resulting product having methoxy and bromo groups can be utilized as a building block for the synthesis of unsymmetrically substituted 9-silafluorene-containing π-conjugated molecules.

Lewis acid-catalyzed synthesis of silafluorene derivatives from biphenyls and dihydrosilanes via a double sila-Friedel–Crafts reaction

The synthesis of silafluorene derivatives from aminobiphenyl compounds and dihydrosilanes via a double sila-Friedel–Crafts reaction using a borane catalyst has been achieved.

The anionic Fries rearrangement: a convenient route to ortho-functionalized aromatics

The scope and mechanism of anionic (hetero-) Fries rearrangements are summarized for various migrating groups and arenes, including applications and computational studies.

Dimethylformamide-stabilised palladium nanoclusters catalysed coupling reactions of aryl halides with hydrosilanes/disilanes

N,N-Dimethylformamide-stabilised Pd nanocluster (NC) catalysed cross-coupling reactions of hydrosilane/disilane have been investigated. In this reaction, the coupling reaction proceeds without ligands with low catalyst loading. N,N-Dimethylacetamide is a crucial solvent in these reactions. The solvent effect was considered by various techniques, such as transmission electron microscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis. The Pd NCs can be recycled five times under both hydrosilane and disilane reaction conditions.

A highly efficient and reusable Pd NCs catalyst system for silylation of aryl halides was developed.

Azasilicon-bridged heterocyclic arylamines: syntheses, structures and photophysical properties

The lithium κ¹-enamides undergo intermolecular cyclization reactions affording bis-azasilicon-bridged heterocyclic arylamines, which were hydrolysed to the saturated 1,4-diimines, and alternatively proceeded a redox reaction to afford the conjugated 1,4-diimines.

Intramolecular Chain Hydrosilylation of Alkynylphenylsilanes Using a Silyl Cation as a Chain Carrier

Diorganyl[2-(trimethylsilylethynyl)phenyl]silanes 1a-c and methyl-substituted phenylsilanes 1d and 1e were treated with a small amount of trityl tetrakis(pentafluorophenyl)borate (TPFPB) as an initiator in benzene to afford the corresponding benzosiloles (2a-e) in moderate to good yields. However, no reaction was observed for the reaction using [2-(1-hexynyl)phenyl]diisopropylsilane lf. The methyl substituent was tolerated under the reaction conditions and increased the yield of the corresponding benzosilole depending on the substitution position. From the result using 1f, the current reaction was found to require the trimethylsilyl group, which can stabilize intermediary alkenyl carbocations by the β-silyl effect. The current reaction can be considered an intramolecular chain hydrosilylation of alkynylarylsilanes involving silyl cations as chain carriers. Therefore, the silyl cations generated by hydride abstraction from hydrosilanes 1 with the trityl cation causes intramolecular electrophilic addition to the C-C triple bond to form ethenyl cations, which abstract a hydride from 1 to afford benzosiloles 2 with the regeneration of the silyl cations.

Catalytic Reductive ortho-C-H Silylation of Phenols with Traceless, Versatile Acetal Directing Groups and Synthetic Applications of Dioxasilines

A new, highly selective, bond functionalization strategy, achieved via relay of two transition metal catalysts and the use of traceless acetal directing groups, has been employed to provide facile formation of C-Si bonds and concomitant functionalization of a silicon group in a single vessel. Specifically, this approach involves the relay of Ir-catalyzed hydrosilylation of inexpensive and readily available phenyl acetates, exploiting disubstituted silyl synthons to afford silyl acetals and Rh-catalyzed ortho-C-H silylation to provide dioxasilines. A subsequent nucleophilic addition to silicon removes the acetal directing groups and directly provides unmasked phenol products and, thus, useful functional groups at silicon achieved in a single vessel. This traceless acetal directing group strategy for catalytic ortho-C-H silylation of phenols was also successfully applied to preparation of multisubstituted arenes. Remarkably, a new formal α-chloroacetyl directing group has been developed that allows catalytic reductive C-H silylation of sterically hindered phenols. In particular, this new method permits access to highly versatile and nicely differentiated 1,2,3-trisubstituted arenes that are difficult to access by other catalytic routes. In addition, the resulting dioxasilines can serve as chromatographically stable halosilane equivalents, which allow not only removal of acetal directing groups but also introduce useful functional groups leading to silicon-bridged biaryls. We demonstrated that this catalytic C-H bond silylation strategy has powerful synthetic potential by creating direct applications of dioxasilines to other important transformations, examples of which include aryne chemistry, Au-catalyzed direct arylation, sequential orthogonal cross-couplings, and late-stage silylation of phenolic bioactive molecules and BINOL scaffolds.