Showing papers on "Norbornene published in 2013"

Ortho vs ipso: site-selective Pd and norbornene-catalyzed arene C-H amination using aryl halides.

Abstract: A Pd and norbornene-catalyzed ortho-arene amination via Catellani-type C–H functionalization is reported. Aryl halides are used as substrates; N-benzoyloxyamines and isopropanol are employed as the amine source (oxidant) and reductant respectively. Examples are provided in 50–99% yields with high functional group tolerance. This method gives complementary site selectivity at the ortho- instead of ipso-position of aryl halides.

Palladium-Catalyzed Synthesis of Carbo- and Heterocycles through Norbornene-Mediated ortho C–H Functionalization

Abstract: Direct aromatic functionalization based on the use of a palladium catalyst and norbornene is a useful method to achieve straightforward synthesis of carbo- and heterocyclic compounds. New ring formation occurs through a cascade process triggered by ortho C–H alkylation (inter- and intramolecular) or arylation (homo­- and heterocoupling) of aryl iodides. Up to four new carbon–carbon bonds are generated under palladium control in a single operation. 1 Introduction 2 ortho C–H Alkylation 2.1 Intermolecular ortho C–H Alkylation 2.1.1 Heck Reaction 2.1.2 C–N Coupling 2.1.3 C–H Arylation 2.2 Intramolecular ortho C–H Alkylation 2.2.1 Heck Reaction 2.2.2 Cyanation Coupling 2.3 Coupling Inter- and Intramolecular ortho C–H Alkylation 3 ortho C–H Arylation 3.1 Homocoupling 3.2 Heterocoupling 3.2.1 α-Arylation/CO Addition 3.2.2 Heck Reaction 3.2.3 C–N Coupling 4 Conclusion

Synthesis of pendant nitronyl nitroxide radical-containing poly(norbornene)s as ambipolar electrode-active materials

Abstract: Ambipolar redox-active polymers with a reversible charging and discharging capability were synthesized via ring-opening metathesis polymerization (ROMP) of nitronyl nitroxide radical (NN) mono- and disubstituted norbornenes which exhibited p- and n-type redox processes (i.e., one-electron oxidation and reduction per NN group, respectively), using Grubbs catalyst to avoid side reactions of the radical moiety allowing over 95% of radicals to survive after ROMP. ROMP of the NN monomers was accomplished with well-controlled molecular weights of the resulting NN polymers which were coincident with theoretical values in the ratio of [monomer]/[catalyst] = 25–200, narrow polydispersity index (ca. 1.2), and high yields even with [monomer]/[catalyst] > 600. The living character for the ROMP of the NN monomers also allowed block copolymerization. NN-containing block copolymers were synthesized through sequential ROMP with benzyl ether-containing norbornene in high yields. The NN polymer/carbon composite electrode e...

Alkene Distortion Energies and Torsional Effects Control Reactivities, and Stereoselectivities of Azide Cycloadditions to Norbornene and Substituted Norbornenes

Abstract: The transition structures for 1,3-dipolar cycloadditions of phenyl azide to norbornene derivatives were located with quantum mechanical methods. Calculations were carried out with M06-2X/6-311G(d,p) and SCS-MP2/6-311G(d,p)//M06-2X/6-311G(d,p) methods. The calculated activation barriers strongly correlate with transition state distortion energies (ΔEd⧧) but not with the reaction energies. Strain-promoted reactions are accelerated because it is easy to distort the strained reactants to a pyramidalized transition state geometry; a correlation of cycloaddition rates with substrate distortion was found for the bicyclic and tricyclic alkenes studied here. The stereoselectivities of reactions of norbornene derivatives are controlled primarily by torsional effects that also influence alkene pyramidalization. These reactions are distortion-accelerated.

Synthesis of Dendronized Polymers via Macromonomer Approach by Living ROMP and Their Characterization: From Rod-Like Homopolymers to Block and Gradient Copolymers

Abstract: Dendronized polymers were synthesized from various endo-tricycle[4.2.2.0]deca-3,9-diene (TD) monomers, using a macromonomer approach, via ring-opening metathesis polymerization. The polymerization was achieved in a living manner to give dendronized polymers with high molecular-weights and narrow polydispersity index. The resulting polymers showed highly extended conformations both in solution and in the solid state, even with relatively small third-generation ester dendrons, because of the rigid backbone of TD monomers. Using their rigidity, block and gradient copolymers containing TD and norbornene moieties were synthesized. Diblock copolymers were produced by the sequential addition of two dendronized macromonomers, and gradient copolymers were produced in a simple batch reaction, because large differences in reactivity allowed for the simultaneous one-pot polymerization, favoring TD over norbornene. Polymer conformations were confirmed by both scattering analysis in solution and atomic force microscopy...

Norbornenes in inverse electron-demand Diels-Alder reactions.

Abstract: Significant differences in the reactivity of norbornene derivatives in the inverse electron-demand Diels-Alder reaction with tetrazines were revealed by kinetic studies. Substantial rate enhancement for the exo norbornene isomers was observed. Quantum-chemical calculations were used to rationalize and support the observed experimental data.

Selective C-2 Alkylation of Tryptophan by a Pd(II)/Norbornene-Promoted C–H Activation Reaction

Abstract: A palladium(II)-catalyzed norbornene-mediated regioselective alkylation at the C-2 indole position of N-tert-butyloxycarbonyl (Boc)-protected (S)-tryptophan ethyl ester is reported. The protocol employs mild reaction conditions and is tolerant of a range of functional groups. The reaction proceeds without racemization at the stereogenic center of the amino acid.

Ladderphanes: a new type of duplex polymers.

Abstract: A polymeric ladderphane is a step-like structure comprising multiple layers of linkers covalently connected to two or more polymeric backbones. The linkers can be planar aromatic, macrocyclic metal complexes, or three-dimensional organic or organometallic moieties. Structurally, a DNA molecule is a special kind of ladderphane, where the cofacially aligned base-pair pendants are linked through hydrogen bonding. A greater understanding of this class of molecules could help researchers develop new synthetic molecules capable of a similar transfer of chemical information.In this Account, we summarize our studies of the strategy, design, synthesis, characterization, replications, chemical and photophysical properties, and assembly of a range of double-stranded ladderphanes with many fascinating structures. We employed two norbornene moieties fused with N-arylpyrrolidine to connect covalently with a range of relatively rigid linkers. Ring opening metathesis polymerizations (ROMP) of these bis-norbornenes using ...

Reversible Activity Modulation of Surface-Attached Grubbs Second Generation Type Catalysts Using Redox-Responsive Polymers

Abstract: Redox-responsive polyvinylferrocene-grafted silica nanoparticles have been used for modulating the catalytic activity of surface-attached Grubbs second generation type catalysts for the ring-opening metathesis polymerization (ROMP) of norbornene monomer. A facile and very efficient protocol for the modification of living polyvinylferrocene chains was developed to introduce a suitable functional group for the intended “grafting onto” approach. Grafted particles were characterized by using TEM, SEM/energy dispersive X-ray spectroscopy (EDS), XPS, small-angle X-ray scattering (SAXS), dynamic light scattering (DLS), and cyclic voltammetry, revealing both the presence of redox-responsive polymers and the presence of Grubbs catalyst in the particle exterior. Chemical oxidation protocols for immobilized polymers were applied to deactivate surface-attached catalysts in ROMP protocols, while chemical in situ reduction immediately led to catalyst’s reactivation.

The use of an emulsion templated microcellular poly(dicyclopentadiene-co-norbornene) membrane as a separator in lithium-ion batteries.

Abstract: The preparation of open-cell macroporous membranes made by the ring opening metathesis polymerization (ROMP) of a mixture of norbornene and dicyclopentadiene, and their basic applicability as separators in lithium-ion batteries, is discussed. Cyclic voltammetry (CV) measurements of negative electrodes (graphite) and positive electrodes (LiCoO2 ) are performed and the results prove the absence of parasitic decomposition reactions within the membrane at high oxidative or reductive potentials. Furthermore, LiCoO2 /Li half cell cycling studies of 100 charging/discharging cycles reveal that the newly disclosed separator and conventional commercial polyolefin based separators have similar performance. These results demonstrate that a potential weakness in the newly disclosed separator, namely residual double bonds present in the polymer network, does not limit the use of this material as a separator in lithium-ion batteries.

Palladium-catalyzed cascade reactions of 3-iodochromones with aryl iodides and norbornadiene leading to annulated xanthones

Abstract: An efficient, palladium-catalyzed cascade reaction, which leads to formation of annulated xanthones, was devised. The process, which uses readily available 3-iodochromones, aryl iodides and norbornadiene as starting materials, takes place via a tandem Heck reaction/double C–H activation/retro-Diels–Alder pathway. The high chemoselectivity of the process is mechanistically unique and it serves as a new approach to achieve regioselective control of C–H activation in Pd/norbornene or norbornadiene systems. Its broad substrate scope, including heteroaryl coupling partners, enables access to diverse annulated xanthones.

Polynorbornene Copolymer with Side-Chain Iridium(III) Emitters and Carbazole Hosts: A Single Emissive Layer Material for Highly Efficient Electrophosphorescent Devices

Abstract: Vinyl addition copolymerization of norbornene monomers using a Pd(II) catalyst in combination with 1-octene chain transfer agent efficiently produces well-defined soluble polynorbornene copolymers bearing side-chain (C∧N)2Ir(O∧O) emitters (C∧N = 2-(4,6-difluorophenyl)-pyridine (M3); 2-phenyl-pyridine (M4); 2-(benzo[b]thiophen-2-yl)-pyridine (M5), O∧O = acetylacetonato) and 9,9′-(1,3-phenylene)bis-9H-carbazole (mCP) or 9,9′-(1,1′-biphenyl)-4,4′-diylbis-9H-carbazole (CBP) host moieties (M1 and M2). The catalytic system provides high-molecular-weight copolymers (Mw = 151 000–457 000 g/mol) with a controlled incorporation of monomers. All copolymers possess high thermal stability with high decomposition (Td5 > 400 °C) and glass transition temperatures (Tg > 330 °C). Among the solution-processed devices fabricated based on a single emissive layer comprising the blue-, green-, and red-phosphorescent copolymers (PBn, PGn, and PRn, n = 1–4) with various concentrations of emitters (1.7–13.9 mol %-Ir), the devices ...

Cationic salt-responsive bottle-brush polymers.

Abstract: A class of cationic bottle-brush polymers that show ionic strength-dependent stimuli responsiveness is prepared. Brush polymers with norbornene as backbone and quaternary ammonium (QA)-containing polycaprolactone copolymers as side chains are synthesized by a combination of ring-opening metathesis polymerization, ring-opening polymerization, and click reaction. In water with low ionic strength, brush polymers are soluble due to the strong electrostatic repulsion between cationic QA groups. As the addition of salt to increase ionic strength, single brush polymers undergo a transition from extended conformation to collapsed state and finally become insoluble in solution due to the screening effect of salts that yield the once-dominant electrostatic interactions among QA species to hydrophobic-hydrophobic interactions.

Direct synthesis of cis-dihalido-bis(NHC) complex of nickel(II) and catalytic application in olefin addition polymerization: Effect of halogen co-ligands and density functional theory study

Abstract: Two novel amine-containing N-heterocyclic carbene ligand precursors [H(1a–b)]Br have been prepared in good yield and fully characterized. Direct syntheses of cis- and trans-dihalido-bis(NHC) nickel complexes [Ni(NHC)2X2] (X = Cl, Br) are reported. The solid structures of trans-[Ni(1a–b)2Br2] (2a–b) and cis-[Ni(1a)2Cl2] (3) were determined by single-crystal X-ray analysis and 3 was found to be the first example of cis-configuration coordination of monodentate NHC ligands to a metal center for dihalido-bis(NHC) nickel complexes. DFT calculations were conducted to determine the energy difference between cis- and trans-isomers of complexes 2a and 3 bearing bromide and chloride co-ligands. The cis-[Ni(1a)2Cl2] (cis-3) is 1.77–1.55 kcal mol−1 lower in energy than its trans-isomer in polar solvents including CH2Cl2 and THF, while the trans-[Ni(1a)2Br2] (trans-2a) is more stable than the cis-isomer similarly in the gas phase. The cis nickel complex 3 with two coordinated monodentate NHCs was tested for olefin addition polymerization at standard conditions. It was found that cis-3 was inactive in ethylene polymerization but showed moderate catalytic activities (0.5–3.0 × 106 g of PNB (mol of Ni)−1 h−1) in the addition polymerization of norbornene in the presence of methylaluminoxane (MAO) as cocatalyst.

State of the art of cyclic olefin polymers

Abstract: Highly active metallocenes and other single site catalysts as well as Grubbs and Schrock metathesis catalytic systems have opened up the possibility to polymerize cycloolefins or to copolymerize them with ethene or propene. The polymers obtained show exciting structures and properties. Cycloolefins such as cyclopentene, cyclooctene, norbornene, and their substituted derivatives are incorporated into the polymer chain either by double bonds or by ring-opening metathesis polymerization. Materials with elastomeric properties or tactic polymers with high glass transition temperatures and melting points are obtained with a wide range of microstructures. For example, cycloolefin copolymers and other homo- and copolymers of norbornene are of great academic and industrial interest because of their properties and applications in optoelectronics, lenses, and coatings.

Cobalt metal organic framework as an efficient heterogeneous catalyst for the oxidation of alkanes and alkenes

Abstract: Co(II) metal-organic framework (Co-MOF) containing Co2+ ions, 1,3,5-benzenetricarboxylic acid and N,N-dimethylformamide was prepared and characterized. It was found that the prepared Co-MOF catalyzes the oxidation of alkanes such as fluorene, adamantane, ethylbenzene, diphenylmethane and alkenes such as diphenylethylene, trans-stilbene, cyclohexene, norbornene, styrene and cyclooctene. Details of moderate to excellent conversions and selectivities toward the alkane C–H oxidations and alkene C=C epoxidations will be discussed in this presentation.

Synthesis and evaluation of an 18F-labelled norbornene derivative for copper-free click chemistry reactions.

Abstract: The copper-free click chemistry reaction between norbornene and tetrazine species is known to proceed in a rapid, reliable and selective manner under mild conditions. Due to these attractive properties, this reaction has recently been explored as a generally applicable method of bioconjugation. Here, we report a convenient synthetic procedure towards a novel 18F-labelled norbornene derivative ([181818F]NFB) and have evaluated its ability to undergo strain-promoted copper-free click chemistry reactions with two model tetrazine species: an asymmetric dipyridyl tetrazine derivative (Tz) and a tetrazine thiourea-coupled stabilised bombesin peptide (TT-BBN). In both cases, [181818F]NFB was found to undergo rapid and high-yielding click chemistry reactions. Furthermore, as reactions of this type could also potentially be used in vivo to facilitate the development of a novel pretargeting approach for tumour imaging and therapy, we have also assessed the radiopharmacological profile (bioavailability, biodistribution, blood clearance and metabolic stability) of [181818F]NFB in normal BALB/c mice. This radiolabelled compound exhibits both high bioavailability and metabolic stability with approximately 90% remaining intact up to 30 min following administration.

Palladium-Mediated [2+1] Cycloaddition of Norbornene Derivatives with Ynamides

Abstract: An efficient palladium-catalyzed [2 + 1]cycloaddition between ynamides and norbornenes or norbornadienes is reported. Both phosphapalla- dacycles and palladium/secondary phosphine oxide catalytic systems were found to be competent for the transformation allowing the preparation of ami- nomethylenecyclopropanes. The reaction showed general applicability to various functionalized bicyclo[2.2.1]hept-2-enes and ynamides. A chiral phosphapalladacycle was tested to carry out this transformation in an enantioselective fashion.

Unique norbornene polymer based 'in-field' sensor for As(III)

Abstract: We report the synthesis of norbornene derived rhodamine (Nor-Rh) and thiol (Nor-Th) monomers and their polymerizations. The response of Nor-Rh against As(III) in the presence of potassium iodate and hydrochloric acid is monitored through UV and fluorescence spectroscopy. The observed colorimetric as well as fluorometric changes are attributed to the redox reaction involved in the unique design. Cyclic voltammogram measurements confirm the oxidation of As(III) to As(V) during the sensing event. The response of the sensing event is instantaneous. This novel design is able to sense ppb levels of As(III) very selectively in an aqueous environment. As(III) is trapped when it is passed through a column containing Nor-Th polymers. As(III) free water is tested using a calibration curve from the Nor-Rh response.

Regioselective Direct C–H Alkylation of NH Indoles and Pyrroles by a Palladium/Norbornene-Cocatalyzed Process

Abstract: Nitrogen-containing heterocycles, including 1H-indoles and electron-deficient 1H-pyrroles, undergo a palladium/norbornene-cocatalyzed regioselective alkylation at the C–H bond adjacent to the NH group. A primary alkyl halide is used as the electrophile and the reaction proceeds smoothly under mild conditions to give 2-alkyl-1H-indoles and 2-substituted or 2,3-disubstituted 5-alkyl-1H-pyrroles in good yields.

A New Access Route to Functionalized Cispentacins from Norbornene β‐Amino Acids

Abstract: An efficient and simple new stereocontrolled access route to novel disubstituted cispentacin derivatives with multiple stereogenic centers from norbornene β-lactam has been developed. The synthesis involves olefinic bond functionalization by dihydroxylation followed by oxidative ring cleavage and transformation of the dialdehyde intermediate through a Wittig reaction.

Highly efficient ethylene/norbornene copolymerization by o‐Di(phenyl)phosphanylphenolate‐based half‐titanocene complexes

Abstract: A series of o-di(phenyl)phosphanylphenolate-based half-titanocene complexes CpTiCl2[O-2-R1-4-R2-6-(Ph2P)C6H2] (Cp = C5H5, 2a: R1 = R2 = H; 2b: R1 = F, R2 = H; 2c: R1 = Ph, R2 = H; 2d: R1 = SiMe3, R2 = H; 2e: R1 = tBu, R2 = H; 2f: R1 = R2 = tBu) have been synthesized in high yields (6587%) by treating CpTiCl3 with 1.0 equiv of the deprotonated ligands in THF. The 1H and 31P NMR spectra indicated that the phosphorus is not coordinated to titanium in complexes 2ac, but is coordinated to titanium in complexes 2df. Structures for 2cf were further confirmed by X-ray crystallography. Complex 2c is essentially a four-coordinate tetrahedral geometry, whereas complexes 2d-f adopt five-coordinate distorted squarepyramid geometry around the titanium center. All complexes exhibited low to moderate activities toward homopolymerization of ethylene. Excitingly, they displayed excellent ability to copolymerize ethylene with norbornene, and catalytic activity was more than 100 times larger than that of ethylene homopolymerization in the case of Ph3CB(C6F5)4/iBu3Al as cocatalyst, affording the copolymers with high comonomer incorporations. Moreover, DFT calculations study had been performed to shed light on the active species and the fundamental role of NBE in improving the catalytic activity. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 1585-1594