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Selenium incorporation is a widely used strategy for achieving high mobility semiconductors for a variety of organic optoelectronic devices, but it has received less attention in organic electrochemical transistors (OECTs). Herein, we developed two polythiophene derivatives (Pg2T-S and Pg2T-SVS) containing different selenophene loadings, as well as a selenophene-free polythiophene (Pg2T-T) as the control. The effects of selenium substitution/incorporation on the optical, electrical, electrochemical, and OECT performance of polythiophene-based organic mixed ionic–electronic conductors are systematically investigated. We discovered that introduction of selenium increases quinoidal character and crystallinity, which is beneficial for charge transport but makes ion penetration more challenging. In contrast, increasing selenium content increases the dipole moment and ion–polymer interaction, which is helpful for ion doping and volumetric capacitance but detrimental to charge transport. Therefore, appropriate selenium content should be evaluated to balance the trade-off between charge transfer and volumetric capacitance. As a result, Pg2T-S with moderate selenium loading achieves a high μC* of 332.7 F cm−1 V−1 s−1 with increased μ of 1.31 cm2 V−1 s−1 and maintains the C* value of 254 F cm−3. It also has a quick τon/τoff of 10.76 ms/5.90 ms and outstanding operational stability. Further introducing selenium boosts the dipole moment and ion–polymer interaction and therefore increased C*, but suppressed μ, resulting in inefficient μC*. We indicated that systematic balancing of the effects of selenium incorporation is necessary for the development of mixed ionic–electronic conductors for high-performance OECTs. [ABSTRACT FROM AUTHOR]

Transition-metal-catalyzed reductive coupling reactions have been considered as a powerful tool to convert two electrophiles into value-added products. Numerous related reports have shown the fascinating potential. Mechanistic studies, especially theoretical studies, can provide important implications for the design of novel reductive coupling reactions. In this review, we summarize the representative advancements in theoretical studies on transition-metal-catalyzed reductive coupling reactions and systematically elaborate the mechanisms for the key steps of reductive coupling reactions. The activation modes of electrophiles and the deep insights of selectivity generation are mechanistically discussed. In addition, the mechanism of the reduction of high-oxidation-state catalysts and further construction of new chemical bonds are also described in detail. [ABSTRACT FROM AUTHOR]

Herein, we report a Pd-catalyzed regiospecific cycloaromatization of β-bromoenal and vinyl borate esters to synthesize m-alkenyl substituted benzaldehydes. This allows the construction of complex molecules from simple materials, which may be useful in the search for new optical materials. [ABSTRACT FROM AUTHOR]

Supported nano-silver (nano-Ag) catalysts have been widely used in heterogeneous catalysis. However, their poor thermal stability restricts their practical application. In order to solve this issue, we report a novel supported nano-Ag catalyst by employing the strong metal–support interactions (SMSIs) between the Ag nanoparticles (NPs) and hydroxyapatite (HAP). The home-made HAP was prepared via a facile hydrothermal or co-precipitation method, which can effectively anchor small size Ag NPs prepared by an impregnation method. Taking advantage of the unique confinement effect with different morphology HAP and the protective effect of hydroxyl groups on the HAP surface, highly dispersed Ag NPs were obtained. These Ag/HAP catalysts were characterized by XRD, N2 physical adsorption, SEM, TEM and XPS. It was found that the particle size of Ag NPs was strongly related to the morphology and structure of the HAP supports, and it significantly affects the CO oxidation performance. The nano-Ag catalyst with a lamellar nanosheet structure HAP has the highest content of Ag0, and 100% CO conversion can be achieved at 160 °C. The Ag NPs loaded on HAP nanosheets with a large specific surface area showing excellent CO oxidation activity demonstrating that the strategy may open a new way to design and develop highly dispersed nano-Ag catalysts for heterogeneous catalysis. [ABSTRACT FROM AUTHOR]

Formic acid (HCO2H) is widely used in various chemical processes, applied in fuel cells, and considered as a promising candidate for hydrogen storage. Currently, industrial production of HCO2H mainly depends on fossil resources using multiple processes. Practical HCO2H production from renewable resources for the potential industrial application is rare. Herein, we demonstrate practical dimethyl sulfoxide (DMSO) (1 v%)-promoted selective hydrolysis–oxidation of lignocellulosic biomass to HCO2H, which is demonstrated by recycling experiments of near 10 gram-scale wheat straw with constantly high efficiencies. Mechanism studies on the major unit of lignocellulosic biomass, glucose, disclose that the high selectivity and yield of HCO2H are attributed to the hydrogen bonds of DMSO with generated gem-diol groups from the reaction of glucose, or the intermediates of glycolaldehyde and glyoxal with water (H2O). The formation of hydrogen bonds is indicated both by DFT calculations and IR experiments. [ABSTRACT FROM AUTHOR]

Enynones are powerful synthons for constructing furan derivatives in the presence of transition metal catalysts. Unlike the conventional intramolecular nucleophilic attack with the activation of coinage metals, we propose that enynones undergo an oxidative cyclization process with a Pd(0) species. The full catalytic cycle involves oxidative cyclization, isocyanide insertion, and reductive elimination, which was supported by DFT calculations. Geometric and electronic analyses confirmed the oxidative cyclization process, which proceeds VIA a Pd(II) intermediate. [ABSTRACT FROM AUTHOR]

Density functional theory (DFT) calculation has been used to reveal the mechanism of the Pd-catalyzed disilylation reaction of aryl halides. The DFT calculations indicate that the reaction starts with the oxidative addition of the C–I bond to the Pd(0) catalyst. Concerted metalation–deprotonation (CMD) can then generate a five-membered palladacycle. Insertion of Pd(II) into the Si–Si bond in disilane followed by two sequential steps of reductive eliminations yields the disilylation product and regenerates the Pd(0) catalyst. According to the NPA charge analysis along the reaction coordinates, the formal oxidative addition of the Si–Si bond to palladium could be considered as the insertion of palladium into the Si–Si bond. However, the conventional oxidative addition of the C–I bond to palladium is exactly an oxidation process with the electron transfer from the palladium atom to the C–I bond. Therefore, electron rich Pd(0) is beneficial for the oxidation process, and Pd(II) prone to acquire electrons is beneficial for the insertion process. [ABSTRACT FROM AUTHOR]

In the presence of multiple electrophiles, the reaction sequence is a critical mechanistic problem. Here, we report a theoretical study on the mechanism of phosphine-catalyzed [8+2] cycloaddition of heptafulvenes and allenoate. DFT calculations showed that electrophilicity is the barrier for nucleophilic attack, while it fails in the prediction of priority. [ABSTRACT FROM AUTHOR]

A systemical computational study was performed to explore the mechanism and origin of selectivities on the organocatalytic arylation of azonaphthalenes with α-chloroaldehydes. The calculated results reveal that the nucleophilicity of active sites and the hydrogen bonds respectively regulate chemo- and stereoselectivities and, for the first time, N-heterocyclic carbene (NHC) can act as a multiple functional base (MFB) catalyst in one system. [ABSTRACT FROM AUTHOR]

The mechanism of copper-mediated coupling reactions has aroused widespread interest, and it has been found to not be as simple as initially thought. In this article, we give an overview of the recent advances in this field. Notably, we focus on whether the presence of CuIII is adopted in the catalytic cycle. Attention is paid to the key CuII species, which can be generated by radical-type or single electron transfer (SET) oxidation of CuI. The CuII species can be oxidized to CuIII by SET or using a nucleophilic radical for further reductive elimination. Alternatively, radical-type substitution or bimetallic reductive elimination can avoid formation of CuIII, and coupling reactions can also be achieved. [ABSTRACT FROM AUTHOR]

A mixture of pathways including the use of catalyst was proposed for a dirhodium-mediated triazole activation–cycloaddition. This proposal was supported by the results of density functional theory (DFT) calculations, and was indicated to involve a non-catalyzed cleavage of the triazole N–N bond followed by a dirhodium-assisted denitrogenation. Electron-deficient carboxylates were found to be favourable for the rate-determining denitrogenation step. [ABSTRACT FROM AUTHOR]

The mechanistic investigation of copper-catalysed transformations has been an important and fundamental task. Herein, we report via XAS and EPR spectroscopy that the sodium bis(trimethylsilyl)amide could reduce Cu(II) to a Cu(I) species serving as an electron donor. XAS spectroscopy demonstrates that the newly formed Cu(I) species is the Cu[N(TMS)2]2Na ate complex, in which the nitrogen atoms coordinate with copper linearly. [ABSTRACT FROM AUTHOR]

Here, we report the development of novel PET radiotracer ([11C]CW22) of BET proteins. In vivo imaging results in rodents and nonhuman primates (NHP) demonstrate that [11C]CW22 has excellent brain uptake, good specificity, good selectivity, suitable metabolism, appropriate kinetics and distribution in the brain. Our studies demonstrated that [11C]CW22 exhibits ideal properties as a PET imaging probe of BET proteins for further validation. [ABSTRACT FROM AUTHOR]

Theoretical calculations have been performed to investigate the mechanism and stereoselectivity of rhodium-catalysed intramolecular [3+2] cycloaddition for construction of a substituted hexahydropentalene complex. A new C–C bond cleavage mechanism, retro-Aldol-type, is proposed and verified for this Rh-catalysed [3+2] cycloaddition reaction. [ABSTRACT FROM AUTHOR]

Ru-Catalyzed aromatic C–H bond activation and functionalization have emerged as important topics because they have resulted in remarkable progress in organic synthesis. Both experimental and theoretical studies of their mechanisms are important for the design of new synthetic methodologies. In this review, a mechanistic view of the Ru-mediated C–H bond cleavage step is first given to reveal the C–H bond activation modes, including oxidative addition, metathesis and base-assisted deprotonation. In this process, directing groups play an important role in determining the reactivity of the C–H bond. The C–H bond activation generally leads to the formation of a Ru–C bond, which is further functionalized in the subsequent steps. The mechanisms of Ru-catalyzed arylation, alkylation, and alkenylation of arenes are summarized, and these transformations can be categorized into cross-coupling with electrophiles or oxidative coupling with nucleophiles. In addition, the mechanism of ortho-ruthenation-enabled remote C–H bond functionalization is also discussed. [ABSTRACT FROM AUTHOR]

Herein, we report an efficient and practical strategy for the synthesis of five types of imidazo[2,1-a]isoquinolines via Cp*RhIII-catalyzed [4+2] annulation of 2-arylimidazoles and α-diazoketoesters, whose structural and substituted diversity at 5- or 6-position can be precisely controlled by the α-diazoketoester coupling partners. Compared with previous reports, in this study, we merged two attractive C–C cleavage strategies (retro-Claisen and decarboxylation) into the classical C–H functionalization/condensation process by choosing appropriate ester groups (–COOEt, –COOtBu or –COOiPr) or inexpensive additives (HOAc or KOAc). Moreover, the synthetic efficacies of these methods were demonstrated by the concise synthesis of several bioactive compounds and the late-stage modification of representative drugs. [ABSTRACT FROM AUTHOR]

Density functional theory (DFT) calculation has been used to reveal the mechanism of Pd-catalyzed disilylation of carbene, which is a pathway to construct disilylmethane derivatives. The DFT calculations indicate that the reaction starts with carbenation of a Pd(0) catalyst. Oxidative addition of disilane can then generate a carbene-coordinated disilylpalladium intermediate. Carbene insertion into the Pd–Si bond followed by reductive elimination gives the disilylmethane product and regenerates the Pd(0) catalyst with the formation of two C–Si bonds. The rate-determining step of this reaction is the carbenation step. The computational results show that the phosphine ligand is unfavorable for this type of reaction because of its high dissociation energy. In this type of reaction, a smaller substrate is favorable for the oxidative addition step because the weaker steric repulsion leads to a lower activation free energy of the oxidative addition step. The computational results also reveal that the reactivity of digermane and distannane is higher than that of disilane, which can be attributed to their low bond dissociation energies. [ABSTRACT FROM AUTHOR]

Encapsulation and surface chemical modification are methodologies to enhance the properties of fullerenes for various applications. Herein, density functional theory calculations are performed to study the Diels–Alder (DA) reactivity of anion encapsulated C60, including [X@C60]− (X = F, Cl, Br, or I), [S@C60]2−, and [N@C60]3−. Computational results reveal that encapsulated Cl−, Br−, I−, or S2− anions are located close to the center of the C60 molecule; however, encapsulated F− is displaced from the center. Encapsulated N3− bonds to the inner surface of the carbon cage, which leads to a negative charge transfer to the C60. In [N@C60]3−, C–C bonds near to the encapsulated N atom are more reactive. Our calculations reveal that encapsulated halogen or S anions decrease the DA reactivity because of the stronger closed-shell repulsion of the encapsulated anion. However, encapsulated N3− increases the DA reactivity. The higher distortion energy of the halogen- or S2−-anion encapsulated C60 leads to lower reactivity of the 6-5 bond. Opposite regioselectivity of the DA reaction with [N@C60]3− is attributed to distortion energy of the cyclopentadiene (CPD) moiety. The asymmetrical transition state geometry leads to a lower distortion energy of the CPD moiety. [ABSTRACT FROM AUTHOR]

In this work, we develop an oxidation-induced C–H functionalization strategy, which not only leads to a new avenue to build C–N bonds, but also leads to different site-selectivity compared with “classic directing-groups”. The high selectivity of our new catalytic system originates from the heterogeneous electron-density distribution of the radical cation species which are induced by single electron transfer between the aromatics and oxidant-Cu(ii) species. [ABSTRACT FROM AUTHOR]

In this study, we broke through the directing function of the amide group. The coordination interaction between metal and directing-group enhanced the reactivity of the substrate. Using this strategy, we realized the selective amination of 8-aminoquinolines at the C5 position via employing azoles as the source of amine. Various kinds of 8-aminoquinolines and different substituted azoles were compatible to afford the corresponding C–N coupling products. [ABSTRACT FROM AUTHOR]

Enantioselective alkynylation of cyclic N-sulfonyl α-ketiminoesters with terminal alkynes was developed by using an Ni(ClO4)2/(R)-DTBM-Segphos complex as a catalyst. A range of propargylic amides bearing quaternary stereocenters were afforded in excellent enantioselectivities (up to 97% ee). Theoretical studies revealed that this reaction proceeded via a Friedel–Crafts-type reaction pathway. [ABSTRACT FROM AUTHOR]

While activation of BAX is required for initiating mitochondria-mediated apoptosis, the underlying mechanisms remain unsettled. We studied conformations of BAX protein using pressure- and temperature-resolved ESR techniques and obtained the thermodynamic properties of the conformations. We show that inactive BAX is structurally heterogeneous and exists in equilibrium between two major populations of the conformations, UM and UM′, of which the former is thermodynamically favored at room temperature. An increase in the population of UM′, induced by either pressure or point mutations of BAX, renders BAX susceptible to oligomerization, which leads to cell death. This study uncovers the biological significance of BAX conformations and shows that the pro-apoptotic activity of BAX can be triggered by altering the equilibrium between the two states. It suggests that therapeutic intervention may focus on shifting the balance in the conformational heterogeneity. [ABSTRACT FROM AUTHOR]

Pd-catalyzed selective amine-oriented C8–H bond functionalization/N-dealkylative carbonylation of naphthyl amines has been achieved. The amine group from dealkylation is proposed to be the directing group for promoting this process. It represents a straightforward and easy method to access various biologically important benzo[cd]indol-2(1H)-one derivatives. [ABSTRACT FROM AUTHOR]

The investigation into the active copper(i) catalysts from copper(ii) precursors has become a fundamental and important task in copper catalysis. In this work, we demonstrate that the tBuO− anion serves not only as a base but also as a mediator to promote the reduction of Cu(ii) to Cu(i) in copper catalysis. XAFS and EPR spectroscopy evidence the [Cu(OtBu)3]− ate complex as the key intermediate which undergoes homolytic-cleavage of the O–Cu(ii) bond generating [Cu(OtBu)2]− ate complex. [ABSTRACT FROM AUTHOR]