878 results on '"Richard R. Schrock"'
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2. Synthesis of Cis,syndiotactic A-alt-B Copolymers from Two Enantiomerically Pure Trans-2,3-Disubstituted-5,6-Norbornenes
- Author
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Eun Sil Jang, Jeremy M. John, and Richard R. Schrock
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Chemistry ,QD1-999 - Published
- 2016
- Full Text
- View/download PDF
3. Metathesis by Molybdenum and Tungsten Catalysts
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Richard R. Schrock
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Alkenes ,Alkynes ,Metathesis ,Molybdenum catalysis ,Organic synthesis ,Polymer chemistry tungsten catalysis ,Chemistry ,QD1-999 - Abstract
Carbon–carbon double bonds are an integral part of the chemical industry and are widely found in natural products, from the small and simple (ethylene) to the large and complex. The ability to manipulate carbon–carbon double bonds to make other carbon–carbon double bonds in a catalytic and stereospecific fashion has revolutionized the way organic molecules and polymers are made today. This article outlines the development of modern molybdenum and tungsten alkylidene catalysts that can be designed at a molecular level to achieve a given result. Carbon–carbon triple bonds also can be manipulated in a similar manner with the appropriate alkylidyne catalyst. Although the 'alkene metathesis' and 'alkyne metathesis' reactions are now fifty to sixty years old, many problems remain that will require an even more detailed understanding of these most intricate, superficially simple reactions.
- Published
- 2015
- Full Text
- View/download PDF
4. Reducing Them Down To Charge Them Up: Low Temperature Catalyst Activation
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Richard R. Schrock
- Subjects
Chemistry ,QD1-999 - Published
- 2016
- Full Text
- View/download PDF
5. Ring Contraction of a Tungstacyclopentane Supported on Silica: Direct Conversion of Ethylene to Propylene
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Jessica Rodriguez, Maxime Boudjelel, Leonard J. Mueller, Richard R. Schrock, and Matthew P. Conley
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Colloid and Surface Chemistry ,General Chemistry ,Alkenes ,Ethylenes ,Silicon Dioxide ,Biochemistry ,Catalysis - Abstract
The reaction of W(NAr)(
- Published
- 2022
6. Synthesis of Molybdenum(VI) Tritylimido Alkylidene Complexes
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Bhaskar Paul, Richard R. Schrock, and Veronica Carta
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Inorganic Chemistry ,Organic Chemistry ,Physical and Theoretical Chemistry - Published
- 2022
7. E- and Z-trisubstituted macrocyclic alkenes for natural product synthesis and skeletal editing
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Yucheng Mu, Felix W. W. Hartrampf, Elsie C. Yu, Katherine E. Lounsbury, Richard R. Schrock, Filippo Romiti, and Amir H. Hoveyda
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General Chemical Engineering ,General Chemistry - Published
- 2022
8. A Tungsten Oxo Alkylidene Supported on Sulfated Zirconium Oxide for Olefin Metathesis
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Jessica Rodriguez, Maxime Boudjelel, Richard R. Schrock, and Matthew P. Conley
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Inorganic Chemistry ,Organic Chemistry ,Physical and Theoretical Chemistry - Published
- 2023
9. Synthesis of Mo(IV) para-Substituted Styrene Complexes and an Exploration of Their Conversion to 1-Phenethylidene Complexes
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Sumeng Liu, Matthew P. Conley, and Richard R. Schrock
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Inorganic Chemistry ,Organic Chemistry ,Physical and Theoretical Chemistry - Published
- 2022
10. Interconversion of Molybdenum or Tungsten d2 Styrene Complexes with d0 1-Phenethylidene Analogues
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Maxime Boudjelel, Charlene Tsay, Richard R. Schrock, Matthew P. Conley, and Sumeng Liu
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Diastereomer ,chemistry.chemical_element ,Protonation ,General Chemistry ,Biochemistry ,Medicinal chemistry ,Catalysis ,Adduct ,Styrene ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,Deprotonation ,chemistry ,Molybdenum ,Pyridinium - Abstract
Upon addition of 5-15% PhNMe2H+X- (X = B(3,5-(CF3)2C6H3)4 or B(C6F5)4) to Mo(NAr)(styrene)(OSiPh3)2 (Ar = N-2,6-i-Pr2C6H3) in C6D6 an equilibrium mixture of Mo(NAr)(styrene)(OSiPh3)2 and Mo(NAr)(CMePh)(OSiPh3)2 is formed over 36 h at 45 °C (Keq = 0.36). A plausible intermediate in the interconversion of the styrene and 1-phenethylidene complexes is the 1-phenethyl cation, [Mo(NAr)(CHMePh)(OSiPh3)2]+, which can be generated using [(Et2O)2H][B(C6F5)4] as the acid. The interconversion can be modeled as two equilibria involving protonation of Mo(NAr)(styrene)(OSiPh3)2 or Mo(NAr)(CMePh)(OSiPh3)2 and deprotonation of the α or β phenethyl carbon atom in [Mo(NAr)(CHMePh)(OSiPh3)2]+. The ratio of the rate of deprotonation of [Mo(NAr)(CHMePh)(OSiPh3)2]+ by PhNMe2 in the α position versus the β position is ∼10, or ∼30 per Hβ. The slow step is protonation of Mo(NAr)(styrene)(OSiPh3)2 (k1 = 0.158(4) L/(mol·min)). Proton sources such as (CF3)3COH or Ph3SiOH do not catalyze the interconversion of Mo(NAr)(styrene)(OSiPh3)2 and Mo(NAr)(CMePh)(OSiPh3)2, while the reaction of Mo(NAr)(styrene)(OSiPh3)2 with pyridinium salts generates only a trace (∼2%) of Mo(NAr)(CMePh)(OSiPh3)2 and forms a monopyridine adduct, [Mo(NAr)(CHMePh)(OSiPh3)2(py)]+ (two diastereomers). The structure of [Mo(NAr)(CHMePh)(OSiPh3)2]+ has been confirmed in an X-ray study; there is no structural indication that a β proton is activated through a CHβ interaction with the metal. W(NAr)(CMePh)(OSiPh3)2 is also converted into a mixture of W(NAr)(CMePh)(OSiPh3)2 and W(NAr)(styrene)(OSiPh3)2 (Keq = 0.47 at 45 °C in favor of the styrene complex) with 10% [PhNMe2H][B(C6F5)4] as the catalyst; the time required to reach equilibrium is approximately the same as in the Mo system.
- Published
- 2021
11. Synthesis of Cationic Molybdenum Imido 2-Adamantylidene Complexes from Bispyrrolides via Cationic Pyrrolenine Complexes
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Richard R. Schrock, Bhaskar Paul, and Charlene Tsay
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Inorganic Chemistry ,Chemistry ,Molybdenum ,Organic Chemistry ,Polymer chemistry ,Cationic polymerization ,chemistry.chemical_element ,Physical and Theoretical Chemistry - Published
- 2021
12. Oxo 2-Adamantylidene Complexes of Mo(VI) and W(VI)
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Richard R. Schrock, Feng Zhai, Charlene Tsay, Maxime Boudjelel, and Amir H. Hoveyda
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Inorganic Chemistry ,010405 organic chemistry ,Chemistry ,Molybdenum ,Organic Chemistry ,Polymer chemistry ,chemistry.chemical_element ,Physical and Theoretical Chemistry ,Tungsten ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences - Abstract
Molybdenum and tungsten oxo 2-adamantylidene (Adene) complexes that contain two nonafluoro-tert-butoxide (ORF9) ligands have been prepared through addition of 2-methylene- or 2-ethylideneadamantane...
- Published
- 2021
13. Stereochemical Control Yields Mucin Mimetic Polymers
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Deborah H. Wen, Gerardo Cárcarmo-Oyarce, Tao Yan, Yuan Wei, Katharina Ribbeck, Richard R. Schrock, Michael J. A. Hore, Austin G. Kruger, Dayanne R. Carvalho, Laura L. Kiessling, and Spencer D. Brucks
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chemistry.chemical_classification ,Glycan ,Glycosylation ,biology ,010405 organic chemistry ,General Chemical Engineering ,Mucin ,Virulence ,General Chemistry ,Polymer ,010402 general chemistry ,01 natural sciences ,Mucus ,0104 chemical sciences ,Chemistry ,chemistry.chemical_compound ,chemistry ,Polymerization ,Chemical Sciences ,Self-healing hydrogels ,Biophysics ,biology.protein ,QD1-999 ,Research Article - Abstract
All animals except sponges produce mucus. Across the animal kingdom, this hydrogel mediates surface wetting, viscosity, and protection against microbes. The primary components of mucus hydrogels are mucins—high molecular weight O-glycoproteins that adopt extended linear structures. Glycosylation is integral to mucin function, but other characteristics that give rise to their advantageous biological activities are unknown. We postulated that the extended conformation of mucins is critical for their ability to block microbial virulence phenotypes. To test this hypothesis, we developed synthetic mucin mimics that recapitulate the dense display of glycans and morphology of mucin. We varied the catalyst in a ring-opening metathesis polymerization (ROMP) to generate substituted norbornene-derived glycopolymers containing either cis- or trans-alkenes. Conformational analysis of the polymers based on allylic strain suggested that cis- rather than trans-poly(norbornene) glycopolymers would adopt linear structures that mimic mucins. High-resolution atomic force micrographs of our polymers and natively purified Muc2, Muc5AC, and Muc5B mucins revealed that cis-polymers adopt extended, mucin-like structures. The cis-polymers retained this structure in solution and were more water-soluble than their trans-analogs. Consistent with mucin’s linear morphology, cis-glycopolymers were more potent binders of a bacterial virulence factor, cholera toxin. Our findings highlight the importance of the polymer backbone in mucin surrogate design and underscore the significance of the extended mucin backbone for inhibiting virulence., Carbohydrate-substituted polymers with backbones of the cis-alkene geometry adopt an extended conformation, mimicking natural mucin’s three-dimensional structure and toxin inhibition capacity.
- Published
- 2021
14. Synthesis of Molybdenum Perfluorophenylimido 2-Adamantylidene Complexes
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Charlene Tsay, Richard R. Schrock, and Bhaskar Paul
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Inorganic Chemistry ,chemistry.chemical_compound ,chemistry ,010405 organic chemistry ,Molybdenum ,Organic Chemistry ,chemistry.chemical_element ,Physical and Theoretical Chemistry ,Diethyl ether ,010402 general chemistry ,01 natural sciences ,Medicinal chemistry ,0104 chemical sciences - Abstract
Addition of 2-adamantylMgBr in diethyl ether to Mo(NArF)2(Cl)2(DME) (ArF = C6F5) gave Mo(NArF)2(Ad)2 (2, Ad = 2-adamantyl, DME = 1,2-dimethoxyethane). Addition of HCl and 2,2′-bipyridyl (bipy) to 2...
- Published
- 2021
15. Stereodefined alkenes with a fluoro-chloro terminus as a uniquely enabling compound class
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Qinghe Liu, Yucheng Mu, Tobias Koengeter, Richard R. Schrock, and Amir H. Hoveyda
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Molecular Structure ,General Chemical Engineering ,Stereoisomerism ,General Chemistry ,Alkenes ,Catalysis ,Article - Abstract
Trisubstituted alkenyl fluorides are needed for research in biological chemistry, drug discovery, agrochemical development, and materials science. Among other applications, these entities are secondary amide bond mimics in one stereoisomeric form and induce a peptide turn in the other. Despite notable progress, however, many stereochemically defined trisubstituted fluoro-alkenes either cannot be prepared efficiently, or can be accessed in only one isomeric form. Here, we outline a general solution to this problem by first unveiling a practical, widely applicable, and catalytic strategy for stereodivergent synthesis of olefins bearing a fluoro and chloro terminus. This has been accomplished by cross-metathesis between two trisubstituted olefins, one of which is a purchasable but scarcely utilized trihalo alkene. Subsequent cross-coupling then be used to generate an assortment of trisubstituted alkenyl fluorides. The importance of the advance is highlighted by syntheses of, among others, a fluoro-nematic liquid crystal component, peptide analogs bearing an E- or a Z-amide bond mimic, and all four stereoisomers of difluoro-rumenic ester (anti-cancer).
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- 2022
16. Syntheses of 'Phosphine-Free' Molybdenum Oxo Alkylidene Complexes through Addition of Water to Alkylidyne Complexes
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Richard R. Schrock, Peter Müller, Amir H. Hoveyda, and Feng Zhai
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Inorganic Chemistry ,chemistry.chemical_compound ,chemistry ,010405 organic chemistry ,Organic Chemistry ,Physical and Theoretical Chemistry ,010402 general chemistry ,01 natural sciences ,Medicinal chemistry ,Phosphine ,0104 chemical sciences - Abstract
Addition of 1 equiv of water to Mo(CArp)(ORF9)3 (Arp = p-methoxyphenyl; ORF9 = OC(CF3)3) in the presence of 5% NEt3 (vs Mo) in THF led to the formation of Mo(O)(CHArp)(ORF9)2(THF)2 in good yield. Mo(O)(CHArp)(ORF9)2(THF)2 reacts with 2 equiv of LiOHMT (OHMT = O-2,6-mesityl2C6H3) at room temperature to yield Mo(O)(CHArp)(OHMT)2 and with 2 equiv of NaOTPP (OTPP = 2,3,5,6-tetraphenylphenoxide) to yield Mo(O)(CHArp)(OTPP)2. In the presence of TMEDA (2.5 equiv), Mo(CR)(ORF9)3 (R = Arp, mesityl, or t-Bu) reacts with 1 equiv of water to yield Mo(O)(CHR)(ORF9)2(TMEDA) complexes, from which (when R = t-Bu) TMEDA is readily displaced by 2,2′-bipyridyl to give Mo(O)(CH-t-Bu)(ORF9)2(bipy). Mo(O)(CH-t-Bu)(ORF9)2(bipy) was converted into Mo(O)(CH-t-Bu)Cl2(bipy) readily, from which Mo(O)(CH-t-Bu)Cl(OHMT)(3-Brpy) (3-Brpy = 3-bromopyridine) and Mo(O)(CH-t-Bu)Cl(OHIPT)(3-Brpy) (OHIPT = O-2,6-(2,4,6-i-Pr3C6H2)2C6H3) were prepared. X-ray studies were carried out on Mo(O)(CHArp)(ORF9)2(THF)2, Mo(O)(CH-t-Bu)(ORF9)2(TMEDA), Mo(O)(CHArp)(OTPP)2, Mo(O)(CH-t-Bu)Cl(OHMT)(3-Brpy), and Mo(O)(CH-t-Bu)Cl(OHIPT)(3-Brpy).
- Published
- 2020
17. Synthesis of Molybdenum Imido 2-Adamantylidene Complexes through α Hydrogen Abstraction
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Charlene Tsay, Richard R. Schrock, and Jordan W. Taylor
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010405 organic chemistry ,Chemistry ,Organic Chemistry ,chemistry.chemical_element ,010402 general chemistry ,Hydrogen atom abstraction ,01 natural sciences ,Medicinal chemistry ,0104 chemical sciences ,Inorganic Chemistry ,chemistry.chemical_compound ,Molybdenum ,Physical and Theoretical Chemistry ,Diethyl ether - Abstract
Addition of 2-adamantylMgBr in diethyl ether to Mo(NAr)2(Cl)2(DME) (Ar = 2,6-i-Pr2C6H3) gave Mo(NAr)2(2-Ad)2 (2-Ad = 2-adamantyl, DME = 1,2-dimethoxyethane), from which Mo(NAr)(Adene)(OTf)2(DME) (1...
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- 2020
18. Group 6 High Oxidation State Alkylidene and Alkylidyne Complexes
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Richard R. Schrock, Mathis J. Benedikter, Michael R. Buchmeiser, and Jonas Groos
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Oxidation state ,Chemistry ,Group (periodic table) ,Medicinal chemistry - Published
- 2022
19. Interconversion of Molybdenum or Tungsten d
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Sumeng, Liu, Maxime, Boudjelel, Richard R, Schrock, Matthew P, Conley, and Charlene, Tsay
- Abstract
Upon addition of 5-15% PhNMe
- Published
- 2021
20. Increasing Olefin Metathesis Activity of Silica‐Supported Molybdenum Imido Adamantylidene Complexes through E Ligand σ‐Donation
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Richard R. Schrock, Lukas Lätsch, Bhaskar Paul, Darryl F. Nater, and Christophe Copéret
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Olefin metathesis ,Ligand ,Organic Chemistry ,chemistry.chemical_element ,surface chemistry ,Biochemistry ,Medicinal chemistry ,Catalysis ,adamantylidenes ,Inorganic Chemistry ,molybdenum ,chemistry ,Molybdenum ,electron donation ,olefin metathesis ,surface organometallic chemistry ,Drug Discovery ,Physical and Theoretical Chemistry - Abstract
Molybdenum imido adamantylidene complexes with different substituents on the imido ligand (dipp=2,6-diisopropylphenyl, Ar-F5=C6F5, and Bu-t) having distinct electron donating abilities were investigated for the metathesis of internal and terminal olefins, for both molecular and silica-supported species using standardized protocols. Here we show that surface immobilization of these compounds results in dramatically increased activity compared to their molecular counterparts. Additionally, we show that electron withdrawing imido groups increase the activity of the compound towards terminal olefins while they simultaneously decrease the ability to metathesize internal olefins. Furthermore, these systems also show high stability when used as initiators in olefin metathesis, although the species that display higher initial activity deactivate faster than those that show more a more moderate reaction rate at first. Our catalytic studies, augmented by DFT calculations, show that all investigated compounds have a remarkably small energy difference between the trigonal bipyramidal (TBP) and square planar (SP) configurations of the metallacyclobutane intermediates, which has previously been linked to high activity., Helvetica Chimica Acta, 104 (11), ISSN:0018-019X, ISSN:1522-2675
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- 2021
21. E- and Z-trisubstituted macrocyclic alkenes for natural product synthesis and skeletal editing
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Yucheng, Mu, Felix W W, Hartrampf, Elsie C, Yu, Katherine E, Lounsbury, Richard R, Schrock, Filippo, Romiti, and Amir H, Hoveyda
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Biological Products ,Cyclization ,Stereoisomerism ,Alkenes ,Catalysis - Abstract
Many therapeutic agents are macrocyclic trisubstituted alkenes but preparation of these structures is typically inefficient and non-selective. A possible solution would entail catalytic macrocyclic ring-closing metathesis, but these transformations require high catalyst loading, conformationally rigid precursors and are often low yielding and/or non-stereoselective. Here we introduce a ring-closing metathesis strategy for synthesis of trisubstituted macrocyclic olefins in either stereoisomeric form, regardless of the level of entropic assistance. The goal was achieved by addressing several unexpected difficulties, including complications arising from pre-ring-closing metathesis alkene isomerization. The power of the method is highlighted by two examples. The first is the near-complete reversal of substrate-controlled selectivity in the formation of a macrolactam related to an antifungal natural product. The other is a late-stage stereoselective generation of an E-trisubstituted alkene in a 24-membered ring, en route to the cytotoxic natural product dolabelide C.
- Published
- 2021
22. Silica‐Supported Molybdenum Oxo Alkylidenes: Bridging the Gap between Internal and Terminal Olefin Metathesis
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Feng Zhai, Christophe Copéret, Deni Mance, Margherita Pucino, Amir H. Hoveyda, Christopher P. Gordon, and Richard R. Schrock
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Molybdenum ,Molecular Structure ,Olefin metathesis ,010405 organic chemistry ,Chemistry ,chemistry.chemical_element ,Stereoisomerism ,General Chemistry ,Alkenes ,Tungsten ,Silicon Dioxide ,010402 general chemistry ,Metathesis ,01 natural sciences ,Medicinal chemistry ,Catalysis ,0104 chemical sciences - Abstract
Grafting a molybdenum oxo alkylidene on silica (partially dehydroxylated at 700 °C) affords the first example of a well-defined silica-supported Mo oxo alkylidene, which is an analogue of the putative active sites in heterogeneous Mo-based metathesis catalysts. In contrast to its tungsten analogue, which shows poor activity towards terminal olefins because of the formation of a stable off-cycle metallacyclobutane intermediate, the Mo catalyst shows high metathesis activity for both terminal and internal olefins that is consistent with the lower stability of Mo metallacyclobutane intermediates. This Mo oxo metathesis catalyst also outperforms its corresponding neutral silica-supported Mo and W imido analogues.
- Published
- 2019
23. E- and Z-, di- and tri-substituted alkenyl nitriles through catalytic cross-metathesis
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Ming Joo Koh, Amir H. Hoveyda, Thach T. Nguyen, Richard R. Schrock, and Yucheng Mu
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General Chemical Engineering ,Carboxylic acid ,Alcohol ,Stereoisomerism ,Context (language use) ,Chemistry Techniques, Synthetic ,Alkenes ,010402 general chemistry ,Metathesis ,01 natural sciences ,Chloride ,Article ,Catalysis ,chemistry.chemical_compound ,Coordination Complexes ,Nitriles ,medicine ,Moiety ,Molybdenum ,chemistry.chemical_classification ,010405 organic chemistry ,Synthetic ,Organic Chemistry ,Chemistry Techniques ,General Chemistry ,Combinatorial chemistry ,0104 chemical sciences ,3. Good health ,chemistry ,Chemical Sciences ,medicine.drug - Abstract
Nitriles are found in many bioactive compounds, and are among the most versatile functional groups in organic chemistry. Despite many notable recent advances, however, there are no approaches that may be used for preparation of di- or trisubstituted alkenyl nitriles. Related approaches which are broad in scope and can deliver the desired products in high stereoisomeric purity are especially scarce. Here, we describe the development of several efficient catalytic cross-metathesis strategies, which provide direct access to a considerable range of Z- or E-disubstituted cyano-substituted alkenes or their corresponding trisubstituted variants. Depending on the reaction type, a molybdenum-based monoaryloxide pyrrolide (MAP) or chloride (MAC) complex may be the optimal choice. The utility of the approach, enhanced by an easy-to-apply protocol for utilization of substrates bearing an alcohol or a carboxylic acid moiety, is highlighted in the context of applications to synthesis of biologically active compounds., Graphical Abstract
- Published
- 2019
24. Protonation Studies of Molybdenum(VI) Nitride Complexes That Contain the [2,6-(ArNCH2)2NC5H3]2– Ligand (Ar = 2,6-Diisopropylphenyl)
- Author
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Lasantha A. Wickramasinghe, Peter Müller, Anne K. Hickey, Charlene Tsay, and Richard R. Schrock
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010405 organic chemistry ,Ligand ,Chemistry ,chemistry.chemical_element ,Protonation ,Nitride ,010402 general chemistry ,01 natural sciences ,Medicinal chemistry ,0104 chemical sciences ,Catalysis ,Inorganic Chemistry ,chemistry.chemical_compound ,Molybdenum ,Pyridine ,Physical and Theoretical Chemistry - Abstract
[Ar2N3]Mo(N)(O-t-Bu) (1), which contains the conformationally rigid pyridine-based diamido ligand [2,6-(ArNCH2)2NC5H3]2– (Ar = 2,6-diisopropylphenyl), is a catalyst for the reduction of dinitrogen ...
- Published
- 2019
25. Molybdenum Complexes that Contain a Calix[6]azacryptand Ligand as Catalysts for Reduction of N2 to Ammonia
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Peter Müller, Lasantha A. Wickramasinghe, Richard R. Schrock, and Charlene Tsay
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010405 organic chemistry ,Ligand ,chemistry.chemical_element ,Azacryptand ,010402 general chemistry ,01 natural sciences ,Medicinal chemistry ,0104 chemical sciences ,Catalysis ,Inorganic Chemistry ,Ammonia ,chemistry.chemical_compound ,chemistry ,Molybdenum ,Calixarene ,Physical and Theoretical Chemistry - Abstract
[CAC(OMe)6]Mo(N) (3, where [CAC]3– is a calix[6]azacryptand ligand derived from a [6]calixarene) has been prepared in a reaction between Li3[CAC(OMe)6] and (t-BuO)3Mo(N). An X-ray structural study ...
- Published
- 2018
26. Publisher Correction: Stereodefined alkenes with a fluoro-chloro terminus as a uniquely enabling compound class
- Author
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Qinghe Liu, Yucheng Mu, Tobias Koengeter, Richard R. Schrock, and Amir H. Hoveyda
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General Chemical Engineering ,General Chemistry - Published
- 2022
27. Syntheses of Molybdenum and Tungsten Imido Alkylidene Complexes that Contain a Bidentate Oxo/Thiolato Ligand
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Peter Müller, Charlene Tsay, Richard R. Schrock, Sudarsan VenkatRamani, and Hosein Tafazolian
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Ethylene ,Denticity ,010405 organic chemistry ,Ligand ,Pinacol ,Organic Chemistry ,chemistry.chemical_element ,ROMP ,010402 general chemistry ,Metathesis ,01 natural sciences ,Biochemistry ,Medicinal chemistry ,Catalysis ,Square pyramidal molecular geometry ,0104 chemical sciences ,Inorganic Chemistry ,chemistry.chemical_compound ,chemistry ,Molybdenum ,Drug Discovery ,Physical and Theoretical Chemistry - Abstract
Author(s): Tafazolian, H; VenkatRamani, S; Tsay, C; Schrock, RR; Muller, P | Abstract: 3,3′,5,5′-Tetra-tert-butyl-2′-sulfanyl[1,1′-biphenyl]-2-ol (H2[tBu4OS]) was prepared in 24 % yield overall from the analogous biphenol using standard techniques. Addition of H2[tBu4OS] to Mo(NAr)(CHCMe2Ph)(2,5-dimethylpyrrolide)2 led to formation of Mo(NAr)(CHCMe2Ph)[tBu4OS], which was trapped with PMe3 to give Mo(NAr)(CHCMe2Ph)[tBu4OS](PMe3) (1(PMe3)). An X-ray crystallographic study of 1(PMe3) revealed that two structurally distinct square pyramidal molecules are present in which the alkylidene ligand occupies the apical position in each. Both 1(PMe3)A and 1(PMe3)B are disordered. Mo(NAd)(CHCMe2Ph)(tBu4OS)(PMe3) (2(PMe3); Ad=1-adamantyl) and W(NAr)(CHCMe2Ph)(tBu4OS)(PMe3) (3(PMe3)) were prepared using analogous approaches. 1(PMe3) reacts with ethylene (1 atm) in benzene within 45 minutes to give an ethylene complex Mo(NAr)(tBu4OS)(C2H4) (4) that is isolable and relatively stable toward loss of ethylene below 60 °C. An X-ray study shows that the bond distances and angles for the ethylene ligand in 4 are like those found for bisalkoxide ethylene complexes of the same general type. Complex 1(PMe3) in the presence of one equivalent of B(C6F5)3 catalyzes the homocoupling of 1-decene, allyltrimethylsilane, and allylboronic acid pinacol ester at ambient temperature. 1(PMe3), 2(PMe3), and 3(PMe3) all catalyze the ROMP of rac-endo,exo-5,6-dicarbomethoxynorbornene (rac-DCMNBE) in the presence of B(C6F5)3, but the polyDCMNBE that is formed has a random structure.
- Published
- 2020
28. Molybdenum Disubstituted Alkylidene Complexes
- Author
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Jordan W. Taylor, Charlene Tsay, and Richard R. Schrock
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Inorganic Chemistry ,010405 organic chemistry ,Chemistry ,Molybdenum ,Organic Chemistry ,chemistry.chemical_element ,Physical and Theoretical Chemistry ,010402 general chemistry ,Other Chemical Sciences ,01 natural sciences ,Medicinal chemistry ,0104 chemical sciences - Abstract
Through relatively straightforward techniques that begin with Mo(NAr)(CH-t-Bu)[OCMe(CF3)2]2 (Ar = 2,6-i-Pr2C6H3), we have prepared Mo(NAr)(CMePh)(OMesityl)2, [Mo(NAr)(CMePh)(OC6F5)2]2, Mo(NAr)(CMePh)(OC6F5)2(MeCN), Mo(NAr)(CMePh)(OC6F5)2(bipyridyl), Mo(NAr)(CMePh)(Cl)2(bipyridyl), Mo(NAr)(CMePh)(Cl)(OHMT)(MeCN) (OHMT = O-2,6-(2,4,6-Me3C6H2)2C6H3), and Mo(NAr)(CMePh)(Pyrrolide)(OHMT). X-ray studies reveal that in five compounds the alkylidene isomer (A) is that in which the phenyl group in the alkylidene points toward the imido nitrogen. In Mo(NAr)(CMePh)(OC6F5)2(MeCN) the isomer in which the methyl group points toward the imido nitrogen (isomer B) has cocrystallized with isomer A (12%). In two 14e compounds that contain isomer A, the Mo═C-C angles differ by 30-36°, consistent with a Mo...C-Hβ agostic interaction. Several of the complexes reported here react readily with ethylene, 1-decene, or cyclooctene to give the expected products, thus confirming their viability as initiators or intermediates in metathesis reactions.
- Published
- 2020
29. Syntheses of Molybdenum(VI) Imido Alkylidene Complexes That Contain a Bidentate Dithiolate Ligand
- Author
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Charlene Tsay, Hosein Tafazolian, Richard R. Schrock, and Peter Müller
- Subjects
Denticity ,010405 organic chemistry ,Ligand ,Organic Chemistry ,chemistry.chemical_element ,010402 general chemistry ,01 natural sciences ,Medicinal chemistry ,0104 chemical sciences ,Inorganic Chemistry ,chemistry.chemical_compound ,chemistry ,Molybdenum ,Pyridine ,NAD+ kinase ,Physical and Theoretical Chemistry ,Trifluoromethanesulfonate - Abstract
Zn(DCTC) (DCTC = 3,6-dichlorodithiacatecholate) reacts with Mo(NAd)(CHCMe2Ph)Cl2(PPh2Me) (Ad = 1-adamantyl) to give Mo(NAd)(CHCMe2Ph)(DCTC)(PPh2Me). The reactions between Zn(DCTC) and Mo(NAd)(CH-t-Bu)(OTf)2(dme) or Mo(NAr)(CHCMe2Ph)(OTf)2(dme) (Ar = 2,6-i-Pr2C6H3; OTf = triflate; dme = 1,2-dimethoxyethane) produce [Mo(NAd)(CH-t-Bu)(DCTC)]2 and [Mo(NAr)(CHCMe2Ph)(DCTC)]2, respectively. Complexes that contain a 3,3′,5,5′-tetrasubstituted dithiabiphenolate were prepared in a reaction between Mo(NAr)(CHCMe2Ph)(Me2pyr)2 (Me2pyr = 2,5-dimethylpyrrolide) and the 3,3′,5,5′-tetrasubstituted dithiabiphenols, (3,3′,5,5′-tetrachlorodithiabiphenol (H2Cl4S2), 3,3′,5,5′-tetrabromodithiabiphenol (H2Br4S2), and 3,3′,5,5′-tetra-t-Bu-dithiabiphenol (H2Bu4S2)). The isolated complexes include Mo(NAr)(CHCMe2Ph)(Cl4S2)(pyridine), Mo(NAr)(CHCMe2Ph)(Br4S2)(pyridine), Mo(NAr)(CHCMe2Ph)(Bu4S2)(PMe3), and [Mo(NAr)(CHCMe2Ph)(Cl4S2)]2. Only the dithiabiphenolate derivatives (in the presence of B(C6F5)3) show activity for the metathesi...
- Published
- 2018
30. Synthesis of High-Oxidation-State Mo═CHX Complexes, Where X = Cl, CF3, Phosphonium, CN
- Author
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Charlene Tsay, Peter Müller, Amir H. Hoveyda, Sudarsan VenkatRamani, and Richard R. Schrock
- Subjects
010405 organic chemistry ,Organic Chemistry ,010402 general chemistry ,01 natural sciences ,Medicinal chemistry ,Article ,0104 chemical sciences ,Inorganic Chemistry ,chemistry.chemical_compound ,chemistry ,Oxidation state ,Stereoselectivity ,Phosphonium ,Physical and Theoretical Chemistry ,Other Chemical Sciences - Abstract
Reactions between (Z)-XCH═CHX, where X = Cl, CF3, CN, and Mo(N-t-Bu)(CH-t-Bu)(OHIPT)Cl(PPh2Me) (OHIPT = O-2,6-(2,4,6-i-Pr3C6H2)2C6H3) produce Mo(N-t-Bu)(CHX)(OHIPT)Cl(PPh2Me) complexes. Addition of 2,2′-bipyridyl (Bipy) yields Mo(N-t-Bu)(CHX)(OHIPT)Cl(Bipy) complexes, which could be isolated and structurally characterized. The reaction between Mo(N-t-Bu)(CH-t-Bu)(OHMT)Cl(PPh2Me) (OHMT = O-2,6-(2,4,6-Me3C6H2)2C6H3) and (Z)-ClCH═CHCl in the presence of Bipy produces a mixture that contains both Mo(N-t-Bu)(CHCl)(OHMT)Cl(PPh2Me) and Mo(N-t-Bu)(CHCl)(OHMT)Cl(Bipy), but the relatively insoluble product that crystallizes from toluene-d8 is the phosphoniomethylidene complex [Mo(N-t-Bu)(CHPPh2Me)(OHMT)Cl(Bipy)]Cl. The Mo(N-t-Bu)(CHX)(OHIPT)Cl(PPh2Me) complexes (X = Cl, CF3) were confirmed to initiate the stereoselective cross-metathesis between (Z)-5-decene and (Z)-XCH═CHX.
- Published
- 2018
31. Syntheses of Molybdenum Oxo Alkylidene Complexes through Addition of Water to an Alkylidyne Complex
- Author
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Amir H. Hoveyda, Peter Müller, Richard R. Schrock, Charlene Tsay, and Konstantin V. Bukhryakov
- Subjects
chemistry.chemical_element ,010402 general chemistry ,Metathesis ,01 natural sciences ,Biochemistry ,Medicinal chemistry ,Article ,Catalysis ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,Coordination Complexes ,Cyclooctene ,Molecule ,Char ,Molybdenum ,Molecular Structure ,010405 organic chemistry ,Water ,General Chemistry ,0104 chemical sciences ,Oxygen atom ,chemistry ,Polymerization ,Alkynes ,Chemical Sciences ,Hydroxide - Abstract
Addition of one equiv of water to Mo(CAr)[OCMe(CF3)2]3(1,2-dimethoxyethane) (2, Ar = o-(OMe)C6H4) in the presence of PPhMe2 leads to formation of Mo(O)(CHAr)[OCMe(CF3)2]2(PPhMe2) (3(PPhMe2)) in 34% yield. Addition of one equiv of water alone to 2 produces the dimeric alkylidyne hydroxide complex, {Mo(CAr)[OCMe(CF3)2]2(μ-OH)}2(dme) (4(dme)) in which each bridging hydroxide proton points toward an oxygen atom in an arylmethoxy group. Addition of PMe3 to 4(dme) gives the alkylidene oxo complex, (3(PMe3)), an analogue of 3(PPhMe2) (95% conversion, 66% isolated). Treatment of 3(PMe3) with two equiv of HCl gave Mo(O)(CHAr)Cl2(PMe3) (5), which upon addition of LiO-2,6-(2,4,6-i-Pr3C6H2)2C6H3 (LiOHIPT) gave Mo(O)(CHAr)(OHIPT)Cl(PMe3) (6). Compound 6 in the presence of B(C6F5)3 will initiate the ring-opening metathesis polymerization of cyclooctene, 5,6-dicarbomethoxynorbornadiene (DCMNBD), and rac-5,6-dicarbomethoxynorbornene (DCMNBE), and the homocoupling of 1-decene to 9-octadecene. The poly(DCMNBD) has a cis,syndiotactic structure, whereas poly(DCMNBE) has a cis,syndiotactic,alt structure. X-ray structures were obtained for 3(PPhMe2), 4(dme), and 6.
- Published
- 2018
32. Reduction of Dinitrogen to Ammonia Catalyzed by Molybdenum Diamido Complexes
- Author
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Lasantha A. Wickramasinghe, Richard R. Schrock, Takaya Ogawa, and Peter Müller
- Subjects
010405 organic chemistry ,Chemistry ,Ligand ,Inorganic chemistry ,chemistry.chemical_element ,Selective catalytic reduction ,General Chemistry ,010402 general chemistry ,01 natural sciences ,Biochemistry ,Medicinal chemistry ,Catalysis ,0104 chemical sciences ,chemistry.chemical_compound ,Ammonia ,Colloid and Surface Chemistry ,Molybdenum ,Pyridine ,Butyllithium ,Diethyl ether - Abstract
[Ar2N3]Mo(N)(O-t-Bu), which contains the conformationally rigid pyridine-based diamido ligand, [2,6-(ArNCH2)2NC5H3]2– (Ar = 2,6-diisopropylphenyl), can be prepared from H2[Ar2N3], butyllithium, and (t-BuO)3Mo(N). [Ar2N3]Mo(N)(O-t-Bu) serves as a catalyst or precursor for the catalytic reduction of molecular nitrogen to ammonia in diethyl ether between −78 and 22 °C in a batchwise manner with CoCp*2 as the electron source and Ph2NH2OTf as the proton source. Up to ∼10 equiv of ammonia can be formed per Mo with a maximum efficiency in electrons of ∼43%.
- Published
- 2017
33. EPR/ENDOR and Theoretical Study of the Jahn–Teller-Active [HIPTN3N]MoVL Complexes (L = N–, NH)
- Author
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Brian M. Hoffman, Frank Neese, Michael R. Reithofer, Ajay Sharma, Richard R. Schrock, and Michael Roemelt
- Subjects
Electron nuclear double resonance ,010405 organic chemistry ,Jahn–Teller effect ,Selective catalytic reduction ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences ,law.invention ,Inorganic Chemistry ,Paramagnetism ,Ammonia ,chemistry.chemical_compound ,Crystallography ,Electron transfer ,chemistry ,Computational chemistry ,law ,Diamagnetism ,Physical and Theoretical Chemistry ,Electron paramagnetic resonance - Abstract
The molybdenum trisamidoamine (TAA) complex [Mo] {[3,5-(2,4,6-i-Pr3C6H2)2C6H3NCH2CH2N]Mo} carries out catalytic reduction of N2 to ammonia (NH3) by protons and electrons at room temperature. A key intermediate in the proposed [Mo] nitrogen reduction cycle is nitridomolybdenum(VI), [Mo(VI)]N. The addition of [e–/H+] to [Mo(VI)]N to generate [Mo(V)]NH might, in principle, follow one of three possible pathways: direct proton-coupled electron transfer; H+ first and then e–; e– and then H+. In this study, the paramagnetic Mo(V) intermediate {[Mo]N}− and the [Mo]NH transfer product were generated by irradiating the diamagnetic [Mo]N and {[Mo]NH}+ Mo(VI) complexes, respectively, with γ-rays at 77 K, and their electronic and geometric structures were characterized by electron paramagnetic resonance and electron nuclear double resonance spectroscopies, combined with quantum-chemical computations. In combination with previous X-ray studies, this creates the rare situation in which each one of the four possible stat...
- Published
- 2017
34. Formation of High-Oxidation-State Metal–Carbon Double Bonds
- Author
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Christophe Copéret and Richard R. Schrock
- Subjects
chemistry.chemical_classification ,Double bond ,010405 organic chemistry ,Organic Chemistry ,Tantalum ,chemistry.chemical_element ,010402 general chemistry ,Ring (chemistry) ,Metathesis ,01 natural sciences ,0104 chemical sciences ,Catalysis ,Inorganic Chemistry ,chemistry.chemical_compound ,chemistry ,Oxidation state ,Polymer chemistry ,Organic chemistry ,Ring-opening metathesis polymerisation ,Physical and Theoretical Chemistry ,Organometallic chemistry - Abstract
This tutorial explores the major pathways of forming metal–carbon double bonds in high-oxidation-state alkylidene complexes that began with the alkylidene chemistry of tantalum complexes in the 1970s and continued with the organometallic chemistry of Mo, W, and Re and the development of homogeneous catalysts for the metathesis of olefins. It also explores recent findings in surface organometallic chemistry and discusses the link between molecularly defined and heterogeneous catalysts. Recent results suggest that heterogeneous olefin metathesis catalysts that are activated toward metathesis upon exposure to olefins produce a d0 alkylidene through formation of a metallacyclopentane ring at d2 metal sites followed by “a ring contraction” to a metallacyclobutane, a reaction that was first observed in tantalum chemistry.
- Published
- 2017
35. Syntheses of Molybdenum Adamantylimido and
- Author
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Konstantin V. Bukhryakov, Richard R. Schrock, Amir H. Hoveyda, Sudarsan VenkatRamani, and Charlene Tsay
- Subjects
010405 organic chemistry ,Chemistry ,Inorganic chemistry ,Organic Chemistry ,chemistry.chemical_element ,010402 general chemistry ,01 natural sciences ,Chloride ,Medicinal chemistry ,Article ,0104 chemical sciences ,Catalysis ,Inorganic Chemistry ,chemistry.chemical_compound ,Cyclooctene ,Molybdenum ,Yield (chemistry) ,medicine ,Physical and Theoretical Chemistry ,Other Chemical Sciences ,medicine.drug - Abstract
Reactions between Mo(N-t-Bu)(2)(CH(2)-t-Bu)(2) or Mo(NAdamantyl)(2)(CH(2)CMe(2)Ph)(2) and 3 equiv of HCl in the presence of 1 equiv of PPh(2)Me yield Mo(NR)(CHR’)(PPh(2)Me)Cl(2) complexes, from which Mo(NR)(CHR’)(PPh(2)Me)(OAr)Cl complexes (OAr = a 2,6-terphenoxide) can be prepared. The Mo(NR)(CHR’)(PPh(2)Me)(OAr)Cl complexes were evaluated as cross-metathesis catalysts between cyclooctene and Z-1,2-dichloroethylene. The efficiencies of the test reaction for complexes in which OAr = OTPP, OHMT, OHIPT, or OHTBT (where OTPP is 2,3,5,6-tetraphenylphenoxide, OHMT is hexamethylterphenoxide, OHIPT is hexaisopropylterphenoxide, and OHTBT is hexa-t-butylterphenoxide) maximize when OAr is OHMT or OHIPT. Mo(N-t-Bu)(CH-t-Bu)(PPh(2)Me)Cl(2) is essentially inactive for the reaction between cyclooctene and Z-1,2-dichloroethylene. X-ray structural studies were carried out on Mo(NAd)(CHCMe(2)Ph)(PPh(2)Me)Cl(2), Mo(N-t-Bu)(CH-t-Bu)(PPh(2)Me)(OHMT)Cl, Mo(NAd)(CHCMe(2)Ph)(Cl)(OHTBT)(PMe(3)), and [Mo(NAd)(CHCMe(2)Ph)(PMe(3))(Cl)](2)(μ-O), the product of the reaction between Mo(NAd)(CHCMe(2)Ph)(Cl)(OHTBT)(PMe(3)) and 0.5 equiv of water.
- Published
- 2019
36. Silica‐Supported Molybdenum Oxo Alkylidenes: Bridging the Gap between Internal and Terminal Olefin Metathesis
- Author
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Margherita Pucino, Feng Zhai, Christopher P. Gordon, Deni Mance, Amir H. Hoveyda, Richard R. Schrock, and Christophe Copéret
- Subjects
Molybdenum ,010405 organic chemistry ,Alkylidene ,Oxo groups ,Single-site catalysis ,General Medicine ,010402 general chemistry ,01 natural sciences ,Surface chemistry ,0104 chemical sciences - Abstract
Angewandte Chemie. International Edition, 58 (34), ISSN:1433-7851, ISSN:1521-3773, ISSN:0570-0833
- Published
- 2019
37. Synthesis of Molybdenum(VI) Neopentylidene Neopentylidyne Complexes
- Author
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Peter Müller, Richard R. Schrock, Hosein Tafazolian, and Massachusetts Institute of Technology. Department of Chemistry
- Subjects
Inorganic Chemistry ,chemistry.chemical_compound ,chemistry ,Molybdenum ,Yield (chemistry) ,Organic Chemistry ,chemistry.chemical_element ,Physical and Theoretical Chemistry ,Diethyl ether ,Other Chemical Sciences ,Medicinal chemistry ,Dichloromethane - Abstract
Mo(C-t-Bu)(CH-t-Bu)(Cl)(PMe₂Ph)₂ (1) was prepared as off-white crystals in 26% yield through addition of 2.5 equiv of Mg(CH₂-t-Bu)₂ to Mo(O)[OC(CF₃)₃]₄ in diethyl ether followed by 3 equiv of PMe₂Ph and a workup that includes dichloromethane (the source of Cl). Compound 1 is largely a syn isomer initially that equilibrates to give approximately a 1:1 mixture of syn and anti isomers within 1-2 h. Compound 1 reacts with Li(3,5-dimethylpyrrolide) to give Mo(C-t-Bu)(CH-t-Bu)(η¹-Me₂Pyr)(PMe₂Ph)₂ (2a) as a pale yellow solid in 76% yield, and 2a reacts with Ph3SiOH to give a mixture of syn and anti Mo(C-t-Bu)(CH-t-Bu)(OSiPh3)(PMe₂Ph)₂ (3a) in 84% yield. All three compounds tend to lose PMe2Ph to give 14e monophosphine complexes with the formulas Mo(C-t-Bu)(CH-t-Bu)(X)(PMe₂Ph) (X = Cl, Me₂Pyr, or OSiPh₃), none of which could be isolated. X-ray studies show the structures of 1, 2a, and 3a to be analogous with τ values of 0.45, 0.53, and 0.69, respectively.
- Published
- 2019
38. Synthesis of Tungsten Oxo Alkylidene Biphenolate Complexes and Ring-Opening Metathesis Polymerization of Norbornenes and Norbornadienes
- Author
-
Richard R. Schrock, Peter Müller, Sudarsan VenkatRamani, Tao Yan, and Massachusetts Institute of Technology. Department of Chemistry
- Subjects
010405 organic chemistry ,Chemistry ,Dimer ,Organic Chemistry ,010402 general chemistry ,01 natural sciences ,Medicinal chemistry ,0104 chemical sciences ,Adduct ,Inorganic Chemistry ,chemistry.chemical_compound ,Monomer ,Polymerization ,Ring-opening metathesis polymerisation ,Stereoselectivity ,Physical and Theoretical Chemistry ,Bond cleavage ,Phosphine - Abstract
We have synthesized and characterized tungsten oxo alkylidene biphenolate complexes with the formulas W(O)(CHR)(rac-biphenolate)(PPhMe2) and (R,S)-[W(μ-O)(CHR)(biphenolate)]2 (R = CMe2Ph; biphenolate = L1 or L2 in the text). They behave as initiators for the stereoselective (cis,isotactic) polymerization of 2,3-dicarbomethoxy-5-norbornadiene and eight enantiomerically pure 5-substituted norbornenes with a cis,isotactic precision of 95–98% in most cases. The active initiators are 14e W(O)(CHR)(biphenolate) complexes, which are formed through either dissociation of PPhMe2 from the phosphine adducts or scission of the heterochiral dimer. Addition of B(C6F5)3 (one per W) to (R,S)-[W(μ-O)(CHR)(L1)]2 led to formation of what we propose to be monomeric W[OB(C6F5)3](CHR)(L1) in equilibrium with B(C6F5)3 and (R,S)-[W(μ-O)(CHR)(L1)]2. This mixture decomposed over a period of 1–2 h, was much slower to initiate polymerization than (R,S)-[W(μ-O)(CHR)(L1)]2, and was much less stereoselective. Polymerization of five of the monomers with the imido alkyidene initiator, W(N-2,6-Me2C6H3)(CHCMe2Ph)(rac-L1), gave virtually identical results compared to the results obtained with oxo complexes., National Science Foundation (CHE-1463707)
- Published
- 2019
39. Protonation Studies of Molybdenum(VI) Nitride Complexes That Contain the [2,6-(ArNCH
- Author
-
Anne K, Hickey, Lasantha A, Wickramasinghe, Richard R, Schrock, Charlene, Tsay, and Peter, Müller
- Abstract
[Ar
- Published
- 2019
40. Traceless Protection for More Broadly Applicable Olefin Metathesis
- Author
-
Richard R. Schrock, Yucheng Mu, Thach T. Nguyen, Farid W. van der Mei, and Amir H. Hoveyda
- Subjects
Carboxylic acid ,Homogeneous catalysis ,Alkenes ,stereoselectivity ,010402 general chemistry ,01 natural sciences ,Catalysis ,Ruthenium ,Article ,Organometallic Compounds ,chemistry.chemical_classification ,Molybdenum ,Olefin fiber ,alkenes ,Molecular Structure ,010405 organic chemistry ,Alkene ,Organic Chemistry ,cross-metathesis ,Stereoisomerism ,General Chemistry ,General Medicine ,homogeneous catalysis ,Combinatorial chemistry ,0104 chemical sciences ,Kinetics ,chemistry ,Yield (chemistry) ,Chemical Sciences ,synthetic methods ,Stereoselectivity ,Isopropyl - Abstract
An operationally simple in situ protection/deprotection strategy that significantly expands the scope of kinetically controlled catalytic Z- and E-selective olefin metathesis is introduced. We demonstrate that, prior to the addition of a sensitive Mo- or Ru-based complex, treatment of a hydroxy- or a carboxylic acid-containing olefin with commercially available HB(pin) or readily accessible HB(trip)(2) (pin = pinacolato, trip = 2,4,6-tri(iso-propyl)phenyl) for 15 minutes is sufficient for efficient generation of a desired product. Routine workup leads to quantitative deprotection. A range of stereochemically defined Z- or E-alkenyl chlorides, bromides, fluorides, and boronates or Z-trifluoromethyl-substituted alkenes with a hydroxy- or a carboxylic acid group were thus prepared in 51–97% yield and 93% to >98% stereoselectivity. The substrates, HB(pin), and cross-partners were used as received. We also show that, regardless of whether a polar functional unit is present or not, a small amount of HB(pin) (e.g., 10 mol %) may be used to remove residual water, significantly enhancing efficiency (i.e., lower catalyst loading).
- Published
- 2019
41. Molybdenum Complexes that Contain a Calix[6]azacryptand Ligand as Catalysts for Reduction of N
- Author
-
Lasantha A, Wickramasinghe, Richard R, Schrock, Charlene, Tsay, and Peter, Müller
- Abstract
[CAC(OMe)
- Published
- 2018
42. Molybdenum and Tungsten Alkylidene Complexes That Contain a 2-Pyridyl-Substituted Phenoxide Ligand
- Author
-
Jeremy M. John, Richard R. Schrock, Peter Müller, Peter E. Sues, and Konstantin V. Bukhryakov
- Subjects
Ortho position ,Ethylene ,Olefin metathesis ,010405 organic chemistry ,Ligand ,Organic Chemistry ,Alkane metathesis ,chemistry.chemical_element ,Ether ,Tungsten ,010402 general chemistry ,01 natural sciences ,Medicinal chemistry ,0104 chemical sciences ,Inorganic Chemistry ,chemistry.chemical_compound ,chemistry ,Molybdenum ,Organic chemistry ,Physical and Theoretical Chemistry - Abstract
In the interest of preparing molybdenum and tungsten alkylidene complexes for olefin metathesis that are longer-lived at high temperatures (∼150 °C or above), we synthesized complexes that contain a phenoxide ligand with a 2-pyridyl in one ortho position and a mesityl (Mes) or 2,4,6-i-Pr3C6H2 (Trip) in the other ortho position ([MesON]− or [TripON]−, respectively). The alkylidene (neophylidene) complexes that were prepared include W(O)(CHCMe2Ph)(Me2Pyr)(RON) (R = Mes or Trip), Mo(NC6F5)(CHCMe2Ph)(RON)Cl, Mo(N-2,6-Me2C6H3)(CHCMe2Ph)(RON)Cl, Mo(N-t-Bu)(CHCMe2Ph)(RON)Cl, and M(N-2,6-i-Pr2C6H3)(CHCMe2Ph)(TripON)(OTf) (M = Mo or W). The reaction between Mo(NAr)(CHCMe2Ph)(TripON)(OTf) and ethylene yielded an ethylene complex, Mo(NAr)(C2H4)(TripON)(OTf)(ether). All neophylidene complexes were essentially unreactive toward terminal olefins at 22 °C and showed modest homocoupling activity (at 80 or 100 °C) and alkane metathesis activity (at 150 and 200 °C). W(O)(CHCMe2Ph)(Me2Pyr)(MesON) also stereoselectively poly...
- Published
- 2016
43. Synthesis of Cis,syndiotactic A-alt-B Copolymers from Two Enantiomerically Pure Trans-2,3-Disubstituted-5,6-Norbornenes
- Author
-
Richard R. Schrock, Eun Sil Jang, and Jeremy M. John
- Subjects
010405 organic chemistry ,General Chemical Engineering ,Diastereomer ,Sequence (biology) ,General Chemistry ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences ,Catalysis ,Metal ,lcsh:Chemistry ,chemistry.chemical_compound ,Monomer ,chemistry ,lcsh:QD1-999 ,visual_art ,Tacticity ,Polymer chemistry ,Chemical Sciences ,visual_art.visual_art_medium ,Copolymer ,Chirality (chemistry) - Abstract
Cis,syndiotacticA-alt-B copolymers, where A and B are two enantiomerically pure trans-2,3-disubstituted-5,6-norbornenes with "opposite" chiralities, can be prepared with stereogenic-at-metal initiators of the type M(NR)(CHR')(OR")(pyrrolide). Formation of a high percentage of alternating AB copolymer linkages relies on an inversion of chirality at the metal with each propagating step and a relatively fast formation of an AB sequence as a consequence of a preferred diastereomeric relationship between the chirality at the metal and the chirality of the monomer. This approach to formation of an alternating AB copolymer contrasts dramatically with the principle of forming AB copolymers from achiral monomers and catalysts.
- Published
- 2016
44. Molybdenum and Tungsten Alkylidene and Metallacyclobutane Complexes That Contain a Dianionic Biphenolate Pincer Ligand
- Author
-
Richard R. Schrock, Jeremy M. John, Peter Müller, and Peter E. Sues
- Subjects
Ethylene ,010405 organic chemistry ,Ligand ,Organic Chemistry ,chemistry.chemical_element ,Tungsten ,010402 general chemistry ,Ring (chemistry) ,Photochemistry ,01 natural sciences ,Medicinal chemistry ,0104 chemical sciences ,Pincer movement ,Inorganic Chemistry ,Metal ,chemistry.chemical_compound ,chemistry ,Molybdenum ,visual_art ,visual_art.visual_art_medium ,Physical and Theoretical Chemistry ,Pincer ligand - Abstract
Molybdenum imido alkylidene and tungsten oxo alkylidene complexes that contain a tridentate “pincer” [ONO]2– ligand have been prepared and treated with ethylene to give unsubstituted metallacyclobutane complexes that have a 16e count. Both Mo and W metallacyclobutane complexes exchange C2D4 into the metallacyclobutane ring at 22 °C at a rate that is first order in metal and zero order in C2D4. These metallacycles lose ethylene at least 104–105 times slower than reported 14e unsubstituted Mo and W metallacyclobutane complexes that have been explored in the literature that have a TBP geometry with the metallacyclobutane ring bound in the equatorial positions. Our studies suggest that breaking up the metallacyclobutane ring in these 16e d0 Mo or W complexes is slow because a 14e TBP metallacyclobutane complex cannot be accessed readily.
- Published
- 2016
45. Syntheses of Molybdenum Oxo Benzylidene Complexes
- Author
-
Amir H. Hoveyda, Peter Müller, Charlene Tsay, Konstantin V. Bukhryakov, Feng Zhai, and Richard R. Schrock
- Subjects
Models, Molecular ,Ethylene ,chemistry.chemical_element ,Chemistry Techniques, Synthetic ,010402 general chemistry ,Crystallography, X-Ray ,Ligands ,01 natural sciences ,Biochemistry ,Medicinal chemistry ,Benzylidene Compounds ,Catalysis ,Article ,Metal ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,Models ,Coordination Complexes ,Molybdenum ,Crystallography ,010405 organic chemistry ,Chemistry ,Ligand ,Synthetic ,Molecular ,Chemistry Techniques ,General Chemistry ,Toluene ,Square pyramidal molecular geometry ,0104 chemical sciences ,Oxygen ,Trigonal bipyramidal molecular geometry ,visual_art ,Chemical Sciences ,visual_art.visual_art_medium ,X-Ray ,Phosphine - Abstract
The reaction between Mo(O)(CHAr(o))(OR(F6))(2)(PMe(3)) (Ar(o) = ortho-methoxyphenyl, OR(F6) = OCMe(CF(3))(2)) and two equivalents of LiOHMT (OHMT = O-2,6-(2,4,6-Me(3)C(6)H(2))(2)C(6)H(3)) leads to Mo(O)(CHAr(o))(OHMT)(2), an X-ray structure of which shows it to be a trigonal bipyramidal anti benzylidene complex in which the o-methoxy oxygen is coordinated to the metal trans to the apical oxo ligand. Addition of one equivalent of water (in THF) to the benzylidyne complex, Mo(CAr(p))(OR)(3)(THF)(2) (Ar(p) = para-methoxyphenyl, OR = OR(F6) or OC(CF(3))(3) (OR(F9))) leads to formation of {Mo(CAr(p))(OR)(2)(μ-OH)(THF)}(2)(μ-THF) complexes. Addition of one equivalent of a phosphine (L) to Mo(CAr(p))(OR(F9))(3)(THF)(2) in THF, followed by addition of one equivalent of water, all at room temperature, yields Mo(O)(CHAr(p))(OR(F9))(2)(L) complexes in good yields for several phosphines (e.g., PMe(2)Ph (69% by NMR), PMePh(2) (59%), PEt(3) (69%), or P(i-Pr)(3) (65%)). The reaction between Mo(O)(CHAr(p))(OR(F9))(2)(PEt(3)) and two equivalents of LiOHMT proceeds smoothly at 90 °C in toluene to give Mo(O)(CHAr(p))(OHMT)(2), a four-coordinate syn alkylidene complex. Mo(O)(CHAr(p))(OHMT)(2) reacts with ethylene (1 atm in C(6)D(6)) to give (in solution) a mixture of Mo(O)(CHAr(p))(OHMT)(2), Mo(O)(CH(2))(OHMT)(2), and an unsubstituted square pyramidal metallacyclobutane complex, Mo(O)(CH(2)CH(2)CH(2))(OHMT)(2), along with ethylene and Ar(p)CH=CH(2). Mo(O)(CHAr(p))(OHMT)(2) also reacts with 2,3-dicarbomethoxynorbornadiene to yield syn and anti isomers of the “first-insertion” products that contain a cis C=C bond.
- Published
- 2018
46. Beyond fossil fuel-driven nitrogen transformations
- Author
-
Kara L. Bren, R. Morris Bullock, Patrick L. Holland, Kyle M. Lancaster, Anne K. Jones, Richard M. Crooks, Richard R. Schrock, Sergei V. Lymar, Lance C. Seefeldt, Mercouri G. Kanatzidis, Michael J. Janik, William F. Schneider, Peter H. Pfromm, Paul W. King, Marcetta Y. Darensbourg, Brian M. Hoffman, and Jingguang G. Chen
- Subjects
Multidisciplinary ,Denitrification ,Waste management ,business.industry ,Commodity chemicals ,Fossil fuel ,chemistry.chemical_element ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Environmentally friendly ,Nitrogen ,Article ,0104 chemical sciences ,law.invention ,Steam reforming ,chemistry ,law ,Environmental science ,0210 nano-technology ,business ,Ostwald process ,Nitrogen cycle - Abstract
BACKGROUND The invention of the Haber-Bosch (H-B) process in the early 1900s to produce ammonia industrially from nitrogen and hydrogen revolutionized the manufacture of fertilizer and led to fundamental changes in the way food is produced. Its impact is underscored by the fact that about 50% of the nitrogen atoms in humans today originate from this single industrial process. In the century after the H-B process was invented, the chemistry of carbon moved to center stage, resulting in remarkable discoveries and a vast array of products including plastics and pharmaceuticals. In contrast, little has changed in industrial nitrogen chemistry. This scenario reflects both the inherent efficiency of the H-B process and the particular challenge of breaking the strong dinitrogen bond. Nonetheless, the reliance of the H-B process on fossil fuels and its associated high CO 2 emissions have spurred recent interest in finding more sustainable and environmentally benign alternatives. Nitrogen in its more oxidized forms is also industrially, biologically, and environmentally important, and synergies in new combinations of oxidative and reductive transformations across the nitrogen cycle could lead to improved efficiencies. ADVANCES Major effort has been devoted to developing alternative and environmentally friendly processes that would allow NH 3 production at distributed sources under more benign conditions, rather than through the large-scale centralized H-B process. Hydrocarbons (particularly methane) and water are the only two sources of hydrogen atoms that can sustain long-term, large-scale NH 3 production. The use of water as the hydrogen source for NH 3 production requires substantially more energy than using methane, but it is also more environmentally benign, does not contribute to the accumulation of greenhouse gases, and does not compete for valuable and limited hydrocarbon resources. Microbes living in all major ecosystems are able to reduce N 2 to NH 3 by using the enzyme nitrogenase. A deeper understanding of this enzyme could lead to more efficient catalysts for nitrogen reduction under ambient conditions. Model molecular catalysts have been designed that mimic some of the functions of the active site of nitrogenase. Some modest success has also been achieved in designing electrocatalysts for dinitrogen reduction. Electrochemistry avoids the expense and environmental damage of steam reforming of methane (which accounts for most of the cost of the H-B process), and it may provide a means for distributed production of ammonia. On the oxidative side, nitric acid is the principal commodity chemical containing oxidized nitrogen. Nearly all nitric acid is manufactured by oxidation of NH 3 through the Ostwald process, but a more direct reaction of N 2 with O 2 might be practically feasible through further development of nonthermal plasma technology. Heterogeneous NH 3 oxidation with O 2 is at the heart of the Ostwald process and is practiced in a variety of environmental protection applications as well. Precious metals remain the workhorse catalysts, and opportunities therefore exist to develop lower-cost materials with equivalent or better activity and selectivity. Nitrogen oxides are also environmentally hazardous pollutants generated by industrial and transportation activities, and extensive research has gone into developing and applying reduction catalysts. Three-way catalytic converters are operating on hundreds of millions of vehicles worldwide. However, increasingly stringent emissions regulations, coupled with the low exhaust temperatures of high-efficiency engines, present challenges for future combustion emissions control. Bacterial denitrification is the natural analog of this chemistry and another source of study and inspiration for catalyst design. OUTLOOK Demands for greater energy efficiency, smaller-scale and more flexible processes, and environmental protection provide growing impetus for expanding the scope of nitrogen chemistry. Nitrogenase, as well as nitrifying and denitrifying enzymes, will eventually be understood in sufficient detail that robust molecular catalytic mimics will emerge. Electrochemical and photochemical methods also demand more study. Other intriguing areas of research that have provided tantalizing results include chemical looping and plasma-driven processes. The grand challenge in the field of nitrogen chemistry is the development of catalysts and processes that provide simple, low-energy routes to the manipulation of the redox states of nitrogen.
- Published
- 2018
47. Formation of Alternating trans-A-alt-B Copolymers through Ring-Opening Metathesis Polymerization Initiated by Molybdenum Imido Alkylidene Complexes
- Author
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Hyangsoo Jeong, Richard R. Schrock, and Jeremy M. John
- Subjects
Chemistry ,Norbornadiene ,Organic Chemistry ,ROMP ,Metathesis ,Inorganic Chemistry ,chemistry.chemical_compound ,Polymerization ,Cyclooctene ,Polymer chemistry ,Ring-opening metathesis polymerisation ,Cycloheptene ,Physical and Theoretical Chemistry ,Norbornene - Abstract
Ring-opening metathesis polymerization (ROMP) is used to prepare trans-poly(A-alt-B) polymers from a 1:1 mixture of A and B where A is a cyclic olefin such as cyclooctene (A1) or cycloheptene (A2) and B is a large norbornadiene or norbornene derivative such as 2,3-dicarbomethoxy-7-isopropylidenenorbornadiene (B1) or dimethylspirobicyclo[2.2.1]hepta-2,5-diene-2,3-dicarboxylate-7,1′-cyclopropane (B2). The most successful initiators that were examined are of the type Mo(NR)(CHCMe2Ph)[OCMe(CF3)2]2 (R = 2,6-Me2C6H3 (1) or 2,6-i-Pr2C6H3 (2)). The trans configuration of the AB linkages is proposed to result from the steric demand of B. Both anti-MB and syn-MB alkylidenes are observed during the copolymerization, where B was last inserted into a Mo═C bond, although anti-MB dominates as the reaction proceeds. anti-MB is lower in energy than syn-MB, does not react readily with either A or B, and interconverts slowly with syn-MB through rotation about the Mo═C bond. Syn-MB does not readily react with B, but it does ...
- Published
- 2015
48. Synthesis of Molybdenum and Tungsten Alkylidene Complexes that Contain a tert-Butylimido Ligand
- Author
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Peter Müller, Richard R. Schrock, and Hyangsoo Jeong
- Subjects
Stereochemistry ,Ligand ,Organic Chemistry ,chemistry.chemical_element ,Tungsten ,Oxygen ,Chloride ,Medicinal chemistry ,Inorganic Chemistry ,Metal ,chemistry.chemical_compound ,chemistry ,Molybdenum ,visual_art ,Pyridine ,visual_art.visual_art_medium ,medicine ,Pyridinium ,Physical and Theoretical Chemistry ,medicine.drug - Abstract
A variety of molybdenum or tungsten complexes that contain a tert-butylimido ligand have been prepared. For example, the o-methoxybenzylidene complex W(N-t-Bu)(CH-o-MeOC6H4)(Cl)2(py) was prepared through addition of pyridinium chloride to W(N-t-Bu)2(CH2-o-MeOC6H4)2, while Mo(N-t-Bu)(CH-o-MeOC6H4)(ORF)2(t-BuNH2) complexes (ORF = OC6F5 or OC(CF3)3) were prepared through addition of two equivalents of RFOH to Mo(N-t-Bu)2(CH2-o-MeOC6H4)2. An X-ray crystallographic study of Mo(N-t-Bu)(CH-o-MeOC6H4)[OC(CF3)3]2(t-BuNH2) showed that the methoxy oxygen is bound to the metal and that two protons on the tert-butylamine ligand are only a short distance away from one of the CF3 groups on one of the perfluoro-tert-butoxide ligands (H···F = 2.456(17) and 2.467(17) A). Other synthesized tungsten tert-butylimido complexes include W(N-t-Bu)(CH-o-MeOC6H4)(pyr)2(2,2′-bipyridine) (pyr = pyrrolide), W(N-t-Bu)(CH-o-MeOC6H4)(pyr)(OHMT) (OHMT = O-2,6-(mesityl)2C6H3), W(N-t-Bu)(CH-t-Bu)(OHMT)(Cl)(py) (py = pyridine), W(N-t-Bu)(CH-...
- Published
- 2015
49. Proof of Tacticity of Stereoregular ROMP Polymers through Post Polymerization Modification
- Author
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Richard R. Schrock, Jakub Hyvl, and Benjamin Autenrieth
- Subjects
Inorganic Chemistry ,chemistry.chemical_classification ,Polymers and Plastics ,Polymer science ,Chemistry ,Tacticity ,Organic Chemistry ,Polymer chemistry ,Materials Chemistry ,ROMP ,Polymer ,Post polymerization - Published
- 2015
50. Stereospecific Ring-Opening Metathesis Polymerization (ROMP) of endo-Dicyclopentadiene by Molybdenum and Tungsten Catalysts
- Author
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Antje Ota, Thomas Lehr, Benjamin Autenrieth, Richard R. Schrock, Jonathan C. Axtell, William P. Forrest, Michael R. Buchmeiser, and Hyangsoo Jeong
- Subjects
Polymers and Plastics ,Chemistry ,Organic Chemistry ,chemistry.chemical_element ,ROMP ,Metathesis ,Catalysis ,Inorganic Chemistry ,chemistry.chemical_compound ,Stereospecificity ,Polymerization ,Molybdenum ,Dicyclopentadiene ,Polymer chemistry ,Materials Chemistry ,Ring-opening metathesis polymerisation - Abstract
We report an examination of the ring-opening metathesis polymerization (ROMP) of endo-dicyclopentadiene (DCPD) by 10 well-defined molybdenum-based and 16 tungsten-based alkylidene initiators. Five tungsten-based MAP (monoaryloxide pyrrolide) initiators with the general formula W(X)(CHCMe2Ph)(Me2Pyr)(OAr) (X = arylimido, alkylimido, or oxo; Me2Pyr =2,5-dimethylpyrrolide; OAr = an aryloxide) were found to yield >98% cis, >98% syndiotactic poly(DCPD); they are W(N-t-Bu)(CHCMe3)(pyr)(OHMT) (2, OHMT = O-2,6-(2,4,6-Me3C6H2)2C6H3, pyr = pyrrolide), W(N-2,6-i-Pr2C6H3)(CHCMe2Ph)(pyr)(OHMT) (3), W(O)(CHCMe2Ph)(Me2Pyr)(OHMT)(PPh2Me) (7, Me2Pyr =2,5-dimethylpyrrolide), W(O)(CHCMe2Ph)(Me2Pyr)(ODFT)(PPh2Me) (9, ODFT = O-2,6-(C6F5)2C6H3), and W(O)(CHCMe2Ph)(Me2Pyr)(OTPP)(PMePh2) (10, OTPP = O-2,3,5,6-Ph4C6H). Two biphenolate alkylidene complexes, Mo(N-2,6-Me2C6H3)(CHCMe2Ph)(rac-biphen) (17) and W(N-2,6-Me2C6H3)(CHCMe2Ph)(rac-biphen) (22, biphen =3,3′-(t-Bu)2-5,5′-6,6′-(CH3)4-1,1′-biphenyl-2,2′-diolate), were found to yi...
- Published
- 2015
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