In this tutorial review, we will summarize our recent efforts in transition metal-catalyzed oxidative coupling
via
C-H functionalization of aromatic, benzylic and allylic C-H bonds. Related works ...from other laboratories will be cited where suitable, aiming to give the readers a flavor of this field. Special emphasis is placed on the reaction design and development.
Our recent developments in transition metal-catalyzed oxidative coupling
via
C-H functionalization of aromatic, benzylic and allylic C-H bonds is summarized.
Conspectus Transition-metal catalyzed cross-coupling reactions have emerged as a powerful tool for constructing biaryl compounds. Aryl halides and aryl metallic reagents (typically prepared from aryl ...halides) are used as coupling partners. It would be desirable to replace either aryl halide or aryl metallic reagents used in cross-couplings reactions with more readily available surrogates. Oxidative dehydrogenative cross-coupling between two different “inert” aryl C–H bonds represents an ideal system that would revolutionize cross-coupling chemistry. Furthermore, cross-coupling reactions might be improved by developing new catalytic protocols based on cheap transition-metal catalysts or even transition-metal-free systems to decrease costs and avoid the use of heavy metal and noble transition metals. It would be desirable to promote both catalytic systems and replace either or both coupling partners. We have used different strategies to improve cross-coupling reactions for constructing biaryls, which we categorized into four groups as follows. First, we focused on developing methodologies to be applied to easily produced and naturally abundant arenol-based electrophiles in cross-coupling via C–O activation. We have extended coupling partners to aryl carboxylates and arenols. Direct application of arenes as surrogates for organohalides and organometallic reagents avoids the tedious preparation of these reagents from arenes and considerably reduces the cost of starting materials. We have also explored cross-coupling reactions of arenes with various organometallic reagents, such as arylboronic acids, arylsilanes, and aryl Grignard reagents. Second, we summarize oxidative cross-coupling reactions based on C–H activation with aryl metallic reagents. On the basis of the reactivity patterns of different organometallic reagents, we adapted different catalytic systems to achieve effective cross-coupling reactions. Third, we improved a well-developed cross-coupling between arenes and organohalides through a strategy of replacing one coupling partner and using a new catalytic system. We have applied earth-abundant transition metals, such as Fe, and Co, and even developed transition-metal-free catalytic systems. Finally, our ultimate goal is to construct biaryls by cross dehydrogenative arylation between two different arenes. Owing to the structural similarity of both arenes, in particular two substituted benzenes, the greatest challenges are not only achieving regio- and chemo-selective C–H activation reactions but also matching both the reactivities and selectivities of both substrates to avoid homocouplings of either arene. Through our efforts, we have developed and applied four different strategies by introducing directing groups, controlling electronic and steric properties, and using dual directing strategies. We hope our studies will stimulate interest and new thinking on cross-couplings reactions for building carbon–carbon bonds from readily available and inexpensive chemicals from basic petroleum chemistry and nature.
The cleavage of C-C bonds has been a great challenge owing to their thermodynamic and kinetic stability. To date, the progress made in this area has mainly relied on the reaction of small rings, ...which is driven by releasing ring strain. Encouragingly, more and more examples of the cleavage of non-strained C-C bonds have been reported. This review provides a comprehensive overview of the transition-metal-catalyzed C-C bond activation of relatively stable and unstrained molecules that involves the formation of organometallic intermediates. In the first section we focus on the C-C bond activation achieved through β-carbon elimination, and in the second section the oxidative addition of the C-C bond to low-valent metal is summarized in detail.
In this review, the transition-metal-catalyzed C-C bond activation of relatively stable and unstrained molecules involving organometallic intermediates is discussed in detail.
Electrical control of atom‐thick van der Waals (vdW) ferromagnets is a key toward future magnetoelectric nanodevices; however, state‐of‐the‐art control approaches are volatile. In this work, ...introducing ferroelectric switching as an aided layer is demonstrated to be an effective approach toward achieving nonvolatile electrical control of 2D ferromagnets. For example, when a ferromagnetic monolayer CrI3 and ferroelectric MXene Sc2CO2 come together into multiferroic heterostructures, CrI3 is controlled by polarized states P↑ and P↓ of Sc2CO2. P↑ Sc2CO2 does not change the semiconducting nature of CrI3, but surprisingly P↓ Sc2CO2 makes CrI3 half‐metallic. Nonvolatility of the electrical switching between two oppositely ferroelectric polarized states, therefore, indirectly enables nonvolatile electrical control of CrI3 between ferromagnetic semiconductor and half‐metal. The heterointerface‐induced half‐metallicity in CrI3 is intrinsic without resorting to any chemical functionalization or external physical modification, which is rather beneficial to the practical application. This work paves the way for nonvolatile electrical control of 2D vdW ferromagnets and applications of CrI3 in half‐metal‐based nanospintronics.
In CrI3/MXene Sc2CO2 multiferroic heterostructures, CrI3 is coupled with polarized states P↑ and P↓ of Sc2CO2. P↑ Sc2CO2 does not change the semiconducting nature of CrI3, but P↓ Sc2CO2 makes CrI3 half‐metallic. Thus, nonvolatile electrical control of 2D ferromagnets can be achieved by introducing ferroelectric switching, and heterointerface engineering is an effective method to modulate 2D ferromagnets into half‐metals.
Transition metal (TM)‐based bimetallic spinel oxides can efficiently activate peroxymonosulfate (PMS) presumably attributed to enhanced electron transfer between TMs, but the existing model cannot ...fully explain the efficient TM redox cycling. Here, we discover a critical role of TM−O covalency in governing the intrinsic catalytic activity of Co3−xMnxO4 spinel oxides. Experimental and theoretical analysis reveals that the Co sites significantly raises the Mn valence and enlarges Mn−O covalency in octahedral configuration, thereby lowering the charge transfer energy to favor MnOh–PMS interaction. With appropriate MnIV/MnIII ratio to balance PMS adsorption and MnIV reduction, the Co1.1Mn1.9O4 exhibits remarkable catalytic activities for PMS activation and pollutant degradation, outperforming all the reported TM spinel oxides. The improved understandings on the origins of spinel oxides activity for PMS activation may inspire the development of more active and robust metal oxide catalysts.
The Mn−O covalency was enlarged by the Co sites mainly in the octahedral configuration, which results in a decreased charge transfer energy to favor Mn–PMS interaction and enhance MnIV reduction to boost PMS activation activity of Co‐Mn spinel oxides.
Digital technology can have significant effects on language education. This effect makes the English language teachers teach the subjects better to the students and also improves the quality of ...teachers' education.
The purpose of this research is to evaluate the digital literacy of English language teachers and to investigate the difference between digital literacy and their gender, education level, and teaching experience. To conduct the study, the researcher invited 2,110 EFL teachers to fill out the Teachers' Digital Literacy questionnaire. The researchers used SPPS and AMOS in analyzing the obtained data.
The results of the study indicated that teachers' contextual factors do not influence their digital literacy skills. In addition, the study showed that teachers' attitudes toward technology, their skill to use technology, and their access to technology can significantly affect teachers' digital literacy.
Implications of the study are further discussed in this paper.
Recently, the rapid advance of vehicular networks has led to the emergence of diverse delay-sensitive vehicular applications such as automatic driving, auto navigation. Note that existing ...resource-constrained vehicles cannot adequately meet these demands on low / ultra-low latency. By offloading parts of the vehicles' compute-intensive tasks to the edge servers in proximity, mobile edge computing is envisioned as a promising paradigm, giving rise to the vehicular edge computing networks (VECNs). However, most existing works on task offloading in VECNs did not take the load balancing of the computation resources at the edge servers into account. To address these issues and given the high dynamics of vehicular networks, we introduce fiber-wireless (FiWi) technology to enhance VECNs, due to its advantages on centralized network management and supporting multiple communication techniques. Aiming to minimize the processing delay of the vehicles' computation tasks, we propose a software-defined networking (SDN) based load-balancing task offloading scheme in FiWi enhanced VECNs, where SDN is introduced to provide supports for the centralized network and vehicle information management. Extensive analysis and numerical results corroborate that our proposed load-balancing scheme can achieve superior performance on processing delay reduction by utilizing the edge servers' computation resources more efficiently.
This paper provides a comprehensive survey of techniques for testing machine learning systems; Machine Learning Testing (ML testing) research. It covers 144 papers on testing properties (e.g., ...correctness, robustness, and fairness), testing components (e.g., the data, learning program, and framework), testing workflow (e.g., test generation and test evaluation), and application scenarios (e.g., autonomous driving, machine translation). The paper also analyses trends concerning datasets, research trends, and research focus, concluding with research challenges and promising research directions in ML testing.
Iron overload triggers the ferroptosis in the heart following ischemia/reperfusion (I/R) and transferrin receptor 1 (TfR1) charges the cellular iron uptake. Bioinformatics analysis shows that the ...three molecules of ubiquitin-specific protease 7 (USP7), p53 and TfR1 form a unique pathway of USP7/p53/TfR1. This study aims to explore whether USP7/p53/TfR1 pathway promotes ferroptosis in rat hearts suffered I/R and the underlying mechanisms. The SD rat hearts were subjected to 1 h-ischemia plus 3 h-reperfusion, showing myocardial injury (increase in creatine kinase release, infarct size, myocardial fiber loss and disarray) and up-regulation of USP7, p53 and TfR1 concomitant with an increase of ferroptosis (reflecting by accumulation of iron and lipid peroxidation while decrease of glutathione peroxidase activity). Inhibition of USP7 activated p53 via suppressing deubiquitination, which led to down-regulation of TfR1, accompanied by the decreased ferroptosis and myocardial I/R injury. Next, H9c2 cells underwent hypoxia/reoxygenation (H/R) in vitro to mimic the myocardial I/R model in vivo. Consistent with the results in vivo, inhibition or knockdown of USP7 reduced the H/R injury (decrease of LDH release and necrosis) and enhanced the ubiquitination of p53 along with the decreased levels of p53 and TfR1 as well as the attenuated ferroptosis (manifesting as the decreased iron content and lipid peroxidation while the increased GPX activity). Knockdown of TfR1 inhibited H/R-induced ferroptosis without p53 deubiquitination. Based on these observations, we conclude that a novel pathway of USP7/p53/TfR1 has been identified in the I/R-treated rat hearts, where up-regulation of USP7promotes ferrptosis via activation of the p53/TfR1 pathway.
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•The protein levels of USP7, p53 and TfR1 are all elevated in the I/R-treated rat hearts.•Suppression of USP7 mitigate the myocardial I/R injury via reduction of ferroptosis.•USP7 promotes ferroptosis in the I/R-treated hearts via activation of p53/TfR1 pathway.
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