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1.
Heterocycles containing group 13 and 15 elements such as borazines are an integral part of organic, biomedical and materials chemistry. Surprisingly, heterocycles containing P and Al are rare. We have now utilized phosphaalumenes in reactions with alkynes, alkenes and conjugated double bond systems. With sterically demanding alkynes 1,2-phosphaalumetes were afforded, whereas the reaction with HCCH or HCCSiMe3 gave 1,4-phosphaaluminabarrelenes. Using styrene saturated 1,2-phosphaalumates were formed, which reacted further with additional styrene to give different regio-isomers of 1,4-aluminaphosphorinanes. Using ethylene, a 1,4-aluminaphosphorinane is obtained, while with 1,3-butadiene a bicyclic system containing an aluminacyclopentane and a phosphirane unit was synthesized. The experimental work is supported by theoretical studies to shed light on the mechanism governing the formation of these heterocycles.  相似文献   

2.
Single C−F transformations of aromatic trifluoromethyl compounds are challenging issues due to the strong C−F bond. We have recently developed selective methods for single C−F transformations such as allylation of o-hydrosilyl-substituted benzotrifluorides through the hydride abstraction with trityl cations. Single C−F thiolation and azidation of o-(hydrosilyl)benzotrifluorides were achieved using trityl sulfides and trityl azide catalyzed by Yb(OTf)3. Treatment of o-(hydrosilyl)benzotrifluorides with trityl chloride resulted in single C−F chlorination. The resulting fluorosilyl group served in further transformations including protonation, halogenation, and Hiyama cross-coupling with C−Si cleavage. We also synthesized benzyl fluorides by LiAlH4-reduction of the resulting fluorosilanes and further C−F transformations. These methods enabled us to prepare a broad range of organofluorines from simple benzotrifluorides through C−F and C−Si transformations.  相似文献   

3.
Single atom catalysts (SACs) have attracted much attention in recent years. As an essential group in SACs, M−X−C (X=nonmetallic element) materials have been demonstrated to be efficient in many reactions. However, identifying the active sites on M−X−C, especially under working conditions, is still challenging, which is crucial for chemists to further understand the mechanism underlying the reaction and better design proper SACs for specific reactions. Herein, the types and characterization of M−X−C are comprehensively summarized and discussed in this review. In addition to the basic information above, the challenges and opportunities remaining in this field will be also proposed to present a perspective to the research on the next step.  相似文献   

4.
The direct C−H functionalization of 1,2-benzazaborines, especially asymmetric version, remains a great challenge. Here we report a palladium-catalyzed enantioselective C−H olefination and allylation reactions of 1,2-benzazaborines. This asymmetric approach is a kinetic resolution (KR), providing various C−B axially chiral 2-aryl-1,2-benzazaborines and 3-substituted 2-aryl-1,2-benzazaborines in generally high yields with excellent enantioselectivities (selectivity (S) factor up to 354). The synthetic potential of this reaction is showcased by late-stage modification of complex molecules, scale-up reaction, and applications.  相似文献   

5.
In this study, we revealed the significance of chemical bonding for the photochemically induced mechanism of 2-phenyl tetrazole derivatives generating nitrile imines. The correlated electron localization function shows that the formation of imine nitrile involves two key bond events: (i) the heterolytic C−N breakage taking place in the T1 state and (ii) the homolytic N−N rupture occurring in the T2 excited state. In particular, a cation-radical specie results from the C−N cleavage, whereas the N−N rupture creates a biradical resonant form of imine nitrile. Additionally, we noticed that the substantial pair delocalization of the C−C-N bonded structure could play a significant role in the conversion of the biradical imine nitrile into both the propargylic and allenic forms via the T1→S0 deactivation.  相似文献   

6.
《中国化学快报》2023,34(1):107743
Three eudesmanolide sesquiterpene-phenol hybrids, atramacronoids A?C (1?3), featuring an unusual 6/6/5/5/6 skeleton furnished by forming an unexpected C-8?C-16 linkage, were obtained from the rhizomes of Atractylodes macrocephala. Their structures and absolute configurations were elucidated by spectroscopic data analysis, chemical calculations, combined with X-ray diffractions. The plausible biosynthetic pathways for compounds 1?3 are proposed. Surprisingly, compound 1 exhibited cytotoxicity against SGC-7901 cells by inducing cells apoptosis, which might relate to the promotion of synthesis of neutrophil elastase.  相似文献   

7.
《Chemical physics letters》1999,291(5-6):348-354
Electronic structures for mono- and dianionic species of two promising C36 fullerene isomers, 14 and 15, are investigated by means of the hybrid Hartree–Fock (HF)/density functional (DF) method. Structural deformations, charge distributions, and spin densities upon one- or two-electron reduction are explained in light of the lowest unoccupied molecular orbitals (LUMOs) of each neutral isomer. First electron affinities for the neutral isomers 14 and 15 are predicted to be 2.3 and 2.5 eV, respectively, facilitating n-type doping for C36 solids. The degrees of local aromaticity of the isomers 14 and 15 tend to decrease with reduction in contrast with C60.  相似文献   

8.
Highly selective divergent coupling reactions of benzocyclobutenones and indoles, in which the chemoselectivity is controlled by catalysts, are reported herein. The substrates undergo C2(indole)–C8(benzocyclobutenone) coupling to produce benzylated indoles and benzo[b]carbazoles in the Ni- and Ru-catalyzed reactions. A completely different selectivity pattern C2(indole)–C2(benzocyclobutenone) coupling to form arylated indoles is observed in the Rh-catalyzed reaction. Preliminary mechanistic studies suggest C−H and C−C activations in the reaction pathway. Synthetic utility of this protocol is demonstrated by the selective synthesis of three different types of carbazoles from the representative products.  相似文献   

9.
The reaction of fumaryl fluoride with the superacidic solutions XF/MF5 (X=H, D; M=As, Sb) results in the formation of the monoprotonated and diprotonated species, dependent on the stoichiometric ratio of the Lewis acid to fumaryl fluoride. The salts [C4H3F2O2]+[MF6] (M=As, Sb) and [C4H2X2F2O2]2+([MF6])2 (X=H, D; M=As, Sb) are the first examples with a protonated acyl fluoride moiety. They were characterized by low-temperature vibrational spectroscopy. Low-temperature NMR spectroscopy and single-crystal X-ray structure analyses were carried out for [C4H3F2O2]+[SbF6] as well as for [C4H4F2O2]2+([MF6])2 (M=As, Sb). The experimental results are discussed together with quantum chemical calculations of the cations [C4H4F2O2 ⋅ 2 HF]2+ and [C4H3F2O2 ⋅ HF]+ at the B3LYP/aug-cc-pVTZ level of theory. In addition, electrostatic potential (ESP) maps combined with natural population analysis (NPA) charges were calculated in order to investigate the electron distribution and the charge-related properties of the diprotonated species. The C−F bond lengths in the protonated dication are considerably reduced on account of the +R effect.  相似文献   

10.
Homogeneous gold (Au) complexes have demonstrated tremendous utility in modern organic chemistry; however, their application for the synthesis of polymers remains rare. Herein, we demonstrate the first catalytic application of Au complexes toward the polycondensation of alkyne-containing comonomers and heteroarene nucleophiles. Polymerization occurs through successive intermolecular hydroarylation reactions to produce high molecular weight aromatic copolymers with 1,1-disubstituted alkene backbone linkages. Clear correlations between the rate and degree of polymerization (DP) were established based on catalyst structure and counterion pairing, thus enabling polymerization reactions that proceeded with remarkable efficiency, high reactivity, and exceptional DPs. The reactivity is broad in scope, enabling the copolymerization of highly functionalized aromatic and aliphatic monomers. These results highlight the untapped utility of Au catalysis in providing access to new macromolecular constructs.  相似文献   

11.
l -threonine aldolase (LTA) catalyzes C−C bond synthesis with moderate diastereoselectivity. In this study, with LTA from Cellulosilyticum sp (CpLTA) as an object, a mutability landscape was first constructed by performing saturation mutagenesis at substrate access tunnel amino acids. The combinatorial active-site saturation test/iterative saturation mutation (CAST/ISM) strategy was then used to tune diastereoselectivity. As a result, the diastereoselectivity of mutant H305L/Y8H/V143R was improved from 37.2 %syn to 99.4 %syn. Furthermore, the diastereoselectivity of mutant H305Y/Y8I/W307E was inverted to 97.2 %anti. Based on insight provided by molecular dynamics simulations and coevolution analysis, the Prelog rule was employed to illustrate the diastereoselectivity regulation mechanism of LTA, holding that the asymmetric formation of the C−C bond was caused by electrons attacking the carbonyl carbon atom of the substrate aldehyde from the re or si face. The study would be useful to expand LTA applications and guide engineering of other C−C bond-forming enzymes.  相似文献   

12.
《Analytical letters》2012,45(9):2051-2058
Abstract

The present paper reports a new chemiluminescence system, i.e, acetone-H2O2?C10?, which can be catalyzed by iodide ion (I?). Based on this catalysis, a new chemiluminescence method for the determination of trace iodide ion is proposed. the optimum conditions are reported in this note. the detection limit is 2 × 10?11 g/ml I?, the linear dynamic range is 4 × 10?10 g/ml to 3 × 10?7 g/ml I?, and the variation coefficient at an iodide concentration of 5 × 10?9 g/ml I? (n=10) is 4.6%. the method has been satisfactorily applied to the determination of trace iodide ion in water.  相似文献   

13.
Anilines are potentially high-value arylating agents, but are limited by the low reactivity of the strong C−N bond. We show that the reactive intermediate benzyne can be used to both activate anilines, and set-up an aryl transfer reaction in a single step. The reaction does not require any transition metal catalysts or stoichiometric organometallics, and establishes a metal-free route to valuable biaryl products by functionalizing the aniline C−N bond.  相似文献   

14.
Phase equilibria and critical phenomena in the lithium nitrate-water-acetonitrile ternary system were studied by a visual polythermal method within the range of ?20 to 50°C. In this ternary system, the constituent liquid binary system is characterized by phase separation with an upper critical solution temperature. It was found that the ternary system undergoes phase separation at temperatures below 0.7°C. In the phase diagram within the range of ?1.1 to 0.7°C, a closed phase separation region with two critical points was revealed. The temperature of the formation of the critical tie line of the monotectic state the solid phase of which is the crystalline hydrate LiNO3 · 3H2O was determined (?18.7°C). Depending on the concentration, lithium nitrate has both salting-in and salting-out effect on aqueous acetonitrile mixtures. The plotted isothermal sections of the temperature-concentration prism of the system at fifteen temperatures showed the pattern of the topological transformation of its phase diagram with varying temperature.  相似文献   

15.
During the post-certification stability monitoring of the certified reference material (CRM) BCR-551 (DNPH derivatives dissolved in acetonitrile), a decreased concentration of one of the analytes of this CRM, the DNPH-formaldehyde derivative, was detected in reference samples (stored at ?70 °C), while the concentration of normal “on-sale” samples (stored at ?20 °C) remained stable. This behaviour is contrary to the expectation of better stability at lower temperatures. Apparently, the DNPH-formaldehyde derivative reacts with dinitrophenylhydrazine (DNPH) remaining from the synthesis phase to produce two new substances. These substances have been identified as C13H12N8O8 (substance 1) and C20H16N12O12 (substance 2) which, based on their structure, are suggested to be produced consecutively: DNPH + DNPH-formaldehyde derivative → substance 1 and substance 1 + DNPH-formaldehyde derivative → substance 2. Since acetonitrile freezes at ?45 °C, reference samples are frozen at ?70 °C, while normal samples are still liquid at ?20 °C. We believe that this leads to a cryo-concentration of the solutes above the eutectic point and thus to an increased reaction rate in the reference samples. This case demonstrates that care should be taken when extrapolating stability results towards conditions that never have been tested, especially if phase transitions are involved, even at temperature as low as ?70 °C. Furthermore, a slower degradation rate at lower temperatures can be overcompensated by a higher concentration due to cryo-concentration above the eutectic temperature.  相似文献   

16.
《Chemical physics letters》1987,133(6):525-530
Large scale, vibrational CI calculations using a global ab initio potential energy surface are used to calculate multidimensional Franck-Condon overlaps from the ground vibrational state of HCO and DCO to all final bound and several quasibound vibrational states of HCO and DCO. The resulting Franck-Condon spectra are compared with recent experimental photoelectron spectra of HCO and DCO.  相似文献   

17.
Described herein is an effective and practical modular flow design for the meta-selective C−H arylation of anilines. The design consists of four continuous-flow modules (i.e., diaryliodonium salt synthesis, meta-selective C−H arylation, inline copper extraction, and aniline deprotection) which can be operated either individually or consecutively to provide direct access to meta-arylated anilines. With a total residence time of 1 hour, the desired product could be obtained in high yield and excellent purity without the need for column chromatography, and the residual copper content meets the standards for parenterally administered pharmaceutical substances.  相似文献   

18.
Aromatic organoboron compounds are highly valuable building blocks in organic chemistry. They were mainly synthesized through aromatic C−H and C−Het borylation, in which transition metal-catalysis dominate. In the past decade, with increasing attention to sustainable chemistry, numerous transition metal-free C−H and C−Het borylation transformations have been developed and emerged as efficient methods towards the synthesis of aromatic organoboron compounds. This account mainly focuses on recent advances in transition metal-free aromatic C−H, C−N, C−S, and C−O borylation transformations and provides insights to where further developments are required.  相似文献   

19.
Iron-nitrogen-carbon materials have been known as the most promising non-noble metal catalyst for proton-exchange membrane fuel cells (PEMFCs), but the genuine active sites for oxygen reduction reaction (ORR) are still arguable. Herein, by the thorough density functional theory investigations, we unravel that the planar Fe2N6 site exhibits excellent ORR catalytic activity over both FeN3 and FeN4 sites, and the potential-determining step is determined to be the *OH hydrogenation step with an overpotential of 0.415 V. The ORR activity of Fe2N6 site originates from the low spin magnetic moment (1.11 μB), which leads to high antibonding states and low d-band center of the Fe center, further leads to weak binding strength of *OH species. The density of FeN4 sites only has little influence on the ORR activity owing to the similar interaction between active site and intermediates in ORR. Our research sheds light on the activity origin of iron-nitrogen-carbon materials for ORR.  相似文献   

20.
Solar-driven CO2 hydrogenation into multi-carbon products is a highly desirable, but challenging reaction. The bottleneck of this reaction lies in the C−C coupling of C1 intermediates. Herein, we construct the C−C coupling centre for C1 intermediates via the in situ formation of Co0−Coδ+ interface double sites on MgAl2O4 (Co−CoOx/MAO). Our experimental and theoretical prediction results confirmed the effective adsorption and activation of CO2 by the Co0 site to produce C1 intermediates, while the introduction of the electron-deficient state of Coδ+ can effectively reduce the energy barrier of the key CHCH* intermediates. Consequently, Co−CoOx/MAO exhibited a high C2–4 hydrocarbons production rate of 1303 μmol g−1 h−1; the total organic carbon selectivity of C2–4 hydrocarbons is 62.5 % under light irradiation with a high ratio (≈11) of olefin to paraffin. This study provides a new approach toward the design of photocatalysts used for CO2 conversion into C2+ products.  相似文献   

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