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991.
Song Liu Hong Bin Yang Sung‐Fu Hung Jie Ding Weizheng Cai Linghui Liu Jiajian Gao Xuning Li Xinyi Ren Zhichong Kuang Yanqiang Huang Tao Zhang Bin Liu 《Angewandte Chemie (International ed. in English)》2020,59(2):798-803
Designing effective electrocatalysts for the carbon dioxide reduction reaction (CO2RR) is an appealing approach to tackling the challenges posed by rising CO2 levels and realizing a closed carbon cycle. However, fundamental understanding of the complicated CO2RR mechanism in CO2 electrocatalysis is still lacking because model systems are limited. We have designed a model nickel single‐atom catalyst (Ni SAC) with a uniform structure and well‐defined Ni‐N4 moiety on a conductive carbon support with which to explore the electrochemical CO2RR. Operando X‐ray absorption near‐edge structure spectroscopy, Raman spectroscopy, and near‐ambient X‐ray photoelectron spectroscopy, revealed that Ni+ in the Ni SAC was highly active for CO2 activation, and functioned as an authentic catalytically active site for the CO2RR. Furthermore, through combination with a kinetics study, the rate‐determining step of the CO2RR was determined to be *CO2?+H+→*COOH. This study tackles the four challenges faced by the CO2RR; namely, activity, selectivity, stability, and dynamics. 相似文献
992.
Max S. Coles Gina Quach Jonathon E. Beves Evan G. Moore 《Angewandte Chemie (International ed. in English)》2020,59(24):9522-9526
The development of photocatalytic reactions has provided many novel opportunities to expand the scope of synthetic organic chemistry. In parallel with progress towards uncovering new reactivity, there is consensus that efforts focused on providing detailed mechanistic insight in order to uncover underlying excited‐state reactions are essential to maximise formation of desired products. With this in mind, we have investigated the recently reported sensitization‐initiated electron transfer (SenI‐ET) reaction for the C?H arylation of activated aryl halides. Using a variety of techniques, and in particular nanosecond transient absorption spectroscopy, we are able to distinguish several characteristic signals from the excited‐state species involved in the reaction, and subsequent kinetic analysis under various conditions has facilitated a detailed insight into the likely reaction mechanism. 相似文献
993.
Huisgen's 1,3‐Dipolar Cycloadditions to Fulvenes Proceed via Ambimodal [6+4]/[4+2] Transition States
Fang Liu Yu Chen K. N. Houk 《Angewandte Chemie (International ed. in English)》2020,59(30):12412-12416
Huisgen's 1960 announcement of the concept of 1,3‐dipolar cycloadditions was published the year before Alder's study of the reaction of diazomethane and dimethylfulvene. The diazomethane reaction was studied again in 1970 by Houk et al. and shown to give a [6+4] adduct. Padwa's nitrile ylide cycloaddition to dimethylfulvene (1978) gave [6+4] and [4+2] adducts. We performed computational studies of these reactions with density functional theory (DFT) and show that they involve ambimodal [6+4]/[4+2] transition states that can lead to either type of cycloadduct from one transition state. We dedicate this paper to the extraordinary life and humanity of Rolf Huisgen, and to the undying influence of his discoveries on chemistry. 相似文献
994.
Martin Breugst Hans‐Ulrich Reissig 《Angewandte Chemie (International ed. in English)》2020,59(30):12293-12307
The concept of 1,3‐dipolar cycloadditions was presented by Rolf Huisgen 60 years ago. Previously unknown reactive intermediates, for example azomethine ylides, were introduced to organic chemistry and the (3+2) cycloadditions of 1,3‐dipoles to multiple‐bond systems (Huisgen reaction) developed into one of the most versatile synthetic methods in heterocyclic chemistry. In this Review, we present the history of this research area, highlight important older reports, and describe the evolution and further development of the concept. The most important mechanistic and synthetic results are discussed. Quantum‐mechanical calculations support the concerted mechanism always favored by R. Huisgen; however, in extreme cases intermediates may be involved. The impact of 1,3‐dipolar cycloadditions on the click chemistry concept of K. B. Sharpless will also be discussed. 相似文献
995.
Dr. Anna Fantinati Prof. Vinicio Zanirato Dr. Paolo Marchetti Prof. Claudio Trapella 《ChemistryOpen》2020,9(2):100-170
The aim of this review is to highlight the rich chemistry of α-haloamides originally mainly used to discover new C−N, C−O and C−S bond forming reactions, and later widely employed in C−C cross-coupling reactions with C(sp3), C(sp2) and C(sp) coupling partners. Radical-mediated transformations of α-haloamides bearing a suitable located unsaturated bond has proven to be a straightforward alternative to access diverse cyclic compounds by means of either radical initiators, transition metal redox catalysis or visible light photoredox catalysis. On the other hand, cycloadditions with α-halohydroxamate-based azaoxyallyl cations have garnered significant attention. Moreover, in view of the important role in life and materials science of difluoroalkylated compounds, a wide range of catalysts has been developed for the efficient incorporation of difluoroacetamido moieties into activated as well as unactivated substrates. 相似文献
996.
Dr. Denis Lesage Prof. Anne Milet Dr. Antony Memboeuf Jérôme Blu Dr. Andrew E. Greene Prof. Jean‐Claude Tabet Dr. Yves Gimbert 《Angewandte Chemie (International ed. in English)》2014,53(7):1939-1942
The mechanism of the Pauson–Khand reaction has been studied by mass spectrometry and it has been found, through ion‐molecule reaction with 13CO, that the carbon monoxide incorporated into the product cyclopentenone is one that has been retained within the complex. Theoretical and kinetic calculations support this finding, which provides a complementary explanation for the effect of Pauson–Khand promoters. 相似文献
997.
Dr. W. Hill Harman Dr. Tzu‐Pin Lin Prof. Dr. Jonas C. Peters 《Angewandte Chemie (International ed. in English)》2014,53(4):1081-1086
Bifunctional E? H activation offers a promising approach for the design of two‐electron‐reduction catalysts with late first‐row metals, such as Ni. To this end, we have been pursuing H2 activation reactions at late‐metal boratranes and herein describe a diphosphine–borane‐supported Ni—(H2) complex, [(PhDPBiPr)Ni(H2)], which has been characterized in solution. 1H NMR spectroscopy confirms the presence of an intact H2 ligand. A range of data, including electronic‐structure calculations, suggests a d10 configuration for [(PhDPBiPr)Ni(H2)] as most appropriate. Such a configuration is highly unusual among transition‐metal H2 adducts. The nonclassical H2 adduct is an intermediate in the complete activation of H2 across the Ni? B interaction. Reaction‐coordinate analysis suggests synergistic activation of the H2 ligand by both the Ni and B centers of the nickel boratrane subunit, thus highlighting an important role of the borane ligand both in stabilizing the d10 Ni—(H2) interaction and in the H—H cleavage step. 相似文献
998.
M. Sc. Stephan M. Rummelt Prof. Alois Fürstner 《Angewandte Chemie (International ed. in English)》2014,53(14):3626-3630
In contrast to all other transition‐metal‐catalyzed hydrostannation reactions documented in the literature, the addition of Bu3SnH across various types of alkynes proceeds with excellent trans selectivity, provided the reaction is catalyzed by [Cp*Ru]‐based complexes. This method is distinguished by a broad substrate scope and a remarkable compatibility with functional groups, including various substituents that would neither survive under the conditions of established Lewis acid mediated trans hydrostannations nor withstand free‐radical reactions. In case of unsymmetrical alkynes, a cooperative effect between the proper catalyst and protic functionality in the substrate allows outstanding levels of regioselectivity to be secured as well. 相似文献
999.
Highly Efficient Chemical Process To Convert Mucic Acid into Adipic Acid and DFT Studies of the Mechanism of the Rhenium‐Catalyzed Deoxydehydration
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Dr. Xiukai Li Di Wu Dr. Ting Lu Dr. Guangshun Yi Prof. Haibin Su Dr. Yugen Zhang 《Angewandte Chemie (International ed. in English)》2014,53(16):4200-4204
The production of bulk chemicals and fuels from renewable bio‐based feedstocks is of significant importance for the sustainability of human society. Adipic acid, as one of the most‐demanded drop‐in chemicals from a bioresource, is used primarily for the large‐volume production of nylon‐6,6 polyamide. It is highly desirable to develop sustainable and environmentally friendly processes for the production of adipic acid from renewable feedstocks. However, currently there is no suitable bio‐adipic acid synthesis process. Demonstrated herein is the highly efficient synthetic protocol for the conversion of mucic acid into adipic acid through the oxorhenium‐complex‐catalyzed deoxydehydration (DODH) reaction and subsequent Pt/C‐catalyzed transfer hydrogenation. Quantitative yields (99 %) were achieved for the conversion of mucic acid into muconic acid and adipic acid either in separate sequences or in a one‐step process. 相似文献
1000.
Crystal‐Plane‐Controlled Selectivity of Cu2O Catalysts in Propylene Oxidation with Molecular Oxygen
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Dr. Zhiquan Jiang Xiaorong Pan Liangfeng Luo Prof. Dr. Wei‐Xue Li Prof. Dr. Weixin Huang 《Angewandte Chemie (International ed. in English)》2014,53(19):4856-4861
The selective oxidation of propylene with O2 to propylene oxide and acrolein is of great interest and importance. We report the crystal‐plane‐controlled selectivity of uniform capping‐ligand‐free Cu2O octahedra, cubes, and rhombic dodecahedra in catalyzing propylene oxidation with O2: Cu2O octahedra exposing {111} crystal planes are most selective for acrolein; Cu2O cubes exposing {100} crystal planes are most selective for CO2; Cu2O rhombic dodecahedra exposing {110} crystal planes are most selective for propylene oxide. One‐coordinated Cu on Cu2O(111), three‐coordinated O on Cu2O(110), and two‐coordinated O on Cu2O(100) were identified as the catalytically active sites for the production of acrolein, propylene oxide, and CO2, respectively. These results reveal that crystal‐plane engineering of oxide catalysts could be a useful strategy for developing selective catalysts and for gaining fundamental understanding of complex heterogeneous catalytic reactions at the molecular level. 相似文献