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971.
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
972.
Highly Efficient Chemical Process To Convert Mucic Acid into Adipic Acid and DFT Studies of the Mechanism of the Rhenium‐Catalyzed Deoxydehydration 下载免费PDF全文
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
973.
Crystal‐Plane‐Controlled Selectivity of Cu2O Catalysts in Propylene Oxidation with Molecular Oxygen 下载免费PDF全文
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
974.
Dr. Wai‐Lun Man Jianhui Xie Po‐Kam Lo Dr. William W. Y. Lam Dr. Shek‐Man Yiu Dr. Kai‐Chung Lau Prof. Tai‐Chu Lau 《Angewandte Chemie (International ed. in English)》2014,53(32):8463-8466
Exploring new reactivity of metal nitrides is of great interest because it can give insights to N2 fixation chemistry and provide new methods for nitrogenation of organic substrates. In this work, reaction of a (salen)ruthenium(VI) nitrido complex with various alkynes results in the formation of novel (salen)ruthenium(III) imine complexes. Kinetic and computational studies suggest that the reactions go through an initial ruthenium(IV) aziro intermediate, followed by addition of nucleophiles to give the (salen)ruthenium(III) imine complexes. These unprecedented reactions provide a new pathway for nitrogenation of alkynes based on a metal nitride. 相似文献
975.
Dr. Elena I. Davydova Prof. Dr. Gernot Frenking Dr. Alexey Y. Timoshkin 《Chemphyschem》2014,15(13):2774-2779
Reaction energy profiles for [Me2AlNH2]3 have been computationally explored by using density functional theory. Both intra‐ and intermolecular methane elimination reactions, as well as Al?N bond‐breaking pathways, were considered. The results show that the energy required for Al?N bond breaking in cyclic [Me2AlNH2]3 is of the same order of magnitude as the activation energies for the first (limiting) step of methane elimination (for both mono‐ and bimolecular mechanisms). Thus, dissociative and associative reaction pathways are competitive. Low‐temperature/high‐pressure conditions will favor the bimolecular pathway, whereas at high temperatures, either intramolecular methane elimination or Al?N bond‐breaking dissociative pathways will be operational. 相似文献
976.
Dr. Jia‐Bi Ma Zhen Yuan Jing‐Heng Meng Qing‐Yu Liu Prof. Dr. Sheng‐Gui He 《Chemphyschem》2014,15(18):4117-4125
The reactivity of metal oxide clusters toward hydrocarbon molecules can be changed, tuned, or controlled by doping. Cerium‐doped vanadium cluster cations CeV2O7+ are generated by laser ablation, mass‐selected by a quadrupole mass filter, and then reacted with C2H4 in a linear ion trap reactor. The reaction is characterized by a reflectron time‐of‐flight mass spectrometer. Three types of reaction channels are observed: 1) single oxygen‐atom transfer , 2) double oxygen‐atom transfer , and 3) C?C bond cleavage. This study provides the first bimetallic oxide cluster ion, CeV2O7+, which gives rise to C?C bond cleavage of ethene. Neither CexOy± nor VxOy± alone possess the necessary topological and electronic properties to bring about such a reaction. 相似文献
977.
Claudia Loerbroks Jeaphianne van Rijn Marc‐Philipp Ruby Qiong Tong Prof. Dr. Ferdi Schüth Prof. Dr. Walter Thiel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(38):12298-12309
A joint experimental and computational study on the glucose–fructose conversion in water is reported. The reactivity of different metal catalysts (CrCl3, AlCl3, CuCl2, FeCl3, and MgCl2) was analyzed. Experimentally, CrCl3 and AlCl3 achieved the best glucose conversion rates, CuCl2 and FeCl3 were only mediocre catalysts, and MgCl2 was inactive. To explain these differences in reactivity, DFT calculations were performed for various metal complexes. The computed mechanism consists of two proton transfers and a hydrogen‐atom transfer; the latter was the rate‐determining step for all catalysts. The computational results were consistent with the experimental findings and rationalized the observed differences in the behavior of the metal catalysts. To be an efficient catalyst, a metal complex should satisfy the following criteria: moderate Brønsted and Lewis acidity (pKa=4–6), coordination with either water or weaker σ donors, energetically low‐lying unoccupied orbitals, compact transition‐state structures, and the ability for complexation of glucose. Thus, the reactivity of the metal catalysts in water is governed by many factors, not just the Lewis acidity. 相似文献
978.
The Mechanism of Gold(I)‐Catalyzed Hydroalkoxylation of Alkynes: An Extensive Experimental Study 下载免费PDF全文
Alexander Zhdanko Prof. Dr. Martin E. Maier 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(7):1918-1930
An extensive experimental study of the mechanism of gold(I)‐catalyzed hydroalkoxylation of internal alkynes has been conducted by using NMR spectroscopy. This study was focused on the organogold intermediates, observations of actual catalytic intermediates in situ, and the reaction kinetics that are involved in this reaction. Based on the experimental results, a complete mechanistic picture was established, including on‐ and off‐cycle processes that explain the role of diaurated species. We have shown that gold‐catalyzed hydroalkoxylation of internal alkynes is a reaction that requires only one gold atom for the catalytic cycle, disproving a recent hypothesis regarding the involvement of cooperative gold catalysis. 相似文献
979.
Dynamic Effects Dictate the Mechanism and Selectivity of Dehydration–Rearrangement Reactions of Protonated Alcohols [Me2(R)CCH(OH2)Me]+ (R=Me,Et, iPr) in the Gas Phase 下载免费PDF全文
Dr. Miguel A. F. de Souza Prof. Elizete Ventura Prof. Silmar A. do Monte Prof. José M. Riveros Prof. Ricardo L. Longo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(42):13742-13754
The gas‐phase dehydration–rearrangement (DR) reactions of protonated alcohols [Me2(R)CCH(OH2)Me]+ [R=Me ( ME ), Et ( ET ), and iPr ( I‐PR )] were studied by using static approaches (intrinsic reaction coordinate (IRC), Rice–Ramsperger–Kassel–Marcus theory) and dynamics (quasiclassical trajectory) simulations at the B3LYP/6‐31G(d) level of theory. The concerted mechanism involves simultaneous water dissociation and alkyl migration, whereas in the stepwise reaction pathway the dehydration step leads to a secondary carbocation intermediate followed by alkyl migration. Internal rotation (IR) can change the relative position of the migrating alkyl group and the leaving group (water), so distinct products may be obtained: [Me(R)CCH(Me)Me ??? OH2]+ and [Me(Me)CCH(R)Me ??? OH2]+. The static approach predicts that these reactions are concerted, with the selectivity towards these different products determined by the proportion of the conformers of the initial protonated alcohols. These selectivities are explained by the DR processes being much faster than IR. These results are in direct contradiction with the dynamics simulations, which indicate a predominantly stepwise mechanism and selectivities that depend on the alkyl groups and dynamics effects. Indeed, despite the lifetimes of the secondary carbocations being short (<0.5 ps), IR can take place and thus provide a rich selectivity. These different selectivities, particularly for ET and I‐PR , are amenable to experimental observation and provide evidence for the minor role played by potential‐energy surface and the relevance of the dynamics effects (non‐IRC pathways, IR) in determining the reaction mechanisms and product distribution (selectivity). 相似文献
980.
On the Importance of Decarbonylation as a Side‐Reaction in the Ruthenium‐Catalysed Dehydrogenation of Alcohols: A Combined Experimental and Density Functional Study 下载免费PDF全文
Dr. Nicolas Sieffert Romain Réocreux Patrizia Lorusso Prof. Dr. David J. Cole‐Hamilton Prof. Dr. Michael Bühl 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(14):4141-4155
We report a density functional study (B97‐D2 level) of the mechanism(s) operating in the alcohol decarbonylation that occurs as an important side‐reaction during dehydrogenation catalysed by [RuH2(H2)(PPh3)3]. By using MeOH as the substrate, three distinct pathways have been fully characterised involving either neutral tris‐ or bis‐phosphines or anionic bis‐phosphine complexes after deprotonation. α‐Agostic formaldehyde and formyl complexes are key intermediates, and the computed rate‐limiting barriers are similar between the various decarbonylation and dehydrogenation paths. The key steps have also been studied for reactions involving EtOH and iPrOH as substrates, rationalising the known resistance of the latter towards decarbonylation. Kinetic isotope effects (KIEs) were predicted computationally for all pathways and studied experimentally for one specific decarbonylation path designed to start from [RuH(OCH3)(PPh3)3]. From the good agreement between computed and experimental KIEs (observed kH/kD=4), the rate‐limiting step for methanol decarbonylation has been ascribed to the formation of the first agostic intermediate from a transient formaldehyde complex. 相似文献