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1.
《Helvetica chimica acta》2018,101(3)
Combining Surface Organometallic Chemistry with rigorous olefin purification protocol allows evaluating and comparing the intrinsic activities of Mo and W olefin metathesis catalysts towards different types of olefin substrates. While well‐defined silica‐supported Mo and W imido‐alkylidenes show very similar activities in metathesis of internal olefins, Mo catalysts systematically outperform their W analogs in metathesis of terminal olefins, consistent with the formation of stable unsubstituted W metallacyclobutanes in the presence of ethylene. However, Mo catalysts are more prone to induce olefin isomerization, in particular when ethylene is present, probably because of their propensity to undergo more easily reduction processes. 相似文献
2.
Amir H. Hoveyda Prof. Steven J. Malcolmson Simon J. Meek Dr. Adil R. Zhugralin 《Angewandte Chemie (International ed. in English)》2010,49(1):34-44
Chiral olefin metathesis catalysts enable chemists to access enantiomerically enriched small molecules with high efficiency; synthesis schemes involving such complexes can be substantially more concise than those that would involve enantiomerically pure substrates and achiral Mo alkylidenes or Ru‐based carbenes. The scope of research towards design and development of chiral catalysts is not limited to discovery of complexes that are merely the chiral versions of the related achiral variants. A chiral olefin metathesis catalyst, in addition to furnishing products of high enantiomeric purity, can offer levels of efficiency, product selectivity and/or olefin stereoselectivity that are unavailable through the achiral variants. Such positive attributes of chiral catalysts (whether utilized in racemic or enantiomerically enriched form) should be considered as general, applicable to other classes of transformations. 相似文献
3.
Well‐Defined Single‐Site Monohydride Silica‐Supported Zirconium from Azazirconacyclopropane 下载免费PDF全文
Bilel Hamzaoui Dr. Mohamad El Eter Dr. Edy Abou‐hamad Dr. Yin Chen Dr. Jérémie D. A. Pelletier Prof. Jean‐Marie Basset 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(11):4294-4299
The silica‐supported azazirconacyclopropane ?SiOZr(HNMe2)(η2‐NMeCH2)(NMe2) ( 1 ) leads exclusively under hydrogenolysis conditions (H2, 150 °C) to the single‐site monopodal monohydride silica‐supported zirconium species ?SiOZr(HNMe2)(NMe2)2H ( 2 ). Reactivity studies by contacting compound 2 with ethylene, hydrogen/ethylene, propene, or hydrogen/propene, at a temperature of 200 °C revealed alkene hydrogenation. 相似文献
4.
Dr. Cezary Pietraszuk Dr. Szymon Rogalski Beata Powała Miłosz Miętkiewski Dr. Maciej Kubicki Grzegorz Spólnik Prof. Dr. Witold Danikiewicz Krzysztof Woźniak Aleksandra Pazio Dr. Anna Szadkowska Anna Kozłowska Prof. Dr. Karol Grela 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(21):6465-6469
5.
Alkyne Metathesis with Silica‐Supported and Molecular Catalysts at Parts‐per‐Million Loadings 下载免费PDF全文
Deven P. Estes Martin Casey Alexey Fedorov Matthias Tamm Christophe Copéret 《Angewandte Chemie (International ed. in English)》2016,55(45):13960-13964
Improvement of the activity, stability, and chemoselectivity of alkyne‐metathesis catalysts is necessary before this promising methodology can become a routine method to construct C≡C triple bonds. Herein, we show that grafting of the known molecular catalyst [MesC≡Mo(OtBuF6)3] ( 1 , Mes=2,4,6‐trimethylphenyl, OtBuF6=hexafluoro‐tert‐butoxy) onto partially dehydroxylated silica gave a well‐defined silica‐supported active alkyne‐metathesis catalyst [(≡SiO)Mo(≡CMes)(OtBuF6)2] ( 1 /SiO2‐700). Both 1 and 1 /SiO2‐700 showed very high activity, selectivity, and stability in the self‐metathesis of a variety of carefully purified alkynes, even at parts‐per‐million catalyst loadings. Remarkably, the lower turnover frequencies observed for 1 /SiO2‐700 by comparison to 1 do not prevent the achievement of high turnover numbers. We attribute the lower reactivity of 1 /SiO2‐700 to the rigidity of the surface Mo species owing to the strong interaction of the metal site with the silica surface. 相似文献
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Chunhua Liu Eunsol Park Dr. Yinghua Jin Jie Liu Yanxia Yu Prof. Dr. Wei Zhang Prof. Dr. Shengbin Lei Prof. Dr. Wenping Hu 《Angewandte Chemie (International ed. in English)》2018,57(7):1869-1873
Understanding how the constitutional dynamics of a dynamic combinatorial library (DCL) adapts to surfaces (compared to bulk solution) is of fundamental importance to the design of adaptive materials. Submolecular resolved scanning tunneling microscopy (STM) can provide detailed insights into olefin metathesis at the interface. Analysis of the distribution of products has revealed the important role of environmental pressure, reaction temperature, and substituent effects in surface‐confined olefin metathesis. We also report an unprecedented preferred deposition and assembly of linear polymers, and some specific oligomers, on the surface that are hard to obtain otherwise. 相似文献
8.
Nuria Rendón Dr. Romain Berthoud Dr. Frédéric Blanc Dr. David Gajan Tarun Maishal Dr. Jean‐Marie Basset Dr. Christophe Copéret Dr. Anne Lesage Dr. Lyndon Emsley Prof. Smaranda C. Marinescu Rojendra Singh Dr. Richard R. Schrock Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(20):5083-5089
Silica supports : Well‐defined silica‐supported Mo–alkylidene complexes containing one alkoxy/aryloxy substituent are selectively obtained by grafting onto silica either well‐defined molecular bis(alkoxy) or alkoxyamido complexes (see scheme). These silica‐supported complexes are highly efficient catalyst precursors for the metathesis of acyclic alkenes. However, they display poor performances in ring‐closing metathesis reactions, possibly due to the relatively large siloxy ligand (silica) inducing a greater rigidity.
9.
Sebastien Monfette Markus Eyholzer Prof. Dr. Dominique M. Roberge Prof. Dr. Deryn E. Fogg 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(38):11720-11725
Reported is the first study of the influence of reactor configuration on the efficiency of a challenging ring‐closing metathesis (RCM) reaction. With the intention of increasing the generality of RCM scaleup and reducing its dependence on substrate modification, macrocyclization of an unmodified, low effective‐molarity diene was explored using different reactor types, in conjunction with a commercial, homogeneous Grubbs catalyst. Optimized performance is compared for a conventional batch reactor (BR), a continuous plug‐flow reactor (PFR), and a continuous stirred‐tank reactor (CSTR). In the PFR, maximum conversion is achieved most rapidly, but product yields and selectivity are adversely affected by co‐entrapment of ethylene with the catalyst, substrate, and product in the traveling “plug”. Use of the CSTR, in which ethylene is efficiently swept out, affords an order‐of‐magnitude increase in total turnover numbers, and reduces the required catalyst loadings by 25× relative to the BR (to 0.2 mol %), while improving RCM yields and selectivity to quantitative levels. Continuous‐flow methodologies that support liberation of the ethylene co‐product thus show great promise for industrial uptake of RCM. 相似文献
10.
Inside Back Cover: Well‐Defined Single‐Site Monohydride Silica‐Supported Zirconium from Azazirconacyclopropane (Chem. Eur. J. 11/2015) 下载免费PDF全文
Bilel Hamzaoui Dr. Mohamad El Eter Dr. Edy Abou‐hamad Dr. Yin Chen Dr. Jérémie D. A. Pelletier Prof. Jean‐Marie Basset 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(11):4467-4467
11.
N‐Heterocyclic Carbene,High Oxidation State Molybdenum Alkylidene Complexes: Functional‐Group‐Tolerant Cationic Metathesis Catalysts 下载免费PDF全文
Prof. Michael R. Buchmeiser M. Sc. Suman Sen Dr. Jörg Unold Dr. Wolfgang Frey 《Angewandte Chemie (International ed. in English)》2014,53(35):9384-9388
We synthesized the first N‐heterocyclic carbene (NHC) complexes of Schrock’s molybdenum imido alkylidene bis(triflate) complexes. Unlike existing bis(triflate) complexes, the novel 16‐electron complexes represent metathesis active, functional‐group‐tolerant catalysts. Single‐crystal X‐ray structures of two representatives of this novel class of Schrock catalysts are presented and reactivity is discussed in view of their structural peculiarities. In the presence of monomer (substrate), these catalysts form cationic species and can be employed in ring‐closing metathesis (RCM), ring‐opening metathesis polymerization (ROMP), as well as in the cyclopolymerization of α,ω‐diynes. Monomers containing functional groups, which are not tolerated by the existing variations of Schrock’s catalyst, e.g., sec‐amine, hydroxy, and carboxylic acid moieties, can be used. These catalysts therefore hold great promise in both organic and polymer chemistry, where they allow for the use of protic monomers. 相似文献
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Olefin Metathesis at the Dawn of Implementation in Pharmaceutical and Specialty‐Chemicals Manufacturing 下载免费PDF全文
Carolyn S. Higman Dr. Justin A. M. Lummiss Prof. Deryn E. Fogg 《Angewandte Chemie (International ed. in English)》2016,55(11):3552-3565
The recent uptake of molecular metathesis catalysts in specialty‐chemicals and pharmaceutical manufacturing is reviewed. 相似文献
13.
Dr. Etienne Borré Dr. Mathieu Rouen Isabelle Laurent Magaly Magrez Dr. Fréderic Caijo Dr. Christophe Crévisy Dr. Wladimir Solodenko Loic Toupet René Frankfurter Prof. Dr. Carla Vogt Prof. Dr. Andreas Kirschning Dr. Marc Mauduit 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(51):16369-16382
In this study, a new pyridinium‐tagged Ru complex was designed and anchored onto sulfonated silica, thereby forming a robust and highly active supported olefin‐metathesis pre‐catalyst for applications under batch and continuous‐flow conditions. The involvement of an oxazine–benzylidene ligand allowed the reactivity of the formed Ru pre‐catalyst to be efficiently controlled through both steric and electronic activation. The oxazine scaffold facilitated the introduction of the pyridinium tag, thereby affording the corresponding cationic pre‐catalyst in good yield. Excellent activities in ring‐closing (RCM), cross (CM), and enyne metathesis were observed with only 0.5 mol % loading of the pre‐catalyst. When this powerful pre‐catalyst was immobilized onto a silica‐based cationic‐exchange resin, a versatile catalytically active material for batch reactions was generated that also served as fixed‐bed material for flow reactors. This system could be reused at 1 mol % loading to afford metathesis products in high purity with very low ruthenium contamination under batch conditions (below 5 ppm). Scavenging procedures for both batch and flow processes were conducted, which led to a lowering of the ruthenium content to as little as one tenth of the original values. 相似文献
14.
Chelating Ruthenium Phenolate Complexes: Synthesis,General Catalytic Activity,and Applications in Olefin Metathesis Polymerization 下载免费PDF全文
Anna Kozłowska Dr. Maciej Dranka Prof. Janusz Zachara Eva Pump Prof. Dr. Christian Slugovc Krzysztof Skowerski Prof. Dr. Karol Grela 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(43):14120-14125
Cyclic Ru‐phenolates were synthesized, and these compounds were used as olefin metathesis catalysts. Investigation of their catalytic activity pointed out that, after activation with chemical agents, these catalysts promote ring‐closing metathesis (RCM), enyne and cross‐metathesis (CM) reactions, including butenolysis, with good results. Importantly, these latent catalysts are soluble in neat dicyclopentadiene (DCPD) and show good applicability in ring‐opening metathesis polymeriyation (ROMP) of this monomer. 相似文献
15.
Cationic Silica‐Supported N‐Heterocyclic Carbene Tungsten Oxo Alkylidene Sites: Highly Active and Stable Catalysts for Olefin Metathesis 下载免费PDF全文
Margherita Pucino Dr. Victor Mougel Roman Schowner Dr. Alexey Fedorov Prof. Dr. Michael R. Buchmeiser Prof. Dr. Christophe Copéret 《Angewandte Chemie (International ed. in English)》2016,55(13):4300-4302
Designing supported alkene metathesis catalysts with high activity and stability is still a challenge, despite significant advances in the last years. Described herein is the combination of strong σ‐donating N‐heterocyclic carbene ligands with weak σ‐donating surface silanolates and cationic tungsten sites leading to highly active and stable alkene metathesis catalysts. These well‐defined silica‐supported catalysts, [(≡SiO)W(=O)(=CHCMe2Ph)(IMes)(OTf)] and [(≡SiO)W(=O)(=CHCMe2Ph)(IMes)+][B(ArF)4?] [IMes=1,3‐bis(2,4,6‐trimethylphenyl)‐imidazol‐2‐ylidene, B(ArF)4=B(3,5‐(CF3)2C6H3)4] catalyze alkene metathesis, and the cationic species display unprecedented activity for a broad range of substrates, especially for terminal olefins with turnover numbers above 1.2 million for propene. 相似文献
16.
Dr. Amit A. Nagarkar Mohammad Yasir Dr. Aurelien Crochet Prof. Dr. Katharina M. Fromm Prof. Dr. Andreas F. M. Kilbinger 《Angewandte Chemie (International ed. in English)》2016,55(40):12343-12346
Use of a tandem ring‐opening–ring‐closing metathesis (RORCM) strategy for the synthesis of functional metathesis catalysts is reported. Ring opening of 7‐substituted norbornenes and subsequent ring‐closing metathesis forming a thermodynamically stable 6‐membered ring lead to a very efficient synthesis of new catalysts from commercially available Grubbs’ catalysts. Hydroxy functionalized Grubbs’ first‐ as well as third‐generation catalysts have been synthesized. Mechanistic studies have been performed to elucidate the order of attack of the olefinic bonds. This strategy was also used to synthesize the ruthenium methylidene complex. 相似文献
17.
M. Sc. Roman Savka Sabine Foro Dr. Markus Gallei Prof. Dr. Matthias Rehahn Prof. Dr. Herbert Plenio 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(32):10655-10662
Eight new N‐Hoveyda‐type complexes were synthesized in yields of 67–92 % through reaction of [RuCl2(NHC)(Ind)(py)] (NHC=1,3‐bis(2,4,6‐trimethylphenylimidazolin)‐2‐ylidene (SIMes) or 1,3‐bis(2,6‐diisopropylphenylimidazolin)‐2‐ylidene (SIPr), Ind=3‐phenylindenylid‐1‐ene, py=pyridine) with various 1‐ or 1,2‐substituted ferrocene compounds with vinyl and amine or imine substituents. The redox potentials of the respective complexes were determined; in all complexes an iron‐centered oxidation reaction occurs at potentials close to E=+0.5 V. The crystal structures of the reduced and of the respective oxidized Hoveyda‐type complexes were determined and show that the oxidation of the ferrocene unit has little effect on the ruthenium environment. Two of the eight new complexes were found to be switchable catalysts, in that the reduced form is inactive in the ring‐opening metathesis polymerization of cis‐cyclooctene (COE), whereas the oxidized complexes produce polyCOE. The other complexes are not switchable catalysts and are either inactive or active in both reduced and oxidized states. 相似文献
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Cyclooctane Metathesis Catalyzed by Silica‐Supported Tungsten Pentamethyl [(SiO)W(Me)5]: Distribution of Macrocyclic Alkanes 下载免费PDF全文
Nassima Riache Emmanuel Callens Manoja K. Samantaray Najeh M. Kharbatia Muhammad Atiqullah Jean‐Marie Basset 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(46):15089-15094
Metathesis of cyclic alkanes catalyzed by the new surface complex [(?SiO)W(Me)5] affords a wide distribution of cyclic and macrocyclic alkanes. The major products with the formula CnH2n are the result of either a ring contraction or ring expansion of cyclooctane leading to lower unsubstituted cyclic alkanes (5≤n≤7) and to an unprecedented distribution of unsubstituted macrocyclic alkanes (12≤n≤40), respectively, identified by GC/MS and by NMR spectroscopies. 相似文献
20.
Z‐Selective Cross Metathesis with Ruthenium Catalysts: Synthetic Applications and Mechanistic Implications 下载免费PDF全文
Dr. Myles B. Herbert Prof. Dr. Robert H. Grubbs 《Angewandte Chemie (International ed. in English)》2015,54(17):5018-5024
Olefin cross metathesis is a particularly powerful transformation that has been exploited extensively for the formation of complex products. Until recently, however, constructing Z‐olefins using this methodology was not possible. With the discovery and development of three families of ruthenium‐based Z‐selective catalysts, the formation of Z‐olefins using metathesis is now not only possible but becoming increasingly prevalent in the literature. In particular, ruthenium complexes containing cyclometalated NHC architectures developed in our group have been shown to catalyze various cross metathesis reactions with high activity and, in most cases, near perfect selectivity for the Z‐isomer. The types of cross metathesis reactions investigated thus far are presented here and explored in depth. 相似文献