Showing papers on "Norbornene published in 2009"

Efficient Synthesis of Narrowly Dispersed Brush Polymers via Living Ring-Opening Metathesis Polymerization of Macromonomers

Abstract: Various macromonomers (MMs) were efficiently synthesized through the copper-catalyzed “click” coupling of a norbornene moiety to the chain end of poly(methylacrylate), poly(t-butylacrylate), and polystyrene that were prepared using atom transfer radical polymerization. Ring-opening metathesis polymerization (ROMP) of these MMs was carried out using the highly active, fast-initiating ruthenium catalyst (H2IMes)(pyr)2(Cl)2RuCHPh in THF at room temperature. ROMP of MMs was found to be living with almost quantitative conversions (>90%) of MMs, producing brush polymers with very low polydispersity indices of 1.01−1.07 and high Mn’s of 200−2600 kDa. The efficient ROMP of such MMs provides facile access to a variety of brush polymers and overcomes previous difficulties in the controlled polymerization of MMs. Atomic force microscopy of the brush polymer products revealed extended, wormlike shapes as a result of significant steric repulsion of densely grafted side chains.

Synthesis in the key of Catellani: norbornene-mediated ortho C-H functionalization.

Abstract: In the late 1990s Catellani reported a remarkable palladium-catalyzed domino reaction [1] in the presence of norbornene, in which aryl iodides were alkylated at the ortho positions by alkyl halides followed by a Mizoroki-Heck reaction to afford products of type 1 (Scheme 1) [2–4]. The process allowed for the construction of up to three carbon–carbon bonds in a single reaction using simple, commercially available starting materials. We called this process the Catellani reaction, and in the past decade considerable attention has been focused upon unlocking its synthetic potential. This review will primarily focus upon the mechanistic aspects of the Catellani reaction, followed by an overview of the synthetic scope of molecules currently accessible with this technology.

A Ring-Opening Metathesis Polymerization Route to Alkaline Anion Exchange Membranes: Development of Hydroxide-Conducting Thin Films from an Ammonium-Functionalized Monomer

Abstract: We report the development of a facile ring-opening olefin metathesis route to alkaline anion exchange membranes via the copolymerization of a tetraalkylammonium-functionalized norbornene with dicyclopentadiene. The thin films generated are mechanically strong and exhibit high hydroxide conductivities and exceptional methanol tolerance.

Reactions of an Intramolecular Frustrated Lewis Pair with Unsaturated Substrates: Evidence for a Concerted Olefin Addition Reaction

Abstract: The intramolecular frustrated Lewis pair (mesityl)(2)P-CH(2)-CH(2)-B(C(6)F(5))(2) was generated in situ by HB(C(6)F(5))(2) hydroboration of dimesitylvinylphosphine. The compound reacts with 1-pentyne by C-H bond cleavage. It undergoes a 1,2-addition to the carbonyl group of trans-cinnamic aldehyde to yield a zwitterionic six-membered heterocycle by B-O and P-C bond formation. The Lewis pair regioselectively adds to the electron-rich C=C double bond of ethyl vinyl ether, and it selectively undergoes an exo-cis-2,3-addition to norbornene. A combined experimental/theoretical study suggests that this reaction takes place in an asynchronous concerted fashion with the B-C bond being formed in slight preference to the P-C bond. The addition products were characterized by X-ray crystal structure analyses.

Development and Application of FI Catalysts for Olefin Polymerization: Unique Catalysis and Distinctive Polymer Formation

Abstract: Catalysts contribute to the efficient production of chemicals and materials in almost all processes in the chemical industry. The polyolefin industry is one prominent example of the importance of catalysts. The discovery of Ziegler-Natta catalysts in the 1950s resulted in the production of high-density polyethylenes (PEs) and isotactic polypropylenes (iPPs). Since then, further catalyst development has led to the production of a new series of polyolefins, including linear low-density PEs, amorphous ethylene/1-butene copolymers, ethylene/propylene/diene elastomers, and syndiotactic PPs (sPPs). Polyolefins are now the most important and the most produced synthetic polymers. This Account describes a family of next-generation olefin polymerization catalysts (FI catalysts) that are currently being used in the commercial production of value-added olefin-based materials. An FI catalyst is a heteroatom-coordinated early transition metal complex that combines a pair of nonsymmetric phenoxy-imine [O(-), N] chelating ligands with a group 4 transition metal. The catalytically active species derived from FI catalysts is highly electrophilic and can assume up to five isomeric structures based on the coordination of the phenoxy-imine ligand. In addition, the accessibility of the ligands of the FI catalysts and their amenability to modification offers an opportunity for the design of diverse catalytic structures. FI catalysts exhibit many unique chemical characteristics: precise control over chain transfers (including highly controlled living ethylene and propylene polymerizations), extremely high selectivity for ethylene, high functional group tolerance, MAO- and borate-free polymerization catalysis, significant morphology polymer formation, controlled multimodal behavior, high incorporation ability for higher alpha-olefins and norbornene, and highly syndiospecific and isospecific polymerizations of both propylene and styrene. These reactions also occur with very high catalyst efficiency. The reaction products include a wide variety of unique olefin-based materials, many of which were previously unavailable via other means of polymerization. We have produced selective vinyl- and Al-terminated PEs, ultrahigh molecular weight linear PEs, regio- and stereoirregular high molecular weight poly(higher alpha-olefin)s, ethylene- and propylene-based telechelic polymers, a wide array of polyolefinic block copolymers from ethylene, propylene, and higher alpha-olefins, and ultrafine noncoherent PE particles. FI catalysts are important from the organometallic, catalytic, and polymer science points of view, and the chemical industry is now using them for the production of value-added olefin-based materials. We anticipate that future research on FI catalysts will produce additional olefin-based materials with unique architectures and material properties and will offer scientists the chance to further study olefin polymerization catalysis and related reaction mechanisms.

A direct route to cyclic organic nanostructures via ring-expansion metathesis polymerization of a dendronized macromonomer.

Abstract: Cyclic organic nanostructures were prepared via ring-expansion metathesis polymerization of a dendronized norbornene macromonomer The strategy provides a direct, efficient route to nanoscale rings in a single operation AFM imaging confirmed toroidal features having diameters of ca 35−40 nm

The norbornene shuttle: multicomponent domino synthesis of tetrasubstituted helical alkenes through multiple C--H functionalization.

Abstract: Shall we dance? Within the proposed mechanism for the palladium-catalyzed title reaction, the strained alkene norbornene (or norbornadiene) enters and exits the catalytic cycle in a catalytic "square dance", acting as both a promoter and a coupling partner in the formation of four carbon-carbon bonds, two of them by challenging C--H activation processes.

One-Pot Synthesis of Brush-Like Polymers via Integrated Ring-Opening Metathesis Polymerization and Polymerization of Amino Acid N-Carboxyanhydrides

Abstract: We report here the integration of ring-opening metathesis polymerization (ROMP) and ring-opening polymerization of the amino acid N-carboxyanhydride (NCA) to allow facile synthesis of brush-like polymers containing polypeptide as the brush side chains. ROMP of N-trimethylsilyl norbornenes rendered the preparation of poly(norbornene)s bearing pendant N-TMS groups. With no need to purify the resulting polymers, such macromolecular initiators could subsequently initiate controlled NCA polymerizations. Brush-like poly(norbornene)s with grafted polypeptides or block copolypeptides were readily obtained with controlled molecular weights and narrow molecular weight distributions. Because numerous ROMP and NCA monomers are widely available, this novel polymerization technique will allow easy access to numerous brush-like hybrid macromolecules with unprecedented properties and broad applications.

Norbornene-Based Copolymers Containing Platinum Complexes and Bis(carbazolyl)benzene Groups in Their Side-Chains

Abstract: Two norbornene-functionalized tetradentate cyclometalated platinum(II) complexes were synthesized and copolymerized with a bis(carbazolyl)benzene-based comonomer using ring-opening metathesis polymerization (ROMP). The copolymers are soluble in common solvents and the molecular weights of these copolymers can be well controlled as a result of the living character of the ROMP. The photophysical and electrochemical properties of the copolymers were compared to their corresponding small molecules. The copolymers showed almost identical photophysical and electrochemical properties demonstrating the inertness of the polymer backbone toward the photophysical properties of the tethered platinum complexes. All complexes exhibit bright photoluminescence in the green region with lifetimes around 0.4 μs and solution phosphorescence quantum efficiencies as high as 0.56, which suggest that these materials could be interesting for OLED applications.

Tunable, Temperature‐Responsive Polynorbornenes with Side Chains Based on an Elastin Peptide Sequence

Abstract: Random copolymers made by living ring-opening metathesis polymerization of norbornene monomers containing either the elastin peptide sequence -(VPGVG)- or pentaethylene glycol (see scheme; Mes=mesityl, pyr=pyridine) exhibit a lower critical solution temperature (LCST). The LCST can be easily modified by varying the ratio of the co-monomers in the polymer feed.

Fe(OTf)(3)-catalyzed addition of sp C-H bonds to olefins.

Abstract: We have developed a novel acid-catalyzed addition of acetylenes to olefins in the presence of catalytic triflic acid or its metal salts. Among the various triflates, the catalytic activities depend on the cation and decrease in the order Fe3+ > Al3+ ≫ H+, In3+, Sc3+ ≫ Cu2+, Ag+. In general, “hard” acids gave higher yields than “soft” acids such as copper and silver triflates. Among relatively hard acids, Fe(OTf)3 was the best catalyst, which is also the case for ester formation from carboxylic acids and olefins. Our procedure is unique and attractive for the following reasons: (i) The reaction proceeds even for isolated C═C double bonds, as in norbornene. (ii) The reaction is promoted by acid catalysts and does not include an oxidation−reduction cycle for transition metals. (iii) Moreover, these catalysts are inexpensive, abundant, and less toxic than precious-metal-based catalysts. The reaction proceeds even under air and does not require precious metals.

γ-Agostic Species as Key Intermediates in the Vinyl Addition Polymerization of Norbornene with Cationic (allyl)Pd Catalysts: Synthesis and Mechanistic Insights

Abstract: Several cationic (allyl)Pd(II) complexes were synthesized and shown to be highly active for (2,3)-vinyl addition polymerization of norbornene (NB) to yield polymers with low molecular weight distributions (MWDs) ranging from 1.2−1.4. Despite the low MWDs, slow initiation was followed by rapid propagation preventing molecular weight control of the poly(norbornene). Several intermediates in these polymerizations initiated with [(2-R-allyl)Pd(mesitylene)]+ complexes were fully characterized (NMR and X-ray diffraction). Consistent with previous observations the allyl and NB units couple in cis-exo fashion to yield a σ,π-complex capped by mesitylene. Mesitylene is readily displaced by NB to form an agostic intermediate in which NB acts as a bidentate ligand and binds to the cationic Pd center via the π-system and a γ-agostic interaction with the syn hydrogen at C7. The identity of this complex was established by NMR spectroscopy and single-crystal X-ray diffraction. It is significant since it suggests bidentat...

Recent Progress in the Vinylic Polymerization and Copolymerization of Norbornene Catalyzed by Transition Metal Catalysts

Abstract: Here progress in the development of the catalytic addition polymerization and copolymerization of norbornene by various transition-metal complexes is described. A full literature account is given in this review mostly covering the years of 2000 to the early of 2009. The interest in vinyl homo-polynorbornene is driven by its dielectric and mechanical properties for the technical application as an interlevel dielectric in microelectronics applications. For comparison, the norbornene/olefin copolymerization is also considered. The metal catalysts of Ti, Cr, Zr, V, Fe, Co, Ni, Pd and Cu are introduced and methylalumoxane (MAO) or perfluorinated borane, e.g. B(C 6 F 5 ) 3 , cocatalysts are presented in terms of their activity and ligand effects are emphasized.

Copolymerization of ethylene with norbornene catalyzed by cationic rare earth metal fluorenyl functionalized N-heterocyclic carbene complexes.

Abstract: Rare earth metal bis(alkyl) complexes attached by fluorenyl modified N-heterocyclic carbene (NHC) (Flu-NHC)Ln(CH2SiMe3)2 (Flu-NHC = (C13H8CH2CH2(NCHCCHN)C6H2Me3-2,4,6); Ln = Sc (2a); Y (2b); Ho (2c); Lu (2d)), (tBuFlu-NHC)Ln(CH2SiMe3)2 (tBuFlu-NHC = 2,7-tBu2C13H6CH2CH2(NCHCCHN)C6H2Me3-2,4,6; Ln = Sc (1a); Lu (1d)) and attached by indenyl modified N-heterocyclic carbene (Ind-NHC)Ln(CH2SiMe3)2 (Ind-NHC = C9H6CH2CH2(NCHCCHN)C6H2Me3-2,4,6; Ln = Sc (3a); Lu (3d)), under the activation of AliBu3 and [Ph3C][B(C6F5)4], showed varied catalytic activities toward homo- and copolymerization of ethylene and norbornene. Among which the scandium complexes, in spite of ligand type, exhibited medium to high catalytic activity for ethylene polymerization (105 g molSc−1 h−1 atm−1), but all were almost inert to norbornene polymerization. Remarkably, higher activity was found for the copolymerization of ethylene and norbornene when using Sc based catalytic systems, which reached up to 5 × 106 g molSc−1 h−1 atm−1 with 2a. The composition of the isolated copolymer was varying from random to alternating according to the feed ratio of the two monomers (rE = 4.1, rNB = 0.013). The molecular structure of complex 1d was characterized by X-ray analysis. The influences of structural factors of complexes and polymerization conditions on both the catalytic activity and the norbornene content in the copolymer were discussed.

Iron(III) aroylhydrazone complexes: Structure, electrochemical studies and catalytic activity in oxidation of olefins

Abstract: Tridentate Schiff base ligands derived from aromatic aldehydes and benzhydrazide, and their iron complexes [Fe(L1)(HL1)] 1, [Fe(HL1)Cl2(CH3OH)]·(CH3OH) 2 and [Fe(HL2)Cl2(H2O)] 3 have been prepared and characterized (H2L1 = (E)-N′-(2-hydroxy-3-methoxybenzylidene)benzohydrazide, H2L2 = (E)-N′-(5-bromo-2-hydroxybenzylidene)benzohydrazide). The crystal structure of 2 has been determined. The electrochemical properties of these complexes have been investigated by cyclic voltammetric technique in acetonitrile solutions. Electrochemical studies have revealed quasi-reversibility for these compounds. The catalytic potential of these complexes has been tested for the oxidation of cyclooctene using tert-butylhydroperoxide (TBHP) as oxidant. The effects of the molar ratio of oxidant to substrate, the temperature, the co-catalyst concentration and the solvent have been studied. Excellent selectivities have been obtained for the epoxidation of cyclohexene, cyclooctene, norbornene, cis- and trans-stilbene.

Comparison of liquid-phase olefin epoxidation catalysed by dichlorobis-(dimethylformamide)dioxomolybdenum(VI) in homogeneous phase and grafted onto MCM-41

Abstract: A mesoporous silica-supported molybdenum oxide catalyst with a loading of 0.17 Mo/nm 2 was prepared by liquid phase deposition of MoO 2 Cl 2 (dmf) 2 ( 1 ) onto MCM-41 (dmf = dimethylformamide). Powder X-ray diffraction and N 2 adsorption studies of Mo-MCM-41 indicate that the texture properties of the support were preserved during the grafting experiment. On the basis of evidence from FTIR spectroscopy, 13 C and 29 Si MAS NMR, and Mo K-edge EXAFS, the Mo atoms in this catalyst are mainly present as isolated {MoO 2 [(–O) 3 SiO] 2 (dmf) 2 } species, with a small contribution from oxo-bridged dimers. Catalysis tests show that complex 1 and Mo-MCM-41 are highly active oxidation catalysts for liquid-phase epoxidation of unfunctionalised olefins using tert -butylhydroperoxide as oxidant, from ambient to 55 °C. The high stability and recyclability of the heterogeneous Mo-MCM-41 catalyst is attributed to the strong metal oxide–support interaction. With cyclooctene, 1-octene, trans -2-octene and norbornene substrates, the corresponding epoxides were the only observed reaction products. The reactions of the other substrates gave by-products such as 8,9- p -menthen-1,2-diol from ( R )-(+)-limonene, campholenic aldehyde from α-pinene, and benzaldehyde from styrene. The addition of dichloromethane as a co-solvent had a beneficial effect on catalytic performance, and in the case of ( R )-(+)-limonene allowed the epoxide to be formed as the only reaction product.

Synthesis and characterization of side-chain liquid crystalline polymers bearing cholesterol mesogen

Abstract: A series of new norbornene carboxylic cholesteryl ester monomers with and without alkyl spacers, NBCh, and NBCh-n, respectively, were synthesized. New side-chain liquid crystalline homopolymers, PNBCh and PNBCh-n, were cleanly prepared using NBCh and NBCh-n, respectively, with Grubbs 2nd generation catalyst. Molecular and structural characterization of monomers and polymers were carried out by nuclear magnetic resonance, NMR, Fourier transform infrared, FT-IR, spectroscopy, and gel permeation chromatography, GPC. The thermal and liquid crystalline properties of the homopolymers were investigated by differential scanning calorimetry, DSC, thermogravimetric analysis, TGA, and polarized optical microscopy, POM. Small angle and wide angle X-ray studies of PNBCh-n in powder and fiber states not only confirmed the formation of smectic A mesophases, but also established their morphologies. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2690–2701, 2009

Orthogonally Self‐Assembled Multifunctional Block Copolymers

Abstract: We report the synthesis of telechelic poly(norbornene) and poly(cyclooctene) homopolymers by ring-opening metathesis polymerization (ROMP) and their subsequent functionalization and block copolymer formation based on noncovalent interactions. Whereas all the poly(norbornene)s contain either a metal complex or a hydrogen-bonding moiety along the polymer side-chains, together with a single hydrogen-bonding-based molecular recognition moiety at one terminal end of the polymer chain. These homopolymers allow for the formation of side-chain-functionalized AB and ABA block copolymers through self-assembly. The orthogonal natures of all side- and main-chain self-assembly events were demonstrated by 1H NMR spectroscopy and isothermal titration calorimetry. The resulting fully functionalized block copolymers are the first copolymers combining both side- and main-chain self-assembly, thereby providing a high degree of control over copolymer functionalization and architecture and bringing synthetic materials one step closer to the dynamic self-assembly structures found in nature.

Alternating Ring-Opening Metathesis Copolymerization of Amino Acid Derived Norbornene Monomers Carrying Nonprotected Carboxy and Amino Groups Based on Acid−Base Interaction

Abstract: Amino acid derived norbornene monomers having carboxy (1) and amino groups (2) were synthesized and subjected to ring-opening metathesis copolymerization with various feed ratios using the Grubbs second generation ruthenium catalyst. The Mn’s of the copolymers ranged from 5300 to 9400 (Mw/Mn = 1.40−1.69). The monomer conversion and Mn of the copolymer were maximized when the monomer feed ratio was 1:1. The monomer unit ratios in the copolymers were almost 1:1 at 10% conversion, irrespective of the feed ratios. The monomer reactivity ratios r1 and r2 were estimated to be 0.08 and 0.02, which confirmed that alternating copolymerization occurred. It is considered that alternating copolymerization is brought about by the acid−base interaction between the monomers and/or between the propagating polymer end and the incoming monomer.

Synthesis and Catalytic Properties in Olefin Epoxidation of Octahedral Dichloridodioxidomolybdenum(VI) Complexes Bearing N,N-Dialkylamide Ligands: Crystal Structure of [Mo2O4(μ2-O)Cl2(dmf)4]

Abstract: The catalytic performance of the complexes [MoO2Cl2(L)2] [L = N,N-dimethylformamide (dmf), N,N-dimethylacetamide (dma), N,N-dimethylpropionamide (dmpa), N,N-diethylformamide (def) and N,N-diphenylformamide (dpf)] was examined in the epoxidation of cis-cyclooctene with tert-butyl hydroperoxide (tbhp) at 55 °C and in the absence of a cosolvent. The complexes showed high turnover frequencies in the range of 561–577 mol molMo–1 h–1, giving the epoxide as the only product in ≥98 % yield after 6 h. The reaction rates decreased significantly in consecutive runs carried out by recharging the reactors with olefin and oxidant. On the basis of the IR spectroscopic characterisation of the solids recovered at the end of the catalytic reactions, the decrease in activity is attributed to the formation of dioxido(μ-oxido)molybdenum(VI) dimers. Accordingly, the treatment of [MoO2Cl2(dmf)2] with an excess amount of tbhp led to the isolation of [Mo2O4(μ2-O)Cl2(dmf)4], which was characterised by single-crystal X-ray diffraction and found to exhibit a catalytic performance very similar to that found in the second runs for the mononuclear complexes. The kinetics of the reaction of [MoO2Cl2(dmf)2] with tbhp was further examined by UV/Vis spectroscopy, allowing rate constants and activation parameters to be determined. For the dpf adduct, the effect of different solvents on cyclooctene epoxidation and the epoxidation of other olefins, namely, (R)-(+)-limonene, α-pinene and norbornene, were investigated. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)