Showing papers on "Norbornene published in 2017"
TL;DR: The approach disclosed in this work constitutes a powerful strategy for the synthesis of polymers spanning the linear-to-bottlebrush regimes with controlled grafting density and side chain distribution, molecular attributes that dictate micro- and macroscopic properties.
Abstract: Control over polymer sequence and architecture is crucial to both understanding structure–property relationships and designing functional materials. In pursuit of these goals, we developed a new synthetic approach that enables facile manipulation of the density and distribution of grafts in polymers via living ring-opening metathesis polymerization (ROMP). Discrete endo,exo-norbornenyl dialkylesters (dimethyl DME, diethyl DEE, di-n-butyl DBE) were strategically designed to copolymerize with a norbornene-functionalized polystyrene (PS), polylactide (PLA), or polydimethylsiloxane (PDMS) macromonomer mediated by the third-generation metathesis catalyst (G3). The small-molecule diesters act as diluents that increase the average distance between grafted side chains, generating polymers with variable grafting density. The grafting density (number of side chains/number of norbornene backbone repeats) could be straightforwardly controlled by the macromonomer/diluent feed ratio. To gain insight into the copolymer ...
121 citations
TL;DR: In this article, the two ferrocenyl units in an α-diimine palladium catalyst can be oxidized in a stepwise fashion, which can be used to modulate the catalyst properties during the homopolymerization of ethylene and 1-hexene, as well as the copolymerizations of polyethylene with norbornene, methyl acrylate, and 5-norbornene-2-yl acetate.
Abstract: The majority of work in the field of olefin polymerization catalysis has been focused on ligand modifications. In this work, we describe an alternative strategy for the modulation of olefin polymerization and copolymerization processes. The two ferrocenyl units in an α-diimine palladium catalyst can be oxidized in a stepwise fashion. This stepwise redox control can be used to modulate the catalyst properties during the homopolymerization of ethylene and 1-hexene, as well as the copolymerizations of ethylene with norbornene, methyl acrylate, and 5-norbornene-2-yl acetate. Moreover, polymer microstructure and polydispersity can be controlled during these stepwise oxidation processes.
90 citations
TL;DR: In this paper, the effect of substitution on biaryl-based phosphine-sulfonate nickel catalysts is investigated, and a series of [κ 2-(P,O)-2-(P-PhAr)-1-benzenesulfonato]NiPh(PPh3) nickel complexes are prepared and applied to the polymerization of ethylene as well as its copolymerizations with polar functionalized norbornene comonomers.
69 citations
TL;DR: The meta-C-H arylation of free phenylacetic acid was realized using 2-carbomethoxynorbornene (NBE-CO2 Me) as a transient mediator and both the modified norbornene and the mono-protected 3-amino-2-hydroxypyridine type ligand are crucial for this auxiliary-free meta-HArylation reaction.
Abstract: The meta-C-H arylation of free phenylacetic acid was realized using 2-carbomethoxynorbornene (NBE-CO2 Me) as a transient mediator. Both the modified norbornene and the mono-protected 3-amino-2-hydroxypyridine type ligand are crucial for this auxiliary-free meta-C-H arylation reaction. A series of phenylacetic acids, including mandelic acid and phenylglycine, react smoothly with various aryl iodides to provide the meta-arylated products in high yields.
60 citations
TL;DR: Highly cis-specific (living) ROMPs of norbornene have been achieved by V(CHSiMe3)(N-2,6-X2C6H3)[OC(CF3)3](PMe3)2 (X = H, Cl), and the activity increased at high temperature without a decrease in cis specificity in the presence of PMe3.
Abstract: Reported examples for synthesis of vanadium–alkylidene complexes and some selected reactions have been summarized. (Imido)vanadium(V)–alkylidene complexes exhibit catalytic activities for ring-opening metathesis polymerization (ROMP) of cyclic olefins; V(CHSiMe3)(N-2,6-Cl2C6H3)(OC6F5)(PMe3)2 exhibited remarkable catalytic activities for ROMPs of norbornene derivatives, polymerized cyclopentene and cis-cyclooctene. Highly cis-specific (living) ROMPs of norbornene have been achieved by V(CHSiMe3)(N-2,6-X2C6H3)[OC(CF3)3](PMe3)2 (X = H, Cl), and the activity increased at high temperature (50 and 80 °C) without a decrease in cis specificity (98%) in the presence of PMe3.
59 citations
TL;DR: In this paper, the first gold(III)-arene complexes were synthesized and characterized by NMR spectroscopy, X-ray diffraction, and DFT calculations.
Abstract: The synthesis and characterization of the first gold(III)–arene complexes are described. Well-defined (P,C)-cyclometalated gold(III)–aryl complexes were prepared and characterized by NMR spectroscopy. These complexes swiftly and cleanly reacted with norbornene and ethylene to provide cationic gold(III)–alkyl complexes, in which the remote phenyl ring was η2-coordinated to gold. The interaction between the aromatic ring and the gold(III) center was thoroughly analyzed by NMR spectroscopy, X-ray diffraction, and DFT calculations. The π–arene coordination was found to significantly influence the stability and reactivity of low coordinated gold(III) alkyl species.
43 citations
TL;DR: In this paper, the structures of the first insertion products (syn/anti, cis/trans) in the ring-opening metathesis polymerization (ROMP) of norbornene derivatives using both neutral and cationic molybdenum imido alkylidene N-heterocyclic carbene (NHC) complexes based on an O-chelating NHC were identified.
Abstract: The structures of the first insertion products (syn/anti, cis/trans) in the ring-opening metathesis polymerization (ROMP) of norbornene derivatives using both neutral and cationic molybdenum imido alkylidene N-heterocyclic carbene (NHC) complexes based on an O-chelating NHC, i.e., [Mo(N-2,6-Me2-C6H3)(N-mesityl-N′-2-O-1-C6H4-imidazolin-2-ylidene)(CHCMe2Ph)(OTf)] (1), [Mo(N-2,6-iPr2-C6H3)(N-2,6-iPr2-C6H3-N′-2-O-1-C6H4-imidazolin-2-ylidene)(CHCMe2Ph)(OTf)] (2), and [Mo(N-2,6-iPr2-C6H3)(N-2,6-iPr2-C6H3-N′-2-O-1-C6H4-imidazolin-2-ylidene)(CH3CN)(CHCMe2Ph)+ (B(ArF)4–)] (3), have been identified. Also, syn/anti interconversion rates of catalysts 1–3 have been determined in acetonitrile. Correlation of these values with the rate constants of polymerization revealed the importance of a balanced ratio between these two values. Disrupting that balance by changing the solvent or the monomer or by switching to a similar, but more ROMP-active catalyst leads to significant changes in the cis/trans contents of the result...
39 citations
TL;DR: In this paper, the authors explored whether graphene oxide after modification with copper coordinated amino acids could attain an excellent catalytic activity for the epoxidation of norbornene, and the results showed that the prepared novel catalysts showed good performance compared with reported catalysts in other works.
37 citations
TL;DR: Rhodium-catalyzed alkylation reactions of C-H bonds (hydroarylation) in aromatic amides that contain an 8-aminoquinoline as a directing group with alkenes are discussed in this paper.
Abstract: Rhodium-catalyzed alkylation reactions of C-H bonds (hydroarylation) in aromatic amides that contain an 8-aminoquinoline as a directing group with alkenes are discussed. Various alkenes, including acrylic esters, styrenes, α,β-unsaturated butyrolactones, dihydrofurans, maleimides, and norbornene derivatives are applicable to this C-H alkylation. The reaction with norbornene gives unusual endo-hydroarylation products in a high degree of selectivity. The use of a carboxylic acid as an additive dramatically increases both the reactivity and the selectivity of the reaction. The results of deuterium-labeling experiments suggest that hydrometalation or carbometalation, which are commonly accepted mechanisms for C-H alkylation reactions, are not involved. Instead, the reaction appears to proceed through a rhodium carbene intermediate generated from the alkene.
37 citations
TL;DR: In this paper, polynorbornenes with different crosslinker contents were prepared using ring-opening metathesis polymerization (ROMP), and the results obtained showed that the proton conductivity, water uptake and swelling ratio of the membranes were all lowered as the crosslink density was enhanced.
35 citations
TL;DR: In this paper, the authors used CANAL to synthesize ladder polymers consisting of rigid and kinked norbornyl benzocyclobutene backbones and bearing various functional groups, such as alcohol, amine, ester, carbamate, amide, benzyl bromide, azide and heterocycles.
Abstract: Rigid ladder polymers represent a unique polymer architecture but have limited synthetic accessibility and structural diversity. Using catalytic arene-norbornene annulation (CANAL) polymerization, we synthesized ladder polymers consisting of rigid and kinked norbornyl benzocyclobutene backbones and bearing various functional groups, such as alcohol, amine, ester, carbamate, amide, benzyl bromide, azide, and heterocycles. The incorporation of functional groups was achieved by either copolymerization of functionalized ladder-type dinorbornenes or postpolymerization functionalization. Functionalization of ladder polymers allows modification of their solubility, compatibility, and other properties, expanding their utilities. These ladder polymers remain microporous and highly glassy, which are desirable for separation and high-temperature applications.
TL;DR: The results clearly suggest that hydrometalation or carbometalation are not involved as the key step in the present reaction, and suggest that the reaction involves a rhodium carbene complex generated from norbornene as theKey intermediate.
Abstract: Hydroarylation is an environmentally attractive strategy which incorporates all of the atoms contained in the substrates into the desired products. Almost all the hydroarylations of norbornene reported to date involve an exo-selective reaction. Here we show the endo-selective hydroarylation of norbornene in the Rh(I)-catalyzed reaction of aromatic amides. The addition of sterically bulky carboxylic acids enhances the endo-selectivity of the reaction. The results of deuterium-labeling experiments show that both the ortho-carbon and the ortho-hydrogen atoms of aromatic amides were attached to the same carbon atom of the norbornane skeleton in the hydroarylation product. These results clearly suggest that hydrometalation or carbometalation, which are commonly accepted mechanisms for the catalytic hydroarylation of C-H bonds, are not involved as the key step in the present reaction, and suggest that the reaction involves a rhodium carbene complex generated from norbornene as the key intermediate.
TL;DR: In this article, two palladium complexes (NHC)Pd(allyl)Cl (naphthoquinimidazolylidene, Ar = 2.6-Me2-C6H3, 2,6-iPr2-c6H 3) bearing a redox-active naphthoequinone moiety were prepared and characterized.
Abstract: Two palladium complexes (NHC)Pd(allyl)Cl (NHC = 1,3-Ar2-naphthoquinimidazolylidene, Ar = 2,6-Me2-C6H3, 2,6-iPr2-C6H3) bearing a redox-active naphthoquinone moiety, were prepared and characterized. Electro-chemistry cyclic voltammetry and NMR studies showed that these palladium complexes could be easily reduced and re-oxidized using CoCp2 and [FeCp2][BAF] (BAF = tetrakis(3,5-bis(trifluoromethyl)phenyl)borate) reagents. The properties of these neutral and reduced palladium complexes in norbornene, 5-norbornene-2-yl acetate and 1-chloro-1-octyne polymerization were studied. The neutral complexes were active in all of these polymerization reactions in the presence of Na[BAF]. In contrast, the reduced analogues showed very low activity under the same conditions. As such, switchable polymerization could be realized in this catalytic system.
TL;DR: Benzylic AdoMet analogs enable highly efficient enzymatic transfer of norbornenes to nucleic acids and subsequent tetrazine ligation.
Abstract: Site-specific alkylation of complex biomolecules is critical for late-stage product diversification as well as post-synthetic labeling and manipulation of proteins and nucleic acids. Promiscuous methyltransferases in combination with analogs of S-adenosyl-L-methionine (AdoMet) can functionalize all major classes of biomolecules. We show that benzylic moieties are transferred by Ecm1 with higher catalytic efficiency than the natural AdoMet. A relative specificity of up to 80% is achieved when a norbornene moiety is placed in para-position, enabling for the first time enzymatic norbornene transfer to specific positions in DNA and RNA— even in cell lysate. Subsequent tetrazine ligation of the stable norbornene moiety is fast, efficient, biocompatible and – in combination with an appropriate tetrazine – fluorogenic.
TL;DR: The proposed method addresses the condensation/amination of free-N-H-bearing substrates in acetone monoarylations and the synthesis of extremely congested 2,6-disubstituted aryl acetones.
TL;DR: In the present study, anionic polymerization techniques were employed for the synthesis of low molecular weight poly(ethylene oxide) (PEO) macromonomers bearing norbornenyl end groups that were characterized by SEC, MALDI-TOF and NMR spectroscopy.
Abstract: Branched polymers are a valuable class of polymeric materials. In the present study, anionic polymerization techniques were employed for the synthesis of low molecular weight poly(ethylene oxide) (PEO) macromonomers bearing norbornenyl end groups. The macromonomers were characterized by SEC, MALDI-TOF and NMR spectroscopy. Subsequent ring opening metathesis polymerization (ROMP) of the macromonomers using ruthenium catalysts (Grubbs catalysts of the 1st, 2nd and 3rd generations) afforded the corresponding polymacromonomers. The effects of the macromonomer molecular weight, the type of the catalyst, the nature of the solvent, the monomer concentration and the polymerization temperature on the molecular characteristics of the branched polymers were examined in detail. The crystallization behavior of the macromonomers and the corresponding polymacromonomers were studied by Differential Scanning Calorimetry (DSC). The thermal stability and the kinetics of the thermal decomposition of the samples were also studied by Thermogravimetric Analysis (TGA). The activation energies of the thermal decomposition were analyzed using the Ozawa⁻Flynn⁻Wall and Kissinger methodologies.
TL;DR: Trimethylammonium-containing (TMA) polynorbornene is synthesized via ring-opening metathesis polymerization for study as an anion exchange membrane (AEM) in solid state alkaline fuel cells as discussed by the authors.
TL;DR: Well-defined molecular brushes bearing polypeptides as side chains were prepared by a “grafting through” synthetic strategy with two-dimensional control over the brush molecular architectures through aminolysis of PBLA side chains for facile installment of functional moieties onto the molecular brushes.
Abstract: Well-defined molecular brushes bearing polypeptides as side chains were prepared by a “grafting through” synthetic strategy with two-dimensional control over the brush molecular architectures. By integrating N-carboxyanhydride ring-opening polymerizations (NCA ROPs) and ring-opening metathesis polymerizations (ROMPs), desirable segment lengths of polypeptide side chains and polynorbornene brush backbones were independently constructed in controlled manners. The N2 flow accelerated NCA ROP was utilized to prepare polypeptide macromonomers with different lengths initiated from a norbornene-based primary amine, and those macromonomers were then polymerized via ROMP. It was found that a mixture of dichloromethane and an ionic liquid were required as the solvent system to allow for construction of molecular brush polymers having densely-grafted peptide chains emanating from a polynorbornene backbone, poly(norbornene-graft-poly(β-benzyl-l-aspartate)) (P(NB-g-PBLA)). Highly efficient postpolymerization modificat...
TL;DR: The synthesis of norbornene derivatives containing alkyne or biotin affinity tags are reported to facilitate the use of these probes in chemical biology and proteomics.
TL;DR: First- and second-generation Percec-type dendronized ferrocenyl norbornene macromonomers containing, respectively, three and nine ferrocENyl termini are synthesized and polymerized by ring-opening metathesis polymerization using Grubbs' third-generation olefin met athesis catalyst with several monomer/catalyst feed ratios between 10 and 50.
Abstract: First- and second-generation Percec-type dendronized ferrocenyl norbornene macromonomers containing, respectively, three and nine ferrocenyl termini are synthesized and polymerized by ring-opening metathesis polymerization using Grubbs' third-generation olefin metathesis catalyst with several monomer/catalyst feed ratios between 10 and 50. The rate of polymerization is highly dependent on the generation of the dendronized macromonomers, but all these ring-opening metathesis polymerization reactions are controlled, and near-quantitative monomer conversions are achieved. The numbers of ferrocenyl groups obtained are in agreement with the theoretical ones according to the cyclic voltammetry studies as determined using the Bard–Anson method.
TL;DR: Control and complete deprotection of the benzyl groups using trimethylsilyl iodide resulted in poly(l-glutamic acid) based brush polymers with molecular weights up to 3.6 MDa, which may potentially be used to prepare size-controlled unimolecular polymeric nanomedicine for drug delivery applications.
Abstract: We report the synthesis and characterization of high-molecular weight poly(L-glutamic acid) based brush polymers. Utilizing a combination of ring-opening metathesis polymerization of norbornene based monomers and ring-opening polymerization of γ-benzyl-L-glutamate N-carboxyanhydride, high-molecular weight γ-benzyl protected poly(L-glutamic acid) brush polymers are synthesized. Controlled and complete deprotection of the benzyl groups using trimethylsilyl iodide resulted in poly(L-glutamic acid) based brush polymers with molecular weights up to 3.6 MDa, which may potentially be used to prepare size-controlled unimolecular polymeric nanomedicine for drug delivery applications. Camptothecin brush poly(L-glutamic acid) conjugates were prepared and their stability, drug release kinetics, and in vitro toxicity were studied.
TL;DR: In this article, a combined cis-specific ring-opening metathesis polymerization (ROMP) of norbornene with terminal olefins (1-hexene, allyltrimethylsilane (ATMS), etc.) was achieved at 80 °C in the presence of V(CHSiMe3)(N-2,6-Cl2C6H3)[OC(CF3)3](PMe3)2.
TL;DR: In this article, the synthesis of low viscosity liquid α,ω-bis(trialkoxysilyl) telechelic copolyolefins (DF) via ring-opening metathesis polymerization (ROMP)/cross-metathesis (CM) is reported.
TL;DR: The gelatin based dynamic hydrogels demonstrated controllable stiffness over a 9.5 kPa–17.8 kPa range and are candidates for studying dynamic cell processes, for example fibrosis.
TL;DR: It is found that norbornene not only acts as the removable scaffold in Catellani-Lautens-type reactions, but also plays the role of suppressing the competitive migratory insertion of ethyl acetate.
Abstract: The Pd-catalyzed cross-coupling of aryl iodide, benzoic anhydride and ethyl acrylate provided a useful alternative to synthesize alkenylated aryl ketones with good selectivity and functional-group tolerance. In this manuscript, density functional theory (DFT) calculations were performed to address the detailed reaction mechanism. Computational results support the experimentally proposed Pd(0)–Pd(II)–Pd(IV) catalytic cycle and further clarify that the rate-determining step is the oxidative addition of benzoic anhydride, the regioselectivity-determining step is the migratory insertion of ethyl acrylate and the following β-H elimination determines the stereoselectivity. The regioselectivity can be attributed to the steric and electronic effect of ethyl acrylate and the stereoselectivity can be explained by the steric repulsion between the toluene moiety and the CO2Et moiety. Furthermore, we found that norbornene not only acts as the removable scaffold in Catellani–Lautens-type reactions, but also plays the role of suppressing the competitive migratory insertion of ethyl acetate. Norbornene insertion and ethyl acetate insertion are found to have close free energy barriers, which shed light on the origin of using stoichiometric amounts of norbornene.
TL;DR: A ring-opening metathesis polymerization catalyst supported by a redox-active N-heterocyclic carbene was synthesized and found to undergo reversible reduction, but upon reduction, the selectivity was found to reverse.
Abstract: A ring-opening metathesis polymerization catalyst supported by a redox-active N-heterocyclic carbene was synthesized and found to undergo reversible reduction. In its neutral form, the catalyst polymerized 1,5-cis,cis-cyclooctadiene at a higher rate than that of a norbornene derivative; however, upon reduction, the selectivity was found to reverse. Utilizing this oxidation state dependent selectivity, a series of copolymers with controlled compositions, microstructures, and physical properties were prepared by redox-switching the catalyst over the course of a series of polymerization reactions.
TL;DR: In this article, a new heterogeneous catalyst containing a copper(II) Schiff base complex covalently immobilized on the surface of silica-coated Fe3O4 nanoparticles was synthesized.
Abstract: A new heterogeneous catalyst containing a copper(II) Schiff base complex covalently immobilized on the surface of silica-coated Fe3O4 nanoparticles (Fe3O4@SiO2-Schiff base-Cu(II)) was synthesized. Characterization of this catalyst was performed using various techniques. The catalytic potential of the catalyst was investigated for the oxidation of various alkenes (styrene, α-methylstyrene, cyclooctene, cyclohexene and norbornene) and alcohols (benzyl alcohol, 3-methoxybenzyl alcohol, 3-chlorobenzyl alcohol, benzhydrol and n-butanol) using tert-butyl hydroperoxide as oxidant. The catalytic investigations revealed that Fe3O4@SiO2-Schiff base-Cu(II) was especially efficient for the oxidation of norbornene and benzyl alcohol. The results showed that norbornene epoxide and benzoic acid were obtained with 100 and 87% selectivity, respectively. Moreover, simple magnetic recovery from the reaction mixture and reuse for several times with no significant loss in catalytic activity were other advantages of this catalyst
06 Dec 2017
TL;DR: On the basis of V nuclear magnetic resonance, electron spin resonance, and V K-edge X-ray absorption near-edge structure (XANES) spectra of the catalyst solution, the observed difference in the catalyst performance in the presence of MAO and Me2AlCl cocatalyst should be due to the formation of different catalytically active species with different oxidation states.
Abstract: (Imido)vanadium(V) dichloride complexes containing 2-(2′-benzimidazolyl)-6-methylpyridine ligand (L) of type V(NR)Cl2(L) [R = 1-adamantyl (Ad, 1), C6H5 (2), and 2,6-Me2C6H3 (3)] have been prepared, and their structures were determined by X-ray crystallography as distorted trigonal bipyramidal structures around vanadium. Reactions with ethylene using 1–3 in the presence of methylaluminoxane (MAO) afforded a mixture of oligomer and polymers, and the compositions were affected by the imido ligand employed. By contrast, 1–3 exhibited remarkable catalytic activities for ethylene polymerization in the presence of Me2AlCl; the phenylimido complex (2) exhibited the highest activity [80 100 kg-PE/mol-V·h turn over frequency (TOF, 2 850 000 h–1, 792 s–1)]. The ethylene copolymerizations with norbornene afforded ultrahigh-molecular-weight copolymers with uniform molecular weight distributions and compositions [e.g., Mn = 1.71–2.66 × 106, Mw/Mn = 2.27–2.53]. On the basis of V nuclear magnetic resonance (51V NMR), ele...
TL;DR: In this paper, the NiL2Br2 catalyst exhibited high activity towards homopolymerization and copolymerization of norbornene(NB) and butyl methacrylate (BMA) and was confirmed to be vinyl-addition copolymers and noncrystalline.
TL;DR: A palladium-catalyzed direct C2-arylation reaction of free (N H) indoles has been developed based on a norbornene-mediated C H activation process on the indole ring which features high regioselectivity and excellent functional group tolerance.