Copper catalyzed regioselective and stereospecific coupling between aziridines and in situ generated pyridine Grignard reagents is reported. This method provides β-pyridylethylamines with diverse ...structures and functionalities from aziridines and iodopyridines. β-Pyridylethylamines are potential scaffolds for the synthesis of biologically active compounds often found in pharmaceuticals. The synthesis of challenging chiral dihydroazaindoles was also achieved through mild one-pot reaction conditions via aziridine opening followed by nucleophilic cyclization.
In this study, an insightful understanding of the correlations of the molecular level micro-defects structure and catalytic performance of palladium species supported on polyvinyl alcohol ...(Pd(II)@PVA) membrane heterogeneous catalyst have been studied with positronium probe and other structural characterization methods. The micro-defects size both in crystalline region (Dc) and amorphous region (Da) of PVA matrix increases gradually with the Pd species loading and membrane catalyst recycle times. As a result of a synergism of micro-defects enlargement caused by solvents swelling and highly thermal motions of macromolecular segments at high temperature, a number of instantaneously connected micro-defects channel rather than a single micro-defect in the real reaction state might provide enough open spaces for the coupling reactions. This catalysis mechanism from the aspect of molecular level micro-defects structure is powerfully supported by comparing the catalytic performances of a common Pd(II)@PVA membrane catalyst and a PVA layer sealed Pd(II)@PVA membrane catalyst applied in Heck reactions. As the recycle times increases, the compactness and regularity of PVA molecular chain segments stacking decreases obviously, which promotes the Pd leaching and causes gradually decrease in catalytic efficiency of the recycled Pd(II)@PVA membrane catalyst. The mechanical properties, morphology, crystalline behavior, and swelling properties of the Pd(II)@PVA membrane catalysts are also characterized and explained in view of the changes of molecular level micro-defects structure.
•Positronium probe is used in the characterization of molecular level micro-defects of Pd(II)@PVA catalyst.•A number of instantaneously connected micro-defects channel provides open spaces for the reactions.•The proposed catalysis mechanism in molecular level is powerfully supported by the catalytic performance assessments.
This paper focuses on improving tracking performance of totally uncoupled compliant micromanipulator based on robust control method of elliptical hysteresis model. The hysteresis model and hysteresis ...compensation model for proposed mechanism based on Piezoelectric transducer (PZT) are established by using elliptical model method. The values of elliptical hysteresis model parameters are identified by simulating method with different frequencies of control input. The uncertainty model is also established, the values of corresponding estimated parameters are conformed by experiment method. Based on the uncertainty model and elliptical hysteresis model, the robust tracking control method is presented and utilized to evaluate the tracking performance of proposed mechanism under inputting different tracking curves. The proposed method can accurately control the output displacement and improve tracking performance of this mechanism, which are validated and carried out by using experimental studies. Additionally, the coupling errors between two directions are kept within 0.14% and the tracking errors for different curves are within 2.5%.
A characterization of organophilic montmorillonite (OMMT) supports and organophilic montmorillonite supported palladium (Pd@OMMT) catalytic composites was carried out using positron annihilation ...lifetime spectroscopy (PALS) and X-ray diffraction (XRD). XRD method supplies the fundamental information on the interlayer spacing of OMMT. And PALS method supplies the complementary information on the free volume voids variations inside the interlayer space of OMMT, which is occupied with organic cations and Pd species. In PALS analyzing, the size of the channel-like free volume voids inside the interlayer space of OMMT are estimated by both cuboidal and cylindrical free volume voids models from o-Ps lifetime. The OMMT and Pd@OMMT composites show bigger interlayer spacing values (by XRD) but smaller free volume void size values (by PALS) than MMT. It should be due to the fact that the interlayer space becomes more crowded after organic modifier intercalation and Pd immobilization inside the interlayer space of MMT. The prepared Pd@OMMT catalytic composites show high activity and good recyclability in typical Heck coupling reactions. The correlations between the microstructure and catalytic performances of the organophilic montmorillonites supported palladium catalytic composites were discussed.
•A combined PALS and XRD thoroughly characterization of layered OMMT and Pd@OMMT catalytic composite was done.•Channel-like micro defects in the interlayer space of the layered OMMT were estimated by both cuboids and cylinders models.•PALS can effectively complement other techniques used in the microstructure characterization of catalytic materials.
Due to their unique properties, dihydroazaindoles are important fragments of active pharmaceutical ingredients and are of great interest in the pharmaceutical industry. In this manuscript, a scalable ...and economical process for the synthesis of a complex (R)-2-(4-fluorophenyl)-2-methyl-2,3-dihydro-1H-pyrrolo2,3-bpyridine-5-carboxylic acid ( R )-1 on multikilogram scale is described. The synthesis was advanced through a second-generation synthetic strategy that did not rely on chiral Supercritical Fluid Chromatography separation, which was the highest cost driver. Through systematic screening of chemical resolution, we found that compound ( R )-1 can be isolated with high (>99%) enantiomeric excess. Furthermore, the mother liquor from the first resolution process was recyclable to racemize the S-isomer into ( R )-1 and ( S ) - 1 mixtures, which could be used for an additional chemical resolution process. The precious palladium (Pd) complexes could be reduced from 20 mol % to 1 mol %, and the long lead time building blocks were safely prepared in-house. Advanced intermediates were efficiently synthesized by reducing isolation steps through one-pot process development. The regulatory starting material compound ( R )-1·HCl was isolated with a high purity profile after di-p-toluoyl-d-tartaric acid salt breaking and HCl salt formation.
The microstructure of poly (vinyl alcohol)/ montmorillonite (PVA/MMT) matrices and Pd@PVA/MMT catalytic composite was characterized by positron annihilation spectroscopy (PAS) and other techniques, ...such as high resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), thermo-gravimetric analysis (TGA), and X-ray photo electron spectroscopy (XPS). XRD and HR-TEM results showed that 20% was the saturation loading percentage of PVA intercalation into MMT. Ortho-positronium (o-Ps) annihilations were mainly distributed in the interlayer spacing of MMT and/or open spaces (free volume) of PVA. Below the saturation loading percentage of PVA (≤ 20%), it was found that the o-Ps annihilation lifetime became shorter after the intercalation of PVA chains into MMT layers. With further addition of PVA, the o-Ps annihilation lifetime became longer after the formation of exfoliated structure. The 20%-PVA/MMT matrix has been selected as the platform to further immobilize Pd specie for preparing novel 0.2%-Pd@20%-PVA/MMT catalytic composite. The effects of Pd immobilization on the microstructure of PVA/MMT matrices were also sensitively detected by PAS. The mean size of the micro-defects (from Tao-Eldrup model) increased from 0.28 nm (20%-PVA/MMT) to 0.29 nm (0.2%-Pd2+@20%-PVA/MMT or 0.2%-Pd0@20%-PVA/MMT), respectively. This increase in the size of the micro-defects of 20%-PVA/MMT matrix after Pd immobilization was mainly due to the replacement of the inter-molecular hydrogen bodings of PVA chains by the interactions formed between the PVA chains and Pd species. The prepared 0.2%-Pd0@20%-PVA/MMT catalytic composite showed excellent catalytic efficiency and recyclability in both Heck-type and Sonogashira-type coupling reactions. The correlations between the microstructure and performance of the 0.2%-Pd0@20%-PVA/MMT composite were thoroughly discussed.
•PAS is successfully used to characterize the micro-defects variation of Pd@PVA/MMT catalytic composites.•Along with other characterization results, a plausible positron annihilation model for Pd@PVA/MMT is proposed.•It is demonstrated the micro-defects of the composite can supply adequate spaces for the reactions.
As an important branch of multimedia content analysis, Surveillance Event Detection (SED) is still a quite challenging task due to high abstraction and complexity such as occlusions, cluttered ...backgrounds and viewpoint changes etc. To address the problem, we propose a unified SED detection framework which divides events into two categories, i.e., short-term events and long-duration events. The former can be represented as a kind of snapshots of static key-poses and embodies an inner-dependencies, while the latter contains complex interactions between pedestrians, and shows obvious inter-dependencies and temporal context. For short-term event, a novel cascade Convolutional Neural Network (CNN)–HsNet is first constructed to detect the pedestrian, and then the corresponding events are classified. For long-duration event, Dense Trajectory (DT) and Improved Dense Trajectory (IDT) are first applied to explore the temporal features of the events respectively, and subsequently, Fisher Vector (FV) coding is adopted to encode raw features and linear SVM classifiers are learned to predict. Finally, a heuristic fusion scheme is used to obtain the results. In addition, a new large-scale pedestrian dataset, named SED-PD, is built for evaluation. Comprehensive experiments on TRECVID SEDtest datasets demonstrate the effectiveness of proposed framework.
Polymeric carbon nitrides (PCNs) have emerged as promising heterogeneous photocatalysts for organic transformations as they are metal-free, inexpensive, and possess tunable bandgaps, with excellent ...chemical stability and photo-stability. However, current application of PCNs in organic synthesis is rather limited to several well-established materials, which limits the scope of reaction patterns and efficiency. We herein report the synthesis and fabrication of two PCN nanosheets by incorporating nanostructure construction, element doping, and vacancy engineering into one hybrid platform. The heteroatom doped PCN nanosheets with vacancies feature highly porous structures with extremely large substrate-catalyst interface areas and enhanced charge separation. The generated heterogeneous catalysts demonstrate impressive photoredox catalytic performances in a variety of organic transformations (e.g., defluoroborylation; 2+2 cycloaddition; C–N, C–S, C–O cross-couplings; and an unprecedented regioselective hydrosilylation), providing efficiencies comparable to reported optimized homogeneous catalysts and exceeding those with commonly utilized PCNs.
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Heteroatom doped polymeric carbon nitrides (PCNs) nanosheets with vacanciesNotable performance for various photoredox transformationsImproved photocatalytic efficiency compared to commonly utilized PCNsAvenue for rational design and development of heterogeneous PCN photocatalysts
Polymeric carbon nitrides (PCNs) are promising heterogeneous photocatalysts. Liu et al. synthesize heteroatom doped PCN nanosheets with vacancies that demonstrate competitive photoredox catalytic performances. The efficiencies are comparable to optimized homogeneous photocatalysts and exceed commonly utilized PCNs. This finding may provide new insights for the design of effective heterogeneous PCN photocatalysts.
The mesoporous phenol-formaldehyde resins (PFR) were synthesized using formaldehyde, phenol, F127 template as raw materials by high temperature hydrothermal method under different temperatures. ...Nitrogen doped mesoporous PFR were synthesized in the same way with another additional raw material HMTA. Two series of carbon materials PCs and PCNs were obtained after calcinating PFR at 700, 800, 900 °C. N2 adsorption analysis indicates that both the two kind of carbon materials have relatively large specific surface area (325–619 cm2/g for PCs and 431–580 cm2/g for PCNs). TEM and XRD analyses prove highly ordered mesoporous structure of the samples. Both the elemental analysis and IR results suggest a high carbon content and the abundant fused-ring structure of the test materials. The positron annihilation spectra show that the corresponding intensity I3 of the longest lifetime component τ3 is less than 2%, indicating that the π electrons in the fused rings with low ionization energy are capable of trapping positrons and inhibiting the formation of o-Ps.
•Two kind of PFR-based carbon materials were synthesized under different temperature.•N2 adsorption, TEM and XRD data indicate ordered mesoporous structure of the samples.•IR and elemental analysis data indicate the fused-ring structure of the materials.•The π-electrons in the fused rings with low ionization energy can quench positrons.•The formation of free and p-Ps annihilation increases, while that of o-Ps decreases.
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