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Sample records for ring-opening metathesis polymerization

  1. Catalytic living ring-opening metathesis polymerization

    NASA Astrophysics Data System (ADS)

    Nagarkar, Amit A.; Kilbinger, Andreas F. M.

    2015-09-01

    In living ring-opening metathesis polymerization (ROMP), a transition-metal-carbene complex polymerizes ring-strained olefins with very good control of the molecular weight of the resulting polymers. Because one molecule of the initiator is required for each polymer chain, however, this type of polymerization is expensive for widespread use. We have now designed a chain-transfer agent (CTA) capable of reducing the required amount of metal complex while still maintaining full control over the living polymerization process. This new method introduces a degenerative transfer process to ROMP. We demonstrate that substituted cyclohexene rings are good CTAs, and thereby preserve the ‘living’ character of the polymerization using catalytic quantities of the metal complex. The resulting polymers show characteristics of a living polymerization, namely narrow molecular-weight distribution, controlled molecular weights and block copolymer formation. This new technique provides access to well-defined polymers for industrial, biomedical and academic use at a fraction of the current costs and significantly reduced levels of residual ruthenium catalyst.

  2. Block copolymer adhesion promoters via ring-opening metathesis polymerization

    DOEpatents

    Kent, Michael S.; Saunders, Randall

    1997-01-01

    Coupling agents based on functionalized block copolymers for bonding thermoset polymers to solid materials. These are polymers which possess at least two types of functional groups, one which is able to attach to and react with solid surfaces, and another which can react with a thermoset resin, which are incorporated as pendant groups in monomers distributed in blocks (typically two) along the backbone of the chain. The block copolymers in this invention are synthesized by living ring-opening metathesis polymerization.

  3. Block copolymer adhesion promoters via ring-opening metathesis polymerization

    DOEpatents

    Kent, M.S.; Saunders, R.

    1997-02-18

    Coupling agents are disclosed based on functionalized block copolymers for bonding thermoset polymers to solid materials. These are polymers which possess at least two types of functional groups, one which is able to attach to and react with solid surfaces, and another which can react with a thermoset resin, which are incorporated as pendant groups in monomers distributed in blocks (typically two) along the backbone of the chain. The block copolymers in this invention are synthesized by living ring-opening metathesis polymerization. 18 figs.

  4. Acidic polysaccharide mimics via ring-opening metathesis polymerization.

    PubMed

    Wathier, Michel; Stoddart, Stephanie S; Sheehy, Matthew J; Grinstaff, Mark W

    2010-11-17

    An efficient and general synthetic strategy for the preparation of high-molecular-weight hydrophilic polymers bearing both carboxylic acid and hydroxyl pendant groups is described. Specifically, poly(5,6-dihydroxyoxanorbornane carboxylic acid) with molecular weight ranging from ∼100 000 to 5 000 000 g/mol was prepared by ring-opening metathesis polymerization of methyl 5-oxanorbornene-2-carboxylate in the presence of Grubbs catalyst II and subsequently modified to tune the hydrophobic/hydrophilic properties by the introduction of either hydroxyl or carboxylic acid functionalities. These polymers mimic the natural acidic polysaccharide alginate and form hydrogels with polylysine. These polymers belong to a class of carbohydrate-like polymers, which are of interest for investigating the relationships between chemical structure and rheological properties as well as for providing new synthetic polysaccharide substitutes for applications in the biotechnology and pharmaceutical industries.

  5. Oxidation-triggered ring-opening metathesis polymerization.

    PubMed

    Savka, Roman; Foro, Sabine; Gallei, Markus; Rehahn, Matthias; Plenio, Herbert

    2013-08-05

    Eight new N-Hoveyda-type complexes were synthesized in yields of 67-92 % through reaction of [RuCl2 (NHC)(Ind)(py)] (NHC=1,3-bis(2,4,6-trimethylphenylimidazolin)-2-ylidene (SIMes) or 1,3-bis(2,6-diisopropylphenylimidazolin)-2-ylidene (SIPr), Ind=3-phenylindenylid-1-ene, py=pyridine) with various 1- or 1,2-substituted ferrocene compounds with vinyl and amine or imine substituents. The redox potentials of the respective complexes were determined; in all complexes an iron-centered oxidation reaction occurs at potentials close to E=+0.5 V. The crystal structures of the reduced and of the respective oxidized Hoveyda-type complexes were determined and show that the oxidation of the ferrocene unit has little effect on the ruthenium environment. Two of the eight new complexes were found to be switchable catalysts, in that the reduced form is inactive in the ring-opening metathesis polymerization of cis-cyclooctene (COE), whereas the oxidized complexes produce polyCOE. The other complexes are not switchable catalysts and are either inactive or active in both reduced and oxidized states. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  6. Organic and composite aerogels through ring opening metathesis polymerization (ROMP)

    NASA Astrophysics Data System (ADS)

    Mohite, Dhairyashil P.

    Aerogels are open-cell nanoporous materials, unique in terms of low density, low thermal conductivity, low dielectric constants and high acoustic attenuation. Those exceptional properties stem from their complex hierarchical solid framework (agglomerates of porous, fractal secondary nanoparticles), but they also come at a cost: low mechanical strength. This issue has been resolved by crosslinking silica aerogels with organic polymers. The crosslinking polymer has been assumed to form a conformal coating on the surface of the skeletal framework by covalent bridging elementary building blocks. However, "assuming" is not enough: for correlating nanostructure with bulk material properties, it is important to know the exact location of the polymer on the aerogel backbone. For that investigation, we synthesized a new norbornene derivative of triethoxysilane (Si-NAD) that can be attached to skeletal silica nanoparticles. Those norbornene-modified silica aerogels were crosslinked with polynorbornene by ring opening metathesis polymerization (ROMP). The detailed correlation between nanostructure and mechanical strength was probed with a wide array of characterization methods ranging from molecular to bulk through nano. Subsequently, it was reasoned that since the polymer dominates the exceptional mechanical properties of polymer crosslinked aerogels, purely organic aerogels with the same nanostructure and interparticle connectivity should behave similarly. That was explored and confirmed by: (a) synthesis of a difunctional nadimide monomer (bis-NAD), and preparation of robust polyimide aerogels by ROMP of its norbornene end-caps; and, (b) synthesis of dimensionally stable ROMP-derived polydicyclopentadiene aerogels by grafting the nanostructure with polymethylmethacrylate (PMMA) via free radical chemistry.

  7. Controlled Ring-Opening Metathesis Polymerization by Molybdenum and Tungsten Alkylidene Complexes

    DTIC Science & Technology

    1988-07-29

    weights and low polydispersities (as low as 1.03) consistent with a living catalyst system employing 50, 100, 200, and 400 eq of monomer. The reactions are...secondary metathesis of polymer chains Bulky alkoxide ligands Wittig-like reaction Ring-opening metathesis polymerization (ROMP) Feast monomer Cyclic...olefins Retro Diels-Alder reaction Norbornene (NBE) Low temperature column chromatography Endo-,endo-5,6-dicarbomethoxynorbornene Discrete, soluble

  8. Thermoset polymers via ring opening metathesis polymerization of functionalized oils

    DOEpatents

    Larock, Richard C; Henna, Phillip H; Kessier, Michael R

    2012-11-27

    The invention provides a method for producing a thermosetting resin from renewable oils, the method comprising supplying renewable oil molecules containing strained ring alkene moieties; reacting the alkene moieties with cyclic alkenes to create a polymer; and repeating the above two steps until the resin having desired characteristics are obtained. Also provided is a thermoset resin comprising functionalized renewable oil polymerized with a co-monomer.

  9. Functional Materials from Nanostructured Block Polymers Prepared via Ring-opening Metathesis Polymerization

    NASA Astrophysics Data System (ADS)

    Pitet, Louis Marcel

    The structural and molecular versatility afforded to polymeric materials by ruthenium catalysts during ring-opening metathesis polymerization (ROMP) cannot be exaggerated. This dissertation describes the synthesis of functionalized polyolefins via ROMP with particular emphasis on designing straightforward approaches to materials in which the molecular structure is meticulously controlled. Moreover, large portions of the body are dedicated to describing functionalized polyolefins as precursors to more complex multicomponent block copolymers. Block copolymers having various components derived from mechanistically incompatible feedstocks were designed with translational targets in mind, including toughening agents for brittle plastics, and free-standing nanoporous membranes. Several fundamental structure-property relationships were also explored for the newly synthesized materials.

  10. Preparation of Bottlebrush Polymers via a One-Pot Ring-Opening Polymerization (ROP) and Ring-Opening Metathesis Polymerization (ROMP) Grafting-Through Strategy.

    PubMed

    Radzinski, Scott C; Foster, Jeffrey C; Matson, John B

    2016-04-01

    Bottlebrush polymers are synthesized using a tandem ring-opening polymerization (ROP) and ring-opening metathesis polymerization (ROMP) strategy. For the first time, ROP and ROMP are conducted sequentially in the same pot to yield well-defined bottlebrush polymers with molecular weights in excess of 10(6) Da. The first step of this process involves the synthesis of a polylactide macromonomer (MM) via ROP of d,l-lactide initiated by an alcohol-functionalized norbornene. ROMP grafting-through is then carried out in the same pot to produce the bottlebrush polymer. The applicability of this methodology is evaluated for different MM molecular weights and bottlebrush backbone degrees of polymerization. Size-exclusion chromatographic and (1)H NMR spectroscopic analyses confirm excellent control over both polymerization steps. In addition, bottlebrush polymers are imaged using atomic force microscopy and stain-free transmission electron microscopy on graphene oxide.

  11. Combining Ring-Opening Metathesis Polymerization and Cyclic Ester Ring-Opening Polymerization To Form ABA Triblock Copolymers from 1,5-Cyclooctadiene and D,L-Lactide

    SciTech Connect

    Pitet, Louis M.; Hillmyer, Marc A.

    2009-07-31

    ABA triblock copolymers were synthesized by combining ring-opening metathesis polymerization (ROMP) of 1,5-cyclooctadiene (COD) with ring-opening polymerization of D,L-lactide. Hydroxyl-functionalized telechelic polyCOD was prepared by taking advantage of chain transfer during ROMP of COD using the acyclic chain transfer agent cis-1,4-diacetoxy-2-butene. These hydroxy-terminated macroinitiators were used as initiators for the polymerization of lactide to form a series of triblock copolymers with compositions in the range 0.24 {le} f{sub PLA} {le} 0.89 and molecular weights ranging from 22 to 196 kg mol{sup -1}. The ordered-state morphologies of the triblocks were determined using small-angle X-ray scattering; well-ordered microstructures were observed for several samples, in accordance with the predicted dependence of morphology on composition. The mechanical properties of these materials were also investigated by performing tensile measurements; the triblocks were considerably tougher than poly(D,L-lactide), most markedly in samples with low polyCOD midblock content.

  12. Facile synthesis of brush poly(phosphoamidate)s via one-pot tandem ring-opening metathesis polymerization and atom transfer radical polymerization.

    PubMed

    Ding, Liang; Qiu, Jun; Wei, Jun; Zhu, Zhenshu

    2014-09-01

    Poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA)-based brush poly(phosphoamidate)s are successfully synthesized by a combination of ring-opening metathesis polymerization (ROMP) and atom transfer radical polymerization (ATRP) following either a commutative two-step procedure or a straightforward one-pot process using Grubbs ruthenium-based catalysts for tandem catalysis. Compared with the traditional polymerization method, combining ROMP and ATRP in a one-pot process allows the preparation of brush copolymers characterized by a relatively moderate molecular weight distribution and quantitative conversion of monomer. Moreover, the surface morphologies and aggregation behaviors of these polymers are studied by AFM and TEM measurements.

  13. Enantioseparation of glycyl-dipeptides by CEC using particle-loaded monoliths prepared by ring-opening metathesis polymerization (ROMP).

    PubMed

    Gatschelhofer, Christina; Schmid, Martin G; Schreiner, Karin; Pieber, Thomas R; Sinner, Frank M; Gübitz, Gerald

    2006-11-30

    Novel particle-loaded monolithic capillary electrochromatography (CEC) phases for chiral separations were prepared via ring-opening metathesis polymerization (ROMP) within the confines of fused silica columns with 200 microm i.d. using norborn-2-ene (NBE), 1,4,4a,5,8,8a-hexahydro-1,4,5,8,exo,endo-dimethanonaphthalene (DMN-H6) as monomers, 2-propanol and toluene as porogens, RuCl2(PCy3)2(CHPh) as initiator and silica-based particles containing the chiral selector. By suspending silica particles bearing the chiral selector in the polymerization mixture, particle-based monoliths are easily prepared. This approach has several advantages compared to particle-based separation media: (i) the concept of particle-based monoliths is broadly applicable, as any silica-based chiral phase can be used; (ii) they are inexpensive to prepare; and (iii) the manufacturing process is very simple, no sophisticated packing procedures or the preparation of end frits are required. To show the usefulness of this concept for chiral CEC, the chiral separation performance of particle-loaded CEC monoliths bearing teicoplanin aglycone, chemically bonded to 3 microm silica gel, was investigated for a set of glycyl-dipeptides. Particle-loaded ROMP CEC monoliths showed good separation performance for glycyl-dipeptides.

  14. Cis-Selective Ring-Opening Metathesis Polymerization with Ruthenium Catalysts

    PubMed Central

    Keitz, Benjamin K.; Fedorov, Alexey; Grubbs, Robert H.

    2012-01-01

    Using a C-H activated, ruthenium-based metathesis catalyst, the cis selective ROMP of several monocyclic alkenes, as well as norbornene and oxanorbornene-type monomers is reported. The cis content of the isolated polymers depended heavily on monomer structure and temperature. By lowering the temperature, cis content as high as 96% could be obtained. PMID:22239675

  15. Dual responsive polymeric nanoparticles prepared by direct functionalization of polylactic acid-based polymers via graft-from ring opening metathesis polymerization.

    PubMed

    Veccharelli, Kate M; Tong, Venus K; Young, Jennifer L; Yang, Jerry; Gianneschi, Nathan C

    2016-01-11

    Polylactic acid (PLA) has found widespread use in plastics and in biomedical applications due to its biodegradability into natural benign products. However, PLA-based materials remain limited in usefulness due to difficulty of incorporating functional groups into the polymer backbone. In this paper, we report a strategy for PLA functionalization that establishes the preparation of highly derivatized materials in which ring opening metathesis polymerization (ROMP) is employed as a graft-from polymerization technique utilizing a norbornene-modified handle incorporated into the PLA backbone. As a demonstration of this new synthetic methodology, a PLA-derived nanoparticle bearing imidazole units protected with a photolabile group was prepared. The morphology of this material could be controllably altered in response to exposure of UV light or acidic pH as a stimulus. We anticipate that this graft-from approach to derivatization of PLA could find broad use in the development of modified, biodegradable PLA-based materials.

  16. Artificial Informational Polymers and Nanomaterials from Ring-Opening Metathesis Polymerization

    NASA Astrophysics Data System (ADS)

    James, Carrie Rae

    Inspired by naturally occurring polymers (DNA, polypeptides, polysaccharides, etc.) that can self-assemble on the nanoscale into complex, information-rich architectures, we have synthesized nucleic acid based polymers using ROMP. These polymers were synthesized using a graft-through strategy, whereby nucleic acids bearing a strained cyclic olefin were directly polymerized. This is the first example of the graft-through polymerization of nucleic acids. Our approach takes advantage of non-charged peptide nucleic acids (PNAs) as elements to incorporate into ROMP polymer backbones. PNA is a synthetic nucleic acid analogue known for its increased affinity and specificity for complementary DNA or RNA. To accomplish the graft-through polymerization of PNA, we conjugated PNA to strained cyclic olefins using solid phase peptide conjugation chemistry. These PNA monomers were then directly polymerized into homo and block copolymers forming brushes, or comb-like arrangements, of information. Block copolymer amphiphiles of these materials, where the PNA brush served as the hydrophilic portion, were capable of self-assembly into spherical nanoparticles (PNA NPs). These PNA NPs were then studied with respect to their ability to hybridize complementary DNA sequences, as well as their ability to undergo cellular internalization. PNA NPs consisting of densely packed brushes of nucleic acids possessed increased thermal stability when mixed with their complementary DNA sequence, indicating a greater DNA binding affinity over their unpolymerized PNA counterparts. In addition, by arranging the PNA into dense brushes at the surface of the nanoparticle, Cy5.5 labeled PNA NPs were able to undergo cellular internalization into HeLa cells without the need for an additional cellular delivery device. Importantly, cellular internalization of PNA has remained a significant challenge in the literature due to the neutrally charged amino-ethyl glycine backbone of PNA. Therefore, this represents a

  17. Glycopolymers Prepared by Ring-Opening Metathesis Polymerization Followed by Glycoconjugation Using a Triazole-Forming "Click" Reaction.

    PubMed

    Okoth, Ronald; Basu, Amit

    2016-01-01

    We describe a protocol for the preparation of glycopolymers derived from the ring-opening polymerization of a norbornene carboxylic acid derivative. Polymerization is followed by attachment of a linker and subsequent glycoconjugation via a triazole-forming azide-alkyne click reaction. The use of a protected amine-terminating agent allows for the attachment of a probe molecule such as a fluorescein dye. The syntheses of a neutral galactopolymer as well a polyanionic poly-3-O-sulfo-galactopolymer are described.

  18. Optimal Hydrophobicity in Ring-Opening Metathesis Polymerization-Based Protein Mimics Required for siRNA Internalization.

    PubMed

    deRonde, Brittany M; Posey, Nicholas D; Otter, Ronja; Caffrey, Leah M; Minter, Lisa M; Tew, Gregory N

    2016-06-13

    Exploring the role of polymer structure for the internalization of biologically relevant cargo, specifically siRNA, is of critical importance to the development of improved delivery reagents. Herein, we report guanidinium-rich protein transduction domain mimics (PTDMs) based on a ring-opening metathesis polymerization scaffold containing tunable hydrophobic moieties that promote siRNA internalization. Structure-activity relationships using Jurkat T cells and HeLa cells were explored to determine how the length of the hydrophobic block and the hydrophobic side chain compositions of these PTDMs impacted siRNA internalization. To explore the hydrophobic block length, two different series of diblock copolymers were synthesized: one series with symmetric block lengths and one with asymmetric block lengths. At similar cationic block lengths, asymmetric and symmetric PTDMs promoted siRNA internalization in the same percentages of the cell population regardless of the hydrophobic block length; however, with 20 repeat units of cationic charge, the asymmetric block length had greater siRNA internalization, highlighting the nontrivial relationships between hydrophobicity and overall cationic charge. To further probe how the hydrophobic side chains impacted siRNA internalization, an additional series of asymmetric PTDMs was synthesized that featured a fixed hydrophobic block length of five repeat units that contained either dimethyl (dMe), methyl phenyl (MePh), or diphenyl (dPh) side chains and varied cationic block lengths. This series was further expanded to incorporate hydrophobic blocks consisting of diethyl (dEt), diisobutyl (diBu), and dicyclohexyl (dCy) based repeat units to better define the hydrophobic window for which our PTDMs had optimal activity. High-performance liquid chromatography retention times quantified the relative hydrophobicities of the noncationic building blocks. PTDMs containing the MePh, diBu, and dPh hydrophobic blocks were shown to have superior

  19. Cobaltocenium-containing block copolymers: ring-opening metathesis polymerization, self-assembly and precursors for template synthesis of inorganic nanoparticles.

    PubMed

    Ren, Lixia; Zhang, Jiuyang; Hardy, Christopher G; Ma, Shuguo; Tang, Chuanbing

    2012-04-13

    Side-chain cobaltocenium-containing block copolymers are prepared by ring-opening metathesis polymerization (ROMP). These block copolymers include one cobaltocenium-containing block, with the second block being either a nonmetal-containing segment or a cobaltocenium-containing segment with different counterions. These block copolymers are self-assembled into spherical core/shell micelles in solutions. A template strategy is used to prepare cobalt (II or III)-containing nanoparticles by treating the self-assembled micelles via UV/ozonolysis and pyrolysis. Characterization by X-ray photon spectroscopy and X-ray diffraction indicates that these nanoparticles consist of different oxidants of cobalt, depending on the chemical compositions of block copolymers. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. Surface-initiated ring-opening metathesis polymerization (SI-ROMP) to attach a tethered organic corona onto CdSe/ZnS core/shell quantum dots.

    PubMed

    Vatansever, Fatma; Hamblin, Michael R

    2016-10-01

    Core-shell CdSe/ZnS quantum dots (QDs) are useful as tunable photostable fluorophores for multiple applications in industry, biology, and medicine. However, to achieve the optimum optical properties, the surface of the QDs must be passivated to remove charged sites that might bind extraneous substances and allow aggregation. Here we describe a method of growing an organic polymer corona onto the QD surface using the bottom-up approach of surface-initiated ring-opening metathesis polymerization (SI-ROMP) with Grubbs catalyst. CdSe/ZnS QDs were first coated with mercaptopropionic acid by displacing the original trioctylphosphine oxide layer, and then reacted with 7-octenyl dimethyl chlorosilane. The resulting octenyl double bonds allowed the attachment of ruthenium alkylidene groups as a catalyst. A subsequent metathesis reaction with strained bicyclic monomers (norbornene-dicarbonyl chloride (NDC), and a mixture of NDC and norbornenylethylisobutyl-polyhedral oligomeric silsesquioxane (norbornoPOSS)) allowed the construction of tethered organic homo-polymer or co-polymer layers onto the QD. Compounds were characterized by FT-IR, 1H-NMR, X-ray photoelectron spectroscopy, differential scanning calorimetry, and transmission electron microscopy. Atomic force microscopy showed that the coated QDs were separate and non-aggregated with a range of diameter of 48-53 nm.

  1. Surface-initiated ring-opening metathesis polymerization (SI-ROMP) to attach a tethered organic corona onto CdSe/ZnS core/shell quantum dots

    NASA Astrophysics Data System (ADS)

    Vatansever, Fatma; Hamblin, Michael R.

    2016-10-01

    Core-shell CdSe/ZnS quantum dots (QDs) are useful as tunable photostable fluorophores for multiple applications in industry, biology, and medicine. However, to achieve the optimum optical properties, the surface of the QDs must be passivated to remove charged sites that might bind extraneous substances and allow aggregation. Here we describe a method of growing an organic polymer corona onto the QD surface using the bottom-up approach of surface-initiated ring-opening metathesis polymerization (SI-ROMP) with Grubbs catalyst. CdSe/ZnS QDs were first coated with mercaptopropionic acid by displacing the original tri-octylphosphine oxide layer, and then reacted with 7-octenyl dimethyl chlorosilane. The resulting octenyl double bonds allowed the attachment of ruthenium alkylidene groups as a catalyst. A subsequent metathesis reaction with strained bicyclic monomers (norbornene-dicarbonyl chloride (NDC), and a mixture of NDC and norbornenylethylisobutyl-polyhedral oligomeric silsesquioxane (norbornoPOSS)) allowed the construction of tethered organic homo-polymer or co-polymer layers onto the QD. Compounds were characterized by FT-IR, 1H-NMR, X-ray photoelectron spectroscopy, differential scanning calorimetry, and transmission electron microscopy. Atomic force microscopy showed that the coated QDs were separate and non-aggregated with a range of diameter of 48-53 nm.

  2. A Bicyclo[4.2.0]octene-Derived Monomer Provides Completely Linear Alternating Copolymers via Alternating Ring-Opening Metathesis Polymerization (AROMP).

    PubMed

    Tan, Li; Parker, Kathlyn A; Sampson, Nicole S

    2014-10-14

    Strained bicyclic carbomethoxy olefins were utilized as substrates in alternating ring-opening metathesis polymerization and found to provide low-dispersity polymers with novel backbones. The polymerization of methyl bicyclo[4.2.0]oct-7-ene-7-carboxylate with cyclohexene in the presence of the fast-initiating Grubbs catalyst (H2IMes)(3-Br-Pyr)2Cl2Ru=CHPh leads to a completely linear as well as alternating copolymer, as demonstrated by NMR spectroscopy, isotopic labeling, and gel permeation chromatography. In contrast, intramolecular chain-transfer reactions were observed with [5.2.0] and [3.2.0] bicyclic carbomethoxy olefins, although to a lesser extent than with the previously reported monocyclic cyclobutenecarboxylic ester monomers [Song A.; Parker K. A.; Sampson N. S.J. Am. Chem. Soc.2009, 131, 3444]. Inclusion of cyclohexyl rings fused to the copolymer backbone minimizes intramolecular chain-transfer reactions and provides a framework for creating alternating functionality in a one-step polymerization.

  3. Separation of planar chiral ferrocene derivatives on beta-cyclodextrin-based polymer supports prepared via ring-opening metathesis graft-polymerization.

    PubMed

    Mayr, Betina; Schottenberger, Herwig; Elsnerb, Olaf; Buchmeiser, Michael R

    2002-10-11

    A series of beta-cyclodextrin (beta-CD) based chiral stationary phases (CSPs) were synthesized by ring-opening metathesis graft polymerization of various norborn-2-ene (NBE) substituted CDs. Chiral selectors based on endo/exo-6-O-(norborn-2-ene-5-ylmethoxymethylsilyl)-beta-CD, tris(endo/exo-6-O-norborn-2-ene-5-ylmethoxymethylsilyl)-beta-CD, tetrakis(endolexo-6-0-norborn-2-ene-5-ylmethoxymethylsilyl)-beta-CD, hexakis(endo/exo-6-O-norborn-2-ene-5-ylmethoxymethylsilyl)-beta-CD and tetrakis(endo-6-O-norborn-2-ene-5-carboxyl)-beta-CD were grafted onto Nucleosil 300-5 using well-established grafting procedures. CSPs were investigated for their separation capabilities for a series of the planar chiral ferrocene derivatives, rac-ferroceno[2,3a]inden-1-one (1a, 1b), rac-6-(3-hydroxy-3-methylbut-1-yn-1-yl)ferroceno[2,3a]inden-1-one (2a, 2b), rac-ferrocene[2,3a]indene (3a, 3b), rac-endo 1-methoxy-1-allylferroceno[2,3a]indene (4a, 4b) and rac-1,4-dihydroxybutylferrocene (5a, 5b). Compounds la, lb and 2a, 2b bearing a carbonyl group were successfully separated on these CSPs, while compounds 3-5 do not undergo enantioselective interaction under the conditions applied. General aspects of separation as well as mechanistic implementations are discussed.

  4. Synthesis of Poly(norbornene-methylamine), a Biomimetic of Chitosan, by Ring-Opening Metathesis Polymerization (ROMP)

    PubMed Central

    Li, Na; Wang, Huanhuan; Qu, Xiaosai; Chen, Yu

    2017-01-01

    ROMP is an effective method for preparing functional polymers due to its having characteristics of “living” polymerization and rapid development of catalysts. In the present work, poly(norbornene-methylamine), a mimic of chitosan, was synthesized via ROMP reaction. The amino-protected product, 5-norbornene-2-(N-methyl)-phthalimide, was prepared by a reaction of 5-norbornene-2-methylamine with phthalic anhydride, which was then subjected to the ROMP reaction in the presence of Hoveyda-Grubbs 2nd catalyst to afford poly(norbornene-(N-methyl)-phthalimide). The target product, poly(norbornene-methylamine), was obtained by deprotection reaction of poly(norbornene-(N-methyl)-phthalimide). The products in each step were characterized by FTIR and 1H-NMR, and their thermal stabilities were determined by TG analysis. The effects of molar ratio between monomer ([M]/[I]) and catalyst on the average relative molecular weight (Mn¯) and molecular weight distribution of the produced polymer products were determined by gel permeation chromatography (GPC). It was found that the Mn¯ of poly(norbornene-(N-methyl)-phthalimide) was controllable and exhibited a narrow polydispersity index (PDI) (~1.10). The synthesis condition of 5-norbornene-2-(N-methyl)-phthalimide was optimized by determining the yields at different reaction temperatures and reaction times. The highest yield was obtained at a reaction temperature of 130 °C and a reaction time of 20 min. Our work provides a new strategy to synthesize polymers with controllable structures and free –NH2 groups via ROMP. PMID:28708109

  5. Synthesis of Side Chain Liquid Crystal Polymers by Living Ring Opening Metathesis Polymerization. 4. Synthesis of Amorphous and Side Chain Liquid Crystal AB Block Copolymers

    DTIC Science & Technology

    1992-05-01

    Metathesis Polymerization. 4. Synthesis of C N00014-89-JI542 Amorphous and Side Chain Liquid Crystal AB Block Copolym rs 6. AUTHOR(S) Zen Komiya, Coleen ...Liquid Crystal AB Block Copolymers by Zen Komiya, Coleen Pugh: and Richard R. Schrock* Submitted to Macromolecules F r fCarnegie Mellon University...Amorphous and Side Chain Liquid Crystal AB Block Copolymers by Zen Komiya, Coleen Pught, and Richard R. Schrock* Contribution from Department of Chemistry 6

  6. Tandem Ring-Opening-Ring-Closing Metathesis for Functional Metathesis Catalysts.

    PubMed

    Nagarkar, Amit A; Yasir, Mohammad; Crochet, Aurelien; Fromm, Katharina M; Kilbinger, Andreas F M

    2016-09-26

    Use of a tandem ring-opening-ring-closing metathesis (RORCM) strategy for the synthesis of functional metathesis catalysts is reported. Ring opening of 7-substituted norbornenes and subsequent ring-closing metathesis forming a thermodynamically stable 6-membered ring lead to a very efficient synthesis of new catalysts from commercially available Grubbs' catalysts. Hydroxy functionalized Grubbs' first- as well as third-generation catalysts have been synthesized. Mechanistic studies have been performed to elucidate the order of attack of the olefinic bonds. This strategy was also used to synthesize the ruthenium methylidene complex. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. Synthesis of Side Chain Liquid Crystal Polymers by Living Ring Opening Metathesis Polymerization. 3. Influence of Molecular Weight, Interconnecting Unit and Substituent on the Mesomorphic behavior of Polymers with Laterally Attached Mesogens

    DTIC Science & Technology

    1992-04-08

    Metathesis Polymerization. 3. In- fluence of Molecular Weight, Interconnecting Unit ... 6. AUTHOR(S) Coleen Pugh and Richard R. Schrock 7. PERFORMING...Unit and Substituent on the Mesomorphic Behavior of Polymers with Laterally Attached Mesogens. by Coleen Pugh t and Richard R. Schrock Submitted to...Mesogens. by Coleen Pugh+ and Richard R. Schrock* Contribution from Department of Chemistry 6-331 Massachusetts Institute of Technology Cambridge

  8. Control of Grafting Density and Distribution in Graft Polymers by Living Ring-Opening Metathesis Copolymerization.

    PubMed

    Lin, Tzu-Pin; Chang, Alice B; Chen, Hsiang-Yun; Liberman-Martin, Allegra L; Bates, Christopher M; Voegtle, Matthew J; Bauer, Christina A; Grubbs, Robert H

    2017-03-15

    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 sequence and architecture, self-propagation and cross-propagation rate constants were determined according to a terminal copolymerization model. These kinetic analyses suggest that copolymerizing a macromonomer/diluent pair with evenly matched self-propagation rate constants favors randomly distributed side chains. As the disparity between macromonomer and diluent homopolymerization rates increases, the reactivity ratios depart from unity, leading to an increase in gradient tendency. To demonstrate the effectiveness of our method, an array of monodisperse polymers (PLA(x)-ran-DME(1-x))n bearing variable grafting densities (x = 1.0, 0.75, 0.5, 0.25) and total backbone degrees of polymerization (n = 167, 133, 100, 67, 33) were synthesized. The approach disclosed in this work therefore constitutes a powerful strategy for the synthesis of polymers spanning the linear-to-bottlebrush regimes with controlled grafting density and side chain distribution, molecular

  9. Reactive triblock polymers from tandem ring-opening polymerization for nanostructured vinyl thermosets

    SciTech Connect

    Amendt, Mark A.; Pitet, Louis M.; Moench, Sarah; Hillmyer, Marc A.

    2013-03-07

    Multiply functional hydroxyl telechelic poly(cyclooctene-s-5-norbornene-2-methylene methacrylate) was synthesized by ring opening metathesis (co)polymerization of cis-cyclooctene and 5-norbornene-2-methylene methacrylate using the second generation Grubbs catalyst in combination with a symmetric chain transfer agent bearing hydroxyl functionality. The resulting hydroxyl-telechelic polymer was used as a macroinitiator for the ring opening transesterification polymerization of d,l-lactide to form reactive poly(lactide)-b-poly(cyclooctene-s-5-norbornene-2-methylene methacrylate)-b-poly(lactide) triblock polymers. Subsequently, the triblocks were crosslinked by free radical copolymerization with several vinyl monomers including styrene, divinylbenzene, methyl methacrylate, and ethyleneglycol dimethacrylate. Certain conditions led to optically transparent thermosets with mesoscale phase separation as evidenced by small angle X-ray scattering, differential scanning calorimetry and transmission electron microscopy. Disordered, bicontinuous structures with nanoscopic domains were generated in several cases, rendering the samples attractive for size-selective membrane applications.

  10. Ring-opening Polymerization of Epoxidized Soybean Oil

    USDA-ARS?s Scientific Manuscript database

    Ring opening polymerization of epoxidized soybean oil (ESO) initiated by boron trifluoride diethyl etherate, (BF3•OEt2), in methylene chloride was conducted in an effort to develop useful biodegradable polymers. The resulting polymers (PESO) were characterized using Infrared (IR), differential scan...

  11. Synthesis of Side Chain Liquid Crystal Polymers by Living Ring Opening Metathesis Polymerization. 1. Influence of Molecular Weight, Polydispersity, and Flexible Spacer Length (n=2-8) on the Thermotropic behavior of the Resulting Polymers

    DTIC Science & Technology

    1992-03-31

    Budget. Paperwork peduc t ~O l~oect(0104. 01111). Wasnhinqtol Dic 20oi 4- TITLE AND SUBTITLE Ap.i FUNIN N92_UMBcncaRpotS1 Synthesis of Side Chain...metathesis polymerization of 5-carbo(n-[(4’-methoxy-4- biphenylyl)oxy]alkyl)bicyclo[2.2.1]hept-2-ene (1-n, n=2-8) by Mo(CH- t -Bu)(NAr) (0- t -Bu)2(Ar=2,6...C6H3- t -Pr 2) is described. Polymers with degrees of polymeri- zation from 5 to 100 and narrow molecular weight distributions (Mw/Mnz1.05-1.24) were

  12. Precision Synthesis of Alternating Copolymers via Ring-Opening Polymerization of 1-Substituted Cyclobutenes.

    PubMed

    Parker, Kathlyn A; Sampson, Nicole S

    2016-03-15

    Investigation of complex molecular systems depends on our ability to correlate physical measurements with molecular structure. Interpretation of studies that rely on synthetic polymers is generally limited by their heterogeneity; i.e., there is variation in the number and arrangement of the monomeric building blocks that have been incorporated. Superior physics and biology can be performed with materials and tools that exert precise control over the sequence and spacing of functional groups. An interest in functional ligands combined with a desire to control the orientation and stereochemistry of monomer incorporation led to the design of new substrates for ruthenium-catalyzed ring-opening metathesis polymerization (ROMP). We discovered that ROMP of cyclobutene-1-carboxamides provides uniform and translationally invariant polymers. In contrast, cyclobutene-1-carboxylate esters ring open upon treatment with ruthenium catalyst, but they are stable to homopolymerization. However, in the presence of cyclohexene monomers, they undergo alternating ROMP (AROMP or alt-ROMP) to give copolymers with a precisely controlled sequence. The alternating cyclobutene ester/cyclohexene pair provides access to functional group spacing larger than is possible with homopolymers. This can be desirable; for example, polymers with a regular 8-10 Å backbone spacing of cationic charge and with between four and eight cationic groups were the most effective antibacterial agents and had low cytotoxicity. Moreover, the AROMP chemistry allows alternation of two functional moieties: one associated with the cyclohexene and one attached to the cyclobutene. In the case of antibacterial copolymers, the alternating chemistry allowed variation of hydrophobicity via the cyclohexene while maintaining a constant cation spacing through the cyclobutene. In the case of copolymers that bear donor and acceptor groups, strict alternation of the groups increased intrachain charge transfer. Like cyclobutene-1

  13. Precision Synthesis of Alternating Copolymers via Ring-Opening Polymerization of 1-Substituted Cyclobutenes

    PubMed Central

    2016-01-01

    Conspectus Investigation of complex molecular systems depends on our ability to correlate physical measurements with molecular structure. Interpretation of studies that rely on synthetic polymers is generally limited by their heterogeneity; i.e., there is variation in the number and arrangement of the monomeric building blocks that have been incorporated. Superior physics and biology can be performed with materials and tools that exert precise control over the sequence and spacing of functional groups. An interest in functional ligands combined with a desire to control the orientation and stereochemistry of monomer incorporation led to the design of new substrates for ruthenium-catalyzed ring-opening metathesis polymerization (ROMP). We discovered that ROMP of cyclobutene-1-carboxamides provides uniform and translationally invariant polymers. In contrast, cyclobutene-1-carboxylate esters ring open upon treatment with ruthenium catalyst, but they are stable to homopolymerization. However, in the presence of cyclohexene monomers, they undergo alternating ROMP (AROMP or alt-ROMP) to give copolymers with a precisely controlled sequence. The alternating cyclobutene ester/cyclohexene pair provides access to functional group spacing larger than is possible with homopolymers. This can be desirable; for example, polymers with a regular 8–10 Å backbone spacing of cationic charge and with between four and eight cationic groups were the most effective antibacterial agents and had low cytotoxicity. Moreover, the AROMP chemistry allows alternation of two functional moieties: one associated with the cyclohexene and one attached to the cyclobutene. In the case of antibacterial copolymers, the alternating chemistry allowed variation of hydrophobicity via the cyclohexene while maintaining a constant cation spacing through the cyclobutene. In the case of copolymers that bear donor and acceptor groups, strict alternation of the groups increased intrachain charge transfer. Like

  14. Thermodynamic Presynthetic Considerations for Ring-Opening Polymerization.

    PubMed

    Olsén, Peter; Odelius, Karin; Albertsson, Ann-Christine

    2016-03-14

    The need for polymers for high-end applications, coupled with the desire to mimic nature's macromolecular machinery fuels the development of innovative synthetic strategies every year. The recently acquired macromolecular-synthetic tools increase the precision and enable the synthesis of polymers with high control and low dispersity. However, regardless of the specificity, the polymerization behavior is highly dependent on the monomeric structure. This is particularly true for the ring-opening polymerization of lactones, in which the ring size and degree of substitution highly influence the polymer formation properties. In other words, there are two important factors to contemplate when considering the particular polymerization behavior of a specific monomer: catalytic specificity and thermodynamic equilibrium behavior. This perspective focuses on the latter and undertakes a holistic approach among the different lactones with regard to the equilibrium thermodynamic polymerization behavior and its relation to polymer synthesis. This is summarized in a monomeric overview diagram that acts as a presynthetic directional cursor for synthesizing highly specific macromolecules; the means by which monomer equilibrium conversion relates to starting temperature, concentration, ring size, degree of substitution, and its implications for polymerization behavior are discussed. These discussions emphasize the importance of considering not only the catalytic system but also the monomer size and structure relations to thermodynamic equilibrium behavior. The thermodynamic equilibrium behavior relation with a monomer structure offers an additional layer of complexity to our molecular toolbox and, if it is harnessed accordingly, enables a powerful route to both monomer formation and intentional macromolecular design.

  15. Sol-gel chemistry by ring-opening polymerization

    SciTech Connect

    RAHIMIAN,KAMYAR; LOY,DOUGLAS A.

    2000-02-07

    Sol-gel processing of materials is plagued by shrinkage during polymerization of the alkoxide monomers and processing (aging and drying) of the resulting gels. The authors have developed a new class of hybrid organic-inorganic materials based on the solventless ring-opening polymerization (ROP) of monomers bearing the 2,2,5,5-tetramethyl-2,5-disilaoxacyclopentyl group, which permits them to drastically reduce shrinkage in sol-gel processed materials. Because the monomers are polymerized through a chain growth mechanism catalyzed by base rather than the step growth mechanism normally used in sol-gel systems, hydrolysis and condensation products are entirely eliminated. Furthermore, since water is not required for hydrolysis, an alcohol solvent is not necessary. Monomers with two disilaoxacyclopentyl groups, separated by a rigid phenylene group or a more flexible alkylene group, were prepared through disilylation of the corresponding diacetylenes, followed by ring closure and hydrogenation. Anionic polymerization of these materials, either neat or with 2,2,5,5-tetramethyl-2,5-disila-1-oxacyclopentane as a copolymer, affords thermally stable transparent gels with no visible shrinkage. These materials provide an easy route to the introduction of sol-gel type materials in encapsulation of microelectronics, which they have successfully demonstrated.

  16. Ring-opening polymerization by lithium catalysts: an overview.

    PubMed

    Sutar, Alekha Kumar; Maharana, Tungabidya; Dutta, Saikat; Chen, Chi-Tien; Lin, Chu-Chieh

    2010-05-01

    This critical review summarizes recent developments in the preparation and application of lithium catalysts/initiators such as, alkyl lithium, alkoxy lithium and bimetallic lithium compounds for ring-opening polymerization (ROP). The ROP of cyclic esters, cyclic carbonates, cyclo-silazanes, cyclo-silanes, cyclo-siloxanes, cyclo-carboxylate, cyclic phosphirene and quinodimethanes are covered in this review. The present paper emphasizes the polymerization kinetics and the control exhibited by the different types of lithium initiators/catalysts. For the cases where useful properties, such as high molecular weight, narrow PDI, or stereocontrol, have been observed, a more detailed examination of the mechanistic studies of the catalysts/initiators are provided. Furthermore, this review also focuses on the synthesis of block copolymers and graft copolymers by ROP principle. The topics covered in this review regarding lithium compounds toward ROP will be of interest to inorganic, organic and organometallic chemists, material, polymer and catalytic scientists due to its unique mode of activation as compared to transition and inner transition-metals. In addition, use of these compounds in catalysis is steadily growing, because of the complementary reactivity toward ROP as compared to other metals. Finally, some aspects and opportunities which may be of interest in the future are suggested (143 references).

  17. Accuracy of a new ring-opening metathesis elastomeric dental impression material with spray and immersion disinfection.

    PubMed

    Kronström, Mats H; Johnson, Glen H; Hompesch, Richard W

    2010-01-01

    A new elastomeric impression material has been formulated with a ring-opening metathesis chemistry. In addition to other properties of clinical significance, the impression accuracy must be confirmed. The purpose of this study was to compare the accuracy of the new elastomeric impression material with vinyl polysiloxane and polyether following both spray and immersion disinfection. Impressions of a modified dentoform with a stainless steel crown preparation in the lower right quadrant were made, and type IV gypsum working casts and dies were formed. Anteroposterior (AP), cross-arch (CA), buccolingual (BL), mesiodistal (MD), occlusogingivobuccal (OGB), and occlusogingivolingual (OGL) dimensions were measured using a microscope. Working cast and die dimensions were compared to those of the master model. The impression materials were a newly formulated, ring-opening metathesis-polymerization impression material (ROMP Cartridge Tray and ROMP Volume Wash), vinyl polysiloxane (VPS, Aquasil Ultra Monophase/LV), and a polyether (PE, Impregum Penta Soft/Permadyne Garant L). Fifteen impressions with each material were made, of which 5 were disinfected by spray for 10 minutes (CaviCide), 5 were disinfected by immersion for 90 minutes (ProCide D), and 5 were not disinfected. There were significant cross-product interactions with a 2-way ANOVA, so a 1-way ANOVA and Dunnett's T3 multiple comparison test were used to compare the dimensional changes of the 3 impression materials, by disinfection status and for each location (alpha=.05). For ROMP, there were no significant differences from the master, for any dimension, when comparing the control and 2 disinfectant conditions. No significant differences were detected among the 3 impression materials for CA, BL, and MD. The working die dimensions of OGB and OGL for VPS with immersion disinfection were significantly shorter than with PE and ROMP (P<.05). Overall, the AP dimension was more accurate than CA, and the BL of working dies

  18. Preparation of Soypolymers by Ring-opening Polymerization of Epoxdized Soybean Oil

    USDA-ARS?s Scientific Manuscript database

    Ring opening polymerization of epoxidized soybean oil (ESO) initiated by boron trifluoride diethyl etherate in methylene chloride was conducted in an effort to develop useful biodegradable polymers. The resulting polymers (PESO) were characterized using Infrared (IR), differential scanning calorime...

  19. Chiral bora[1]ferrocenophanes: syntheses, mechanistic insights, and ring-opening polymerizations.

    PubMed

    Sadeh, Saeid; Bhattacharjee, Hridaynath; Khozeimeh Sarbisheh, Elaheh; Quail, J Wilson; Müller, Jens

    2014-12-01

    A series of new boron-bridged [1]ferrocenophanes ([1]FCPs) was prepared by salt-metathesis reactions between enantiomerically pure dilithioferrocenes and amino(dichloro)boranes (Et2 NBCl2 , iPr2 NBCl2 , or tBu(Me3 Si)NBCl2 ). The dilithioferrocenes were prepared in situ by lithium-bromine exchange from the respective planar-chiral dibromides (Sp ,Sp )-[1-Br-2-(HR2 C)H3 C5 ]2 Fe (R=Me or Et). In most of the cases, mixtures of the targeted [1]FCPs 4 and the unwanted 1,1'-bis(boryl)ferrocenes 5 were formed. The product ratio depends on the bulkiness of the amino group, the speed of addition of the amino(dichloro)borane, the alkyl group on Cp rings, and in particular on the reaction temperature. The formation of strained [1]FCPs is strongly favored by increased reaction temperatures. Secondly, CHEt2 groups at Cp rings favored the formation of the targeted [1]FCPs stronger than CHMe2 groups. These discoveries open up new possibilities to further suppress the formation of unwanted byproducts by a careful choice of the reaction temperature and through tailoring the bulkiness of CHR2 groups on ferrocene. Thermal ring-opening polymerizations of selected boron-bridged [1]FCPs gave metallopolymers with a Mw of 10 kDa (GPC).

  20. Catalysts and methods for ring opening metathesis polymerization

    DOEpatents

    Schrock, Richard Royce; Autenrieth, Benjamin

    2017-04-04

    The present invention, among other things, provides highly syndiotactic poly(dicyclopentadiene) and/or hydrogenated poly(dicyclopentadiene), compositions thereof, and compounds and methods for preparing the same. In some embodiments, a provided compound is a compound of formula I, II or III. In some embodiments, a provided method comprises providing a compound of formula I, II or III.

  1. Ring-Opening Polymerization of Lactide to Form a Biodegradable Polymer

    ERIC Educational Resources Information Center

    Robert, Jennifer L.; Aubrecht, Katherine B.

    2008-01-01

    In this laboratory activity for introductory organic chemistry, students carry out the tin(II) bis(2-ethylhexanoate)/benzyl alcohol mediated ring-opening polymerization of lactide to form the biodegradable polymer polylactide (PLA). As the mechanism of the polymerization is analogous to that of a transesterification reaction, the experiment can be…

  2. Catalyzed ring-opening polymerization of epoxidized soybean oil by hydrated and anhydrous fluoroantimonic acids

    USDA-ARS?s Scientific Manuscript database

    Ring-opening polymerization of epoxidized soybean oil (ESO) catalyzed by the super acid, fluroantimonic acid hexahydrate (HSbF6-6H2O), and the anhydrous form (HSbF6) in ethyl acetate was conducted in an effort to develop useful biodegradable polymers. The resulting polymerized ESO (SA-RPESO and SAA-...

  3. Ring-Opening Polymerization of Lactide to Form a Biodegradable Polymer

    ERIC Educational Resources Information Center

    Robert, Jennifer L.; Aubrecht, Katherine B.

    2008-01-01

    In this laboratory activity for introductory organic chemistry, students carry out the tin(II) bis(2-ethylhexanoate)/benzyl alcohol mediated ring-opening polymerization of lactide to form the biodegradable polymer polylactide (PLA). As the mechanism of the polymerization is analogous to that of a transesterification reaction, the experiment can be…

  4. Fast and selective ring-opening polymerizations by alkoxides and thioureas

    NASA Astrophysics Data System (ADS)

    Zhang, Xiangyi; Jones, Gavin O.; Hedrick, James L.; Waymouth, Robert M.

    2016-11-01

    Ring-opening polymerization of lactones is a versatile approach to generate well-defined functional polyesters. Typical ring-opening catalysts are subject to a trade-off between rate and selectivity. Here we describe an effective catalytic system combining alkoxides with thioureas that catalyses rapid and selective ring-opening polymerizations. Deprotonation of thioureas by sodium, potassium or imidazolium alkoxides generates a hydrogen-bonded alcohol adduct of the thiourea anion (thioimidate). The ring-opening polymerization of L-lactide mediated by these alcohol-bonded thioimidates yields highly isotactic polylactide with fast kinetics and living polymerization behaviour, as evidenced by narrow molecular weight distributions (Mw/Mn < 1.1), chain extension experiments and minimal transesterifications. Computational studies indicate a bifunctional catalytic mechanism whereby the thioimidate activates the carbonyl of the monomer and the alcohol initiator/chain end to effect the selective ring-opening of lactones and carbonates. The high selectivity of the catalyst towards monomer propagation over transesterification is attributed to a selective activation of monomer over polymer chains.

  5. Zinc-Catalyzed Highly Isoselective Ring Opening Polymerization of rac-Lactide

    PubMed Central

    2015-01-01

    A family of chiral zinc amido-oxazolinate complexes are shown to be highly active and isoselective initiators for the ring-opening polymerization (ROP) of rac-lactide, yielding isotactic stereoblock polylactides (PLA) with Pm up to 0.91. This represents the highest isoselectivity observed with zinc-based catalysts for ROP of rac-lactide. PMID:25068079

  6. Ring-opening polymerization of cyclic esters by an enantiopure heteroscorpionate rare earth initiator.

    PubMed

    Otero, Antonio; Fernández-Baeza, Juan; Lara-Sánchez, Agustín; Alonso-Moreno, Carlos; Márquez-Segovia, Isabel; Sánchez-Barba, Luis F; Rodríguez, Ana M

    2009-01-01

    With a sting in its tail: An enantiopure neodymium complex (see scheme) acts as an efficient single-site initiator for the controlled ring-opening polymerization of rac-lactide, forming isotactic polyester. The heteroscorpionate complex was characterized spectroscopically and by X-ray diffraction.

  7. Organocatalytic Ring-Opening Polymerization of Trimethylene Carbonate to Yield a Biodegradable Polycarbonate

    ERIC Educational Resources Information Center

    Chan, Julian M. W.; Zhang, Xiangyi; Brennan, Megan K.; Sardon, Haritz; Engler, Amanda C.; Fox, Courtney H.; Frank, Curtis W.; Waymouth, Robert M.; Hedrick, James L.

    2015-01-01

    In this laboratory experiment, students work in pairs to synthesize a simple aliphatic polycarbonate via ring-opening polymerization of trimethylene carbonate using 1,8-diazabicyclo[5.4.0]undec-7-ene and thiourea as organocatalysts. Following polymer isolation, students cool the material in a dry ice/acetone bath to observe its glass-transition…

  8. Boron Trifluoride Catalized Ring-Opening Polymerization of Epoxidized Soybean Oil in Liquid Carbon Dioxide

    USDA-ARS?s Scientific Manuscript database

    Boron trifluoride diethyl etherate (BF3.OEt2) catalyzed ring-opening polymerization of epoxidized soybean oil (ESO), in liquid carbon dioxide, was conducted in an effort to develop useful biobased biodegradable polymers. The resulting polymers (RPESO) were characterized by FTIR spectroscopy, differ...

  9. Lewis Acid Catalyzed Ring-opening Polymerization of Epoxidized Soybean Oil in Liquid Carbon Dioxide

    USDA-ARS?s Scientific Manuscript database

    Ring-opening polymerization of epoxidized soybean oil (ESO) catalyzed by boron trifluoride diethyl etherate (BF3•OEt2), in liquid carbon dioxide, was conducted in an effort to develop useful biobased biodegradable polymers. The resulting polymers (RPESO) were characterized by FTIR spectroscopy, diff...

  10. Organocatalytic Ring-Opening Polymerization of Trimethylene Carbonate to Yield a Biodegradable Polycarbonate

    ERIC Educational Resources Information Center

    Chan, Julian M. W.; Zhang, Xiangyi; Brennan, Megan K.; Sardon, Haritz; Engler, Amanda C.; Fox, Courtney H.; Frank, Curtis W.; Waymouth, Robert M.; Hedrick, James L.

    2015-01-01

    In this laboratory experiment, students work in pairs to synthesize a simple aliphatic polycarbonate via ring-opening polymerization of trimethylene carbonate using 1,8-diazabicyclo[5.4.0]undec-7-ene and thiourea as organocatalysts. Following polymer isolation, students cool the material in a dry ice/acetone bath to observe its glass-transition…

  11. Radical Ring-Opening Polymerization: Scope, Limitations, and Application to (Bio)Degradable Materials.

    PubMed

    Tardy, Antoine; Nicolas, Julien; Gigmes, Didier; Lefay, Catherine; Guillaneuf, Yohann

    2017-02-08

    Cyclic monomers bearing either vinyl or exomethylene groups have the ability to be polymerized through a radical pathway via a ring-opening mechanism (addition-fragmentation process), leading to the introduction of functionalities in the polymer backbone. Radical ring-opening polymerization (rROP) combines the advantages of both ring-opening polymerization and radical polymerization, that is the preparation of polymers bearing heteroatoms in the backbone but with the ease and robustness of a radical process. This current review presents a comprehensive description of rROP by detailing: (i) the various monomers that polymerize through rROP; (ii) the main parameters that govern the rROP mechanism; (iii) the copolymerization by conventional or controlled/living radical polymerization between rROP monomers and traditional vinyl monomers to obtain copolymers with advanced properties; (iv) the different applications (low shrinkage materials and preparation of (bio)degradable materials) of rROP monomer-containing materials, and (v) the main alternatives to rROP to induce degradability to materials obtained by a radical polymerization.

  12. INVESTIGATION OF THE SURFACE PROPERTIES OF POLYMERIC SOAPS OBTAINED BY RING-OPENING POLYMERIZATION OF EPOXIDIZED SOYBEAN OIL

    USDA-ARS?s Scientific Manuscript database

    Epoxidized soybean oil (ESO) was converted to a polysoap via a two-step synthetic procedure of catalytic ring-opening polymerization (PESO), followed by hydrolysis with a base (HPESO). Various molecular weights of PESO and HPESO were prepared by varying the reaction temperature and/or catalyst conc...

  13. Lipase-catalyzed ring-opening polymerization of lactones to polyesters and its mechanistic aspects.

    PubMed

    Namekawa, S; Suda, S; Uyama, H; Kobayashi, S

    1999-01-01

    Lipase catalysis induced a ring-opening polymerization of lactones with different ring-sizes. Small-size (four-membered) and medium-size lactones (six- and seven-membered) as well as macrolides (12-, 13-, 16-, and 17-membered) were subjected to lipase-catalyzed polymerization. The polymerization behaviors depended primarily on the lipase origin and the monomer structure. The macrolides showing much lower anionic polymerizability were enzymatically polymerized faster than epsilon-caprolactone. The granular immobilized lipase derived from Candida antartica showed extremely efficient catalysis in the polymerization of epsilon-caprolactone. Single-step terminal functionalization of the polyester was achieved by initiator and terminator methods. The enzymatic polymerizability of lactones was quantitatively evaluated by Michaelis-Menten kinetics.

  14. Synthesis of NLO polycarbonates via the ring-opening polymerization of macrocyclic prepolymers

    NASA Astrophysics Data System (ADS)

    Kulig, Joseph B.; Moore, Collin G.; Brittain, William J.; Gilmour, Sandra; Perry, Joseph W.

    1994-05-01

    The synthesis and characterization of polycarbonates and polyformals is described. Copolymers of bisphenol A (BPA) and either a triphenyloxazole (1) or phenylquinoxaline (2) monomer were prepared. The polycarbonate copolymers were prepared by ring-opening polymerization of macrocyclic prepolymers using a solvent-free process. Preliminary electro- optic measurements have been performed on the polycarbonate copolymers of BPA and 1. Polyformals have also been prepared by a conventional polymerization process involving the reaction of dichloromethane with different feed ratios of BPA and either 1 or 2. The glass transition temperature of either the polyformals or polycarbonates is dramatically increased by increasing mole fractions of monomers 1 and 2.

  15. Zwitterionic ring-opening polymerization for the synthesis of high molecular weight cyclic polymers.

    PubMed

    Brown, Hayley A; Waymouth, Robert M

    2013-11-19

    Cyclic polymers are an intriguing class of macromolecules. Because of the constraints of the cyclic topology and the absence of chain ends, the properties of these molecules differ from those of linear polymers in ways that remain poorly understood. Cyclic polymers present formidable synthetic challenges because the entropic penalty of coupling the chain ends grows exponentially with increasing molecular weight. In this Account, we describe recent progress in the application of zwitterionic ring-opening polymerization (ZROP) as a strategy for the synthesis of high molecular weight, cyclic polymers. Zwitterionic ring-opening polymerization involves the addition of neutral organic nucleophiles to strained heterocyclic monomers; under appropriate conditions, cyclization of the resultant macrozwitterions generates cyclic macromolecules. We discuss the mechanistic and kinetic features of these zwitterionic ring-opening reactions and the conditions that influence the efficiency of the initiation, propagation, and cyclization to generate high molecular weight cyclic polymers. N-Heterocyclic carbenes (NHC) are potent nucleophiles and relatively poor leaving groups, two features that are important for the generation of high molecular weight polymers. Investigations of the nature of the monomer and nucleophile have helped researchers understand the factors that govern the reactivity of these systems and their impact on the molecular weight and molecular weight distributions of the resulting cyclic polymers. We focus primarily on ZROP mediated by N-heterocyclic carbene nucleophiles but also discuss zwitterionic polymerizations with amidine, pyridine, and imidazole nucleophiles. The ZROP of N-carboxyanhydrides with N-hetereocyclic carbenes generates a family of functionalized cyclic polypeptoids. We can synthesize gradient lactone copolymers by exploiting differences in relative reactivity present in ZROP that differ from those of traditional metal-mediated polymerizations

  16. Modeling of lipase catalyzed ring-opening polymerization of epsilon-caprolactone.

    PubMed

    Sivalingam, G; Madras, Giridhar

    2004-01-01

    Enzymatic ring-opening polymerization of epsilon-caprolactone by various lipases was investigated in toluene at various temperatures. The determination of molecular weight and structural identification was carried out with gel permeation chromatography and proton NMR, respectively. Among the various lipases employed, an immobilized lipase from Candida antartica B (Novozym 435) showed the highest catalytic activity. The polymerization of epsilon-caprolactone by Novozym 435 showed an optimal temperature of 65 degrees C and an optimum toluene content of 50/50 v/v of toluene and epsilon-caprolactone. As lipases can degrade polyesters, a maximum in the molecular weight with time was obtained due to the competition of ring opening polymerization and degradation by specific chain end scission. The optimum temperature, toluene content, and the variation of molecular weight with time are consistent with earlier observations. A comprehensive model based on continuous distribution kinetics was developed to model these phenomena. The model accounts for simultaneous polymerization, degradation and enzyme deactivation and provides a technique to determine the rate coefficients for these processes. The dependence of these rate coefficients with temperature and monomer concentration is also discussed.

  17. Microwave-assisted cationic ring-opening polymerization of 2-oxazolines

    PubMed Central

    Luef, Klaus P.; Hoogenboom, Richard; Schubert, Ulrich S.; Wiesbrock, Frank

    2017-01-01

    Unlike any other polymer class, the (co-)poly(2-oxazoline)s have tremendously benefited from the introduction of microwave reactors into chemical laboratories. This review focuses on the research activities in the area of (co-)poly(2-oxazoline)s prepared by microwave-assisted syntheses and, correspondingly, summarizes the current-state-of the-art of the microwave-assisted synthesis of 2-oxazoline monomers and the microwave-assisted ring-opening (co-)polymerization of 2-oxazolines as well as prominent examples of post-polymerization modification of (co-)poly(2-oxazoline)s. Special attention is attributed to the kinetic analysis of the microwave-assisted polymerization of 2-oxazolines and the discussion of non-thermal microwave effects. PMID:28239203

  18. Solventless sol-gel chemistry through ring-opening polymerization of bridged disilaoxacyclopentanes

    SciTech Connect

    RAHIMIAN,KAMYAR; LOY,DOUGLAS A.

    2000-05-01

    Ring-opening polymerization (ROP) of disilaoxacyclopentanes has proven to be an excellent approach to sol-gel type hybrid organic-inorganic materials. These materials have shown promise as precursors for encapsulation and microelectronics applications. The polymers are highly crosslinked and are structurally similar to traditional sol-gels, but unlike typical sol-gels they are prepared by an organic base or Bronsted acid (formic or triflic acid), without the use of solvents and water, they have low VOC's and show little shrinkage during processing.

  19. Method of polymerizing exo-methylene cyclic organic compounds using homogeneous ring-opening catalysts

    DOEpatents

    Marks, Tobin J.; Yang, Xinmin; Jia, Li

    1994-01-01

    The regiospecific (1,2-Me.sub.2 C.sub.5 H.sub.3).sub.2 ZrMe.sup.+ MeB(C.sub.6 F.sub.5).sub.3.sup.- mediated ring-opening polymerization of methylenecyclobutane and its copolymerization with ethylene to polyolefins of microstructure--{CH.sub.2 CH.sub.2 CH.sub.2 C(CH.sub.2)]--.sub.n and {--[CH.sub.2 CHR]--.sub.x [CH.sub.2 CH.sub.2 CH.sub.2 C(CH.sub.2)]--.sub.y }.sub.n' respectively, is disclosed.

  20. Synthesis of biodegradable poly-epsilon-caprolactone microspheres by dispersion ring-opening polymerization in supercritical carbon dioxide.

    PubMed

    Grignard, Bruno; Stassin, Fabrice; Calberg, Cédric; Jérôme, Robert; Jérôme, Christine

    2008-11-01

    A series of fluorinated diblock and triblock copolymers of poly(epsilon-caprolactone) and poly(heptadecafluorodecylacrylate) were prepared by combining ring-opening polymerization of epsilon-CL and atom transfer radical polymerization of the acrylate. These copolymers with well-controlled molecular weight and composition were characterized by (1)H NMR spectroscopy and used as stabilizers for the dispersion ring-opening polymerization of epsilon-CL in supercritical carbon dioxide. The effect of composition and architecture of the polymeric stabilizers on the stabilization of PCL microspheres was investigated. Finally, purification of PCL was successfully implemented by reactive supercritical fluid extraction of the tin catalyst.

  1. Effect of initiators on synthesis of poly(L-lactide) by ring opening polymerization

    NASA Astrophysics Data System (ADS)

    Pholharn, D.; Srithep, Y.; Morris, J.

    2017-06-01

    We studied the effect of several aliphatic alcohols, including1-dodecanol, 1-octanol and methanol, as initiators on synthesis of poly(L-lactide) (PLLA) by ring opening polymerization. The reaction starts with L-lactide monomer and uses stannous octoate as catalyst. Fourier transform infrared spectroscopy and X-ray diffraction analysis verified that PLLAs were produced successfully. Weight, number average molecular weight and polydispersity index of PLLAs were measured by gel permeation chromatography. The PLLA initiated by methanol (PLLA-Meth) presented the highest molecular weight and yield percent. From differential scanning calorimetry, PLLA-Meth showed the highest melting temperature at ∼167°C, crystallization temperature at 110°C and degree of crystallinity 80%. The thermal stability was assessed by thermogravimetric analysis: this confirmed that PLLA-Meth was superior with the highest degradation temperature compared to PLLA initiated by other initiators. We concluded that methanol was the most appropriate initiator for PLLA synthesis by ring opening polymerization.

  2. L-Lactide Ring-Opening Polymerization with Tris(acetylacetonate)Titanium(IV) for Renewable Material.

    PubMed

    Kim, Da Hee; Yoo, Ji Yun; Ko, Young Soo

    2016-05-01

    A new Ti-type of catalyst for L-lactide polymerization was synthesized by reaction of titanium(IV) isopropoxide (TTIP) with acetylacetone (AA). Moreover, PLA was prepared by the bulk ring-opening polymerization using synthesized Ti catalyst. Polymerization behaviors were examined depending on monomer/catalyst molar ratio, polymerization temperature and time. The structure of synthesized catalysts was verified with FT-IR and 1H NMR and the properties of poly(L-lactide) (PLLA) were examined by GPC, DSC and FT-IR. There existed about 30 minutes of induction time at the monomer/catalyst molar ratio of 300. The molecular weight (MW) increased as monomer/catalyst molar ratio increased. The MW increased almost linearly as polymerization progressed. Increasing polymerization temperature increased the molecular weight of PLLA as well as monomer/catalyst molar ratio. The melting point (T(m)) of polymers was in the range of 142 to 167 degrees C. Lower T(m) was expected to be resulted from relatively lower molecular weight.

  3. Enantioselective Ring-Opening Polymerization of rac-Lactide Dictated by Densely Substituted Amino Acids.

    PubMed

    Sanchez-Sanchez, Ana; Rivilla, Ivan; Agirre, Maddalen; Basterretxea, Andere; Etxeberria, Agustin; Veloso, Antonio; Sardon, Haritz; Mecerreyes, David; Cossío, Fernando P

    2017-04-05

    Organocatalysis is becoming an important tool in polymer science because of its versatility and specificity. To date a limited number of organic catalysts have demonstrated the ability to promote stereocontrolled polymerizations. In this work we report one of the first examples of chirality transfer from a catalyst to a polymer in the organocatalyzed ring-opening polymerization (ROP) of rac-lactide (rac-LA). We have polymerized rac-LA using the diastereomeric densely substituted amino acids (2S,3R,4S,5S)-1-methyl-4-nitro-3,5-diphenylpyrrolidine-2-carboxylic acid (endo-6) and (2S,3S,4R,5S)-1-methyl-4-nitro-3,5-diphenylpyrrolidine-2-carboxylic acid (exo-6), combined with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as a cocatalyst. Both diastereoisomers not only showed the ability to synthesize enriched isotactic polylactide with a Pm higher than 0.90 at room temperature but also were able to preferentially promote the polymerization of one of the isomers (l or d) with respect to the other. Thus, exo-6 preferentially polymerized l-lactide, whereas endo-6 preferred d-lactide as the substrate. Density functional theory calculations were conducted to investigate the origins of this unique stereocontrol in the polymerization, providing mechanistic insight and explaining why the chirality of the catalyst is able to define the stereochemistry of the monomer insertion.

  4. Stereorigid OSSO-Type Group 4 Metal Complexes in the Ring-Opening Polymerization of rac-Lactide.

    PubMed

    Lapenta, Rosita; Buonerba, Antonio; De Nisi, Assunta; Monari, Magda; Grassi, Alfonso; Milione, Stefano; Capacchione, Carmine

    2017-03-20

    The synthesis and characterization of a series of group 4 metal complexes of general formula {OSSOX}M(OR)2 (X = R = (t)Bu, M = Zr (1); X = cumyl, M = Zr, R = (t)Bu (2); X = cumyl, M = Ti, R = (i)Pr (4); X = cumyl, M = Hf, R = (t)Bu (5)) and {OSSOX}2Zr (X = Cl (3)) supported by o-phenylene-bridged bis(phenolato) ligands (OSSOtBu-H = 6,6'-((1,2-phenylenebis(sulfanediyl))bis(methylene))bis(2,4-di-tert-butyphenol); OSSOCum-H = 6,6'-((1,2-phenylenebis(sulfanediyl))bis(methylene))bis(2,4-bis(2-phenylpropan-2-yl)phenol); OSSOCl-H = 6,6'-((1,2-phenylenebis(sulfanediyl))bis(methylene))bis(2,4-dichlorophenol)) are described herein. Complexes 1-5 were readily obtained by σ-bond metathesis reactions between the proligand and the appropriate homoleptic metal precursor. The reaction with OSSOCl yielded the bis-ligand complex{OSSOCl}2Zr (3) regardless of the OSSOCl-H/Zr(O(t)Bu)4 molar ratio or experimental conditions. All complexes were characterized in solution using NMR spectroscopy and, in the case of 2, by single-crystal X-ray diffraction experiments. These complexes show a fac-fac ligand wrapping and a cis relationship between the other two monodentate ligands; zirconium and hafnium complexes 1-3 and 5 are configurationally stable, whereas titanium complex 4 is fluxional in solution at room temperature. The complexes tested in the ring-opening polymerization (ROP) of racemic-lactide showed, except in the case of 3, moderate rates and good levels of polymerization control. Upon addition of an exogenous alcohol (isopropyl alcohol or tert-butyl alcohol) efficient binary catalytic systems were achieved. Polymerizations were well-controlled, as testified by the linear growth of the molecular weight as polymerization proceeded, narrow polydispersity indices, and molecular weights close to those expected on the basis of added alcohol amounts. Experimental and theoretical evidence is provided that ROP reactions operate according to an activated monomer mechanism.

  5. Synthesis of Block Copolymers of Varying Architecture Through Suppression of Transesterification during Coordinated Anionic Ring Opening Polymerization

    PubMed Central

    Lipik, Vitali T.; Abadie, Marc J. M.

    2012-01-01

    Well-defined di- and triblock copolymers consisting of ε-caprolactone (CL), L-lactide (LA), and trimethylene carbonate (TMC) were synthesized via “PLA first route” in coordinated anionic ring opening polymerization/copolymerization (CAROP) with tin (II) octoate as catalyst. The desired block structure was preserved by use of protective additive α-methylstyrene by preventing the transesterification side-reactions. MALDI-TOF analysis revealed that the protection mechanism is associated with α-methylstyrene and tin (II) octoate complexation. Additionally, it was shown that use of α-methylstyrene in ring opening polymerization allowed the formation of polyesters with high molar mass. PMID:22844286

  6. Mesoporous Molecular Sieves Based Catalysts for Olefin Metathesis and Metathesis Polymerization

    NASA Astrophysics Data System (ADS)

    Balcar, Hynek; Čejka, Jiří

    Heterogeneous catalysts for olefin metathesis using different types of (i) siliceous mesoporous molecular sieves, and (ii) organized mesoporous alumina as supports are reported. The catalysts were prepared either by spreading of transition metal oxidic phase on the support surface or by immobilizing transition metal compounds (mostly organometallic) on the support. The activity of these catalysts in various types of metathesis reactions (i.e. alkene and diene metathesis, metathesis of unsaturated esters and ethers, RCM, ROMP and metathesis polymerization of alkynes) was described. The main advantages of these catalysts consist generally in their high activity and selectivity, easy separation of catalysts from reaction products and the preparation of products free of catalyst residue. The examples of pore size influence on the selectivity in metathesis reactions are also given.

  7. Dual Catalysis for Selective Ring-Opening Polymerization of Lactones: Evolution toward Simplicity.

    PubMed

    Naumann, Stefan; Scholten, Philip B V; Wilson, James A; Dove, Andrew P

    2015-11-18

    Much work has been directed to the design of complex single-site catalysts for ring-opening polymerization (ROP) to enhance both activity and selectivity. More simply, however, cooperative effects between Lewis acids and organocatalytic nucleophiles/Lewis bases provide a powerful alternative. In this study we demonstrate that the combination of N-heterocyclic carbenes, 1,8-diazabicycloundec-7-ene (DBU) and 4-dimethylaminopyridine (DMAP) with simple Lewis acids enables the ROP of the macrolactone pentadecalactone in a rapid and efficient manner. Remarkably, regardless of the nature of the nucleophile, the order of activity was observed to be MgX2 ≫ YCl3 ≫ AlCl3 and MgI2 > MgBr2 > MgCl2 in every case. The minimal influence of the organobase on polymerization activity allows for the use of simple and inexpensive precursors. Furthermore, extension of the study to other cyclic (di)ester monomers reveals the choice of Lewis acid to lead to monomer selective ROP activity and hence control over copolymer composition by choice of Lewis acid. This approach could lead to the realization of complex polymer structures with tunable physical properties from simple catalyst combinations.

  8. Heteroscorpionate rare-earth initiators for the controlled ring-opening polymerization of cyclic esters.

    PubMed

    Otero, Antonio; Lara-Sánchez, Agustín; Fernández-Baeza, Juan; Alonso-Moreno, Carlos; Márquez-Segovia, Isabel; Sánchez-Barba, Luis F; Castro-Osma, José A; Rodríguez, Ana M

    2011-05-07

    A series of neutral rare-earth metal amides containing different achiral and chiral heteroscorpionate ligands was synthesized and characterized and these compounds were employed in the polymerization of cyclic esters. Thus, treatment of [Ln{N(SiHMe(2))(2)}(3)(thf)(2)] (Ln = Nd, Sm) with acetamide or thioacetamide heteroscorpionate ligands for 2 h at 0 °C afforded the α-agostic silylamido dimeric rare-earth compounds [Ln{N(SiHMe(2))(2)}(NNE)](2) (Ln = Nd and Sm; NNE = heteroscorpionate ligands, E = O, S) (1-8), some as enantiopure complexes. Complexes 1-8 contain dianionic heteroscorpionate pseudoallyl ligands resulting from C-H activation of the bridging methine group of the bis(pyrazol-1-yl)methane moiety and subsequent coordination to the metal center. However, when the reaction was carried out for 1 h at lower temperature new bis(silylamido) dimeric lanthanide compounds [Ln{N(SiHMe(2))(2)}(2)(NNE)](2) (Ln = Nd and Sm; E = O) (9 and 10) were obtained. The structures of the complexes were determined by spectroscopic methods and the X-ray crystal structures of 1, and 4 were also established. Neodymium complexes are active initiators for the ring-opening polymerization (ROP) of lactide (LA) and lactones, giving rise to medium-high molar mass polymers under mild conditions and with narrow polydispersities. These complexes were well suited for achieving well-controlled polymerization through an insertion-coordination mechanism. Achiral and racemic complexes did not affect stereocontrol in the polymerizarion of rac-LA but the enantiomerically pure complex 1 was found to exhibit a homosteric preference for one of the two enantiomers of rac-LA at low conversions.

  9. Newly Developed Techniques on Polycondensation, Ring-Opening Polymerization and Polymer Modification: Focus on Poly(Lactic Acid)

    PubMed Central

    Hu, Yunzi; Daoud, Walid A.; Cheuk, Kevin Ka Leung; Lin, Carol Sze Ki

    2016-01-01

    Polycondensation and ring-opening polymerization are two important polymer synthesis methods. Poly(lactic acid), the most typical biodegradable polymer, has been researched extensively from 1900s. It is of significant importance to have an up-to-date review on the recent improvement in techniques for biodegradable polymers. This review takes poly(lactic acid) as the example to present newly developed polymer synthesis techniques on polycondensation and ring-opening polymerization reported in the recent decade (2005–2015) on the basis of industrial technique modifications and advanced laboratory research. Different polymerization methods, including various solvents, heating programs, reaction apparatus and catalyst systems, are summarized and compared with the current industrial production situation. Newly developed modification techniques for polymer properties improvement are also discussed based on the case of poly(lactic acid). PMID:28773260

  10. Different mechanisms at different temperatures for the ring-opening polymerization of lactide catalyzed by binuclear magnesium and zinc alkoxides.

    PubMed

    Sun, Yangyang; Cui, Yaqin; Xiong, Jiao; Dai, Zhongran; Tang, Ning; Wu, Jincai

    2015-10-07

    Two binuclear magnesium and zinc alkoxides supported by a bis-salalen type dinucleating heptadentate Schiff base ligand were synthesized and fully characterized. The two complexes are efficient initiators for the ring-opening polymerization (ROP) of L-lactide, affording polymers with narrow polydispersities and desirable molecular weights. Interestingly, the mechanisms for the ROP of lactide are different at different temperatures. At a high temperature of 130 °C, a coordination-insertion mechanism is reasonable for the bulk melt polymerization of lactide. At a low temperature, the alkoxide cannot initiate the ROP reaction; however, upon the addition of external benzyl alcohol into the system, the ROP of lactide can smoothly proceed via an "activated monomer" mechanism. In addition, these complexes display slight stereo-selectivity for the ring-opening polymerization of rac-lactide, affording partially isotactic polylactide in toluene with a Pm value of 0.59.

  11. Ring-opening polymerization of cyclic esters by phenoxy-thioether complexes derived from biocompatible metals.

    PubMed

    Pilone, Alessia; Lamberti, Marina; Mazzeo, Mina; Milione, Stefano; Pellecchia, Claudio

    2013-09-28

    A series of novel Mg(II) and Zn(II) complexes of the form LMX or L2M, supported by phenoxy-thioether ligands bearing different substituents at the ortho position of the thiophenol rings [L(-) = 4,6-tBu2-OC6H2-2-CH2S(2-R-C6H4)(-)] [M = Zn, R = H, X = N(SiMe3)2 (1) and X = Et (2); M = Mg, X = n-Bu, R = H (3), R = CH3 (4), R = Br (5); M = Mg, R = H (6)], were synthesized and characterized. Reaction of the proper zinc precursor (Zn[N(SiHMe2)2]2 or ZnEt2) with one equivalent of the phenoxy-thioether proligand produced the corresponding amido (1) and ethyl (2) zinc complexes in high yields. The monoalkylmagnesium complexes (3-5) were all obtained by butane elimination reaction of the dialkylmagnesium reagent, Mg(n-Bu)2, with one equivalent of the proligand in good yields. The homoleptic complex 6 was obtained by reaction of 0.5 equivalent of Mg(n-Bu)2 and the proper proligand. Variable temperature (1)H NMR studies performed on 2 and 3 demonstrated that the named complexes are involved in fluxional processes concerning a fast conformational change of the six-membered metallacycle. DOSY (Diffusion Ordered SpectroscopY) (1)H experiments and ligand scrambling strongly suggested that complexes 1-6 exist as dimeric species in solution. All complexes were active as catalysts in the ring-opening polymerization of cyclic esters. In particular, magnesium complexes showed superior ε-caprolactone and lactide ROP behavior in terms of activity, control of molecular weights and molecular weight distributions.

  12. High throughput synthesis of polyesters using entropically driven ring-opening polymerizations.

    PubMed

    Kamau, Stephen D; Hodge, Philip; Williams, Richard T; Stagnaro, Paola; Conzatti, Lucia

    2008-01-01

    Copolyesters were synthesized in a high throughput (HT) manner and in high yield on ca. a 90 mg scale using entropically driven ring-opening polymerizations (ED-ROPs). This synthetic approach is a valuable addition to the HT polymer synthesis arsenal in that it allows condensation-type polymers with relatively large repeat units, such as those in poly(ethylene terephthalate) and poly(butylene terephthalate), to be obtained easily. The synthetic procedure involved taking mixtures of the appropriate macrocyclic oligoesters and heating them together under neat conditions at 250-300 degrees C for 2 h in the presence of 0.1 mol % of di- n-butyltin oxide or tetra- n-butylammonium tetrafluoroborate. In most cases Mw values were >25,000 and, as expected for ED-ROPs, the polydispersity indices were close to 2.0. Higher molecular weights could be obtained by using longer reaction times, but this might lead to product decomposition. The method worked well for esters formally derived from aliphatic or aromatic acids and alcohols, but less well for esters derived from phenols. Attempts were also made to synthesize copolymers by mixing together the two homopolymers and heating with a catalyst. These reactions were successful in a few instances, but generally, they were not. This is probably because the homopolymers did not mix well. An aluminum reaction block with 36 wells lined with Teflon cups, that fitted snugly in a cylindrical Buchi oven, was the most successful method for carrying out syntheses in an HT manner.

  13. Comparative Theoretical Study of the Ring-Opening Polymerization of Caprolactam vs Caprolactone Using QM/MM Methods

    SciTech Connect

    Elsasser, Brigitta M.; Schoenen, Iris; Fels, Gregor

    2013-06-07

    Candida antarctica lipase B (CALB) efficiently catalyzes the ring-opening polymerization of lactones to high molecular weight products in good yield. In contrast, an efficient enzymatic synthesis of polyamides has so far not been described in the literature. This obvious difference in enzyme catalysis is the subject of our comparative study of the initial steps of a CALB catalyzed ring-opening polymerization of ε- caprolactone and ε-caprolactam. We have applied docking tools to generate the reactant state complex and performed quantum mechanical/molecular mechanical (QM/MM) calculations at the density functional theory (DFT) PBE0 level of theory to simulate the acylation of Ser105 by the lactone and the lactam, respectively, via the corresponding first tetrahedral intermediates. We could identify a decisive difference in the accessibility of the two substrates in the ring-opening to the respective acyl enzyme complex as the attack of ε-caprolactam is hindered because of an energetically disfavored proton transfer during this part of the catalytic reaction while ε-caprolactone is perfectly processed along the widely accepted pathway using the catalytic triade of Ser105, His224, and Asp187. Since the generation of an acylated Ser105 species is the crucial step of the polymerization procedure, our results give an explanation for the unsatisfactory enzymatic polyamide formation and opens up new possibilities for targeted rational catalyst redesign in hope of an experimentally useful CALB catalyzed polyamide synthesis.

  14. beta-Diketiminate aluminium complexes: synthesis, characterization and ring-opening polymerization of cyclic esters.

    PubMed

    Gong, Shaogang; Ma, Haiyan

    2008-07-07

    A series of aluminium alkyl complexes (BDI)AlEt(2) (3a-m) bearing symmetrical or unsymmetrical beta-diketiminate ligand (BDI) frameworks were obtained from the reaction of triethyl aluminium and the corresponding beta-diketimine. The monomeric structure of the aluminium complex 3k was confirmed by an X-ray diffraction study, which shows that the aluminium center is coordinated by both of the nitrogen donors of the chelating diketiminate ligand and the two ethyl groups in a distorted tetrahedral geometry. Attempt to synthesize beta-diketiminate aluminium alkoxide complexes by the reactions of monochloride complex "(BDI-2a)AlMeCl" (4) with alkali salts of 2-propanol gave unexpectedly an aluminoxane [(BDI-2a)AlMe](2)(micro-O) (7) as characterized by X-ray diffraction methods. Complexes 3a-m and [(2,6-(i)Pr(2)C(6)H(3)NCMe)(2)HC]AlEt(2) (8) were found to catalyze the ring-opening polymerization (ROP) of epsilon-caprolactone with moderate activities. The steric and electronic characteristics of the ancillary ligands have a significant influence on the polymerization performance of the corresponding aluminium complexes. The introduction of electron-donating substituents at the para-positions of the aryl rings in the ligand resulted in an apparent decrease in catalytic activity. Complex 3h showed the highest activity among the investigated aluminium complexes due to the high electrophilicity of the metal center induced by the meta-trifluoromethyl substituents on the aryl rings. The increase of steric hindrance of the ligand by introducing ortho-substituents onto the phenyl moieties also resulted in a decrease in the catalytic activity. Although the viscosity average molecular weights (M(eta)) of the obtained poly(caprolactone)s increased with the enhancement of monomer conversion, the ROPs of epsilon-caprolactone initiated by complexes 3a-m and 8 were not well-controlled, as judged from the broad molecular weight distributions (PDI = 1.66-3.74, M(w)/M(n)) of the obtained

  15. Bidirectional cross metathesis and ring-closing metathesis/ring opening of a C 2-symmetric building block: a strategy for the synthesis of decanolide natural products

    PubMed Central

    Kunz, Oliver

    2013-01-01

    Summary Starting from the conveniently available ex-chiral pool building block (R,R)-hexa-1,5-diene-3,4-diol, the ten-membered ring lactones stagonolide E and curvulide A were synthesized using a bidirectional olefin-metathesis functionalization of the terminal double bonds. Key steps are (i) a site-selective cross metathesis, (ii) a highly diastereoselective extended tethered RCM to furnish a (Z,E)-configured dienyl carboxylic acid and (iii) a Ru–lipase-catalyzed dynamic kinetic resolution to establish the desired configuration at C9. Ring closure was accomplished by macrolactonization. Curvulide A was synthesized from stagonolide E through Sharpless epoxidation. PMID:24367418

  16. Tetraphenolate niobium and tantalum complexes for the ring opening polymerization of ε-caprolactone.

    PubMed

    Al-Khafaji, Yahya; Sun, Xinsen; Prior, Timothy J; Elsegood, Mark R J; Redshaw, Carl

    2015-07-21

    Reaction of the pro-ligand α,α,α',α'-tetra(3,5-di-tert-butyl-2-hydroxyphenyl-p-)xylene-para-tetraphenol (p-L(1)H4) with two equivalents of [NbCl5] in refluxing toluene afforded, after work-up, the complex {[NbCl3(NCMe)]2(μ-p-L(1))}·6MeCN (1·6MeCN). When the reaction was conducted in the presence of excess ethanol, the orange complex {[NbCl2(OEt)(NCMe)]2(μ-p-L(1))}·3½MeCN·0.614toluene (2·3½MeCN·0.614toluene) was formed. A similar reaction using [TaCl5] afforded the yellow complex {[TaCl2(OEt)(NCMe)]2(μ-p-L(1))}·5MeCN (3·5MeCN). In the case of the meta pro-ligand, namely α,α,α',α'tetra(3,5-di-tert-butyl-2-hydroxyphenyl-m-)xylene-meta-tetraphenol (m-L(2)H4) only the use of [Nb(O)Cl3(NCMe)2] led to the isolation of crystalline material, namely the orange bis-chelate complex {[Nb(NCMe)Cl(m-L(2)H2)2]}·3½MeCN (4·3½MeCN) or {[Nb(NCMe)Cl(m-L(2)H2)2]}·5MeCN (4·5MeCN). The molecular structures of 1-4 and the tetraphenols L(1)H4 and m-L(2)H4·2MeCN have been determined. Complexes 1-4 have been screened as pre-catalysts for the ring opening polymerization of ε-caprolactone, both with and without benzyl alcohol or solvent present, and at various temperatures; conversion rates were mostly excellent (>96%) with good control either at >100 °C over 20 h (in toluene) or 1 h (neat).

  17. Ring-opening polymerization of ε-caprolactone catalyzed by sulfonic acids: computational evidence for bifunctional activation.

    PubMed

    Susperregui, Nicolas; Delcroix, Damien; Martin-Vaca, Blanca; Bourissou, Didier; Maron, Laurent

    2010-10-01

    The mechanism of ring-opening of ε-caprolactone by methanol catalyzed by trifluoromethane and methane sulfonic acids has been studied computationally at the DFT level of theory. For both elementary steps, the sulfonic acid was predicted to behave as a bifunctional catalyst. The nucleophilic addition proceeds via activation of both the monomer and the alcohol. The ring-opening involves the cleavage of the endo C-O bond of the tetrahedral intermediate with concomitant proton transfer. In both cases, the sulfonic acid acts as a proton shuttle via its acidic hydrogen atom and basic oxygen atoms. The computed activation barriers are consistent with the relatively fast polymerizations observed experimentally at room temperature with both catalysts.

  18. Spontaneously Healable Thermoplastic Elastomers Achieved through One-Pot Living Ring-Opening Metathesis Copolymerization of Well-Designed Bulky Monomers.

    PubMed

    Yang, Ji-Xing; Long, Ying-Yun; Pan, Li; Men, Yong-Feng; Li, Yue-Sheng

    2016-05-18

    We report here a series of novel spontaneously healable thermoplastic elastomers (TPEs) with a combination of improved mechanical and good autonomic self-healing performances. Hard-soft diblock and hard-soft-hard triblock copolymers with poly[exo-1,4,4a,9,9a,10-hexahydro-9,10(1',2')-benzeno-l,4-methanoanthracene] (PHBM) as the hard block and secondary amide group containing norbornene derivative polymer as the soft block were synthesized via living ring-opening metathesis copolymerization by use of Grubbs third-generation catalyst through sequential monomer addition. The microstructure, mechanical, self-healing, and surface morphologies of the block copolymers were thoroughly studied. Both excellent mechanical performance and self-healing capability were achieved for the block copolymers because of the interplayed physical cross-link of hard block and dynamic interaction formed by soft block in the self-assembled network. Under an optimized hard block (PHBM) weight ratio of 5%, a significant recovery of tensile strength (up to 100%) and strain at break (ca. 85%) was achieved at ambient temperature without any treatment even after complete rupture. Moreover, the simple reaction operations and well-designed monomers offer versatility in tuning the architectures and properties of the resulting block copolymers.

  19. Cyclic alternating ring-opening metathesis polymerization (CAROMP). Rapid access to functionalized cyclic polymers.

    PubMed

    Song, Airong; Parker, Kathlyn A; Sampson, Nicole S

    2010-09-03

    Catalysis of alternating ROMP with (H(2)IMes)Cl(2)Ru=CHPh(OiPr), the second generation Hoveyda-Grubbs catalyst, provided an entirely cyclic alternating polymer. Conditions for the cyclic AROMP were used to prepare a polymer in which one of the repeat units bore a primary alkyl chloride that was used for further elaboration.

  20. New Applications of Ring-Opening Metathesis Polymerization for Grafting Alkylene Oxide-Based Copolymers

    NASA Astrophysics Data System (ADS)

    Spurcaciu, Bogdan; Buzdugan, Emil; Nicolae, Cristian; Ghioca, Paul; Iancu, Lorena; Dragutan, Valerian; Dragutan, Ileana

    This research tackles the challenges of innovative modification of poly(allyl alkylene oxides) by ROMP to produce new materials. Firstly, binary and ternary copolymers, poly(epichlorohydrin-allyl glycidyl ether) (ECH-AGE) and poly (epichlorohydrin-propylene oxide-allyl glycidyl ether) (ECH-PO-AGE), have been prepared using as initiator a catalytic system consisting of an alkyl aluminium, controlled amounts of water and different compounds (ethers, diols, phosphines, salicylic acid derivatives, organozincs) acting as cocatalysts. Among catalysts explored in these copolymerizations most productive showed to be the systems triisobutylaluminium (TIBA), water and Zn(DIPS)2 or Zn(acac)2. Copolymers which have become thus available were subsequently grafted onto the pendent allylic groups by ROMP with cycloolefins (cyclooctene, norbornene, cyclododecene) involving ruthenium based catalysts.

  1. Synthesis and Purification of Tunable High Tg Electro-Optical Polymers by Ring Opening Metathesis Polymerization

    DTIC Science & Technology

    2011-09-01

    the residual Ru, Soxhlet extraction was performed with MeOH. The resulting material contained 110 ppm Ru, an improvement over repeated precipitations...ppm) 1 Once precipitated 97 240 2 Twice precipitated 91 160 3 Thrice precipitated 77 140 4 Precipitate, Soxhlet extraction , precipitate 86 110...adsorbed. Maynard and Grubbs used a polar, water soluble phosphine ligand to bind Ru and partition the complex into water via extraction (21

  2. Fluoroantimonic acid hexahydrate (HSbF6-6H2O) catalysis: The ring-opening polymerization of epoxidized soybean oil

    USDA-ARS?s Scientific Manuscript database

    Ring-opening polymerization of epoxidized soybean oil (ESO) catalyzed by a super acid, fluroantimonic acid hexahydrate (HSbF6-6H2O), in ethyl acetate was conducted in an effort to develop useful biodegradable polymers. The resulting polymerized ESO (SA-RPESO) were characterized by using infrared (IR...

  3. Rare earth complexes of phenoxy-thioether ligands: synthesis and reactivity in the ring opening polymerization of cyclic esters.

    PubMed

    Mazzeo, Mina; Tramontano, Roberta; Lamberti, Marina; Pilone, Alessia; Milione, Stefano; Pellecchia, Claudio

    2013-07-07

    The potential of the phenoxy-thioether moieties as ancillary ligands in the coordination chemistry of group 3 metals was explored. The amine elimination reactions between yttrium and scandium amido precursors {M [N(SiHMe2)2]3 (THF)n} with the proligands {4,6-tBu2-OC6H2-2-CH2S(2-R-C6H4)}H [R = H (L1-H), CH3 (L2-H), Br (L3-H), CF3 (L4-H)], bearing different substituents at the ortho position of the thiophenol aryl ring, were studied. The outcome of aminolysis reactions gave different results depending on the structure of the proligand and the reaction conditions. Heteroleptic scandium and yttrium amido complexes with general formula {(L)2M [N(SiHMe2)2] (THF)n} were prevailingly obtained from phenoxy-thioether proligands L1-H and L4-H. In contrast, homoleptic yttrium complexes bearing three phenoxy-thioether ligands were favored with L2-H and L3-H. The activities of all the synthesized complexes toward the ring-opening polymerization of ε-caprolactone and L- and rac-lactide were investigated, also in combination with an alcohol as an external chain transfer agent. Polyesters with controlled molecular parameters (Mn, end groups) and low polydispersities were obtained. The monoinsertion adduct, produced by the reaction of {(L1)2ScN(SiHMe2)2} and 1 equiv. of ε-caprolactone, was isolated proving that a coordination-insertion mechanism of ring-opening polymerization was operative. In the polymerization of rac-lactide, yttrium complexes exerted a high degree of stereocontrol producing heterotactic polylactides (P(r) up to 0.91).

  4. Preparation of stereoregular isotactic poly(mandelic acid) through organocatalytic ring-opening polymerization of a cyclic O-carboxyanhydride.

    PubMed

    Buchard, Antoine; Carbery, David R; Davidson, Matthew G; Ivanova, Petya K; Jeffery, Ben J; Kociok-Köhn, Gabriele I; Lowe, John P

    2014-12-08

    Poly(mandelic acid) (PMA) is an aryl analogue of poly(lactic acid) (PLA) and a biodegradable analogue of polystyrene. The preparation of stereoregular PMA was realized using a pyridine/mandelic acid adduct (Py⋅MA) as an organocatalyst for the ring-opening polymerization (ROP) of the cyclic O-carboxyanhydride (manOCA). Polymers with a narrow polydispersity index and excellent molecular-weight control were prepared at ambient temperature. These highly isotactic chiral polymers exhibit an enhancement of the glass-transition temperature (T(g)) of 15 °C compared to the racemic polymer, suggesting potential future application as high-performance commodity and biomedical materials.

  5. Degradable and comb-like PEG-based copolymers by nitroxide-mediated radical ring-opening polymerization.

    PubMed

    Delplace, Vianney; Tardy, Antoine; Harrisson, Simon; Mura, Simona; Gigmes, Didier; Guillaneuf, Yohann; Nicolas, Julien

    2013-10-14

    Three cyclic ketene acetals, 2-methylene-1,3-dioxepane (MDO), 5,6-benzo-2-methylene-1,3-dioxepane (BMDO), and 2-methylene-4-phenyl-1,3-dioxolane (MPDL), have been copolymerized with oligo(ethylene glycol) methyl ether methacrylate and a small amount of acrylonitrile (or styrene) at 90 °C by nitroxidemediated radical ring-opening polymerization, as a convenient way to prepare degradable PEG-based copolymers for biomedical applications. MPDL was the best candidate, enabling high monomer conversions to be reached and well-defined PEG-based copolymers with adjustable amount of ester groups in the main chain to be synthesized, leading to nearly complete hydrolytic degradation (5% KOH aqueous solution, ambient temperature). The noncytotoxicity of the obtained copolymers was shown on three different cell lines (i.e., fibroblasts, endothelial cells and macrophages), representing a promising approach for the design of degradable precursors for PEGylation and bioconjugation via the NMP technique.

  6. Ring-Opening Polymerization of L-Lactide to Cyclic Poly(Lactide) by Zeolitic Imidazole Framework-8 Catalyst.

    PubMed

    Luo, Zhixiong; Chaemchuen, Somboon; Zhou, Kui; Verpoort, Francis

    2017-09-18

    The catalytic activity of ZIF-8 in the ring-opening polymerization of L-lactide without solvents or co-catalysts is presented for the first time. Two different synthetic strategies have been applied for synthesizing ZIF-8, either under solvothermal condition or by spray-drying procedure. Their catalytic activities are found to be correlating with the presence of open active sites in ZIF-8 structure. The structural defects which afford active acid and basic sites are supposed to cooperatively catalyze the reaction. ZIF-8 assembled by spray-drying technique, displays a superior catalytic activity at temperature of 160 °C, leading to the formation of high molecular weight cyclic polylactide. The ZIF-8 catalysts could be recycled and reused without any significant loss of catalytic activity. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. Synthesis of eight-shaped poly(ethylene oxide) by the combination of Glaser coupling with ring-opening polymerization.

    PubMed

    Wang, Guowei; Fan, Xiaoshan; Hu, Bin; Zhang, Yannan; Huang, Junlian

    2011-10-18

    The eight-shaped poly(ethylene oxide) (PEO) is synthesized by a combination of Glaser coupling with ring-opening polymerization (ROP). Firstly, the star-shaped (PEO-OH)(4) is synthesized by ROP of ethylene oxide (EO) using pentaerythritol as an initiator and diphenylmethyl potassium (DPMK) as a deprotonated agent, and then the alkyne group is introduced onto the PEO arm-end to give (PEO-Alkyne)(4) in a NaH/tetrahydrofuran (THF) system. The intramolecular cyclization is carried out by a Glaser coupling reaction in a pyridine/CuBr/N,N,N',N",N"-pentamethyldiethylenetriamine (PMDETA) system at room temperature in an air atmosphere, and eight-shaped PEO was formed with high efficiency (almost 100%). The target polymers and intermediates were well characterized by SEC, MALDI-TOF MS, (1)H NMR and FT-IR in detail. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Synthesis, characterization and catalytic activity of Ag-acidfuchsin nanohybrid system towards the ring opening polymerization of ε-caprolactone.

    PubMed

    Meenarathi, B; Palanikumar, S; Kannammal, L; Anbarasan, R

    2015-01-25

    The acidfuchsin (AF) decorated Ag nanoparticle (NP) was synthesized and its ability towards the ring opening polymerization (ROP) of ε-caprolactone (CL) was studied under N2 atmosphere at 160 °C in the presence of stannous octoate (SO) as a catalyst. Both the nanohybrid and nanocomposites were characterized by various analytical tools like Fourier transform infrared (FTIR) spectroscopy, UV-visible spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, fluorescence spectroscopy, gel permeation chromatography (GPC), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The number of binding site from the fluorescence spectrum confirmed that all the functional groups present in AF might have been involved in the ROP of CL. Copyright © 2014 Elsevier B.V. All rights reserved.

  9. Bis(phosphinic)diamido yttrium amide, alkoxide, and aryloxide complexes: an evaluation of lactide ring-opening polymerization initiator efficiency.

    PubMed

    Platel, Rachel H; White, Andrew J P; Williams, Charlotte K

    2011-08-15

    The synthesis and characterization of a series of bis(phosphinic)diamido yttrium alkoxide, amide, and aryloxide initiators are reported. The new complexes are characterized using multinuclear nuclear magnetic resonance (NMR) spectroscopy, elemental analysis, and, in some cases, X-ray crystallography. The alkoxide complexes are all dimeric in both the solid state and in solution, as are the amide complexes substituted with iso-propyl or phenyl groups on the phosphorus atoms. On the other hand, increasing the steric hindrance of the phosphorus substituents (tert-butyl), enables isolation of mononuclear yttrium amide complexes with either 2,2-dimethylpropylene or ethylene diamido ligand backbones. The complex of 2,6-di-tert-butyl-4-methylphenoxide is also mononuclear. All the new complexes are efficient initiators for rac-lactide ring-opening polymerization. The polymerization kinetics are compared and pseudo first order rate constants, k(obs), determined. The polymerization control is also discussed, by monitoring the number-averaged molecular weight, M(n), and polydispersity index, PDI, obtained using gel permeation chromatography (GPC). The alkoxide complexes are the most efficient initiators, showing very high rates and good polymerization control, behavior consistent with rapid rates of initiation. The phenoxide and amide complexes are less efficient as manifest by nonlinear regions in the kinetic plots, lower values for k(obs), and reduced polymerization control. One of the mononuclear yttrium amide complexes shows heteroselectivity in the polymerization of rac-lactide; however, this effect is reduced on changing the initiating group to phenoxide or on changing the ancillary ligand diamido backbone group.

  10. Salen complexes of zirconium and hafnium: synthesis, structural characterization, controlled hydrolysis, and solvent-free ring-opening polymerization of cyclic esters and lactides.

    PubMed

    Saha, Tanmoy Kumar; Ramkumar, Venkatachalam; Chakraborty, Debashis

    2011-04-04

    Dinuclear salen compounds of zirconium and hafnium are efficient initiators for the solvent-free ring-opening polymerization of cyclic ester monomers and lactides. There is a correlation between the theoretical and experimental number-average molecular weights (M(n)'s) in these polymerizations. Polymerization of β-butyrolactone gives poly(3-hydroxybutyrate) with a good M(n) and molecular weight distribution.

  11. Recent Developments of Versatile Photoinitiating Systems for Cationic Ring Opening Polymerization Operating at Any Wavelengths and under Low Light Intensity Sources.

    PubMed

    Lalevée, Jacques; Mokbel, Haifaa; Fouassier, Jean-Pierre

    2015-04-20

    Photoinitiators (PI) or photoinitiating systems (PIS) usable in light induced cationic polymerization (CP) and free radical promoted cationic polymerization (FRPCP) reactions (more specifically for cationic ring opening polymerization (ROP)) together with the involved mechanisms are briefly reviewed. The recent developments of novel two- and three-component PISs for CP and FRPCP upon exposure to low intensity blue to red lights is emphasized in details. Examples of such reactions under various experimental conditions are provided.

  12. Metathesis catalysts and methods thereof

    DOEpatents

    Schrock, Richard Royce; Yuan, Jian

    2016-04-19

    The present application provides, among other things, novel compounds for metathesis reactions, and methods for preparing and using provided compounds. In some embodiments, the present invention provides compounds having the structure of formula I or II. In some embodiments, the present invention provides methods for preparing a compound of formula I or II. In some embodiments, the present invention provides methods for using a provided compound. In some embodiments, a provided compound is useful for stereoselective ring-opening metathesis polymerization. In some embodiments, a provided metathesis method provides cis and/or isotactic polymers.

  13. Carbohydrate-Based Initiators for the Cationic Ring-Opening Polymerization of 2-Ethyl-2-Oxazoline.

    PubMed

    Weber, Christine; Gottschaldt, Michael; Hoogenboom, Richard; Schubert, Ulrich S

    2016-01-01

    The advancement in the field of living and controlled polymerization techniques provides the opportunity for careful bottom-up design of polymers for biomedical applications according to their specific needs. This contribution describes the detailed methodology to functionalize poly(2-ethyl-2-oxazoline), a polymer with properties very similar to polyethylene glycol, in a stereo-selective manner with a range of carbohydrates that can serve as biological targeting units. The obtained building blocks can subsequently be applied for the synthesis of more complex polymeric architectures.

  14. High activity of an indium alkoxide complex toward ring opening polymerization of cyclic esters.

    PubMed

    Quan, Stephanie M; Diaconescu, Paula L

    2015-06-14

    An indium complex supported by a ferrocene-derived Schiff base ligand has an unprecedented high activity toward ε-caprolactone, δ-valerolactone, and β-butyrolactone. l-Lactide, d,l-lactide, and trimethylene carbonate polymerizations also showed moderate to high activity.

  15. Dinuclear vs. mononuclear complexes: accelerated, metal-dependent ring-opening polymerization of lactide.

    PubMed

    Normand, M; Roisnel, T; Carpentier, J-F; Kirillov, E

    2013-12-25

    Dinuclear complexes of aluminum and indium with a bis(phenoxy-imine) platform have been synthesized and used in the polymerization of lactide. Kinetic studies demonstrate that the dialuminum precursor provides a more favorable reaction pathway in terms of activation free energy than that of directly related monoaluminum systems. No similar trend is observed with the corresponding diindium-monoindium systems, which is attributed to a dissimilar ROP mechanism.

  16. Metal-chelating polymers by anionic ring-opening polymerization and their use in quantitative mass cytometry.

    PubMed

    Illy, Nicolas; Majonis, Daniel; Herrera, Isaac; Ornatsky, Olga; Winnik, Mitchell A

    2012-08-13

    Metal-chelating polymers (MCPs) are important reagents for multiplexed immunoassays based on mass cytometry. The role of the polymer is to carry multiple copies of individual metal isotopes, typically as lanthanide ions, and to provide a reactive functionality for convenient attachment to a monoclonal antibody (mAb). For this application, the optimum combination of chain length, backbone structure, end group, pendant groups, and synthesis strategy has yet to be determined. Here we describe the synthesis of a new type of MCP based on anionic ring-opening polymerization of an activated cyclopropane (the diallyl ester of 1,1-cyclopropane dicarboxylic acid) using a combination of 2-furanmethanethiol and a phosphazene base as the initiator. This reaction takes place with rigorous control over molecular weight, yielding a polymer with a narrow molecular weight distribution, reactive pendant groups for introducing a metal chelator, and a functional end group with orthogonal reactivity for attaching the polymer to the mAbs. Following the ring-opening polymerization, a two-step transformation introduced diethylenetriaminepentaacetic acid (DTPA) chelating groups on each pendant group. The polymers were characterized by NMR, size exclusion chromatography (SEC), and thermogravimetric analysis (TGA). The binding properties toward Gd(3+) as a prototypical lanthanide (Ln) ion were also studied by isothermal titration calorimetry (ITC). Attachment to a mAb involves a Diels-Alder reaction of the terminal furan with a bismaleimide, followed by a Michael addition of a thiol on the mAb, generated by mild reduction of a disulfide bond in the hinge region. Polymer samples with a number average degree of polymerization of 35, with a binding capacity of 49.5 ± 6 Ln(3+) ions per chain, were loaded with 10 different types of Ln ions and conjugated to 10 different mAbs. A suite of metal-tagged Abs was tested by mass cytometry in a 10-plex single cell analysis of human adult peripheral blood

  17. Directed Growth of Polymer Nanorods Using Surface-Initiated Ring-Opening Polymerization of N-Allyl N-Carboxyanhydride.

    PubMed

    Lu, Lu; Lahasky, Samuel H; Zhang, Donghui; Garno, Jayne C

    2016-02-17

    A stepwise chemistry route was used to prepare arrays of polymer nanostructures of poly(N-allyl glycine) on Si(111) using particle lithography. The nanostructures were used for studying surface reactions with advanced measurements of atomic force microscopy (AFM). In the first step to fabricate the surface platform, isolated nanopores were prepared within a thin film of octadecyltrichlorosilane (OTS). The OTS served as a surface resist, and the areas of nanopores provided multiple, regularly shaped sites for further reaction. An initiator, (3-aminopropyl)triethoxysilane (APTES), was grown selectively inside the nanopores to define sites for polymerization. The initiator attached selectively to the sites of nanopores indicating OTS prevented nonspecific adsorption. Surface-initiated ring-opening polymerization of N-allyl N-carboxyanhydride with APTES produced polymer nanorods on the nanodots of APTES presenting amine functional groups. The surface changes for each step were monitored using high resolution atomic force microscopy (AFM). Slight variations in the height of the poly(N-allyl glycine) nanorods were observed which scale correspondingly to the initial dimensions of nanopores. The distance between adjacent polymer nanorods was controlled by the size of mesoparticle masks used in the experiment. This surface platform has potential application in biotechnology for smart coatings or biosensors.

  18. Grafting of cellulose fibers with poly(epsilon-caprolactone) and poly(L-lactic acid) via ring-opening polymerization.

    PubMed

    Lönnberg, Hanna; Zhou, Qi; Brumer, Harry; Teeri, Tuula T; Malmström, Eva; Hult, Anders

    2006-07-01

    In this study, ring-opening polymerization (ROP) of epsilon-caprolactone (epsilon-CL) and L-lactide (L-LA) has been performed from cellulose fibers. The hydroxyl groups on cellulose act as initiators in the polymerization, and the polymers are covalently bonded to the cellulose fiber. As an attempt to introduce more available hydroxyl groups on the surface, and thereby obtain higher grafting efficiency in the ROP of epsilon-CL and L-LA, unmodified paper was modified with xyloglucan-bis(methylol)-2-methylpropanamide (XG-bis-MPA) and 2,2-bis(methylol)propionic acid (bis-MPA), respectively. The grafted substrates were characterized via Fourier transform infrared spectroscopy (FTIR), contact angle measurement, atomic force microscopy, and enzymatic degradation. The results showed a successful grafting of poly(epsilon-caprolactone) (PCL) and poly(L-lactic acid) (PLLA) from the cellulose fiber surfaces. Furthermore, the results showed an improved grafting efficiency after activation of the cellulose surface with bis-MPA, and showed that the amount of grafted polymer could be controlled by the ratio of added free initiator to monomer.

  19. Highly active and stereoselective zirconium and hafnium alkoxide initiators for solvent-free ring-opening polymerization of rac-lactide.

    PubMed

    Chmura, Amanda J; Davidson, Matthew G; Frankis, Catherine J; Jones, Matthew D; Lunn, Matthew D

    2008-03-21

    Under solvent-free conditions (at 130 degrees C), zirconium and hafnium amine tris(phenolate) alkoxides are extremely active, well-controlled, single-site initiators for the ring-opening polymerization of rac-lactide, yielding highly heterotactic polylactide.

  20. Ring-opening polymerization of epoxidized soybean oil catalyzed by the superacid, Fluroantimonic acid hexahydrate (HSbF6-6H2O)

    USDA-ARS?s Scientific Manuscript database

    Ring-opening polymerization of epoxidized soybean oil (ESO) catalyzed by the super acid, fluroantimonic acid hexahydrate (HSbF6-6H2O), in ethyl acetate was conducted. The resulting polymers, SA-RPESO, were characterized using infrared spectroscopy, differential scanning calorimetry, thermogravimetri...

  1. Z-Selective Ruthenium Metathesis Catalysts: Comparison of Nitrate and Nitrite X-type Ligands

    PubMed Central

    Pribisko, Melanie A.; Ahmed, Tonia S.; Grubbs, Robert H.

    2014-01-01

    Two new Ru-based metathesis catalysts, 3 and 4, have been synthesized for the purpose of comparing their catalytic properties to those of their cis-selective nitrate analogues, 1 and 2. Although catalysts 3 and 4 exhibited slower initiation rates than 1 and 2, they maintained high cis-selectivity in homodimerization and ring-opening metathesis polymerization reactions. Furthermore, the nitrite catalysts displayed higher cis-selectivity than 2 for ring-opening metathesis polymerizations, and 4 delivered higher yields of polymer. PMID:25484484

  2. Facile preparation of a stable and functionalizable hybrid monolith via ring-opening polymerization for capillary liquid chromatography.

    PubMed

    Lin, Hui; Ou, Junjie; Tang, Shouwan; Zhang, Zhenbin; Dong, Jing; Liu, Zhongshan; Zou, Hanfa

    2013-08-02

    An organic-inorganic hybrid monolith was prepared by a single-step ring-opening polymerization of octaglycidyldimethylsilyl polyhedral oligomeric silsesquioxane (POSS) with poly(ethylenimine) (PEI). The obtained hybrid monoliths possessed high ordered 3D skeletal microstructure with dual retention mechanism that exhibits reversed-phase (RP) mechanism under polar mobile phase and hydrophilic-interaction liquid chromatography (HILIC) retention mechanism under less polar mobile phase. The high column efficiencies of 110,000N/m can be achieved for separation of alkylbenzenes in capillary reversed-phase liquid chromatography (cLC). Due to the robust property of hybrid monolith and the rich primary and secondary amino groups on its surface, the resulting hybrid monolith was easily modified with γ-gluconolactone and physically coated with cellulose tris(3,5-dimethylphenylcarbamate) (CDMPC), respectively. The former was successfully applied for HILIC separation of neutral, basic and acidic polar compounds as well as small peptides, and the latter for enantioseparation of racemates in cLC. The high column efficiencies were achieved in all of those separations. These results demonstrated that the hybrid monolith (POSS-PEI) possessed high stability and good surface tailorbility, potentially being applied for other research fields.

  3. Completely recyclable biopolymers with linear and cyclic topologies via ring-opening polymerization of γ-butyrolactone

    NASA Astrophysics Data System (ADS)

    Hong, Miao; Chen, Eugene Y.-X.

    2016-01-01

    Ring-opening polymerization (ROP) is a powerful synthetic methodology for the chemical synthesis of technologically important biodegradable aliphatic polyesters from cyclic esters or lactones. However, the bioderived five-membered γ-butyrolactone (γ-BL) is commonly referred as ‘non-polymerizable’ because of its low strain energy. The chemical synthesis of poly(γ-butyrolactone) (PγBL) through the ROP process has been realized only under ultrahigh pressure (20,000 atm, 160 °C) and only produces oligomers. Here we report that the ROP of γ-BL can, with a suitable catalyst, proceed smoothly to high conversions (90%) under ambient pressure to produce PγBL materials with a number-average molecular weight up to 30 kg mol-1 and with controlled linear and/or cyclic topologies. Remarkably, both linear and cyclic PγBLs can be recycled back into the monomer in quantitative yield by simply heating the bulk materials at 220 °C (linear polymer) or 300 °C (cyclic polymer) for one hour, which thereby demonstrates the complete recyclability of PγBL.

  4. Completely recyclable biopolymers with linear and cyclic topologies via ring-opening polymerization of γ-butyrolactone.

    PubMed

    Hong, Miao; Chen, Eugene Y-X

    2016-01-01

    Ring-opening polymerization (ROP) is a powerful synthetic methodology for the chemical synthesis of technologically important biodegradable aliphatic polyesters from cyclic esters or lactones. However, the bioderived five-membered γ-butyrolactone (γ-BL) is commonly referred as 'non-polymerizable' because of its low strain energy. The chemical synthesis of poly(γ-butyrolactone) (PγBL) through the ROP process has been realized only under ultrahigh pressure (20,000 atm, 160 °C) and only produces oligomers. Here we report that the ROP of γ-BL can, with a suitable catalyst, proceed smoothly to high conversions (90%) under ambient pressure to produce PγBL materials with a number-average molecular weight up to 30 kg mol(-1) and with controlled linear and/or cyclic topologies. Remarkably, both linear and cyclic PγBLs can be recycled back into the monomer in quantitative yield by simply heating the bulk materials at 220 °C (linear polymer) or 300 °C (cyclic polymer) for one hour, which thereby demonstrates the complete recyclability of PγBL.

  5. Bimetallic salen aluminum complexes: cooperation between reactive centers in the ring-opening polymerization of lactides and epoxides.

    PubMed

    Isnard, Florence; Lamberti, Marina; Lettieri, Luana; D'auria, Ilaria; Press, Konstantin; Troiano, Rubina; Mazzeo, Mina

    2016-10-12

    Three dinuclear aluminum alkyl complexes of the general formula LAl2Me4, where L are salen ligands with an alkyl backbone of different lengths between the nitrogen atoms (1,3-propylene (1), 1,5-pentylene (2) and 1,12-dodecaylene (3)), have been prepared through alkane elimination reactions between each ligand and two equivalents of AlMe3. The related hemi-salen aluminum complex 4 was prepared by an analogous reaction between a phenoxy-imine ligand and a single equivalent of AlMe3. The activities of these aluminum complexes in the ring-opening polymerization (ROP) of rac-lactide and of several epoxides have been investigated and compared. The dinuclear complex 1, bearing the salen ligand with the shortest alkyl bridge, was the most active in the ROP of LA producing isotactic enriched PLA. Otherwise, the other complexes (2 and 3), in which the metal centers are remote, produced atactic PLA with inferior activity. Analogous differences in terms of activity emerged in the ROP of epoxides. The comparison of the catalytic behavior of the dinuclear complexes as well as their mononuclear counterparts suggests the cooperation between the two aluminum metal centers of the dinuclear species in which these are close enough.

  6. Mechanistic Investigations of the Stereoselective Rare Earth Metal-Mediated Ring-Opening Polymerization of β-Butyrolactone.

    PubMed

    Altenbuchner, Peter T; Kronast, Alexander; Kissling, Stefan; Vagin, Sergei I; Herdtweck, Eberhardt; Pöthig, Alexander; Deglmann, Peter; Loos, Robert; Rieger, Bernhard

    2015-09-21

    Poly(3-hydroxybutyrate) (PHB) is produced by numerous bacteria as carbon and energy reserve storage material. Whereas nature only produces PHB in its strictly isotactic (R) form, homogeneous catalysis, when starting from racemic (rac) β-butyrolactone (BL) as monomer, can in fact produce a wide variety of tacticities. The variation of the metal center and the surrounding ligand structure enable activity as well as tacticity tuning. However, no homogeneous catalyst exists to date that is easy to modify, highly active, and able to produce PHB with high isotacticities from rac-β-BL. Therefore, in this work, the reaction kinetics of various 2-methoxyethylamino-bis(phenolate) lanthanide (Ln=Sm, Tb, Y, Lu) catalysts are examined in detail. The order in monomer and catalyst are determined to elucidate the reaction mechanism and the results are correlated with DFT calculations of the catalytic cycle. Furthermore, the enthalpies and entropies of the rate-determining steps are determined through temperature-dependent in situ IR measurements. Experimental and computational results converge in one specific mechanism for the ring-opening polymerization of BL and even allow us to rationalize the preference for syndiotactic PHB.

  7. Development of high-speed reactive processing system for carbon fiber-reinforced polyamide-6 composite: In-situ anionic ring-opening polymerization

    SciTech Connect

    Kim, Sang-Woo; Seong, Dong Gi; Yi, Jin-Woo; Um, Moon-Kwang

    2016-05-18

    In order to manufacture carbon fiber-reinforced polyamide-6 (PA-6) composite, we optimized the reactive processing system. The in-situ anionic ring-opening polymerization of ε-caprolactam was utilized with proper catalyst and initiator for PA-6 matrix. The mechanical properties such as tensile strength, inter-laminar shear strength and compressive strength of the produced carbon fiber-reinforced PA-6 composite were measured, which were compared with the corresponding scanning electron microscope (SEM) images to investigate the polymer properties as well as the interfacial interaction between fiber and polymer matrix. Furthermore, kinetics of in-situ anionic ring-opening polymerization of ε-caprolactam will be discussed in the viewpoint of increasing manufacturing speed and interfacial bonding between PA-6 matrix and carbon fiber during polymerization.

  8. Synthesis of (13)C-perlabeled cellulose with more than 99% isotopic enrichment by a cationic ring-opening polymerization approach.

    PubMed

    Adelwöhrer, Christian; Takano, Toshiyuki; Nakatsubo, Fumiaki; Rosenau, Thomas

    2009-10-12

    (13)C-Perlabeled cellulose was obtained in a seven-step approach from (13)C(6)-labeled d-glucose with a cationic ring-opening polymerization as the key step. Isopropylidene protection, benzylation of the remaining free 3-O-position and subsequent deprotection afforded 3-O-benzyl-(13)C(6)-glucose (2). Regioselective bis-pivaloylation followed by subsequent ortho-esterification provided the precursor for the cationic ring-opening polymerization, 3-O-benzyl-(13)C(6)-glucopyranose 1,2,4-orthopivalate (4). The actual polymerization step gave a stereo- and regioregular (13)C-perlabeled (1-->4)-beta-glucopyranan derivative, which was deprotected into fully labeled (13)C-cellulose, as the cellulose II allomorph with a DP of 40, in an overall 28% yield. All reaction steps were optimized beforehand with nonlabeled compounds toward high yields and high reproducibility and the final compound was comprehensively analytically characterized.

  9. Comparative Study of Aluminum Complexes Bearing N,O- and N,S-Schiff Base in Ring-Opening Polymerization of ε-Caprolactone and L-Lactide.

    PubMed

    Chang, Meng-Chih; Lu, Wei-Yi; Chang, Heng-Yi; Lai, Yi-Chun; Chiang, Michael Y; Chen, Hsing-Yin; Chen, Hsuan-Ying

    2015-12-07

    A series of Al complexes bearing Schiff base and thio-Schiff base ligands were synthesized, and their application for the ring-opening polymerization of ε-caprolactone (CL) and l-lactide (LA) was studied. It was found that steric effects of the ligands caused higher polymerization rate and most importantly the Al complexes with N,S-Schiff base showed significantly higher polymerization rate than Al complexes with N,O-Schiff base (5-12-fold for CL polymerization and 2-7-fold for LA polymerization). The reaction mechanism of CL polymerization was investigated by density functional theory (DFT). The calculations predicted a lower activation energy for a process involved with an Al complex bearing an N,S-Schiff base ligand (17.6 kcal/mol) than for that of an Al complex bearing an N,O-Schiff base ligand (19.0 kcal/mol), and this magnitude of activation energy reduction is comparable to the magnitude of rate enhancement observed in the experiment. The reduction of activation energy was attributed to the catalyst-substrate destabilization effect. Using a sulfur-containing ligand to decrease the activation energy in the ring-opening polymerization process may be a new strategy to design a new Al complex with high catalytic activity.

  10. Rapid Synthesis of a Lipocationic Polyester Library via Ring-Opening Polymerization of Functional Valerolactones for Efficacious siRNA Delivery.

    PubMed

    Hao, Jing; Kos, Petra; Zhou, Kejin; Miller, Jason B; Xue, Lian; Yan, Yunfeng; Xiong, Hu; Elkassih, Sussana; Siegwart, Daniel J

    2015-07-29

    The ability to control chemical functionality is an exciting feature of modern polymer science that enables precise design of drug delivery systems. Ring-opening polymerization of functional monomers has emerged as a versatile method to prepare clinically translatable degradable polyesters.1 A variety of functional groups have been introduced into lactones; however, the direct polymerization of tertiary amine functionalized cyclic esters has remained elusive. We report a strategy that enabled the rapid synthesis of >130 lipocationic polyesters directly from functional monomers without protecting groups. These polymers are highly effective for siRNA delivery at low doses in vitro and in vivo.

  11. Cyclic poly(alpha-peptoid)s and their block copolymers from N-heterocyclic carbene-mediated ring-opening polymerizations of N-substituted N-carboxylanhydrides.

    PubMed

    Guo, Li; Zhang, Donghui

    2009-12-23

    N-Heterocyclic carbene (NHC)-mediated ring-opening polymerization (ROP) of N-substituted N-carboxylanhydride ((N)R-NCA) yields cyclic poly(alpha-peptoid)s with controlled molecular weights (M(n) = 3-30 kg mol(-1)) and narrow molecular weight distributions (PDI = 1.04-1.12). The reactions exhibit characteristics of a living polymerization with minimal chain transfer. This enables the facile synthesis of cyclic diblock copoly(alpha-peptoid)s through sequential monomer addition. The cyclic polymer architectures were verified by MALDI-TOF mass spectrometry and intrinsic viscosity measurements. Mark-Houwink-Sakurada plot analyses revealed that cyclic poly(alpha-peptoid)s prepared from NHC-mediated polymerizations exhibit lower intrinsic viscosities than their linear analogues prepared from primary amine-initiated polymerizations. The ratio of their intrinsic viscosities is consistent with the former being mostly cyclic.

  12. Synthesis of epoxybenzo[d]isothiazole 1,1-dioxides via a reductive-Heck, metathesis-sequestration protocol†‡

    PubMed Central

    Asad, Naeem; Hanson, Paul R.; Long, Toby R.; Rayabarapu, Dinesh K.; Rolfe, Alan

    2011-01-01

    An atom-economical purification protocol, using solution phase processing via ring-opening metathesis polymerization (ROMP) has been developed for the synthesis of tricyclic sultams. This chromatography-free method allows for convenient isolation of reductive-Heck products and reclamation of excess starting material via sequestration involving metathesis catalysts and a catalyst-armed Si-surface. PMID:21727956

  13. Hybrid scorpionate/cyclopentadienyl magnesium and zinc complexes: synthesis, coordination chemistry, and ring-opening polymerization studies on cyclic esters.

    PubMed

    Garcés, Andrés; Sánchez-Barba, Luis F; Alonso-Moreno, Carlos; Fajardo, Mariano; Fernández-Baeza, Juan; Otero, Antonio; Lara-Sánchez, Agustín; López-Solera, Isabel; Rodríguez, Ana María

    2010-03-15

    only accessible by protonolysis of the bis(amide) complexes [M{N(SiMe(3))(2)}(2)] (M = Mg, Zn) and the mixed ligand complex [EtZnOAr)] with the hybrid ligand bpzcpH to afford [Zn(R){kappa(2)-eta(1)(pi)-bpzcp}] (R = N(SiMe(3))(2) 13, R = 2,4,6-Me(3)C(6)H(2)O 14) and [Mg{N(SiMe(3))(2)}(kappa(2)-eta(5)-bpzcp)] (15). Finally, alkyl and alkoxide-containing complexes 1-10 and 14 can act as highly effective single-component living initiators for the ring-opening polymerization of epsilon-caprolactone and lactides over a wide range of temperatures. Epsilon-caprolactone is polymerized within minutes to give high molecular weight polymers with medium-broad polydispersities (M(n) > 10(5), M(w)/M(n) = 1.45). Lactide afforded poly(lactide) materials with medium molecular weights and polydispersities as narrow as M(w)/M(n) = 1.02. Additionally, polymerization of L-lactide occurred without racemization in the propagation process and offered highly crystalline, isotactic poly(L-lactides) with very high melting temperatures (T(m) = 165 degrees C). Microstructural analysis of poly(rac-lactide) by (1)H NMR spectroscopy revealed that propagations occur without appreciable levels of stereoselectivity. Polymer end group analysis showed that the polymerization process is initiated by alkyl transfer to the monomer.

  14. Preparation of a unique glucan with large intervals in molecular weight distribution. Controlled ring-opening polymerization of O-permethylcyclodextrin.

    PubMed

    Suzuki, Masato; Shimazaki, Tomofumi

    2003-02-07

    O-Permethylated cyclodextrins (MeCDs) were found to be polymerizable with the initiator-activator system of HI-I2 or HI-ZnX2, undergoing ring-cleavage to give linear 1-->4-glucan. Among several conditions investigated, HI-ZnCl2 in CH2Cl2 at 0 degree C proved most effective to control this cationic ring-opening polymerization (CROP). The MALDI-TOF-MS spectrum revealed that the molecular weight distribution of the glucan obtained from gamma-MeCD uniquely consisted of large, regular intervals, each of which were identical to the molecular weight of gamma-MeCD (1634).

  15. Group IV complexes containing the benzotriazole phenoxide ligand as catalysts for the ring-opening polymerization of lactides, epoxides and as precatalysts for the polymerization of ethylene.

    PubMed

    Pappuru, Sreenath; Chokkapu, Eswara Rao; Chakraborty, Debashis; Ramkumar, Venkatachalam

    2013-12-14

    A series of Ti(IV), Zr(IV) and Hf(IV) benzotriazole phenoxide (BTP) complexes were synthesized and characterized by various spectroscopic techniques, elemental analysis and X-ray crystallography. The monosubstituted Zr(IV) BTP complexes [(μ-L)Zr(O(i)Pr)3]2 1-3 [L = (C1)BTP-H (1), (TCl)BTP-H (2), (pent)BTP-H (3)] and tetrasubstituted Zr(IV), Hf(IV) complexes ZrL4 4-6 [L = (C1)BTP-H (4), (TCl)BTP-H (5), (pent)BTP-H (6)] and HfL4 7-9 [L = (C1)BTP-H (7), (TCl)BTP-H (8), (pent)BTP-H (9)] were prepared by the reaction of Zr(O(i)Pr)4·((i)PrOH) and Hf(O(t)Bu)4 in toluene with the respective ligands in different stoichiometric proportions. The reaction between BTP and TiCl4 and ZrCl4 and HfCl4 in a 2 : 1 stoichiometric reaction resulted in the formation of disubstituted group IV chloride complexes L2MCl2 10-12 [L = (C1)BTP-H, M = Ti, Zr and Hf]. The molecular structures of complexes 1, 4, 7, 10, 11, and 12 were determined by single-crystal X-ray studies. The X-ray structure of 1 reveals a dimeric Zr(IV) complex containing a Zr2O2 core bridged through the oxygen atoms of the phenoxide groups. Each Zr atom is distorted from an octahedral symmetry. These complexes were found to be active towards the ring-opening polymerization (ROP) of L-lactide (L-LA) and rac-lactide (rac-LA). Complex 1 produced highly heterotactic poly(lactic acid) (PLA) from rac-LA under melt conditions with narrow molecular weight distributions (MWDs) and well controlled number average molecular weights (M(n)). Additionally, epoxide polymerizations using rac-cyclohexene oxide (CHO), rac-propylene oxide (PO), and rac-styrene oxide (SO) were also carried out with these complexes. The yield and molecular weight of the polymer was found to increase with the extension of reaction time. Compounds 1-12 were activated by methylaluminoxane (MAO) and show good activity for ethylene polymerization and produced high molecular weight polyethylene.

  16. Zirconium and hafnium complexes bearing pyrrolidine derived salalen-type {ONNO} ligands and their application for ring-opening polymerization of lactides.

    PubMed

    Duan, Yu-Lai; Hu, Zhi-Jian; Yang, Bo-Qun; Ding, Fei-Fei; Wang, Wei; Huang, Yong; Yang, Ying

    2017-08-29

    The reactions of pyrrolidine derived salalen-type {ONNO} ligands (S)-L(1-3)-H2 with 1 equiv. M(O(i)Pr)4(HO(i)Pr) (M = Zr or Hf) in diethyl ether yielded complexes [L(1-3)M(O(i)Pr)2] (L = L(1), M = Zr (1); L = L(2), M = Zr (2), Hf (3); L = L(3), M = Zr (4), Hf (5)). All of these complexes were well characterized by NMR spectroscopy, elemental analyses and single-crystal X-ray analysis in the case of complexes 1 and 3-5. X-ray structural determination revealed that these complexes were analogous mononuclear species and had a similar structure in which the metal centers were six-coordinated to two oxygen atoms and two nitrogen atoms of one ligand and two oxygen atoms of two isopropoxy groups. All of these complexes efficiently initialized the ring-opening polymerization of lactides to afford polymers with controlled molecular weight and narrow polydispersity. Furthermore, the ring-opening polymerization of rac-lactide catalyzed by complexes 1-5 afforded isotactic-enriched polymers in solution (Pm = 0.74-0.80) and under melt conditions (Pm = 0.63-0.72).

  17. Developments in the use of rare earth metal complexes as efficient catalysts for ring-opening polymerization of cyclic esters used in biomedical applications

    NASA Astrophysics Data System (ADS)

    Cota, Iuliana

    2017-04-01

    Biodegradable polymers represent a class of particularly useful materials for many biomedical and pharmaceutical applications. Among these types of polyesters, poly(ɛ-caprolactone) and polylactides are considered very promising for controlled drug delivery devices. These polymers are mainly produced by ring-opening polymerization of their respective cyclic esters, since this method allows a strict control of the molecular parameters (molecular weight and distribution) of the obtained polymers. The most widely used catalysts for ring-opening polymerization of cyclic esters are tin- and aluminium-based organometallic complexes; however since the contamination of the aliphatic polyesters by potentially toxic metallic residues is particularly of concern for biomedical applications, the possibility of replacing organometallic initiators by novel less toxic or more efficient organometallic complexes has been intensively studied. Thus, in the recent years, the use of highly reactive rare earth initiators/catalysts leading to lower polymer contamination has been developed. The use of rare earth complexes is considered a valuable strategy to decrease the polyester contamination by metallic residues and represents an attractive alternative to traditional organometallic complexes.

  18. Alternating Sequence Controlled Copolymer Synthesis of α-Hydroxy Acids via Syndioselective Ring-Opening Polymerization of O-Carboxyanhydrides Using Zirconium/Hafnium Alkoxide Initiators.

    PubMed

    Sun, Yangyang; Jia, Zhaowei; Chen, Changjuan; Cong, Yong; Mao, Xiaoyang; Wu, Jincai

    2017-08-09

    The ring-opening polymerization (ROP) of O-carboxyanhydrides (OCAs) can give diverse poly(α-hydroxy acid)s (PAHAs) with different functional groups because of easy modification of the side group of OCAs, which can extend applications of PAHAs widely. The stereoselective polymerization of O-carboxyanhydrides and further sequence controlled alternating copolymerization of OCAs were still big challenges until now for lack of suitable catalysts/initiators. In this work, a highly syndioselective ROP of OCAs system as the first stereoselective example in this area is reported using zirconium/hafnium alkoxides as initiators with the highest Pr value up to 0.95. Furthermore, these initiators were successfully applied in the precisely alternating sequence controlled copolymerization of PheOCA and Tyr(Bn)OCA, and alternating copolymerization of LacOCA and PheOCA was also achieved.

  19. A Ruthenium Catalyst for Olefin Metathesis Featuring an Anti-Bredt N-Heterocyclic Carbene Ligand

    PubMed Central

    Martin, David; Marx, Vanessa M.

    2016-01-01

    A ruthenium complex bearing an “anti-Bredt” N-heterocyclic carbene was synthesized, characterized and evaluated as a catalyst for olefin metathesis. Good conversions were observed at room temperature for the formation of di- and tri-substituted olefins by ring-closing metathesis. It also allowed for the ring-opening metathesis polymerization of cyclooctadiene, as well as for the cross-metathesis of cis-1,4-diacetoxy-2-butene with allyl-benzene, with enhanced Z/E kinetic selectivity over classical NHC-based catalysts. PMID:27594819

  20. Shape-Persistent, Thermoresponsive Polypeptide Brushes Prepared by Vapor Deposition Surface-Initiated Ring-Opening Polymerization of α-Amino Acid N -Carboxyanhydrides

    SciTech Connect

    Shen, Yong; Desseaux, Solenne; Aden, Bethany; Lokitz, Bradley S.; Kilbey, S. Michael; Li, Zhibo; Klok, Harm-Anton

    2015-04-20

    We report that surface-grafting thermoresponsive polymers allows the preparation of thin polymer brush coatings with surface properties that can be manipulated by variation of temperature. In most instances, thermoresponsive polymer brushes are produced using polymers that dehydrate and collapse above a certain temperature. This report presents the preparation and properties of polymer brushes that show thermoresponsive surface properties, yet are shape-persistent in that they do not undergo main chain collapse. The polymer brushes presented here are obtained via vapor deposition surface-initiated ring-opening polymerization (SI-ROP) of γ-di- or tri(ethylene glycol)-modified glutamic acid N-carboxyanhydrides. Vapor deposition SI-ROP of γ-di- or tri(ethylene glycol)-modified L- or D-glutamic acid N-carboxyanhydrides affords helical surface-tethered polymer chains that do not show any changes in secondary structure between 10 and 70 °C. QCM-D experiments, however, revealed significant dehydration of poly(γ-(2-(2-methoxyethoxy)ethyl)-l-glutamate) (poly(L-EG2-Glu)) brushes upon heating from 10 to 40 °C. At the same time, AFM and ellipsometry studies did not reveal significant variations in film thickness over this temperature range, which is consistent with the shape-persistent nature of these polypeptide brushes and indicates that the thermoresponsiveness of the films is primarily due to hydration and dehydration of the oligo(ethylene glycol) side chains. The results we present here illustrate the potential of surface-initiated NCA ring-opening polymerization to generate densely grafted assemblies of polymer chains that possess well-defined secondary structures and tunable surface properties. These polypeptide brushes complement their conformationally unordered counterparts that can be generated via surface-initiated polymerization of vinyl-type monomers and represent another step forward to biomimetic surfaces and interfaces.

  1. Shape-Persistent, Thermoresponsive Polypeptide Brushes Prepared by Vapor Deposition Surface-Initiated Ring-Opening Polymerization of α-Amino Acid N -Carboxyanhydrides

    DOE PAGES

    Shen, Yong; Desseaux, Solenne; Aden, Bethany; ...

    2015-04-20

    We report that surface-grafting thermoresponsive polymers allows the preparation of thin polymer brush coatings with surface properties that can be manipulated by variation of temperature. In most instances, thermoresponsive polymer brushes are produced using polymers that dehydrate and collapse above a certain temperature. This report presents the preparation and properties of polymer brushes that show thermoresponsive surface properties, yet are shape-persistent in that they do not undergo main chain collapse. The polymer brushes presented here are obtained via vapor deposition surface-initiated ring-opening polymerization (SI-ROP) of γ-di- or tri(ethylene glycol)-modified glutamic acid N-carboxyanhydrides. Vapor deposition SI-ROP of γ-di- or tri(ethylene glycol)-modifiedmore » L- or D-glutamic acid N-carboxyanhydrides affords helical surface-tethered polymer chains that do not show any changes in secondary structure between 10 and 70 °C. QCM-D experiments, however, revealed significant dehydration of poly(γ-(2-(2-methoxyethoxy)ethyl)-l-glutamate) (poly(L-EG2-Glu)) brushes upon heating from 10 to 40 °C. At the same time, AFM and ellipsometry studies did not reveal significant variations in film thickness over this temperature range, which is consistent with the shape-persistent nature of these polypeptide brushes and indicates that the thermoresponsiveness of the films is primarily due to hydration and dehydration of the oligo(ethylene glycol) side chains. The results we present here illustrate the potential of surface-initiated NCA ring-opening polymerization to generate densely grafted assemblies of polymer chains that possess well-defined secondary structures and tunable surface properties. These polypeptide brushes complement their conformationally unordered counterparts that can be generated via surface-initiated polymerization of vinyl-type monomers and represent another step forward to biomimetic surfaces and interfaces.« less

  2. Well-Defined Redox-Active Polymers and Block Copolymers Prepared by Living Ring-Opening Metathesis Polymerization

    DTIC Science & Technology

    1992-02-04

    appears more promising since functionalized derivatives are relatively easy to synthesize in wide variety by Diels - Alder reactions and since well...norbornene skeleton as shown in eq 2. The acid group, which facilitated the Diels - Alder reaction, was later turned into a carbomethoxy group, which is not...R.R. Schrock 13a TYPE OF REPORT 13b TIME COVERED 14 DATE OF REPORT (Year, Month, Day) 1s PA 4CO ,)NT technical FROM _0 TO _9__ 92/2/4 16 SUPPLEMENTARY

  3. Antimicrobial polymers prepared by ring-opening metathesis polymerization: manipulating antimicrobial properties by organic counterion and charge density variation.

    PubMed

    Lienkamp, Karen; Madkour, Ahmad E; Kumar, Kushi-Nidhi; Nüsslein, Klaus; Tew, Gregory N

    2009-11-02

    The synthesis and characterization of a series of poly(oxanorbornene)-based synthetic mimics of antimicrobial peptides (SMAMPs) is presented. In the first part, the effect of different organic counterions on the antimicrobial properties of the SMAMPs was investigated. Unexpectedly, adding hydrophobicity by complete anion exchange did not increase the SMAMPs' antimicrobial activity. It was found by dye-leakage studies that this was due to the loss of membrane activity of these polymers caused by the formation of tight ion pairs between the organic counterions and the polymer backbone. In the second part, the effect of molecular charge density on the biological properties of a SMAMP was investigated. The results suggest that, above a certain charge threshold, neither minimum inhibitory concentration (MIC90) nor hemolytic activity (HC50) is greatly affected by adding more cationic groups to the molecule. A SMAMP with an MIC90 of 4 microg mL(-1) against Staphylococcus aureus and a selectivity (=HC50/MIC90) of 650 was discovered, the most selective SMAMP to date.

  4. Mechanochemical Ring-Opening Polymerization of Lactide: Liquid-Assisted Grinding for the Green Synthesis of Poly(lactic acid) with High Molecular Weight.

    PubMed

    Ohn, Nuri; Shin, Jihoon; Kim, Sung Sik; Kim, Jeung Gon

    2017-09-22

    Mechanochemical polymerization of lactide is carried out by using ball milling. Mechanical energy from collisions between the balls and the vessel efficiently promotes an organic-base-mediated metal- and solvent-free solid-state polymerization. Investigation of the parameters of the ball-milling synthesis revealed that the degree of lactide ring-opening polymerization could be modulated by the ball-milling time, vibration frequency, mass of the ball media, and liquid-assisted grinding. Liquid-assisted grinding was found to be an especially important factor for achieving a high degree of mechanochemical polymerization. Although polymer-chain scission from the strong collision energy prevented mechanical-force-driven high-molecular-weight polymer synthesis, the addition of only a small amount of liquid enabled sufficient energy dissipation and poly(lactic acid) was thereby obtained with a molecular weight of over 1×10(5)  g mol(-1) . © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. From syndiotactic homopolymers to chemically tunable alternating copolymers: highly active yttrium complexes for stereoselective ring-opening polymerization of β-malolactonates.

    PubMed

    Jaffredo, Cédric G; Chapurina, Yulia; Guillaume, Sophie M; Carpentier, Jean-François

    2014-03-03

    Alternating copolymers constitute an attractive class of materials. It was shown previously that highly alternated poly(β-hydroxyalkanoate)s (PHAs) can be prepared by ring-opening polymerization (ROP) of mixtures of two different enantiomerically pure 4-alkyl-β-propiolactones. However, the approach could not be extended to PHAs with chemically tunable functional groups, which is highly desirable to access original advanced materials. Reported herein is the first highly syndioselective and controlled ROP of racemic allyl and benzyl β-malolactonates (MLA(R); R=allyl, benzyl) using an yttrium complex supported by a tetradentate dichloro-substituted bis(phenolate) ligand. This highly active catalyst allows the nearly perfect alternating copolymerization of MLA(Allyl) and MLA(Benzyl). Hydrogenolysis of the benzyloxycarbonyl or functionalization of the allyl pendant groups opens a route towards a new class of functional alternating copolymers.

  6. Lactide as the Playmaker of the ROP Game: Theoretical and Experimental Investigation of Ring-Opening Polymerization of Lactide Initiated by Aminonaphtholate Zinc Complexes.

    PubMed

    Jędrzkiewicz, Dawid; Adamus, Grażyna; Kwiecień, Michał; John, Łukasz; Ejfler, Jolanta

    2017-02-06

    A family of homo- and heteroleptic zinc complexes bearing aminonaphtholate ligands was synthesized and fully characterized. Using NMR spectroscopy and DFT calculation, bis-alkoxy-bridged complexes [LZn(μ-OR)]2 were confirmed to have dimeric structures in solution, analogous to those obtained via X-ray crystallography. Surprisingly, a detailed experimental and theoretical study of the catalytic activity of [LZn(μ-OR)]2 in the ring-opening polymerization (ROP) of lactides showed that although well-defined alkoxy dimers possess a single-site structural motif, the most active initiator is obtained during in situ alcoholysis of the alkylzinc precursor. These results indicate that rational ancillary and alkoxy ligand design that takes into account its mutual interaction on monomer coordination may be key to the synthesis of new high-performance ROP catalysts.

  7. Amino-Functionalized Multiwalled Carbon Nanotubes Lead to Successful Ring-Opening Polymerization of Poly(ε-caprolactone): Enhanced Interfacial Bonding and Optimized Mechanical Properties.

    PubMed

    Roumeli, Eleftheria; Papageorgiou, Dimitrios G; Tsanaktsis, Vasilios; Terzopoulou, Zoe; Chrissafis, Konstantinos; Avgeropoulos, Apostolos; Bikiaris, Dimitrios N

    2015-06-03

    In this work, the synthesis, structural characteristics, interfacial bonding, and mechanical properties of poly(ε-caprolactone) (PCL) nanocomposites with small amounts (0.5, 1.0, and 2.5 wt %) of amino-functionalized multiwalled carbon nanotubes (f-MWCNTs) prepared by ring-opening polymerization (ROP) are reported. This method allows the creation of a covalent-bonding zone on the surface of nanotubes, which leads to efficient debundling and therefore satisfactory dispersion and effective load transfer in the nanocomposites. The high covalent grafting extent combined with the higher crystallinity provide the basis for a significant enhancement of the mechanical properties, which was detected in the composites with up to 1 wt % f-MWCNTs. Increasing filler concentration encourages intrinsic aggregation forces, which allow only minor grafting efficiency and poorer dispersion and hence inferior mechanical performance. f-MWCNTs also cause a significant improvement on the polymerization reaction of PCL. Indeed, the in situ polymerization kinetics studies reveal a significant decrease in the reaction temperature, by a factor of 30-40 °C, combined with accelerated the reaction kinetics during initiation and propagation and a drastically reduced effective activation energy.

  8. Synthesis of N,N,O-chelate zinc and aluminum complexes and their catalysis in the ring-opening polymerization of ε-caprolactone and rac-lactide.

    PubMed

    Kong, Wei-Li; Chai, Zuo-Yun; Wang, Zhong-Xia

    2014-10-14

    Zinc and aluminum complexes supported by N,N,O-chelate ligands were synthesized and characterized. The zinc complexes [Zn(Et){2-{OC(R(1))=CH}-6-(3,5-Me2C3HN2)C5H3N}]2 (R(1) = Ph, 1a; R(1) = Bu(t), 1b) were synthesized by reaction of ligand precursors 2-{R(1)C(O)CH2}-6-(3,5-Me2C3HN2)C5H3N (R(1) = Ph, HL(1); R(1) = Bu(t), HL(2)) with ZnEt2. The aluminum complexes [Al(R)2{2-{OC(Ph)=CH}-6-(3,5-Me2C3HN2)C5H3N}] (R = Me, 2a; R = Et, 2b) were synthesized by reaction of HL(1) with AlMe3 or AlEt3. Similar treatment of the ligand precursor 2-{Ph2C(OH)CH2}-6-(3,5-Me2C3HN2)C5H3N (HL(3)) with AlMe3 or AlEt3 afforded aluminum complexes [Al(R)2{2-{OC(Ph)2CH2}-6-(3,5-Me2C3HN2)C5H3N}] (R = Me, 3a; R = Et, 3b). The complexes were characterized by (1)H and (13)C{(1)H} NMR spectroscopy, elemental analyses and single crystal X-ray diffraction (for 1a, 1b, 2b and 3a). All the complexes are active to catalyze the ring-opening polymerization of ε-caprolactone in the presence of BnOH, leading to polycaprolactone with good molecular weight control and relatively narrow molecular weight distribution. The zinc complexes/BnOH showed good catalytic activity for the ring-opening polymerization of rac-lactide, displaying good molecular weight control and very narrow molecular weight distributions. The PLA catalyzed by complex 1a/BnOH showed somewhat hetero-stereoselectivity with Pr up to 0.73 when the polymerization was performed in THF at 0 °C. Complex 1a/BnOH also catalyzed block copolymerization of ε-CL and rac-LA with good molecular weight control of the polymer. Kinetic studies of the polymerization reactions were performed.

  9. Lewis acid catalyzed ring-opening polymerization of natural epoxy oil (Euphorbia oil) in carbon dioxide media

    USDA-ARS?s Scientific Manuscript database

    In an attempt to build up useful application of plant oil based polymers, natural epoxy oil (euphorbia oil-EuO) was polymerized in liquid carbon dioxide in the presence of Lewis acid catalyst [Boron trifluoride diethyl etherate (BF3•OEt2)]. The resulting polymers (RPEuO) were characterized by FTIR ...

  10. Highly heteroselective ring-opening polymerization of racemic lactide initiated by divalent ytterbium complexes bearing amino bis(phenolate) ligands.

    PubMed

    Yang, Sheng; Du, Zhu; Zhang, Yong; Shen, Qi

    2012-10-09

    Polymerization of racemic lactide initiated by divalent ytterbium complexes supported by either dimethylamino-amino bis(phenolate) or methoxy-amino bis(phenolate) ligands proceeds rapidly at room temperature in a living fashion to give heterotactic polylactide with the racemic enchainment of monomer units P(r) ranging from 0.97-0.99.

  11. PMLABe diol synthesized by ring-opening polymerization of racemic benzyl β-malolactonate initiated by rare-earth trisborohydride complexes: an experimental and DFT study.

    PubMed

    Jaffredo, Cédric G; Schmid, Matthias; Del Rosal, Iker; Mevel, Teddy; Roesky, Peter W; Maron, Laurent; Guillaume, Sophie M

    2014-10-27

    Polymer diols are a class of polymeric building blocks of high interest for the synthesis of complex macromolecular edifices. Rare-earth borohydride complexes are known as efficient initiators for the ring-opening polymerization (ROP) of cyclic esters, directly affording α,ω-dihydroxy-telechelic polyesters. Here, were report the direct synthesis of poly(benzyl β-malolactonate) (PMLABe) diols, from the ROP of racemic (benzyl β-malolactonate) (rac-MLABe), a valuable and renewable monomer, initiated by the homoleptic [Ln(BH4 )3 (thf)3 ] (Ln=La, Nd, and Sm) complexes. These initiators enabled the controlled ROP of this β-lactone, affording well-defined syndiotactic-enriched (Pr ≈0.83) PMLABes (Mn up to 21 300 g mol(-1) , ÐM ≈1.5) as evidenced by size exclusion chromatography, (1) H and (13) C NMR spectroscopy, and MALDI-ToF mass spectrometry analyses. The first and second insertions of rac-MLABe, as assessed by DFT calculations, revealed more favorable stationary front-side than migratory back-side insertions, the thermodynamically and kinetically competitive ROP on two distinct arms with that on a one arm-only, and the thermodynamically slightly favored formation of syndiotactic-enriched PMLABes.

  12. Green polymer chemistry: investigating the mechanism of radical ring-opening redox polymerization (R3P) of 3,6-dioxa-1,8-octanedithiol (DODT).

    PubMed

    Rosenthal-Kim, Emily Q; Puskas, Judit E

    2015-04-13

    The mechanism of the new Radical Ring-opening Redox Polymerization (R3P) of 3,6-dioxa-1,8-octanedithiol (DODT) by triethylamine (TEA) and dilute H2O2 was investigated. Scouting studies showed that the formation of high molecular weight polymers required a 1:2 molar ratio of DODT to TEA and of DODT to H2O2. Further investigation into the chemical composition of the organic and aqueous phases by 1H-NMR spectroscopy and mass spectrometry demonstrated that DODT is ionized by two TEA molecules (one for each thiol group) and thus transferred into the aqueous phase. The organic phase was found to have cyclic disulfide dimers, trimers and tetramers. Dissolving DODT and TEA in water before the addition of H2O2 yielded a polymer with Mn = 55,000 g/mol, in comparison with Mn = 92,000 g/mol when aqueous H2O2 was added to a DODT/TEA mixture. After polymer removal, MALDI-ToF MS analysis of the residual reaction mixtures showed only cyclic oligomers remaining. Below the LCST for TEA in water, 18.7 °C, the system yielded a stable emulsion, and only cyclic oligomers were found. Below DODT/TEA and H2O2 1:2 molar ratio mostly linear oligomers were formed, with <20% cyclic oligomers. The findings support the proposed mechanism of R3P.

  13. Synthesis and characterization of photoluminescent hybrids of poly( ɛ-caprolactone)-grafted-polyhedral oligosilsesquioxane by using a combination of ring-opening polymerization and click chemistry

    NASA Astrophysics Data System (ADS)

    Cao, Xuan Thang; Showkat, Ali Md; Bach, Long Giang; Jeong, Yeon Tae; Kim, Jong Soo; Lim, Kwon Taek; Gal, Yeong-Soon

    2015-01-01

    Photoluminescent hybrids of poly( ɛ-caprolactone) (PCL), polyhedral oligosilsesquioxane (POSS) and terbium ions (Tb3+) were synthesized by using a combination of ring-opening polymerization (ROP), click chemistry and coordination chemistry. Initially, acetylene functionalized PCL (alkyne-PCL-COOH) was prepared by using ROP of ɛ-caprolactone with propargyl alcohol, and azide-substituted POSS (POSS-N3) was prepared by using the reaction of chloropropyl-heptaisobutyl-substituted POSS with NaN3. The click reaction between alkyne-PCL-COOH and POSS-N3 afforded POSS-g-PCL, which was subsequently coordinated with Tb3+ ions in the presence of 1,10-phenanthroline to produce POSS-g-PCL-Tb3+-Phen. The structures and compositions of the hybrids were investigated by using 1H nuclear magnetic resonance (NMR), Fourier-transform infrared spectroscopy (FT-IR), Field emission scanning electron microscope (FE-SEM), Transmission electron microscopy (TEM), and Thermogravimetric analysis (TGA). The optical properties of POSS-g-PCL-Tb3+-Phen complexes were characterized by using photoluminescence spectroscopy, which showed four high emission bands centered at 489, 545, 584, and 620 nm with excitation at 330 nm. The emission spectra of the europium-ion-coordinated hybrids, POSS-g-PCL-Eu3+-Phen, had four high-intensity peaks, 594, 617, 652 and 686 nm, for an excitation wavelength of 352 nm.

  14. Organocatalysts for the controlled "immortal" ring-opening polymerization of six-membered-ring cyclic carbonates: a metal-free, green process.

    PubMed

    Helou, Marion; Miserque, Olivier; Brusson, Jean-Michel; Carpentier, Jean-François; Guillaume, Sophie M

    2010-12-10

    Six-membered cyclic carbonates, namely trimethylene carbonate (TMC), 3,3-dimethoxytrimethylene carbonate (DMTMC) and 3-benzyloxytrimethylene carbonate (BTMC), undergo controlled "immortal" ring-opening polymerization (iROP) under mild conditions (bulk, 60-150 °C), by using organocatalysts, including an amine [4-N,N-dimethylaminopyridine (DMAP)], a guanidine [1,5,7-triazabicyclo-[4.4.0]dec-5-ene (TBD)], or a phosphazene [2-tert-butylimino-2-diethylamino-1,3-dimethylperhydro-1,3,2-diazaphosphorine (BEMP)], in the presence of an alcohol [benzyl alcohol (BnOH), 1,3-propanediol (PPD), glycerol (GLY)] that acts as both a co-initiator and a chain-transfer agent. Remarkably, such organocatalysts remain highly active in the iROP of technical-grade, unpurified TMC. Under optimized conditions, as much as 100,000 equivalents of TMC were fully converted by as little as 10 ppm of BEMP with the simultaneous growth of as many as 200 polymer chains, allowing the preparation of high molar mass poly(trimethylene carbonate)s (up to 45,800 g mol(-1)). These catalyst systems enable among the highest activities (TOF=55,800 h(-1)) and productivities (TON=95,000) ever reported for the ROP of TMC.

  15. Syntheses, characterization, and in vitro degradation of ethyl cellulose-graft-poly(epsilon-caprolactone)-block-poly(L-lactide) copolymers by sequential ring-opening polymerization.

    PubMed

    Yuan, Weizhong; Yuan, Jinying; Zhang, Fengbo; Xie, Xuming

    2007-04-01

    Well-defined ethyl cellulose-graft-poly(epsilon-caprolactone) (EC-g-PCL) graft copolymers were successfully synthesized via ring-opening polymerization (ROP) of epsilon-caprolactone (CL) with an ethyl cellulose (EC) initiator and a tin 2-ethylhexanoate (Sn(Oct)2) catalyst in xylene at 120 degrees C. Then, novel ethyl cellulose-graft-poly(epsilon-caprolactone)-block-poly(L-lactide) (EC-g-PCL-b-PLLA) graft-block copolymers were prepared by ROP of L-lactide (L-LA) with a hydroxyl-terminated EC-g-PCL macroinitiator and Sn(Oct)2 catalyst in bulk at 120 degrees C. Various graft and block lengths of EC-g-PCL and EC-g-PCL-b-PLLA copolymers were obtained by adjusting the molar ratios of CL monomer to EC and the L-LA monomer to CL. The thermal properties and crystalline morphologies of EC-g-PCL and EC-g-PCL-b-PLLA copolymers were different from those of linear PCL. The in vitro degradation rate of EC-g-PCL-b-PLLA was faster than those of linear PCL and EC-g-PCL due to the presence of PLLA blocks.

  16. Controlled synthesis, optical properties and cytotoxicity studies of CdSe-poly(lactic acid) multifunctional nanocomposites by ring-opening polymerization.

    PubMed

    Islam, Md Rafiqul; Bach, Long Giang; Vo, Thanh-Sang; Lee, Doh C; Lim, Kwon Taek

    2014-08-01

    A facile synthetic route has been developed for the covalent grafting of biocompatible poly(lactic acid) (PLA) onto CdSe Quantum Dots (QDs) using surface initiated ring opening polymerization (ROP) to afford CdSe-g-PLA nanocomposites. At first, 2-mercaptoethanol (ME) capped CdSe QDs were synthesized through a wet chemical process. The surface initiated ROP of lactide was accomplished with Sn(Oct)2 to give CdSe-g-PLA nanocomposites having surface hydroxyl functionality. FT-IR data suggested that a robust covalent bond was formed between ME capped CdSe QDs and polymer moieties. The grafting density of PLA on CdSe QDs was found to be moderate as measured by TGA analysis. The CdSe QDs were well dispersed in CdSe-g-PLA nanocomposites matrices as captured by TEM. The cubic phase crystal structure of CdSe QDs in the nanocomposites was determined by XRD. The optical properties of the CdSe-g-PLA nanocomposites were investigated by UV-vis and photoluminescence spectroscopy which suggested their potentialities as optical materials in biomedical application. Cell viability studies revealed that the biocompatibility of CdSe QDs was improved upon PLA immobilization.

  17. Titanium, aluminum and zinc complexes containing diamine-bis(benzotriazole phenolate) ligands: Synthesis, structural characterization and catalytic studies for ring-opening polymerization of ε-caprolactone

    NASA Astrophysics Data System (ADS)

    Liu, Zheng-Tang; Li, Chen-Yu; Chen, Jhy-Der; Liu, Wan-Ling; Tsai, Chen-Yen; Ko, Bao-Tsan

    2017-04-01

    Structurally diverse metal complexes bearing diamine-bis(benzotriazole phenolate) (DiBTP) ligands have been synthesized and fully characterized by single crystal X-ray crystallography. The reaction of Ti(OiPr)4 with C8MEADiBTP-H2 or C8BEADiBTP-H2 (1.0 mol equiv.) generated the monomeric titanium alkoxy complexes [(C8MEADiBTP)Ti(OiPr)2] (1) and [(C8BEADiBTP)Ti(OiPr)2] (2), respectively. Moreover, C8BEADiBTP-H2 reacted with 2.0 molar equiv. of AlMe3 to give the tetra-coordinated di-aluminum complex [(C8BEADiBTP)Al2Me4] (3). Zinc complex [(C8BEADiBTP)Zn2Et2] (4) could be obtained by the alkane elimination of ZnEt2 (2.0 equiv.) with C8BEADiBTP-H2 as the pro-ligand under similar synthetic methods in good yield. Single-crystal X-ray diffraction indicates that 3 is a bimetallic aluminum dimethyl complex with a tetradentate C8BEADiBTP moiety chelating two metal atoms, whereas complex 4 displays the dinuclear feature containing both tetra- and penta-coordinated zinc atoms bonded by one ONNON-pentadentate C8BEADiBTP ligand. Catalytic studies for ring-opening polymerization of ε-caprolactone of complex 1-4 were systematic explored; the comparative studies of such polymerization were also discussed.

  18. Rare-earth metal complexes supported by 1,omega-dithiaalkanediyl-bridged bis(phenolato) ligands: synthesis, structure, and heteroselective ring-opening polymerization of rac-lactide.

    PubMed

    Ma, Haiyan; Spaniol, Thomas P; Okuda, Jun

    2008-04-21

    Monomeric yttrium and lutetium bis(phenolato) complexes [Ln(OSSO){N(SiHMe 2) 2}(THF)] (Ln = Y, Lu) were prepared from the reaction of silylamido complexes [Ln{N(SiHMe 2) 2} 3(THF) 2] with 1 equiv of tetradentate 1,omega-dithiaalkanediyl-bridged bis(phenol) (OSSO)H 2 1- 9 in moderate to high yields. In contrast to the rigid configuration of scandium analogues, the yttrium complexes 2b and 3b and the lutetium complex 3c that contain a C 2 bridge between the two sulfur donors of the ligand are symmetric in solution. The monomeric nature of these complexes was indicated by an X-ray diffraction study of the yttrium complex 6b. The yttrium center in 6b is coordinated to the tetradentate [OSSO]-type ligand, one silylamido group and one THF ligand with the two oxygen donors of the [OSSO]-type ligand located trans. Corresponding bis(phenolato) silylamido complexes of larger rare-earth metals could not be obtained from similar reactions: Reaction of [La{N(SiHMe 2) 2} 3(THF) 2] with 1,2-xylylene-linked bis(phenol) gave a dinuclear lanthanum complex 6d of the formula [La 2(OSSO) 3] with two inequivalent eight-coordinate metal centers. The yttrium and lutetium complexes efficiently initiated the ring-opening polymerization (ROP) of lactides in THF. The heteroselectivity during the ROP of rac-lactide was enhanced when the steric demand of the bis(phenolato) ligand was increased, either by extending the bridge length or by introducing bulky ortho-substituents in the phenoxy units. A C 3 bridge within the ligand backbone is essential to allow configurational interconversion of the active site between Lambda and Delta configuration during polymerization, allowing accommodation of both enantiomers of the monomer in an alternating fashion.

  19. Heteroscorpionate rare-earth metal zwitterionic complexes: syntheses, characterization, and heteroselective catalysis on the ring-opening polymerization of rac-lactide.

    PubMed

    Zhang, Zhichao; Cui, Dongmei

    2011-10-04

    Novel neutral phosphine-modified heteroscorpionate ligand (3,5-Me(2)Pz)(2)CHPPh(2) (1) and its derivatives oxophosphine (2) and iminophosphine (3) heteroscorpionates were synthesized for the first time. These neutral heteroscorpionate ligands displayed unique chemistry towards rare-earth metal tris(alkyl)s [Ln(CH(2)SiMe(3))(3)(thf)(2)] (Ln=Y, Lu, Sc). The reaction between compound 1 and [Ln(CH(2)SiMe(3))(3)(thf)(2)] afforded heteroscorpionate rare-earth metal trialkyl adduct complexes 4a-c. Compounds 2 and 3 were treated with [Ln(CH(2)SiMe(3))(3)(thf)(2)] to give the unprecedented zwitterionic heteroscorpionate rare-earth metal dialkyls 5 and 6, respectively. In the process, the heteroscorpionates transferred to the carbanions by means of methine C-H bond cleavage that was attributed to the presence of the electron-withdrawing groups. In addition the ligand and central metal showed a concerted effect on both the catalytic activity and specific selectivity of complexes 4-6 for the ring-opening polymerization (ROP) of rac-lactide (rac-LA). All the adduct complexes 4 were nonselective and gave atactic polylactide (PLA), probably due to the dissociation of ligand 1 from the active metal center during the polymerization. Strikingly, zwitterionic complexes 5 catalyzed rapid ROP of rac-LA to produce PLAs with heterotacticity up to 0.87. However, the zwitterionic complexes 6 were less active and less selective than 5, which might be on account of the stronger coordination of the tetradentate ligand. Complexes 5 represent rare examples of the selective ROP of rac-LA mediated by rare-earth metal complexes supported by non-bisphenolate ligands.

  20. Scandium versus yttrium{amino-alkoxy-bis(phenolate)} complexes for the stereoselective ring-opening polymerization of racemic lactide and β-butyrolactone.

    PubMed

    Chapurina, Yulia; Klitzke, Joice; Casagrande, Osvaldo de L; Awada, Mouhamad; Dorcet, Vincent; Kirillov, Evgueni; Carpentier, Jean-François

    2014-10-14

    Scandium and yttrium amide complexes Ln{ONXO(R1,R2)}(N(SiHMe2)2)(THF)n (Ln = Sc, n = 0 or Y, n = 1; X = NMe2 or OMe; R(1) = Cumyl or p-Cl-Cumyl; R(2) = Me or Cumyl) were prepared by aminolysis of Ln[N(SiHMe2)2]3(THF) with the corresponding tetradentate diamino- or alkoxy-amino-bis(phenol) pro-ligands {ONXO(R1,R2)}H2. In the solid state and in toluene solution, the scandium complexes are monomeric and 5-coordinated, while the analogous yttrium complexes all bear an extra THF-coordinated molecule and are 6-coordinated. Sc{ONXO(R1,R2)}(N(SiHMe2)2) complexes are single-site initiators for the ring-opening polymerization (ROP) of racemic lactide but are less active than their yttrium analogues Y{ONXO(R1,R2)}(N(SiHMe2)2)(THF); also, in contrast to the latter ones, they are inactive in the ROP of the more demanding racemic β-butyrolactone. On the other hand, the scandium amide complexes feature a significantly improved control over the ROP of lactide, yielding PLAs with much narrower molecular weight distributions (Đ(M) < 1.1 for Sc vs. 1.5-2.0 for Y). The yttrium complex with the very bulky o,p-dicumyl-substituted ligand is more heteroselective than its scandium analogue (P(r) = 0.88 vs. 0.83), while the opposite is observed with complexes based on p-methyl-substituted ligands (P(r) = 0.50 in toluene or 0.72-0.75 in THF for Y vs. P(r) = 0.75-0.83 for Sc in toluene). These reactivity and selectivity trends are rationalized by a much more sterically crowded coordination sphere in scandium than in yttrium complexes.

  1. Preparation of polyhedral oligomeric silsesquioxane-based hybrid monolith by ring-opening polymerization and post-functionalization via thiol-ene click reaction.

    PubMed

    Liu, Zhongshan; Ou, Junjie; Lin, Hui; Wang, Hongwei; Dong, Jing; Zou, Hanfa

    2014-05-16

    A polyhedral oligomeric silsesquioxane (POSS) hybrid monolith was simply prepared by using octaglycidyldimethylsilyl POSS (POSS-epoxy) and cystamine dihydrochloride as monomers via ring-opening polymerization. The effects of composition of prepolymerization solution and polycondensation temperature on the morphology and permeability of monolithic column were investigated in detail. The obtained POSS hybrid monolithic column showed 3D skeleton morphology and exhibited high column efficiency of ∼71,000 plates per meter in reversed-phase mechanism. Owing to this POSS hybrid monolith essentially possessing a great number of disulfide bonds, the monolith surface would expose thiol groups after reduction with dithiothreitol (DTT), which supplied active sites to functionalize with various alkene monomers via thiol-ene click reaction. The results indicated that the reduction with DTT could not destroy the 3D skeleton of hybrid monolith. Both stearyl methylacrylate (SMA) and benzyl methacrylate (BMA) were selected to functionalize the hybrid monolithic columns for reversed-phase liquid chromatography (RPLC), while [2-(methacryloyloxy)ethyl]-dimethyl-(3-sulfopropyl)-ammonium hydroxide (MSA) was used to modify the hybrid monolithic column in hydrophilic interaction chromatography (HILIC). These modified hybrid monolithic columns could be successfully applied for separation of small molecules with high efficiency. It is demonstrated that thiol-ene click reaction supplies a facile way to introduce various functional groups to the hybrid monolith possessing thiol groups. Furthermore, due to good permeability of the resulting hybrid monoliths, we also prepared long hybrid monolithic columns in narrow-bore capillaries. The highest column efficiency reached to ∼70,000 plates using a 1-m-long column of 75μm i.d. with a peak capacity of 147 for isocratic chromatography, indicating potential application in separation and analysis of complex biosamples. Copyright © 2014

  2. Zirconium and hafnium complexes containing N-alkyl substituted amine biphenolate ligands: coordination chemistry and living ring-opening polymerization catalysis.

    PubMed

    Liang, Lan-Chang; Lin, Sheng-Ta; Chien, Chia-Cheng; Chen, Ming-Tsz

    2013-07-07

    The coordination chemistry of zirconium and hafnium complexes containing the tridentate amine biphenolate ligands [RN(CH2-2-O-3,5-C6H2(tBu)2)2](2-) ([R-ONO](2-); R = tBu (1a), iPr (1b), nPr (1c)) featuring distinct N-alkyl substituents is described. Alcoholysis of Zr(OiPr)4(HOiPr) or Hf(OiPr)4(HOiPr) with H2[1a] in diethyl ether solutions at -35 °C generates the corresponding five-coordinate [1a]M(OiPr)2 (M = Zr (2a), Hf (3a)) in high isolated yield. Similar reactions employing H2[1b] produce six-coordinate [1b]M(OiPr)2(HOiPr) (M = Zr (2b·HOiPr), Hf (3b·HOiPr)) as an isopropanol adduct. Repetitive trituration of 2b·HOiPr and 3b·HOiPr with diethyl ether gives five-coordinate 2b and 3b, respectively. Treatment of M(OiPr)4(HOiPr) with H2[1c] under similar conditions affords six-coordinate [1c]M(OiPr)2(HOiPr) (M = Zr (2c·HOiPr), Hf (3c·HOiPr)), subsequent recrystallization of which from acetonitrile-diethyl ether solutions leads to acetonitrile adducts 2c·MeCN and 3c·MeCN. Reactivity studies of these zirconium and hafnium complexes revealed that they are all active catalysts for ring-opening polymerization of ε-caprolactone. Among them, the N-isopropyl derived complexes are most reactive. Polymerizations catalyzed by 2b, 3b and 3c·MeCN were proved to be living. The X-ray structures of 2a·HOiPr, 2a·MeCN, 2c·HOiPr, 2c·MeCN, and 3c·MeCN are presented.

  3. Synthesis of amphiphilic tadpole-shaped linear-cyclic diblock copolymers via ring-opening polymerization directly initiating from cyclic precursors and their application as drug nanocarriers.

    PubMed

    Wan, Xuejuan; Liu, Tao; Liu, Shiyong

    2011-04-11

    We report on the facile synthesis of well-defined amphiphilic and thermoresponsive tadpole-shaped linear-cyclic diblock copolymers via ring-opening polymerization (ROP) directly initiating from cyclic precursors, their self-assembling behavior in aqueous solution, and the application of micellar assemblies as controlled release drug nanocarriers. Starting from a trifunctional core molecule containing alkynyl, hydroxyl, and bromine moieties, alkynyl-(OH)-Br, macrocyclic poly(N-isopropylacrylamide) (c-PNIPAM) bearing a single hydroxyl functionality was prepared by atom transfer radical polymerization (ATRP), the subsequent end group transformation into azide functionality, and finally the intramacromolecular ring closure reaction via click chemistry. The target amphiphilic tadpole-shaped linear-cyclic diblock copolymer, (c-PNIPAM)-b-PCL, was then synthesized via the ROP of ε-caprolactone (CL) by directly initiating from the cyclic precursor. In aqueous solution at 20 °C, (c-PNIPAM)-b-PCL self-assembles into spherical micelles consisting of hydrophobic PCL cores and well-solvated coronas of cyclic PNIPAM segments. For comparison, linear diblock copolymer with comparable molecular weight and composition, (l-PNIPAM)-b-PCL, was also synthesized. It was found that the thermoresponsive coronas of micelles self-assembled from (c-PNIPAM)-b-PCL exhibit thermoinduced collapse and aggregation at a lower critical thermal phase transition temperature (T(c)) compared with those of (l-PNIPAM)-b-PCL. Temperature-dependent drug release profiles from the two types of micelles of (c-PNIPAM)-b-PCL and (l-PNIPAM)-b-PCL loaded with doxorubicin (Dox) were measured, and the underlying mechanism for the observed difference in releasing properties was proposed. Moreover, MTT assays revealed that micelles of (c-PNIPAM)-b-PCL are almost noncytotoxic up to a concentration of 1.0 g/L, whereas at the same polymer concentration, micelles loaded with Dox lead to ∼60% cell death. Overall, chain

  4. The Olefin Metathesis Reactions Combined with Organo-Iron Arene Activation Towards Dendrimers, and Polymers

    NASA Astrophysics Data System (ADS)

    Astruc, Didier; Martinez, Victor

    The subjects treated in the two lectures of the North Atlantic Treaty Organization (NATO) summer course are (1) the combination of arene activation and perfunctionalization using organo-iron chemistry with olefin metathesis incuding metathesis of dendritic polyolefin molecules; (2) the synthesis of metallodendritic benzylidene complexes that catalyse ring-opening metathesis polymerization (ROMP) under ambient conditions and the formation of dendritic stars; (3) the use of stoichiometric and catalytic electron-transfer processes with standard reservoirs of electrons (reductants) or electron holes (oxidants) iron complexes to achieve noteworthy metathesis reactions or synthesize compounds that are useful in metathesis. Only the two first topics are treated in this chapter, and interested readers can find references concerning the third aspect called in the introduction and subsequently cited in the reference list.

  5. Synthesis of Novel μ-Star Copolymers with Poly(N-Octyl Benzamide) and Poly(ε-Caprolactone) Miktoarms through Chain-Growth Condensation Polymerization, Styrenics-Assisted Atom Transfer Radical Coupling, and Ring-Opening Polymerization.

    PubMed

    Huang, Chih-Feng; Aimi, Junko; Lai, Kuan-Yu

    2017-02-01

    Star copolymers are known to phase separate on the nanoscale, providing useful self-assembled morphologies. In this study, the authors investigate synthesis and assembly behavior of miktoarm star (μ-star) copolymers. The authors employ a new strategy for the synthesis of unprecedented μ-star copolymers presenting poly(N-octyl benzamide) (PBA) and poly(ε-caprolactone) (PCL) arms: a combination of chain-growth condensation polymerization, styrenics-assisted atom transfer radical coupling, and ring-opening polymerization. Gel permeation chromatography, mass-analyzed laser desorption/ionization mass spectrometry, and (1) H NMR spectroscopy reveal the successful synthesis of a well-defined (PBA11 )2 -(PCL15 )4 μ-star copolymer (Mn,NMR ≈ 12 620; Đ = 1.22). Preliminary examination of the PBA2 PCL4 μ-star copolymer reveals assembled nanofibers having a uniform diameter of ≈20 nm. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  6. Composite materials with improved properties in compression. Appendix 5. Synthesis and anionic ring-opening polymerization of 1-germa-1,1- dimethyl(3,4,c) thieno cyclopentane. Interim report

    SciTech Connect

    Zhou, S.Q.; Weber, W.P.

    1990-05-09

    While there has been extensive work on several types of polymers having silicon in the main chain due to their scientific and industrial importance, few studies on polymers containing germanium in the backbone have been reported. Despite this limited research, polygermanes have been observed to have interesting properties. For example, they have been found to be photoactive. They undergo photobleaching as well as to have thermochromic properties. Most recently, germylenes, stable divalent germanium species, have been found to undergo a novel oxidation-reduction copolymerization with benzoquinones. Anionic ring opening polymerization of I yields III, a carbogermanium polymer in which both carbon and germanium atoms make up the polymer backbone.

  7. Chromatographic assessment of two hybrid monoliths prepared via epoxy-amine ring-opening polymerization and methacrylate-based free radical polymerization using methacrylate epoxy cyclosiloxane as functional monomer.

    PubMed

    Wang, Hongwei; Ou, Junjie; Lin, Hui; Liu, Zhongshan; Huang, Guang; Dong, Jing; Zou, Hanfa

    2014-11-07

    Two kinds of hybrid monolithic columns were prepared by using methacrylate epoxy cyclosiloxane (epoxy-MA) as functional monomer, containing three epoxy moieties and one methacrylate group. One column was in situ fabricated by ring-opening polymerization of epoxy-MA and 1,10-diaminodecane (DAD) using a porogenic system consisting of isopropanol (IPA), H2O and ethanol at 65°C for 12h. The other was prepared by free radical polymerization of epoxy-MA and ethylene dimethacrylate (EDMA) using 1-propanol and 1,4-butanediol as the porogenic solvents at 60°C for 12h. Two hybrid monoliths were investigated on the morphology and chromatographic assessment. Although two kinds of monolithic columns were prepared with epoxy-MA, their morphologies looked rather different. It could be found that the epoxy-MA-DAD monolith possessed higher column efficiencies (25,000-34,000plates/m) for the separation of alkylbenzenes than the epoxy-MA-EDMA monolith (12,000-13,000plates/m) in reversed-phase nano-liquid chromatography (nano-LC). Depending on the remaining epoxy or methacrylate groups on the surface of two pristine monoliths, the epoxy-MA-EDMA monolith could be easily modified with 1-octadecylamine (ODA) via ring-opening reaction, while the epoxy-MA-DAD monolith could be modified with stearyl methacrylate (SMA) via free radical reaction. The chromatographic performance for the separation of alkylbenzenes on SMA-modified epoxy-MA-DAD monolith was remarkably improved (42,000-54,000 plates/m) when compared with that on pristine epoxy-MA-DAD monolith, while it was not obviously enhanced on ODA-modified epoxy-MA-EDMA monolith when compared with that on pristine epoxy-MA-EDMA monolith. The enhancement of the column efficiency of epoxy-MA-DAD monolith after modification might be ascribed to the decreased mass-transfer resistence. The two kinds of hybrid monoliths were also applied for separations of six phenols and seven basic compounds in nano-LC.

  8. A computational insight into a metal mediated pathway for the ring-opening polymerization (ROP) of lactides by an ionic {(NHC)2Ag}(+)X(-) (X = halide) type N-heterocyclic carbene (NHC) complex.

    PubMed

    Stephen, Raji; Sunoj, Raghavan B; Ghosh, Prasenjit

    2011-10-21

    A metal mediated coordination-insertion pathway for the ring-opening polymerization (ROP) of L-lactide by an ionic {(NHC)(2)Ag}(+)X(-) (X = halide) type silver complex of N-heterocyclic carbene (NHC) has been investigated using the density functional theory (DFT) method. A clear insight into the lactide insertion process could be obtained by modeling two consecutive monomer addition steps with the first one mimicking chain initiation with the second representing a propagation step. In particular, in each of the cycles, the reaction initiates with the formation of a lactide coordinated species, [1+LL] and [2+LL] that transforms into a metal bound cyclic lactide intermediate, I([1+LL]→2) and I([2+LL]→3), which subsequently ring opens to give the lactide inserted products, 2 and 3. The estimated overall activation barrier for the initiation step is 42.0 kcal mol(-1) while the same for the propagation step is 31.5 kcal mol(-1). Studies on higher monomer insertions showed a decrease in the relative product energies as anticipated for an addition polymerization pathway.

  9. N-heterocyclic carbene-induced zwitterionic ring-opening polymerization of ethylene oxide and direct synthesis of alpha,omega-difunctionalized poly(ethylene oxide)s and poly(ethylene oxide)-b-poly(epsilon-caprolactone) block copolymers.

    PubMed

    Raynaud, Jean; Absalon, Christelle; Gnanou, Yves; Taton, Daniel

    2009-03-11

    An N-heterocyclic carbene (NHC), namely, 1,3-bis-(diisopropyl)imidazol-2-ylidene (1), was demonstrated to bring about the metal-free ring-opening polymerization of ethylene oxide at 50 degrees C in dimethyl sulfoxide, in absence of any other reagents. Poly(ethylene oxide) (PEO) of polydispersities <1.2 and molar masses perfectly matching the [monomer]/[(1)] ratio could thus be obtained in quantitative yields, attesting to the controlled/living character of such carbene-initiated polymerizations. It is argued that (1) adds to ethylene oxide to form a zwitterionic species, namely 1,3-bis-(diisopropyl)imidazol-2-ylidinium alkoxide, that further propagates by a zwitterionic ring-opening polymerization (ZROP) mechanism. Through an appropriate choice of terminating agent NuH or NuSiMe(3) at the completion of the polymerization, a variety of end-functionalized PEO chains could be generated. In particular, alpha,omega-bis(hydroxy)-telechelic PEO, alpha-benzyl,omega-hydroxy, and alpha-azido,omega-hydroxy-difunctionalized PEOs were synthesized by NHC (1)-initiated ZROP, using H(2)O, PhCH(2)OH, and N(3)SiMe(3) as terminating agent, respectively. Characterization of these alpha,omega-difunctionalized PEOs by techniques such as (1)H NMR spectroscopy, MALDI-TOF spectrometry, and size exclusion chromatography confirmed the quantitative introduction of functional groups at both alpha and omega positions of the PEO chains and the formation of very narrow molar mass polymers. Finally, the synthesis of a poly(ethylene oxide)-b-poly(epsilon-caprolactone) diblock copolymer by sequential ZROP of the corresponding monomers was successfully achieved using (1) as organic initiator without isolation of the PEO block intermediate.

  10. Switching from Controlled Ring-Opening Polymerization (cROP) to Controlled Ring-Closing Depolymerization (cRCDP) by Adjusting the Reaction Parameters That Determine the Ceiling Temperature

    PubMed Central

    2016-01-01

    Full control over the ceiling temperature (Tc) enables a selective transition between the monomeric and polymeric state. This is exemplified by the conversion of the monomer 2-allyloxymethyl-2-ethyl-trimethylene carbonate (AOMEC) to poly(AOMEC) and back to AOMEC within 10 h by controlling the reaction from conditions that favor ring-opening polymerization (Tc > T0) (where T0 is the reaction temperature) to conditions that favor ring-closing depolymerization (Tc < T0). The ring-closing depolymerization (RCDP) mirrors the polymerization behavior with a clear relation between the monomer concentration and the molecular weight of the polymer, indicating that RCDP occurs at the chain end. The Tc of the polymerization system is highly dependent on the nature of the solvent, for example, in toluene, the Tc of AOMEC is 234 °C and in acetonitrile Tc = 142 °C at the same initial monomer concentration of 2 M. The control over the monomer to polymer equilibrium sets new standards for the selective degradation of polymers, the controlled release of active components, monomer synthesis and material recycling. In particular, the knowledge of the monomer to polymer equilibrium of polymers in solution under selected environmental conditions is of paramount importance for in vivo applications, where the polymer chain is subjected to both high dilution and a high polarity medium in the presence of catalysts, that is, very different conditions from which the polymer was formed. PMID:27783494

  11. Thermally Stable, Latent Olefin Metathesis Catalysts

    PubMed Central

    Thomas, Renee M.; Fedorov, Alexey; Keitz, Benjamin K.

    2011-01-01

    Highly thermally stable N-aryl,N-alkyl N-heterocyclic carbene (NHC) ruthenium catalysts were designed and synthesized for latent olefin metathesis. These catalysts showed excellent latent behavior toward metathesis reactions, whereby the complexes were inactive at ambient temperature and initiated at elevated temperatures, a challenging property to achieve with second generation catalysts. A sterically hindered N-tert-butyl substituent on the NHC ligand of the ruthenium complex was found to induce latent behavior toward cross-metathesis reactions, and exchange of the chloride ligands for iodide ligands was necessary to attain latent behavior during ring-opening metathesis polymerization (ROMP). Iodide-based catalysts showed no reactivity toward ROMP of norbornene-derived monomers at 25 °C, and upon heating to 85 °C gave complete conversion of monomer to polymer in less than 2 hours. All of the complexes were very stable to air, moisture, and elevated temperatures up to at least 90 °C, and exhibited a long catalyst lifetime in solution at elevated temperatures. PMID:22282652

  12. Photoresponsive Polymeric Reversible Nanoparticles via Self-Assembly of Reactive ABA Triblock Copolymers and Their Transformation to Permanent Nanostructures

    PubMed Central

    Ding, Liang; Li, Juan; Jiang, Ruiyu; Song, Wei

    2016-01-01

    Azobenzene-functionalized ABA triblock copolymers with controlled molecular weights are prepared first via a sequential ring-opening metathesis polymerization and acyclic diene metathesis polymerization in one-pot, which are readily converted, by a facile esterification, to the modified ABA triblock copolymers. Then, these reactive triblock copolymers can spontaneously self-assemble in a selective solvent to form reproducible and reversible polymeric core-shell nanoparticles. Finally, the stable and permanent shell-crosslinked nanoparticles are obtained by an intramolecular crosslinking reaction in dilute solution under UV light irradiation. These as-prepared polymeric nanoparticles and their precursor incorporating azobenzene chromophores exhibit distinct photoresponsive performance and morphological variation. PMID:28774100

  13. 1-n-Butyl-3-methylimidazolium-2-carboxylate: a versatile precatalyst for the ring-opening polymerization of ε-caprolactone and rac-lactide under solvent-free conditions

    PubMed Central

    Hoppe, Astrid; Sadaka, Faten; Brachais, Claire-Hélène; Boni, Gilles; Couvercelle, Jean-Pierre

    2013-01-01

    Summary The ring-opening polymerization of ε-caprolactone (ε-CL) and rac-lactide (rac-LA) under solvent-free conditions and using 1-n-butyl-3-methylimidazolium-2-carboxylate (BMIM-2-CO2) as precatalyst is described. Linear and star-branched polyesters were synthesized by successive use of benzyl alcohol, ethylene glycol, glycerol and pentaerythritol as initiator alcohols, and the products were fully characterized by 1H and 13C{1H} NMR spectroscopy, gel permeation chromatography (GPC), and differential scanning calorimetry (DSC). BMIM-2-CO2 acts as an N-heterocyclic carbene precursor, resulting from in situ decarboxylation, either by heating under vacuo (method A) or by addition of NaBPh4 (method B). Possible catalytic and deactivation mechanisms are proposed. PMID:23616809

  14. Bis(imino)diphenylamido rare-earth metal dialkyl complexes: synthesis, structure, and catalytic activity in living ring-opening ε-caprolactone polymerization and copolymerization with γ-butyrolactone.

    PubMed

    Du, Gaixia; Wei, Yanling; Zhang, Wei; Dong, Yuping; Lin, Zhengguo; He, Huan; Zhang, Shaowen; Li, Xiaofang

    2013-01-28

    Bis(imino)diphenylamido rare-earth metal dialkyl complexes [o-(2,6-(i)Pr(2)-C(6)H(3)-N=C-C(6)H(4))(2)-N]Ln(CH(2)SiMe(3))(2) (1: Ln = Sc; 2: Ln = Lu; 3: Ln = Y) have been synthesized in good yields and structurally characterized by elemental analysis, NMR spectroscopy, and single-crystal X-ray diffraction studies. They serve as highly efficient single-component catalysts both for the living ring-opening ε-caprolactone polymerization and random copolymerization with γ-butyrolactone, with the activity being dependent on the steric hindrance around the metal center, yielding high molecular weight PCLs or P(CL-co-BL)s with narrow molecular weight distributions.

  15. Soluble, Highly Conjugated Derivatives of Polyacetylene from the Ring-Opening Metathesis Polymerization of Monosubstituted Cyclooctatetraenes: Synthesis and the Relationship Between Polymer Structure and Physical Properties

    DTIC Science & Technology

    1993-01-15

    Figure 11). For various side groups , the geometry of these oligomers was optimized and the effect of the side group upon the conformation of the main...iin general, secondary or tertiary groups immediately adjacent to the main chain remain ",,,i’le in the trans form and are, in most cases, still...thermal isomerization was monitored by visible absorption spectroscopy. Polymers containing, in general, secondary or tertiary groups immediately

  16. Ring opening metathesis polymerization-derived block copolymers bearing chelating ligands: synthesis, metal immobilization and use in hydroformylation under micellar conditions

    PubMed Central

    Pawar, Gajanan M; Weckesser, Jochen

    2010-01-01

    Summary Norborn-5-ene-(N,N-dipyrid-2-yl)carbamide (M1) was copolymerized with exo,exo-[2-(3-ethoxycarbonyl-7-oxabicyclo[2.2.1]hept-5-en-2-carbonyloxy)ethyl]trimethylammonium iodide (M2) using the Schrock catalyst Mo(N-2,6-Me2-C6H3)(CHCMe2Ph)(OCMe(CF3)2)2 [Mo] to yield poly(M1-b-M2). In water, poly(M1-b-M2) forms micelles with a critical micelle-forming concentration (cmc) of 2.8 × 10−6 mol L−1; Reaction of poly(M1-b-M2) with [Rh(COD)Cl]2 (COD = cycloocta-1,5-diene) yields the Rh(I)-loaded block copolymer poly(M1-b-M2)-Rh containing 18 mg of Rh(I)/g of block copolymer with a cmc of 2.2 × 10−6 mol L−1. The Rh-loaded polymer was used for the hydroformylation of 1-octene under micellar conditions. The data obtained were compared to those obtained with a monomeric analogue, i.e. CH3CON(Py)2RhCl(COD) (C1, Py = 2-pyridyl). Using the polymer-supported catalyst under micellar conditions, a significant increase in selectivity, i.e. an increase in the n:iso ratio was accomplished, which could be further enhanced by the addition of excess ligand, e.g., triphenylphosphite. Special features of the micellar catalytic set up are discussed. PMID:20502652

  17. Synthetic mimics of antimicrobial peptides--a versatile ring-opening metathesis polymerization based platform for the synthesis of selective antibacterial and cell-penetrating polymers.

    PubMed

    Lienkamp, Karen; Tew, Gregory N

    2009-11-09

    Natural macromolecules exhibit an extensive arsenal of properties, many of which have proven difficult to recapitulate in simpler synthetic systems. Over the last couple of years, foldamers have emerged as one important step toward increased functionality in synthetic systems. While the great majority of work in this area has focused on folded structures, hence the name, more recent progress has centered on polymers that mimic protein function. These efforts have resulted in the design of relatively simple macromolecules; one example are the synthetic mimics of antimicrobial peptides (SMAMPs) that capture the central physicochemical features of their natural archetypes irrespective of the specific folded form. Here we present our recent efforts to create polymers which display biological activity similar to natural proteins, including antimicrobial and cell-penetrating peptides.

  18. Triblock Terpolymers by Simultaneous Tandem Block Polymerization (STBP).

    PubMed

    Freudensprung, Ines; Klapper, Markus; Müllen, Klaus

    2016-02-01

    A route of synthesizing triblock terpolymers in a one-pot, "one-step" polymerization approach is presented. The combination of two distinct polymerization techniques through orthogonal catalyst/initiator functionalities attached to a polymeric linker furnishes novel pathways to ABC-terpolymers. Both polymerizations have to be compatible regarding mechanisms, chosen monomers, and solvents. Here, an α,ω-heterobifunctional poly(ethylene glycol) serves as poly-meric catalyst/initiator to obtain triblock terpolymers of poly(norbornene)-b-poly(ethylene glycol)-b-poly(L-lactic acid) PNB-PEG-PLLA via simultaneous ring opening metathesis poly-merization and ring opening polymerization in a fast one-pot polymerization. Structural characterization of the polymers is provided via (1)H-, DOSY-, and (1)H,(1)H-COSY-NMR, while solution and thin film self-assembly are investigated by dynamic light scattering and atomic force microscopy.

  19. Preparation of cadmium selenide-polyolefin composites from functional phosphine oxides and ruthenium-based metathesis.

    PubMed

    Skaff, Habib; Ilker, M Firat; Coughlin, E Bryan; Emrick, Todd

    2002-05-22

    Cadmium selenide nanoparticles, prepared by known methods, were stabilized with functional phosphine oxide 1, then used to support the polymerization of cyclic olefins radially outward from the surface by ruthenium-catalyzed ring-opening metathesis polymerization (ROMP). The conversion of compound 1 into the new metathesis catalyst 3 by carbene exchange and the subsequent polymerization of cyclic olefins were observed spectroscopically by (1)H NMR to afford for example CdSe-polycyclooctene composite 6. Transmission electron micrographs on thin films of these composites showed good nanoparticle dispersion. This is in stark contrast to the substantial nanoparticle aggregation observed when similar polymerizations were performed in the presence of conventional TOPO-covered nanoparticles. The methods reported here to prepare composite product 6 are applicable to other cyclic olefins, and suggest that this chemistry will be useful for incorporating CdSe nanoparticles into a wide variety of polymer matrices.

  20. The catalytic performance of metal complexes immobilized on SBA-15 in the ring opening polymerization of ε-caprolactone with different metals (Ti, Al, Zn and Mg) and immobilization procedures.

    PubMed

    Pérez, Yolanda; del Hierro, Isabel; Zazo, Lydia; Fernández-Galán, Rafael; Fajardo, Mariano

    2015-03-07

    A family of heterogeneous catalysts has been prepared by employing different strategies: firstly by direct reaction or grafting of titanium, zinc, aluminium and magnesium precursors with dehydrated SBA-15 and secondly by reaction of the metallic derivatives with a hybrid SBA-15 mesoporous material, which possesses a new covalently bonded linker based on an amino alcohol chelate ligand. These materials have been characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), N2 adsorption-desorption, FT-IR and multi-nuclear NMR spectroscopy. The catalytic performance of the prepared materials has been studied in the ring opening polymerization of ε-caprolactone and compared with that of their homogeneous counterparts. Conversion values obtained by using homogeneous and heterogeneous catalysts depend on the metal precursor and the synthetic procedure. The most active heterogeneous Ti-SBA-15, Zn-SBA-15 and Zn-PADO-HMDS-SBA-15 catalysts produced poly(ε-caprolactone) with a narrow molecular weight distribution, close to one. In all cases polymerization was confirmed to proceed via a coordination insertion mechanism after end group analysis by (1)H NMR.

  1. Functional Degradable Polymers by Radical Ring-Opening Copolymerization of MDO and Vinyl Bromobutanoate: Synthesis, Degradability and Post-Polymerization Modification.

    PubMed

    Hedir, Guillaume G; Bell, Craig A; O'Reilly, Rachel K; Dove, Andrew P

    2015-07-13

    The synthesis of vinyl bromobutanoate (VBr), a new vinyl acetate monomer derivative obtained by the palladium-catalyzed vinyl exchange reaction between vinyl acetate (VAc) and 4-bromobutyric acid is reported. The homopolymerization of this new monomer using the RAFT/MADIX polymerization technique leads to the formation of novel well-defined and controlled polymers containing pendent bromine functional groups able to be modified via postpolymerization modification. Furthermore, the copolymerization of vinyl bromobutanoate with 2-methylene-1,3-dioxepane (MDO) was also performed to deliver a range of novel functional degradable copolymers, poly(MDO-co-VBr). The copolymer composition was shown to be able to be tuned to vary the amount of ester repeat units in the polymer backbone, and hence determine the degradability, while maintaining a control of the final copolymers' molar masses. The addition of functionalities via simple postpolymerization modifications such as azidation and the 1,3-dipolar cycloaddition of a PEG alkyne to an azide is also reported and proven by (1)H NMR spectroscopy, FTIR spectroscopy, and SEC analyses. These studies enable the formation of a novel class of hydrophilic functional degradable copolymers using versatile radical polymerization methods.

  2. Mono-BHT heteroleptic magnesium complexes: synthesis, molecular structure and catalytic behavior in the ring-opening polymerization of cyclic esters.

    PubMed

    Nifant'ev, I E; Shlyakhtin, A V; Bagrov, V V; Minyaev, M E; Churakov, A V; Karchevsky, S G; Birin, K P; Ivchenko, P V

    2017-09-28

    Numerous heteroleptic 2,6-di-tert-butyl-4-methylphenolate (BHT) magnesium complexes have been synthesized by treatment of (BHT)MgBu(THF)2 with various alcohols. Molecular structures of the complexes have been determined by X-ray diffraction. The magnesium coordination number in [(BHT)Mg(μ-OBn)(THF)]2 (3) and [(BHT)Mg(μ-O-tert-BuC6H4)(THF)]2 (4) is equal to 4. Complexes formed from esters of glycolic and lactic acids, [(BHT)Mg(μ-OCH2COOEt)(THF)]2 (5) and [(BHT)Mg(μ-OCH(CH3)COOCH2COO(t)Bu)(THF)]2 (6) contain chelate fragments with pentacoordinated magnesium. Compounds 3-6 contain THF molecules coordinated to magnesium atoms. Complex {(BHT)Mg[μ-O(CH2)3CON(CH3)2]}2 (7) does not demonstrate any tendency to form an adduct with THF. It has been experimentally determined that complexes 3 and 5 are highly active catalysts of lactide polymerization. The activity of 4 is rather low, and complex 7 demonstrates moderate productivity. According to DOSY NMR experiments, compounds 3 and 5 retain their dimeric structures even in THF. The free energies of model dimeric [(DBP)Mg(μ-OMe)(Sub)]2 and monomeric (DBP)Mg(OMe)(Sub)2 products on treatment of [(DBP)Mg(μ-OMe)(THF)]2 with a series of σ-electron donors (Sub) have been estimated by DFT calculations. These results demonstrate that the substitution of THF by Sub in a dimeric molecule is an energetically allowed process, whereas the dissociation of dimers is energetically unfavorable. DFT modeling of ε-CL and (dl)-lactide ROP catalyzed by dimeric and monomeric complexes showed that a cooperative effect of two magnesium atoms occurs within the ROP for binuclear catalytic species. A comparison of the reaction profiles for ROP catalyzed by binuclear and mononuclear species allowed us to conclude that the binuclear mechanism is favorable in early stages of ROP initiated by dimers 3 and 5.

  3. Recent applications of ring-rearrangement metathesis in organic synthesis

    PubMed Central

    Meshram, Milind; Khedkar, Priti; Banerjee, Shaibal; Deodhar, Deepak

    2015-01-01

    Summary Ring-rearrangement metathesis (RRM) involves multiple metathesis processes such as ring-opening metathesis (ROM)/ring-closing metathesis (RCM) in a one-pot operation to generate complex targets. RRM delivers complex frameworks that are difficult to assemble by conventional methods. The noteworthy point about this type of protocol is multi-bond formation and it is an atom economic process. In this review, we have covered literature that appeared during the last seven years (2008–2014). PMID:26664603

  4. Recent applications of ring-rearrangement metathesis in organic synthesis.

    PubMed

    Kotha, Sambasivarao; Meshram, Milind; Khedkar, Priti; Banerjee, Shaibal; Deodhar, Deepak

    2015-01-01

    Ring-rearrangement metathesis (RRM) involves multiple metathesis processes such as ring-opening metathesis (ROM)/ring-closing metathesis (RCM) in a one-pot operation to generate complex targets. RRM delivers complex frameworks that are difficult to assemble by conventional methods. The noteworthy point about this type of protocol is multi-bond formation and it is an atom economic process. In this review, we have covered literature that appeared during the last seven years (2008-2014).

  5. Dinuclear magnesium, zinc and aluminum complexes supported by bis(iminopyrrolide) ligands: synthesis, structures, and catalysis toward the ring-opening polymerization of ε-caprolactone and rac-lactide.

    PubMed

    Kong, Wei-Li; Wang, Zhong-Xia

    2014-06-28

    Synthesis and characterization of novel dinuclear magnesium, zinc and aluminum complexes supported by bis(iminopyrrolide) ligands and their catalysis toward the ring-opening polymerization (ROP) of ε-caprolactone (ε-CL) and rac-lactide (rac-LA) were carried out. The ligand precursors [(5-Bu(t)-2-C4H2NH)CH=N(CH2)2]2NH (H2L(Bu), 1) and [(2-C4H3NH)CH=N(CH2)2]2NH (H2L(H), 2) were prepared by condensation of diethylene triamine with 5-tert-butyl-1H-pyrrole-2-carbaldehyde and 1H-pyrrole-2-carbaldehyde, respectively. Treatment of 1 with 2 equiv. of Bu(n)MgOBn in toluene at 70 °C produced dinuclear magnesium complex [(μ-OBn)2Mg2L(Bu)] (3). Similar treatment of 1 with EtZnOBn generated [(μ-OBn)2Zn2L(Bu)] (4). Reaction of 2 with 2 equiv. of Me2AlOBn in toluene at 70 °C afforded aluminum complex [Me2Al(μ-OBn)2AlL(H)] (5). Complexes 3-5 were characterized by (1)H and (13)C NMR spectroscopy, elemental analyses, and single crystal X-ray diffraction techniques. Each of complexes 3-5 is active for the ROP of ε-CL and rac-LA. Kinetic studies of the polymerization reactions were performed.

  6. Synthesis and characterization of cyclic and linear helical poly(alpha-peptoids)s by N-heterocyclic carbene-mediated ring-opening polymerizations of N-substituted N-carboxyanhydrides.

    PubMed

    Guo, Li; Li, Jinhai; Brown, Zachary; Ghale, Kushal; Zhang, Donghui

    2011-01-01

    Cyclic poly(alpha-peptoid)s [a.k.a. poly(N-R-glycine)] with chiral aromatic side-chains [R = (R)- or (S)-CHMePh] have been synthesized by N-heterocyclic carbene-mediated ring-opening polymerization of N-substituted N-carboxyanhydrides (N(R-NCA)). Their linear analogs have been prepared by primary amine-initiated polymerization of the corresponding N(R-NCA). Poly[(R)/(S)-N-CHMePh-glycine] with polymer molecular weights (MWs) in the range of 4-15 kg mol(-1) and low MW distribution (Polydispersity index (PDI) < 1.15) can be readily accessed by these methods. Their high MW analogs were not obtained due to the competitive formation of cyclic oligomeric species that result from intramolecular transamidation. Intrinsic viscosity measurements confirm the architectural difference between the polymers prepared by the two methods and reveals that both cyclic and linear poly[(S)-N-CHMePh-glycine]s behave as random-coil polymers in 0.1M LiBr/Dimethylformamide (DMF) solution. Circular dichroism analysis suggests that the cyclic and linear poly(alpha-peptoid)s retain polyproline I helix conformations, analogously to previously reported linear oligomers. Differential scanning calorimetry analysis reveals that cyclic and linear poly[(S)-N-CHMePh-glycine] are both amorphous with the glass transition temperature of the cyclic polymers (T(g) = 122 degrees C) being notably higher than that of the linear analogs (T(g) = 112 degrees C) with identical MW. These results are consistent with the absence of chain ends, causing the polymers to have reduced segmental mobilities.

  7. Cationic ruthenium alkylidene catalysts bearing phosphine ligands† †Electronic supplementary information (ESI) available: NMR spectra and metathesis data. CCDC 784488. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c5dt04506a Click here for additional data file. Click here for additional data file.

    PubMed Central

    Endo, Koji

    2016-01-01

    The discovery of highly active catalysts and the success of ionic liquid immobilized systems have accelerated attention to a new class of cationic metathesis catalysts. We herein report the facile syntheses of cationic ruthenium catalysts bearing bulky phosphine ligands. Simple ligand exchange using silver(i) salts of non-coordinating or weakly coordinating anions provided either PPh3 or chelating Ph2P(CH2)nPPh2 (n = 2 or 3) ligated cationic catalysts. The structures of these newly reported catalysts feature unique geometries caused by ligation of the bulky phosphine ligands. Their activities and selectivities in standard metathesis reactions were also investigated. These cationic ruthenium alkylidene catalysts reported here showed moderate activity and very similar stereoselectivity when compared to the second generation ruthenium dichloride catalyst in ring-closing metathesis, cross metathesis, and ring-opening metathesis polymerization assays. PMID:26817990

  8. Synthesis and characterization of dinuclear rare-earth complexes supported by amine-bridged bis(phenolate) ligands and their catalytic activity for the ring-opening polymerization of l-lactide.

    PubMed

    Duan, Yu-Lai; He, Jia-Xuan; Wang, Wei; Zhou, Jing-Jing; Huang, Yong; Yang, Ying

    2016-06-28

    Reactions of amine-bridged bis(phenolate) protio-ligands N,N-bis(3,5-di-tert-butyl-2-hydroxybenzyl)aminoacetic acid (L(1)-H3) and N,N-bis[3,5-bis(α,α'-dimethylbenzyl)-2-hydroxybenzyl]aminoacetic acid (L(2)-H3), with 1 equiv. M[N(SiMe3)2]3 (M = La, Nd, Sm, Gd, Y) in THF at room temperature yielded the neutral rare-earth complexes [M2(L)2(THF)4] (L = L(1), M = La (), Nd (), Sm (), Gd (), Y (); L = L(2), M = La (), Nd (), Sm (), Gd (), Y ()). All of these complexes were characterized by single-crystal X-ray diffraction, elemental analysis and in the case of yttrium and lanthanum complexes, (1)H NMR spectroscopy. The molecular structure of revealed dinuclear species in which the eight-coordinate lanthanum centers were bonded to two oxygen atoms of two THF molecules, to three oxygen atoms and one nitrogen atom of one L(1) ligand, and two oxygen atoms of the carboxyl group of another. Complexes were also dinuclear species containing seven-coordinate metal centers similar to , albeit with bonding to one rather than two carboxyl group oxygens of another ligand. Further treatment of with excess benzyl alcohol provided dinuclear complex [La2(L(1))2(BnOH)6] (), in which each lanthanum ion is eight-coordinate, bonded to three oxygen atoms and one nitrogen atom of one ligand, three oxygen atoms of three BnOH molecules, as well as one oxygen atom of bridging carboxyl group of the other ligand. In the presence of BnOH, complexes efficiently catalyzed the ring-opening polymerization of l-lactide in a controlled manner and gave polymers with relatively narrow molecular weight distributions. The kinetic and mechanistic studies associated with the ROP of l-lactide using /BnOH initiating system have been performed.

  9. Recent advances in metathesis-derived polymers containing transition metals in the side chain

    PubMed Central

    Demonceau, Albert; Fischer, Helmut

    2015-01-01

    Summary This account critically surveys the field of side-chain transition metal-containing polymers as prepared by controlled living ring-opening metathesis polymerization (ROMP) of the respective metal-incorporating monomers. Ferrocene- and other metallocene-modified polymers, macromolecules including metal-carbonyl complexes, polymers tethering early or late transition metal complexes, etc. are herein discussed. Recent advances in the design and syntheses reported mainly during the last three years are highlighted, with special emphasis on new trends for superior applications of these hybrid materials. PMID:26877797

  10. Comments on the ring-opening polymerization of morpholine-2,5-dione derivatives by various metal catalysts and characterization of the products formed in the reactions involving R2SnX2, where X = OPr(i) and NMe2 and R = Bu(n), Ph and p-Me2NC6H4.

    PubMed

    Chisholm, M H; Galucci, J; Krempner, C; Wiggenhorn, C

    2006-02-14

    (3S,6S)-3-Isopropyl-6-methyl-morpholine-2,5-dione (1), and (3S,6S)-3,6-dimethyl-morpholine-2,5-dione (2), do not enter into ring-opening polymerization reactions with metal catalyst precursors commonly employed for lactides, and with Sn(II) octanoate, only low molecular weight oligomers are obtained. Reactions with R2SnX2 compounds, where R = Ph, Bu(n) and p-Me2NC6H4 and X = OPr(i) or NMe2, reveal that ring-opening of the morpholine-2,5-diones does occur, but that polymerization is terminated by the formation of kinetically-inert products such as {Ph2Sn[mu,eta(3)-OCH(Me)CONCH(Pr(i))COOPr(i)]}2 (3), and {[Bu(n))2Sn[mu,eta(3)-OCH(Me)CONCH(Me)CONMe2]}2 (4), with elimination of HX. Ph3SnOPr(i) is seen to react reversibly with morpholine-2,5-diones in toluene-d8 by 1H NMR spectroscopy while (Bu(n))3SnNMe2 reacts by ring opening to give (Bu(n))3SnOCH(Me)C(O)NHCHMeC(O)NMe2. The new organotin compounds have been characterized by 1H, 13C{1H} and 118Sn NMR spectroscopy and compounds 1, 2, 3 and 4 by single crystal X-ray crystallography.

  11. Solvent-free cyclization of linear dienes using olefin metathesis and the Thorpe-Ingold effect

    SciTech Connect

    Forbees, M.D.E.; Myers, T.L.; Maynard, H.D.; Schulz, G.R. ); Patton, J.T.; Smith, D.W. Jr.; Wagener, K.B. )

    1992-12-30

    The olefin metathesis reaction is of great synthetic utility in polymer chemistry. The recent development of ring-opening (ROMP) and acyclic diene (ADMET) metathesis polymerization reactions has opened new avenues for the synthesis of novel polymeric materials. Recently the authors used ADMET to synthesize several photochemically active poly(keto olefins) using the catalyst Mo(CHCMe[sub 2]Ph)(NAr)(OCMe(CF[sub 3])[sub 2])[sub 2] (Ar = 2,6-diisopropylphenyl) (1) developed by Schrock and co-workers in 1990. In the course of that work, they discovered that neat samples of highly substituted dienes will cyclize quantitatively via metathesis to give difunctional five- and seven-membered rings instead of the expected linear polymer. Examples of substituted diene cyclizations by metathesis even in the presence of a solvent are rare. Their systematic exploitation in organic synthesis has therefore been limited to two recent studies by Fu and Grubbs, who cyclized several substituted diene ethers, amines, and amides to unsaturated oxygen and nitrogen heterocycles. Cyclization of unsubstituted dienes in various solvents has been reported, but complete conversion occurred in only a few cases. Formation of cyclic alkene oligomers from back-biting during the ROMP reaction is also known. The reactions reported here are unusual in that they are intermolecular between catalyst and substrate, yet can give 100% yield of product solely from the monomer in the absence of solvent. 13 refs.

  12. One-Pot Synthesis of Polyrotaxanes via Acyclic Diene Metathesis Polymerization of Supramolecular Monomers

    PubMed Central

    Momčilović, Nebojša; Clark, Paul G.; Boydston, Andrew J.; Grubbs, Robert H.

    2011-01-01

    A one-pot synthesis of polyrotaxanes has been developed. The method employs a supramolecular monomer comprising a polymerizable ammonium salt and crown ether, in combination with dynamic ADMet polymerization. Ultimately, highly efficient complexation, polymerization, and end-capping were accomplished in a single operation to yield polyrotaxanes with Mws up to 19.3 kDa and > 80% of the repeat units being complexed. PMID:22023086

  13. Grubbs–Hoveyda type catalysts bearing a dicationic N-heterocyclic carbene for biphasic olefin metathesis reactions in ionic liquids

    PubMed Central

    Koy, Maximilian; Altmann, Hagen J; Autenrieth, Benjamin; Frey, Wolfgang

    2015-01-01

    Summary The novel dicationic metathesis catalyst [(RuCl2(H2ITapMe2)(=CH–2-(2-PrO)-C6H4))2+ (OTf−)2] (Ru-2, H2ITapMe2 = 1,3-bis(2’,6’-dimethyl-4’-trimethylammoniumphenyl)-4,5-dihydroimidazol-2-ylidene, OTf− = CF3SO3 −) based on a dicationic N-heterocyclic carbene (NHC) ligand was prepared. The reactivity was tested in ring opening metathesis polymerization (ROMP) under biphasic conditions using a nonpolar organic solvent (toluene) and the ionic liquid (IL) 1-butyl-2,3-dimethylimidazolium tetrafluoroborate [BDMIM+][BF4 −]. The structure of Ru-2 was confirmed by single crystal X-ray analysis. PMID:26664582

  14. Self-healing polymers---The importance of choosing an adequate healing monomer, and the olefin metathesis polymerization of agricultural oils

    NASA Astrophysics Data System (ADS)

    Mauldin, Timothy C.

    Modern society's immense and ill-fated reliance on petrochemical-based polymeric materials will likely necessitate a shift in polymer production paradigms in the near future. The work presented herein attempts to address this issue via a two-pronged approach. First, efforts to improve the duration of composite materials by incorporation of a self-healing function are discussed, the fruitful application of which can potentially reduce or eliminate the massive carbon footprints associated with the repair/replacement of damaged materials. And second, polymeric materials derived predominately from natural and renewable feedstock---namely vegetable oils---are developed. Early microcapsule-based self-healing materials utilized dicyclopentadiene-filled microcapsules and Grubbs' olefin metathesis catalyst to initiate the healing mechanism. However, the patent-protected catalyst, made from the precious metal ruthenium and sometimes costly ligands, will likely never be inexpensive and therefore limit large-scale applications. Hence, clever approaches to reduce the healing catalyst loading in self-healing polymers are of great interest. To this end, our efforts have revolved around solving the problem of the relatively inefficient use of Grubbs' catalyst during the healing mechanism. Given that the mismatch of the olefin metathesis polymerization and Grubbs' catalyst dissolution (in monomer) kinetics is a known cause of this inefficient use of the catalyst, we attempted to tune the "latency" (i.e. pot life) of the olefin metathesis polymerization to ensure more complete dissolution of catalyst in monomer. In an alternative approach to improving efficient catalyst dissolution, we developed a simple model to predict relative dissolution rates of Grubbs' catalyst in a small library of healing monomers. This model was shown experimentally to be able to aid in the selection of, for example, reactive monomer additives that can yield impressive improvements in catalyst dissolution

  15. Olefin metathesis and quadruple hydrogen bonding: A powerful combination in multistep supramolecular synthesis

    PubMed Central

    Scherman, Oren A.; Ligthart, G. B. W. L.; Ohkawa, Haruki; Sijbesma, Rint P.; Meijer, E. W.

    2006-01-01

    We show that combining concepts generally used in covalent organic synthesis such as retrosynthetic analysis and the use of protecting groups, and applying them to the self-assembly of polymeric building blocks in multiple steps, results in a powerful strategy for the self-assembly of dynamic materials with a high level of architectural control. We present a highly efficient synthesis of bifunctional telechelic polymers by ring-opening metathesis polymerization (ROMP) with complementary quadruple hydrogen-bonding motifs. Because the degree of functionality for the polymers is 2.0, the formation of alternating, blocky copolymers was demonstrated in both solution and the bulk leading to stable, microphase-separated copolymer morphologies. PMID:16877543

  16. Enantioselective Olefin Metathesis with Cyclometalated Ruthenium Complexes

    PubMed Central

    2015-01-01

    The success of enantioselective olefin metathesis relies on the design of enantioenriched alkylidene complexes capable of transferring stereochemical information from the catalyst structure to the reactants. Cyclometalation of the NHC ligand has proven to be a successful strategy to incorporate stereogenic atoms into the catalyst structure. Enantioenriched complexes incorporating this design element catalyze highly Z- and enantioselective asymmetric ring opening/cross metathesis (AROCM) of norbornenes and cyclobutenes, and the difference in ring strain between these two substrates leads to different propagating species in the catalytic cycle. Asymmetric ring closing metathesis (ARCM) of a challenging class of prochiral trienes has also been achieved. The extent of reversibility and effect of reaction setup was also explored. Finally, promising levels of enantioselectivity in an unprecedented Z-selective asymmetric cross metathesis (ACM) of a prochiral 1,4-diene was demonstrated. PMID:25137310

  17. Synthesis and Side Chain Liquid Crystal Polymers by Living Ring Opening Metathesis Polymerization. 5. Influence of Mesogenic Group and Interconnecting Group on the Thermotropic Behavior of the Resulting Polymers

    DTIC Science & Technology

    1992-07-22

    Komiya and Richard R. Schrock Massachusetts Institute of Technology REPORT NUMBER Department of Chemistry , 6-331 N00014 - 92-J-1433 77 Massachusetts...Behavior of the Resulting Polymers. by Zen Komiyat and Richard R. Schrock* Submitted to Macromolecules *Department of Chemistry 6-331 Massachusetts...br, -CH 2 00C-), 5.15-5.55 (br, olefinic H), 6.97 (brd, arom . H), 7.51 (brd, arom . H). 1H NMR of poly(2-n): 8 1.0 (in, terminal t-Bu), 1.2-2.2 (br

  18. Synthesis of Side Chain Liquid Crystal Polymers by Living Ring Opening Metathesis Polymerization. 2. Influence of Molecular Weight, Polydispersity, and Flexible Spacer Length (n=9-12) on the Thermotropic behavior of the Resulting Plymers

    DTIC Science & Technology

    1992-03-31

    In- CN018952 fluence of Molecular Weight, Polydispersilty and ... 6 AUTHOR(S) Zen Komiya, Coleen Pugh, Richard R. Schrock 7. PERFORMING ORGANIZATION...Zen Komiya, Coleen Pught, and Richard R. Schrock Submitted to A,,tA =z soij For Macromolecules NTIS - - D~iC 1 ,C; tCarnegie Mellon University...Spacer Length (n = 9-12) on the Thermotropic Behavior of the Resulting Polymers by Zen Komiya, Coleen Pught, and Richard R. Schrock* Contribution from

  19. Spiropyran polymeric microcapillary coatings for photodetection of solvent polarity.

    PubMed

    Florea, Larisa; McKeon, Aoife; Diamond, Dermot; Benito-Lopez, Fernando

    2013-02-26

    Fused silica microcapillaries were functionalized with spiropyran-polymer brushes using surface-initiated ring-opening metathesis polymerization. Based on the inherited spiropyran properties, the functionalized capillaries were successfully used to photoidentify solvents of different polarity when passing through the microcapillary in continuous flow. In the present study, six different solvents (toluene, tetrahydrofuran, acetone, acetonitrile, ethanol, and methanol) can be easily detected while passing through the modified microcapillary by simply irradiating a portion of it with UV light (365 nm). This converts the closed spiropyran moiety to the open merocyanine form, and as a consequence, the microcapillary gains a distinct color and spectral response depending on the polarity of the solvent. The rate of ring-opening of the spiropyran-polymer brushes coatings has been determined in situ in the presence of different solvents, showing that the coloration rate is also influenced by the solvent polarity and therefore can be used as an additional parameter for solvent sensing.

  20. Adsorption and ring-opening of lactide on the chiral metal surface Pt(321)(S) studied by density functional theory.

    PubMed

    Franke, J-H; Kosov, D S

    2015-01-28

    We study the adsorption and ring-opening of lactide on the naturally chiral metal surface Pt(321)(S). Lactide is a precursor for polylactic acid ring-opening polymerization, and Pt is a well known catalyst surface. We study, here, the energetics of the ring-opening of lactide on a surface that has a high density of kink atoms. These sites are expected to be present on a realistic Pt surface and show enhanced catalytic activity. The use of a naturally chiral surface also enables us to study potential chiral selectivity effects of the reaction at the same time. Using density functional theory with a functional that includes the van der Waals forces in a first-principles manner, we find modest adsorption energies of around 1.4 eV for the pristine molecule and different ring-opened states. The energy barrier to be overcome in the ring-opening reaction is found to be very small at 0.32 eV and 0.30 eV for LL- and its chiral partner DD-lactide, respectively. These energies are much smaller than the activation energy for a dehydrogenation reaction of 0.78 eV. Our results thus indicate that (a) ring-opening reactions of lactide on Pt(321) can be expected already at very low temperatures, and Pt might be a very effective catalyst for this reaction; (b) the ring-opening reaction rate shows noticeable enantioselectivity.

  1. Adsorption and ring-opening of lactide on the chiral metal surface Pt(321)S studied by density functional theory

    NASA Astrophysics Data System (ADS)

    Franke, J.-H.; Kosov, D. S.

    2015-01-01

    We study the adsorption and ring-opening of lactide on the naturally chiral metal surface Pt(321)S. Lactide is a precursor for polylactic acid ring-opening polymerization, and Pt is a well known catalyst surface. We study, here, the energetics of the ring-opening of lactide on a surface that has a high density of kink atoms. These sites are expected to be present on a realistic Pt surface and show enhanced catalytic activity. The use of a naturally chiral surface also enables us to study potential chiral selectivity effects of the reaction at the same time. Using density functional theory with a functional that includes the van der Waals forces in a first-principles manner, we find modest adsorption energies of around 1.4 eV for the pristine molecule and different ring-opened states. The energy barrier to be overcome in the ring-opening reaction is found to be very small at 0.32 eV and 0.30 eV for LL- and its chiral partner DD-lactide, respectively. These energies are much smaller than the activation energy for a dehydrogenation reaction of 0.78 eV. Our results thus indicate that (a) ring-opening reactions of lactide on Pt(321) can be expected already at very low temperatures, and Pt might be a very effective catalyst for this reaction; (b) the ring-opening reaction rate shows noticeable enantioselectivity.

  2. FeCl3 -Catalyzed Ring-Closing Carbonyl-Olefin Metathesis.

    PubMed

    Ma, Lina; Li, Wenjuan; Xi, Hui; Bai, Xiaohui; Ma, Enlu; Yan, Xiaoyu; Li, Zhiping

    2016-08-22

    Exploiting catalytic carbonyl-olefin metathesis is an ongoing challenge in organic synthesis. Reported herein is an FeCl3 -catalyzed ring-closing carbonyl-olefin metathesis. The protocol allows access to a range of carbo-/heterocyclic alkenes with good efficiency and excellent trans diastereoselectivity. The methodology presents one of the rare examples of catalytic ring-closing carbonyl-olefin metathesis. This process is proposed to take place by FeCl3 -catalyzed oxetane formation followed by retro-ring-opening to deliver metathesis products. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. First acyclic diene metathesis polymerization under biphasic conditions using a dicationic ruthenium alkylidene: access to high-molecular-weight polymers with very low ruthenium contamination.

    PubMed

    Zhao, Jing; Wang, Dongren; Autenrieth, Benjamin; Buchmeiser, Michael R

    2015-01-01

    The acyclic diene metathesis (ADMET) polymerization of 6-hydroxy-1,10-undecadiene (M1) and 6-acetoxy-1,10-undecadiene (M2) by the action of two different catalysts, i.e., the second-generation Grubbs-Hoveyda system ([RuCl2(IMesH2)(CH-2-(2-PrO-C6H4)]) (1) and the dicationic ruthenium alkylidene [Ru(DMF)3(IMesH2)(CH-2-(2-PrO-C6H4)] (2, IMesH2 = 1,3-dimesitylimidazolin-2-ylidene) is reported. Biphasic conditions using 1-butyl-2,3-dimethylimidazolium tetrafluoroborate ([BDMIM(+)BF4(-)]) and 1,2,4-trichlorobenzene (TCB) are applied. Under the chosen conditions (T = 75 °C, 20 mbar), the use of catalyst 1 results only in the formation of low-molecular-weight polymers (Mn ≤ 10,000 g mol(-1)), while catalyst 2 allows for the high yield synthesis of high-molecular-weight polymers (Mn ≤ 40,000 g mol(-1), yields ≤ 99%). Irrespective of the catalyst used, all polymers display a high trans-content (>95%). Notably, Ru-contamination of the target polymers without any additional purification is as low as 1.2 ppm with catalyst 2. Together with the high yields and high molecular weights, the low Ru-contaminations clearly illustrate the advantages of the biphasic setup.

  4. Synthesis of interlocked molecules by olefin metathesis

    NASA Astrophysics Data System (ADS)

    Clark, Paul Gregory

    A large body of work in the Grubbs group has focused on the development of functional-group tolerant ruthenium alkylidene catalysts that perform a number of olefin metathesis reactions. These catalysts have seen application in a wide range of fields, including classic total synthesis as well as polymer and materials chemistry. One particular family of compounds, interlocked molecules, has benefitted greatly from these advances in catalyst stability and activity. This thesis describes several elusive and challenging interlocked architectures whose syntheses have been realized through the utilization of different types of ruthenium-catalyzed olefin metathesis reactions. Ring-closing olefin metathesis has enabled the synthesis of a [c2]daisy-chain dimer with the ammonium binding site near the cap of the dimer. A deprotonated DCD possessing such a structural attribute will more forcefully seek to restore coordinating interactions upon reprotonation, enhancing its utility as a synthetic molecular actuator. Dimer functionalization facilitated incorporation into linear polymers, with a 48% size increase of an unbound, extended analogue of the polymer demonstrating slippage of the dimer units. Ongoing work is directed at further materials studies, in particular, exploring the synthesis of macroscopic networks containing the DCD units and analyzing the correlation between molecular-scale extension-contraction manipulations and resulting macro-scale changes. A "clipping" approach to a polycatenated cyclic polymer, a structure that resembles a molecular "charm bracelet", has been described. The use of ring-opening metathesis polymerization of a carbamate monomer in the presence of a chain transfer agent allowed for the synthesis of a linear polymer that was subsequently functionalized and cyclized to the corresponding cyclic analogue. This cyclic polymer was characterized through a variety of techniques, and subjected to further functionalization reactions, affording a cyclic

  5. In Situ Formation of Pyridyl-Functionalized Poly(3-hexylthiophene)s via Quenching of the Grignard Metathesis Polymerization: Toward Ligands for Semiconductor Quantum Dots

    SciTech Connect

    Kochemba, William Michael; Pickel, Deanna L; Sumpter, Bobby G; Chen, Jihua; Kilbey, II, S Michael

    2012-01-01

    The synthesis of well-defined, end-functional poly(3-hexylthiophene)s (P3HTs) by in situ quenching of the Grignard metathesis (GRIM) polymerization is complicated by the extreme tendency to favor difunctional products in all but a few cases. A facile one-pot method for preparing 2-pyridyl and 3-pyridyl P3HTs with high abundance of monofunctional products is established via an examination of the kinetics of the end-functionalization quenching reaction with lithium chloride complexes of 2- and 3-pyridyl Grignard reagents. Density functional theory calculations guide the selection of pyridine as the end group, which provides the capacity to ligate cadmium selenide (CdSe) nanocrystals and arrests aggregation upon thermal annealing when dispersed in a P3HT matrix. The relative abundances of various end-functional products, as ascertained by high-resolution matrix assisted laser desorption ionization time-of-flight mass spectrometry, can be altered through the use of 1-pentene as an additive: GRIM polymerizations quenched with 3-pyridyl and 2-pyridyl Grignard reagents show 5% and 18% abundances of difunctional, pyridyl-capped P3HTs, respectively, when 1-pentene is present at 1000:1 relative to the nickel catalyst. This represents a significant improvement compared to quenching with aryl Grignard reagents, where difunctional products predominate. The ability to manipulate end group compositions coupled with the propensity of pyridyl-functionalized P3HTs to ligate semiconductor quantum dots (SQDs) opens new possibilities for tuning the morphology of conjugated polymer/SQD blends.

  6. All-polymer photovoltaic devices of poly(3-(4-n-octyl)-phenylthiophene) from Grignard Metathesis (GRIM) polymerization.

    PubMed

    Holcombe, Thomas W; Woo, Claire H; Kavulak, David F J; Thompson, Barry C; Fréchet, Jean M J

    2009-10-14

    The synthesis of poly[3-(4-n-octyl)-phenylthiophene] (POPT) from Grignard Metathesis (GRIM) is reported. GRIM POPT is found to have favorable electronic, optical, and processing properties for organic photovoltaics (OPVs). Space-charge limited current and field effect transistor measurements for POPT yielded hole mobilities of 1 x 10(-4) cm(2)/(V s) and 0.05 cm(2)/(V s), respectively. Spincasting GRIM POPT from chlorobenzene yields a thin film with a 1.8 eV band gap, and PC(61)BM:POPT bulk heterojection devices provide a peak performance of 3.1%. Additionally, an efficiency of 2.0% is achieved in an all-polymer, bilayer OPV using poly[2-methoxy-5-(2'-ethylhexyloxy)-1,4-(1-cyanovinylene)phenylene] (CNPPV) as an acceptor. This state-of-the-art all-polymer device is analyzed in comparison to the analogous poly(3-hexylthiophene) (P3HT)/CNPPV device. Counter to expectations based on more favorable energy level alignment, greater active layer light absorption, and similar hole mobility, P3HT/CNPPV devices perform less well than POPT/CNPPV devices with a peak efficiency of 0.93%.

  7. Chain Reaction Polymerization.

    ERIC Educational Resources Information Center

    McGrath, James E.

    1981-01-01

    The salient features and importance of chain-reaction polymerization are discussed, including such topics as the thermodynamics of polymerization, free-radical polymerization kinetics, radical polymerization processes, copolymers, and free-radical chain, anionic, cationic, coordination, and ring-opening polymerizations. (JN)

  8. Chain Reaction Polymerization.

    ERIC Educational Resources Information Center

    McGrath, James E.

    1981-01-01

    The salient features and importance of chain-reaction polymerization are discussed, including such topics as the thermodynamics of polymerization, free-radical polymerization kinetics, radical polymerization processes, copolymers, and free-radical chain, anionic, cationic, coordination, and ring-opening polymerizations. (JN)

  9. Polymerization of monomer-based ferrofluids.

    PubMed

    Bian, Pei; McCarthy, Thomas J

    2010-05-04

    Ferrofluids based on oleate-stabilized nanoparticulate magnetite in cyclic olefin carrier solvents were prepared. Puddles of fluids containing 20-70 wt % magnetite in 1,5-cyclooctadiene or dicyclopentadiene can be moved or positioned on surfaces or in vessels with moderate magnetic fields (inexpensive NdFeB magnets). The surfaces of puddles with concentrations >40 wt % distort in response to magnetic fields applied perpendicular to the puddle surface and exhibit pointed liquid asperities. The liquid surface topography (asperity height and number per unit area) can be controlled by the strength of the applied field. The cyclic olefin carriers can be polymerized by ring-opening metathesis, solidifying the ferrofluid samples in the shape of the magnetically distorted monomeric solvent suspensions.

  10. Towards a universal polymer backbone: design and synthesis of polymeric scaffolds containing terminal hydrogen-bonding recognition motifs at each repeating unit.

    PubMed

    Stubbs, Ludger P; Weck, Marcus

    2003-02-17

    Polymers containing terminal hydrogen-bonding recognition motifs based on diaminotriazine and diaminopyridine groups in their side chains for the self-assembly of appropriate receptors have been prepared by ring-opening metathesis polymerization (ROMP) of norbornenes. A new synthetic method for the preparation of norbornene monomers based on pure alkyl spacers is introduced. These monomers show unprecedented high reactivity using ROMP. To suppress self-association of diaminotriazine-based polymers, polymerizations were run in presence of N-butylthymine. The butylthymine acts as a protecting group via self-assembly onto the hydrogen-bonding sites of the polymeric scaffold, thereby solubilizing the polymer. Diaminopyridine monomers do not require the presence of a protecting group due to their low propensity to dimerize. In addition, they exhibit a high affinity for hydrogen-bonded receptors on both monomeric and polymeric level. These polymers present our first building blocks towards the design and synthesis of a "universal polymer scaffold".

  11. Adsorption and ring-opening of lactide on the chiral metal surface Pt(321){sup S} studied by density functional theory

    SciTech Connect

    Franke, J.-H.; Kosov, D. S.

    2015-01-28

    We study the adsorption and ring-opening of lactide on the naturally chiral metal surface Pt(321){sup S}. Lactide is a precursor for polylactic acid ring-opening polymerization, and Pt is a well known catalyst surface. We study, here, the energetics of the ring-opening of lactide on a surface that has a high density of kink atoms. These sites are expected to be present on a realistic Pt surface and show enhanced catalytic activity. The use of a naturally chiral surface also enables us to study potential chiral selectivity effects of the reaction at the same time. Using density functional theory with a functional that includes the van der Waals forces in a first-principles manner, we find modest adsorption energies of around 1.4 eV for the pristine molecule and different ring-opened states. The energy barrier to be overcome in the ring-opening reaction is found to be very small at 0.32 eV and 0.30 eV for LL- and its chiral partner DD-lactide, respectively. These energies are much smaller than the activation energy for a dehydrogenation reaction of 0.78 eV. Our results thus indicate that (a) ring-opening reactions of lactide on Pt(321) can be expected already at very low temperatures, and Pt might be a very effective catalyst for this reaction; (b) the ring-opening reaction rate shows noticeable enantioselectivity.

  12. Olefin metathesis for effective polymer healing via dynamic exchange of strong carbon-carbon bonds

    DOEpatents

    Guan, Zhibin; Lu, Yixuan

    2015-09-15

    A method of preparing a malleable and/or self-healing polymeric or composite material is provided. The method includes providing a polymeric or composite material comprising at least one alkene-containing polymer, combining the polymer with at least one homogeneous or heterogeneous transition metal olefin metathesis catalyst to form a polymeric or composite material, and performing an olefin metathesis reaction on the polymer so as to form reversible carbon-carbon double bonds in the polymer. Also provided is a method of healing a fractured surface of a polymeric material. The method includes bringing a fractured surface of a first polymeric material into contact with a second polymeric material, and performing an olefin metathesis reaction in the presence of a transition metal olefin metathesis catalyst such that the first polymeric material forms reversible carbon-carbon double bonds with the second polymeric material. Compositions comprising malleable and/or self-healing polymeric or composite material are also provided.

  13. Single Turnover at Molecular Polymerization Catalysts Reveals Spatiotemporally Resolved Reactions.

    PubMed

    Easter, Quinn T; Blum, Suzanne A

    2017-09-11

    Multiple active individual molecular ruthenium catalysts have been pinpointed within growing polynorbornene, thereby revealing information on the reaction dynamics and location that is unavailable through traditional ensemble experiments. This is the first single-turnover imaging of a molecular catalyst by fluorescence microscopy and allows detection of individual monomer reactions at an industrially important molecular ruthenium ring-opening metathesis polymerization (ROMP) catalyst under synthetically relevant conditions (e.g. unmodified industrial catalyst, ambient pressure, condensed phase, ca. 0.03 m monomer). These results further establish the key fundamentals of this imaging technique for characterizing the reactivity and location of active molecular catalysts even when they are the minor components. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. Reactivity ratios, and mechanistic insight for anionic ring-opening copolymerization of epoxides

    PubMed Central

    Lee, Bongjae F.; Wolffs, Martin; Delaney, Kris T.; Sprafke, Johannes K.; Leibfarth, Frank A.; Hawker, Craig J.; Lynd, Nathaniel A.

    2012-01-01

    Reactivity ratios were evaluated for anionic ring-opening copolymerizations of ethylene oxide (EO) with either allyl glycidyl ether (AGE) or ethylene glycol vinyl glycidyl ether (EGVGE) using a benzyl alkoxide initiator. The chemical shift for the benzylic protons of the initiator, as measured by 1H NMR spectroscopy, were observed to be sensitive to the sequence of the first two monomers added to the initiator during polymer growth. Using a simple kinetic model for initiation and the first propagation step, reactivity ratios for the copolymerization of AGE and EGVGE with EO could be determined by analysis of the 1H NMR spectroscopy for the resulting copolymer. For the copolymerization between EO and AGE, the reactivity ratios were determined to be rAGE = 1.31 ± 0.26 and rEO = 0.54 ± 0.03, while for EO and EGVGE, the reactivity ratios were rEGVGE = 3.50 ± 0.90 and rEO = 0.32 ± 0.10. These ratios were consistent with the compositional drift observed in the copolymerization between EO and EGVGE, with EGVGE being consumed early in the copolymerization. These experimental results, combined with density functional calculations, allowed a mechanism for oxyanionic ring-opening polymerization that begins with coordination of the Lewis-basic epoxide to the cation to be proposed. The calculated transition-state energies agree qualitatively with the observed relative rates for polymerization. PMID:23226879

  15. Homobimetallic Ruthenium-N-Heterocyclic Carbene Complexes For Olefin Metathesis

    NASA Astrophysics Data System (ADS)

    Sauvage, Xavier; Demonceau, Albert; Delaude, Lionel

    In this chapter, the synthesis and catalytic activity towards olefin metathesis of homobimetallic ruthenium (Ru)-alkylidene, -cyclodiene or -arene complexes bearing phosphine or N-heterocyclic carbene (NHC) ligands are reviewed. Emphasis is placed on the last category of bimetallic compounds. Three representatives of this new type of molecular scaffold were investigated. Thus, [(p-cymene)Ru(m-Cl)3RuCl (h2-C2H4)(L)] complexes with L = PCy3 (15a), IMes (16a), or IMesCl2 (16b) were prepared. They served as catalyst precursors for cross-metathesis (CM) of various styrene derivatives. These experiments revealed the outstanding aptitude of complex 16a (and to a lesser extent of 16b) to catalyze olefin metathesis reactions. Contrary to monometallic Ru-arene complexes of the [RuCl2(p-cymene)(L)] type, the new homobimetallic species did not require the addition of a diazo compound nor visible light illumination to initiate the ring-opening metathesis of norbornene or cyclooctene. When diethyl 2,2-diallylmalonate and N,N-diallyltosylamide were exposed to 16a,b, a mixture of cycloisomerization and ring-closing metathesis (RCM) products was obtained in a nonselective way. Addition of phenylacetylene enhanced the metathetical activity while completely repressing the cycloisomerization process.

  16. Ring-Opening 1,3-Halochalcogenation of Cyclopropane Dicarboxylates

    PubMed Central

    2016-01-01

    Donor–acceptor cyclopropanes with two geminal carboxylic esters are reacted with chalcogenyl chlorides and bromides to afford ring-opened products bearing the halogen atoms in the 1-position, adjacent to the donor, and the chalcogenyl residue in the 3-position next to the two acceptor groups. A variety of different donors (e.g., aryl, N, and O) are used. The stereospecificity of the reaction is demonstrated by using a chiral starting material. PMID:27966993

  17. Ruthenium—Arene Complexes Derived from NHC•CO2 and NHC•CS2 Zwitterionic Adducts and Their Use in Olefin Metathesis

    NASA Astrophysics Data System (ADS)

    Delaude, Lionel; Demonceau, Albert

    A range of imidazol(in)ium-2-carboxylates and -dithiocarboxylates bearing alkyl or aryl groups on their nitrogen atoms were prepared by reacting the corresponding N-heterocyclic carbenes (NHCs) with either carbon dioxide or carbon disulfide. All the zwitterionic products were characterized by various analytical techniques, including thermogravimetric analysis (TGA). Their ability to act as NHC ligand precursors for in situ catalytic applications was investigated in the ruthenium-promoted ring-opening metathesis polymerization (ROMP) of cyclo-octene. Upon exposure to the [RuCl2(p-cymene)]2 dimer, the NHC CO2 adducts readily dissociated to generate [RuCl2(p-cymene)(NHC)] complexes that were highly active catalyst precursors for olefin metathesis. Conversely, the NHC CS2 betaines retained their zwitterionic nature and led to new cationic complexes of the [RuCl(p-cymene)(NHC CS2)]+PF6 - type that were devoid of any significant catalytic activity in the reaction under consideration

  18. Nitroxide-mediated radical ring-opening copolymerization: chain-end investigation and block copolymer synthesis.

    PubMed

    Delplace, Vianney; Harrisson, Simon; Tardy, Antoine; Gigmes, Didier; Guillaneuf, Yohann; Nicolas, Julien

    2014-02-01

    Well-defined, degradable copolymers are successfully prepared by nitroxide-mediated radical ring opening polymerization (NMrROP) of oligo(ethylene glycol) methyl ether methacrylate (OEGMA) or methyl methacrylate (MMA), a small amount of acrylonitrile (AN) and cyclic ketene acetals (CKAs) of different structures. Phosphorous nuclear magnetic resonance allows in-depth chain-end characterization and gives crucial insights into the nature of the copoly-mer terminal sequences and the living chain fractions. By using a small library of P(OEGMA-co-AN-co-CKA) and P(MMA-co-AN-co-CKA) as macroinitiators, chain extensions with styrene are performed to furnish (amphiphilic) block copolymers comprising a degradable segment.

  19. Intramolecular donor-acceptor cyclopropane ring-opening cyclizations.

    PubMed

    Cavitt, Marchello A; Phun, Lien H; France, Stefan

    2014-02-07

    Cyclization reactions of donor-acceptor (D-A) cyclopropanes are recognized as versatile methods for construction of carbocyclic and heterocyclic scaffolds. In the literature, many examples of these polarized cyclopropanes' reactivity with nucleophiles, electrophiles, and radicals are prevalent. Although intermolecular reactivity of donor-acceptor cyclopropanes is widely reported, reviews that center on their intramolecular chemistry are rare. Thereupon, this tutorial review focalizes on new intramolecular transformations of donor-acceptor cyclopropanes for cycloisomerizations, formal cycloadditions, umpolung reactions, rearrangements and ring-opening lactonizations/lactamizations from 2009 to 2013. Furthermore, the role of D-A acceptor cyclopropanes as reactive subunits in natural product synthesis is underscored.

  20. Catalysts for CO2/epoxide ring-opening copolymerization

    PubMed Central

    Trott, G.; Saini, P. K.; Williams, C. K.

    2016-01-01

    This article summarizes and reviews recent progress in the development of catalysts for the ring-opening copolymerization of carbon dioxide and epoxides. The copolymerization is an interesting method to add value to carbon dioxide, including from waste sources, and to reduce pollution associated with commodity polymer manufacture. The selection of the catalyst is of critical importance to control the composition, properties and applications of the resultant polymers. This review highlights and exemplifies some key recent findings and hypotheses, in particular using examples drawn from our own research. PMID:26755758

  1. Asymmetric catalysis of epoxide ring-opening reactions.

    PubMed

    Jacobsen, E N

    2000-06-01

    The discovery of the metal salen-catalyzed asymmetric ring-opening (ARO) of epoxides is chronicled. A screening approach was adopted for the identification of catalysts for the addition of TMSN(3) to meso-epoxides, and the chiral (salen)CrN(3) complex was identified as optimal. Kinetic and structural studies served to elucidate the mechanism of catalysis, which involves cooperative activation of both epoxide and azide by two different metal centers. Covalently linked bimetallic complexes were constructed on the basis of this insight, and shown to catalyze the ARO with identical enantioselectivity but 1-2 orders of magnitude greater reactivity than the monomeric analogues. Extraordinarily high selectivity is observed in the kinetic resolution of terminal epoxides using the (salen)CrN(3)/TMSN(3) system. A search for a practical method for the kinetic resolution reaction led to the discovery of highly enantiomer-selective hydrolytic ring-opening using the corresponding (salen)Co(III) catalyst. This system displays extraordinary substrate generality, and allows practical access to enantiopure terminal epoxides on both laboratory and industrial scales.

  2. Hexacoordinate Ru-based olefin metathesis catalysts with pH-responsive N-heterocyclic carbene (NHC) and N-donor ligands for ROMP reactions in non-aqueous, aqueous and emulsion conditions

    PubMed Central

    Balof, Shawna L; Nix, K Owen; Olliff, Matthew S; Roessler, Sarah E; Saha, Arpita; Müller, Kevin B; Behrens, Ulrich; Valente, Edward J

    2015-01-01

    Summary Three new ruthenium alkylidene complexes (PCy3)Cl2(H2ITap)Ru=CHSPh (9), (DMAP)2Cl2(H2ITap)Ru=CHPh (11) and (DMAP)2Cl2(H2ITap)Ru=CHSPh (12) have been synthesized bearing the pH-responsive H2ITap ligand (H2ITap = 1,3-bis(2’,6’-dimethyl-4’-dimethylaminophenyl)-4,5-dihydroimidazol-2-ylidene). Catalysts 11 and 12 are additionally ligated by two pH-responsive DMAP ligands. The crystal structure was solved for complex 12 by X-ray diffraction. In organic, neutral solution, the catalysts are capable of performing standard ring-opening metathesis polymerization (ROMP) and ring closing metathesis (RCM) reactions with standard substrates. The ROMP with complex 11 is accelerated in the presence of two equiv of H3PO4, but is reduced as soon as the acid amount increased. The metathesis of phenylthiomethylidene catalysts 9 and 12 is sluggish at room temperature, but their ROMP can be dramatically accelerated at 60 °C. Complexes 11 and 12 are soluble in aqueous acid. They display the ability to perform RCM of diallylmalonic acid (DAMA), however, their conversions are very low amounting only to few turnovers before decomposition. However, both catalysts exhibit outstanding performance in the ROMP of dicyclopentadiene (DCPD) and mixtures of DCPD with cyclooctene (COE) in acidic aqueous microemulsion. With loadings as low as 180 ppm, the catalysts afforded mostly quantitative conversions of these monomers while maintaining the size and shape of the droplets throughout the polymerization process. Furthermore, the coagulate content for all experiments stayed <2%. This represents an unprecedented efficiency in emulsion ROMP based on hydrophilic ruthenium alkylidene complexes. PMID:26664616

  3. Linker-free, silica-bound olefin-metathesis catalysts: applications in heterogeneous catalysis.

    PubMed

    Cabrera, José; Padilla, Robin; Bru, Miriam; Lindner, Ronald; Kageyama, Takeharu; Wilckens, Kristina; Balof, Shawna L; Schanz, Hans-Jörg; Dehn, Richard; Teles, J Henrique; Deuerlein, Stephan; Müller, Kevin; Rominger, Frank; Limbach, Michael

    2012-11-12

    A set of heterogenized olefin-metathesis catalysts, which consisted of Ru complexes with the H(2)ITap ligand (1,3-bis(2',6'-dimethyl-4'dimethyl aminophenyl)-4,5-dihydroimidazol-2-ylidene) that had been adsorbed onto a silica support, has been prepared. These complexes showed strong binding to the solid support without the need for tethering groups on the complex or functionalized silica. The catalysts were tested in the ring-opening-ring-closing-metathesis (RO-RCM) of cyclooctene (COE) and the self-metathesis of methyl oleate under continuous-flow conditions. The best complexes showed a TON>4000, which surpasses the previously reported materials that were either based on the Grubbs-Hoveyda II complex on silica or on the classical heterogeneous Re(2)O(7)/B(2)O(3) catalyst.

  4. Ring-Opening Metathesis Polymerization of (+) and (+ or -)-endo,exo-5,6- Dimethylbicyclo(2.2.1)hept-2-ene by Mo(CH-t-Bu)(N-2,6-C6H3-i-Pr2)(OR)2

    DTIC Science & Technology

    1993-10-20

    and passed through activated alumina prior to use. (-)-Dimenthyl fumarate was prepared by treating fumaric acid and -(-)- menthol (2 equiv) with a...concentrated to a solid, treated with water (650 mL) and extracted with ether (3 x 280 mL) to remove menthol . The aqueous layer was acidified to pH = 1

  5. Reactive ring-opened aldehyde metabolites in benzene hematotoxicity.

    PubMed Central

    Witz, G; Zhang, Z; Goldstein, B D

    1996-01-01

    The hematotoxicity of benzene is mediated by reactive benzene metabolites and possibly by other intermediates including reactive oxygen species. We previously hypothesized that ring-opened metabolites may significantly contribute to benzene hematotoxicity. Consistent with this hypothesis, our studies initially demonstrated that benzene is metabolized in vitro to trans-trans-muconaldehyde (MUC), a reactive six-carbon diene dialdehyde, and that MUC is toxic to the bone marrow in a manner similar to benzene. Benzene toxicity most likely involves interactions among several metabolites that operate by different mechanisms to produce more than one biological effect. Our studies indicate that MUC coadministered with hydroquinone is a particularly potent metabolite combination that causes bone marrow damage, suggesting that the involvement of ring-opened metabolites in benzene toxicity may be related to their biological effects in combination with other benzene metabolites. Studies in our laboratory and by others indicate that MUC is metabolized to a variety of compounds by oxidation or reduction of the aldehyde groups. The aldehydic MUC metabolite 6-hydroxy-trans-trans-2,4-hexadienal (CHO-M-OH), similar to MUC but to a lesser extent, is reactive toward glutathione, mutagenic in V79 cells, and hematotoxic in mice. It is formed by monoreduction of MUC, a process that is reversible and could be of biological significance in benzene bone marrow toxicity. The MUC metabolite 6-hydroxy-trans-trans-2,4-hexadienoic (COOH-M-OH) is an end product of MUC metabolism in vitro. Our studies indicate that COOH-M-OH is a urinary metabolite of benzene in mice, a finding that provides further indirect evidence for the in vivo formation of MUC from benzene. Mechanistic studies showed the formation of cis-trans-muconaldehyde in addition to MUC from benzene incubated in a hydroxyl radical-generating Fenton system. These results suggest that the benzene ring is initially opened to cis

  6. Olefin metathesis in air

    PubMed Central

    Piola, Lorenzo; Nahra, Fady

    2015-01-01

    Summary Since the discovery and now widespread use of olefin metathesis, the evolution of metathesis catalysts towards air stability has become an area of significant interest. In this fascinating area of study, beginning with early systems making use of high oxidation state early transition metal centers that required strict exclusion of water and air, advances have been made to render catalysts more stable and yet more functional group tolerant. This review summarizes the major developments concerning catalytic systems directed towards water and air tolerance. PMID:26664625

  7. Organo-Lewis acid as cocatalyst for cationic homogenous metallocene Ziegler-Natta olefin polymerizations

    DOEpatents

    Marks, Tobin J.; Chen, You-Xian

    2000-01-01

    The synthesis of the organo-Lewis acid perfluorobiphenylborane (PBB) and the activation of metallocenes for the formation of a variety of highly active homogeneous Ziegler-Natta metallocene olefin polymerization, copolymerization and ring-opening polymerization catalysts is described.

  8. Iridium-Catalyzed Asymmetric Ring-Opening of Oxabenzonorbornadienes with N-Substituted Piperazine Nucleophiles.

    PubMed

    Yang, Wen; Luo, Renshi; Yang, Dingqiao

    2015-11-27

    Iridium-catalyzed asymmetric ring-opening of oxabenzonorbornadienes with N-substituted piperazines was described. The reaction afforded the corresponding ring-opening products in high yields and moderate enantioselectivities in the presence of 2.5 mol % [Ir(COD)Cl]₂ and 5.0 mol % (S)-p-Tol-BINAP. The effects of various chiral bidentate ligands, catalyst loading, solvent, and temperature on the yield and enantioselectivity were also investigated. A plausible mechanism was proposed to account for the formation of the corresponding trans-ring opened products based on the X-ray structure of product 2i.

  9. Self-healing of polymeric materials: The effect of the amount of DCPD confined within microcapsules

    NASA Astrophysics Data System (ADS)

    Chipara, Dorina M.; Perez, Alma; Lozano, Karen; Elamin, Ibrahim; Villarreal, Jahaziel; Salinas, Alfonso; Chipara, Mircea

    2013-03-01

    The self-healing SH) of polymers is based on the dispersion of a catalyst and of microcapsules filled with monomer within the polymeric matrix. Sufficiently large external stresses will rupture the microcapsule, releasing the monomer which will diffuse through the polymer and eventually will reach a catalyst particle igniting a polymerization reaction. The classical SH system includes first generation Grubbs catalyst and poly-urea formaldehyde microcapsules filled with DCPD. The polymerization reaction is a ring-opening metathesis. The size and the mechanical features of microcapsules are critical in controlling the SH process. Research was focused on the effect of DCPD on the size and thickness of microcapsules. Microscopy was used to determine the size of microcapsules (typically in the range of 10-4 m) and the thickness of the microcapsules (ranging between 10-6 to 10-8 m). Research revealed a thick disordered layer over a thin and more compact wall. Raman spectroscopy confirmed the confinement of DCPD, TGA measurements aimed to a better understanding of the degradation processes in inert atmosphere, and mechanical tests supported the ignition of self-healing properties. This research has been supported by National Science Foundation under DMR (PREM) grant 0934157.

  10. Therapeutic Delivery of H2S via COS: Small Molecule and Polymeric Donors with Benign Byproducts.

    PubMed

    Powell, Chadwick R; Foster, Jeffrey C; Okyere, Benjamin; Theus, Michelle H; Matson, John B

    2016-10-07

    Carbonyl sulfide (COS) is a gas that may play important roles in mammalian and bacterial biology, but its study is limited by a lack of suitable donor molecules. We report here the use of N-thiocarboxyanhydrides (NTAs) as COS donors that release the gas in a sustained manner under biologically relevant conditions with innocuous peptide byproducts. Carbonic anhydrase converts COS into H2S, allowing NTAs to serve as either COS or H2S donors, depending on the availability of the enzyme. Analysis of the pseudo-first-order H2S release rate under biologically relevant conditions revealed a release half-life of 75 min for the small molecule NTA under investigation. A polynorbornene bearing pendant NTAs made by ring-opening metathesis polymerization was also synthesized to generate a polymeric COS/H2S donor. A half-life of 280 min was measured for the polymeric donor. Endothelial cell proliferation studies revealed an enhanced rate of proliferation for cells treated with the NTA over untreated controls.

  11. Copper(II) tetrafluoroborate catalyzed ring-opening reaction of epoxides with alcohols at room temperature.

    PubMed

    Barluenga, José; Vázquez-Villa, Henar; Ballesteros, Alfredo; González, José M

    2002-08-22

    [reaction: see text] Efficient ring opening of different epoxides by reaction with representative alcohols is presented. These processes were carried out at room temperature and rely on the usefulness of commercial copper tetrafluoroborate as catalyst.

  12. A domino ring-opening/epoxidation of 1,2-dioxines.

    PubMed

    Greatrex, Ben W; Taylor, Dennis K; Tiekink, Edward R T

    2004-04-02

    When allowed to react with alkaline hydrogen peroxide, monocyclic 1,2-dioxines ring-open to their isomeric gamma-hydroxyenone intermediates which are rapidly epoxidized to afford trans-4-hydroxy-2,3-epoxyketones in 21-81% yield. In the case of meso-1,2-dioxines, Co(II) complex catalyzed asymmetric ring-opening of the 1,2-dioxine may be employed to furnish enantioenriched epoxides

  13. Unexpected ring-opening reactions of aziridines with aldehydes catalyzed by nucleophilic carbenes under aerobic conditions.

    PubMed

    Liu, Yan-Kai; Li, Rui; Yue, Lei; Li, Bang-Jing; Chen, Ying-Chun; Wu, Yong; Ding, Li-Sheng

    2006-04-13

    [reaction: see text] The chemoselective ring opening of N-tosyl aziridines with aldehydes catalyzed by an N-heterocyclic carbene was investigated under aerobic conditions. Unexpected carboxylates of 1,2-amino alcohols from the corresponding aldehydes, rather than the acyl anion ring-opened beta-amino ketones, were exclusively obtained. A plausible mechanism for this unprecedented carbene-mediated reaction was also proposed.

  14. Solventless sol-gel chemistry through ring-opening polymerization of bridged disilaoxacyclopentanes

    SciTech Connect

    RAHIMIAN,KAMYAR; LOY,DOUGLAS A.

    2000-04-04

    Disilaoxacyclopentanes have proven to be excellent precursors to sol-gel type materials. These materials have shown promise as precursors for encapsulation and microelectronics applications. The polymers are highly crosslinked and are structurally similar to traditional sol-gels, but unlike typical sol-gels they are prepared without the use of solvents and water, they have low VOC's and show little shrinkage during processing.

  15. Prosodically Driven Metathesis in Mutsun

    ERIC Educational Resources Information Center

    Butler, Lynnika

    2013-01-01

    Among the many ways in which sounds alternate in the world's languages, changes in the order of sounds (metathesis) are relatively rare. Mutsun, a Southern Costanoan language of California which was documented extensively before the death of its last speaker in 1930, displays three patterns of synchronic consonant-vowel (CV) metathesis. Two of…

  16. Prosodically Driven Metathesis in Mutsun

    ERIC Educational Resources Information Center

    Butler, Lynnika

    2013-01-01

    Among the many ways in which sounds alternate in the world's languages, changes in the order of sounds (metathesis) are relatively rare. Mutsun, a Southern Costanoan language of California which was documented extensively before the death of its last speaker in 1930, displays three patterns of synchronic consonant-vowel (CV) metathesis. Two of…

  17. Polymeric ADAM protein mimics interrogate mammalian sperm-egg binding.

    PubMed

    Lee, Younjoo; Sampson, Nicole S

    2009-03-23

    The sperm proteins ADAM2 and ADAM3, members of the ADAM family of proteins, have been implicated in mammalian sperm-egg binding. However, elucidating their roles is complex because of the interdependence of ADAM protein expression in the testis. Hence, multivalent probes containing the three-amino acid binding sequence of ADAM2, glutamate-cysteine-aspartate (ECD), and ADAM3, glutamine-cysteine-aspartate (QCD), were designed, synthesized, and tested to investigate gamete interactions. In this work, ECD polymer mimics were synthesized by ring-opening metathesis polymerization with a faster initiating ruthenium catalyst than previously used. Polymers containing 100 copies of the ECD peptide mimic were found to be the best inhibitors of fertilization. The multivalent QCD polymers were also tested as inhibitors of fertilization. The structure-activity profile was the same as ECD polymers, but the overall potency was lower. Both ECD and QCD polymers require the presence of beta(1) integrin to inhibit fertilization. Next, triblock ABA and ABC copolymers containing both ECD and QCD ligands were synthesized with 96 monomer spacers as their B blocks. Although these polymers had lower densities of ECD and QCD peptides, their potencies correlated with the potencies of their corresponding homopolymers. In addition, no synergy between ECD and QCD mimics was observed. All the data suggest that QCD and ECD bind to the same complex of proteins that includes beta(1) integrin.

  18. Reaction Path Bifurcation in an Electrocyclic Reaction: Ring-Opening of the Cyclopropyl Radical.

    PubMed

    Kramer, Zeb C; Carpenter, Barry K; Ezra, Gregory S; Wiggins, Stephen

    2015-06-25

    Following previous work [J. Chem. Phys. 2013, 139, 154108] on a simple model of a reaction with a post-transition state valley ridge inflection point, we study the chemically important example of the electrocyclic cyclopropyl radical ring-opening reaction using direct dynamics and a reduced dimensional potential energy surface. The overall reaction requires con- or disrotation of the methylenes, but the initial stage of the ring-opening involves substantial internal rotation of only one methylene. The reaction path bifurcation is then associated with the relative sense of rotation of the second methylene. Clear deviations of reactive trajectories from the disrotatory intrinsic reaction coordinate (IRC) for the ring-opening are observed and the dynamical mechanism is discussed. Several features observed in the model system are found to be preserved in the more complex and higher dimensional ring-opening reaction. Most notable is the sensitivity of the reaction mechanism to the shape of the potential manifested as a Newtonian kinetic isotope effect upon deuterium substitution of one of the methylene hydrogens. Dependence of the product yield on frictional dissipation representing external environmental effects is also presented. The dynamics of the post-transition state cyclopropyl radical ring-opening are discussed in detail, and the use of low dimensional models as tools to analyze complicated organic reaction mechanisms is assessed in the context of this reaction.

  19. Metathesis depolymerizable surfactants

    DOEpatents

    Jamison, Gregory M.; Wheeler, David R.; Loy, Douglas A.; Simmons, Blake A.; Long, Timothy M.; McElhanon, James R.; Rahimian, Kamyar; Staiger, Chad L.

    2008-04-15

    A class of surfactant molecules whose structure includes regularly spaced unsaturation in the tail group and thus, can be readily decomposed by ring-closing metathesis, and particularly by the action of a transition metal catalyst, to form small molecule products. These small molecules are designed to have increased volatility and/or enhanced solubility as compared to the original surfactant molecule and are thus easily removed by solvent extraction or vacuum extraction at low temperature. By producing easily removable decomposition products, the surfactant molecules become particularly desirable as template structures for preparing meso- and microstructural materials with tailored properties.

  20. Thorium-mediated ring-opening of tetrahydrofuran and the development of a new thorium starting material: preparation and chemistry of ThI4(DME)2.

    PubMed

    Travia, Nicholas E; Monreal, Marisa J; Scott, Brian L; Kiplinger, Jaqueline L

    2012-12-28

    The thorium(IV) tetraiodide complex ThI(4)(DME)(2) (3) (DME = 1,2-dimethoxyethane) has been prepared in high yield by reacting the corresponding chloride complex ThCl(4)(DME)(2) with an excess of trimethylsilyl iodide (Me(3)SiI) in toluene. This new route avoids the use of thorium metal as a reagent. ThI(4)(DME)(2) (3) exhibits excellent thermal stability compared to ThI(4)(THF)(4) (1), which undergoes rapid ring-opening of THF at ambient temperature to yield the iodobutoxide complex ThI(3)[O(CH(2))(4)I](THF)(3) (2). Subsequent ligand-exchange between 2 and DME affords ThI(3)[O(CH(2))(4)I](DME)(2) (11), which can be converted to 3 with Me(3)SiI. Salt metathesis between 2 and K(L(Me)) (L(Me) = (2,6-(i)Pr(2)C(6)H(3))NC(Me)CHC(Me)N(2,6-(i)Pr(2)C(6)H(3))) cleanly gives (L(Me))ThI(2)[O(CH(2))(4)I](THF) (10), which is a rare example of a thorium β-diketiminate complex. Complexes 2, 10, and 11 represent the first reported examples of THF ring-opening mediated by thorium. The synthetic utility of ThI(4)(DME)(2) (3) is demonstrated by preparation of thorium(IV) alkoxide, amide, and organometallic compounds.

  1. A broadly applicable and practical oligomeric (salen) Co catalyst for enantioselective epoxide ring-opening reactions

    PubMed Central

    White, David E.; Tadross, Pamela M.; Lu, Zhe

    2014-01-01

    The (salen) Co catalyst (4a) can be prepared as a mixture of cyclic oligomers in a short, chromatography-free synthesis from inexpensive, commercially available precursors. This catalyst displays remarkable enhancements in reactivity and enantioselectivity relative to monomeric and other multimeric (salen) Co catalysts in a wide variety of enantioselective epoxide ring-opening reactions. The application of catalyst 4a is illustrated in the kinetic resolution of terminal epoxides by nucleophilic ring-opening with water, phenols, and primary alcohols; the desymmetrization of meso epoxides by addition of water and carbamates; and the desymmetrization of oxetanes by intramolecular ring opening with alcohols and phenols. The favorable solubility properties of complex 4a under the catalytic conditions facilitated mechanistic studies, allowing elucidation of the basis for the beneficial effect of oligomerization. Finally, a catalyst selection guide is provided to delineate the specific advantages of oligomeric catalyst 4a relative to (salen) Co monomer 1 for each reaction class. PMID:25045188

  2. A broadly applicable and practical oligomeric (salen) Co catalyst for enantioselective epoxide ring-opening reactions.

    PubMed

    White, David E; Tadross, Pamela M; Lu, Zhe; Jacobsen, Eric N

    2014-07-08

    The (salen) Co catalyst (4a) can be prepared as a mixture of cyclic oligomers in a short, chromatography-free synthesis from inexpensive, commercially available precursors. This catalyst displays remarkable enhancements in reactivity and enantioselectivity relative to monomeric and other multimeric (salen) Co catalysts in a wide variety of enantioselective epoxide ring-opening reactions. The application of catalyst 4a is illustrated in the kinetic resolution of terminal epoxides by nucleophilic ring-opening with water, phenols, and primary alcohols; the desymmetrization of meso epoxides by addition of water and carbamates; and the desymmetrization of oxetanes by intramolecular ring opening with alcohols and phenols. The favorable solubility properties of complex 4a under the catalytic conditions facilitated mechanistic studies, allowing elucidation of the basis for the beneficial effect of oligomerization. Finally, a catalyst selection guide is provided to delineate the specific advantages of oligomeric catalyst 4a relative to (salen) Co monomer 1 for each reaction class.

  3. Ring-opening reaction of a trifluorinated indolylfulgide: mode-specific photochemistry after pre-excitation

    PubMed Central

    Draxler, Simone; Brust, Thomas; Malkmus, Stephan; DiGirolamo, Jessica A.; Lees, Watson J.; Zinth, Wolfgang; Braun, Markus

    2010-01-01

    Summary The ring-opening reaction of a trifluorinated indolylfulgide has been studied as a function of temperature and optical pre-excitation where it was found that reaction times decreased as temperature increased from 10.3 ps at 12 °C to 7.6 ps at 60 °C. Simultaneously, the quantum yields for the ring-opening reaction grew from 3.1% (12 °C) to 5.0% (60 °C). When the reaction was started from a nonequilibrium state generated by a directly preceding ring-closure process, the ring-opening reaction became faster and the quantum efficiency increased by more than a factor of three. Analysis of the experimental results points to mode-specific photochemistry in that the promoting, photochemically active modes of the photoreaction are efficiently excited by the directly preceding ring-closure reaction. PMID:19562131

  4. H12461. Fluorine as a Regiocontrol Element in the Ring Openings of Bicyclic Aziridiniums

    PubMed Central

    Lam, Yu-hong; Cossy, Janine; Prado, Domingo Gomez; Cochi, Anne

    2013-01-01

    The origin of the variation in the regioselectivity of the nucleophilic ring-opening of a series of bicyclic aziridinium ions derived from N-alkylprolinols was investigated by quantum chemical computations (M06-2X/6-31+G(d,p)—SMD). These aziridiniums differ only in the degree and the stereochemistry of fluoro substitution at C(4). With the azide ion as nucleophile, the ratio of the piperidine to the pyrrolidine product was computed. An electrostatic gauche effect influences the conformation of the adjoining five-membered ring in the fluorinated bicyclic aziridinium. This controls the regioselectivity of the aziridinium ring-opening. PMID:23471532

  5. Transient X-ray fragmentation: probing a prototypical photoinduced ring opening.

    PubMed

    Petrović, Vladimir S; Siano, Marco; White, James L; Berrah, Nora; Bostedt, Christoph; Bozek, John D; Broege, Douglas; Chalfin, Max; Coffee, Ryan N; Cryan, James; Fang, Li; Farrell, Joseph P; Frasinski, Leszek J; Glownia, James M; Gühr, Markus; Hoener, Matthias; Holland, David M P; Kim, Jaehee; Marangos, Jonathan P; Martinez, Todd; McFarland, Brian K; Minns, Russell S; Miyabe, Shungo; Schorb, Sebastian; Sension, Roseanne J; Spector, Limor S; Squibb, Richard; Tao, Hongli; Underwood, Jonathan G; Bucksbaum, Philip H

    2012-06-22

    We report the first study of UV-induced photoisomerization probed via core ionization by an x-ray laser. We investigated x-ray ionization and fragmentation of the cyclohexadiene-hexatriene system at 850 eV during the ring opening. We find that the ion-fragmentation patterns evolve over a picosecond, reflecting a change in the state of excitation and the molecular geometry: the average kinetic energy per ion fragment and H(+)-ion count increase as the ring opens and the molecule elongates. We discuss new opportunities for molecular photophysics created by optical pump x-ray probe experiments.

  6. Novel poly(ethylene oxide)-b-poly(propylene oxide) copolymer-glucose conjugate by the microwave-assisted ring opening of a sugar lactone.

    PubMed

    Glisoni, Romina J; Sosnik, Alejandro

    2014-11-01

    In this work, we investigated for the first time the conjugation of gluconolactone to a poly(ethylene oxide)-poly(propylene oxide) block copolymer by a microwave-assisted ring opening reaction. The glucosylated copolymer was obtained with high yield (90%). A conjugation extent of approximately 100% was achieved within 15 min. The modification reduced the critical micellar concentration and increased the size of the micelles. The agglutination of the modified polymeric micelles by a soluble lectin that binds glucose confirmed the recognizability of the modified nanocarrier. Finally, the solubilization of darunavir, an anti-HIV protease inhibitor, showed a sharp increase of the aqueous solubility from 91 microgram/mL to 14.2 and 18.9 mg/mL for 10% w/v pristine and glucosylated polymeric micelles, respectively. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. Sulfuric acid as a catalyst for ring-opening of biobased bis-epoxides

    USDA-ARS?s Scientific Manuscript database

    Vegetable oils can be relatively and easily transformed into bio-based epoxides. Because of this, the acid-catalyzed epoxide ring-opening has been explored for the preparation of bio-based lubricants and polymers. Detailed model studies are carried out only with mono-epoxide made from methyl oleate,...

  8. An Introductory Organic Chemistry Review Homework Exercise: Deriving Potential Mechanisms for Glucose Ring Opening in Mutarotation

    ERIC Educational Resources Information Center

    Murdock, Margaret; Holman, R. W.; Slade, Tyler; Clark, Shelley L. D.; Rodnick, Kenneth J.

    2014-01-01

    A unique homework assignment has been designed as a review exercise to be implemented near the end of the one-year undergraduate organic chemistry sequence. Within the framework of the exercise, students derive potential mechanisms for glucose ring opening in the aqueous mutarotation process. In this endeavor, 21 general review principles are…

  9. Synthesis of Nitrogen Heterocycles via Photochemical Ring Opening of Pyridazine N-Oxides.

    PubMed

    Portillo, Maribel; Maxwell, Michael A; Frederich, James H

    2016-10-07

    A photochemical method for the direct synthesis of 1H-pyrazoles from pyridazine N-oxides was developed. This chemistry features a regioselective approach to nonsymmetrically substituted pyridazine N-oxides. Herein, we highlight the first strategic use of photoinduced ring-opening reactions of 1,2-diazine N-oxides for the preparative synthesis of nitrogen heterocycles.

  10. Selective Ring Opening of 1-Methylnaphthalene Over NiW-Supported Catalyst Using Dealuminated Beta Zeolite.

    PubMed

    Kim, Eun-Sang; Lee, You-Jin; Kim, Jeong-Rang; Kim, Joo-Wan; Kim, Tae-Wan; Chae, Ho-Jeong; Kim, Chul-Ung; Lee, Chang-Ha; Jeong, Soon-Yong

    2016-02-01

    Nanoporous Beta zeolite was dealuminated by weak acid treatment for reducing the acidity. Bi-functional catalysts were prepared using commercial Beta zeolites and the dealuminated zeolites for acidic function, NiW for metallic function. 1-Methylnaphthalene was selected as a model compound for multi-ring aromatics in heavy oil, and its selective ring opening reaction has been investigated using the prepared bi-functional catalysts with different acidity in fixed bed reaction system. The dealuminated Beta zeolites, which crystal structure and nanoporosity were maintained, showed the higher SiO2/Al2O3 ratio and smaller acidity than their original zeolite. NiW-supported catalyst using the dealuminated Beta zeolite with SiO2/Al203 mole ratio of 55 showed the highest performance for the selective ring opening. The acidity of catalyst seemed to play an important role as active sites for the selective ring opening of 1-methylnaphthalene but there should be some optimum catalyst acidity for the reaction. The acidity of Beta zeolite could be controlled by the acid treatment and the catalyst with the optimum acidity for the selective ring opening could be prepared.

  11. Iridium-Catalyzed Anti-Stereoselective Asymmetric Ring-Opening Reactions of Azabenzonorbornadienes with Carboxylic Acids.

    PubMed

    Zhu, Meina; Chen, Jingchao; He, Xiaobo; Gu, Cuiping; Xu, Jianbin; Fan, Baomin

    2017-03-17

    The first anti-stereoselective asymmetric ring-opening reactions of azabenzonorbornadienes with carboxylic acids have been realized with an iridium catalyst assisted by (n)Bu4NBr. The reaction features broad substrate scope and good functional group tolerance and allows the synthesis of chiral dihydronaphthalene derivatives with high optical purities.

  12. Organocatalytic synthesis of beta-alkylaspartates via beta-lactone ring opening.

    PubMed

    Armstrong, Alan; Geldart, Stephen P; Jenner, Chloe R; Scutt, James N

    2007-10-12

    Cinchona alkaloid-catalyzed reaction of ethyl glyoxylate with substituted ketenes, formed in situ, gives disubstituted beta-lactones in moderate yield and high enantiomeric excess. Subsequent azide ring opening, reduction, and ester hydrolysis allows access to chiral beta-alkyl aspartates.

  13. An Introductory Organic Chemistry Review Homework Exercise: Deriving Potential Mechanisms for Glucose Ring Opening in Mutarotation

    ERIC Educational Resources Information Center

    Murdock, Margaret; Holman, R. W.; Slade, Tyler; Clark, Shelley L. D.; Rodnick, Kenneth J.

    2014-01-01

    A unique homework assignment has been designed as a review exercise to be implemented near the end of the one-year undergraduate organic chemistry sequence. Within the framework of the exercise, students derive potential mechanisms for glucose ring opening in the aqueous mutarotation process. In this endeavor, 21 general review principles are…

  14. Alkene metathesis: the search for better catalysts.

    PubMed

    Deshmukh, Prashant H; Blechert, Siegfried

    2007-06-28

    Alkene metathesis catalyst development has made significant progress over recent years. Research in metathesis catalyst design has endeavoured to tackle three key issues: those of (i) catalyst efficiency and activity, (ii) substrate scope and selectivity--particularly stereoselective metathesis reactions--and (iii) the minimization of metal impurities and catalyst recycling. This article describes a brief history of metathesis catalyst development, followed by a survey of more recent research, with a particular emphasis on ruthenium catalysts.

  15. Polyphosphoester-Camptothecin Prodrug with Reduction-Response Prepared via Michael Addition Polymerization and Click Reaction.

    PubMed

    Du, Xueqiong; Sun, Yue; Zhang, Mingzu; He, Jinlin; Ni, Peihong

    2017-04-26

    Polyphosphoesters (PPEs), as potential candidates for biocompatible and biodegradable polymers, play an important role in material science. Various synthetic methods have been employed in the preparation of PPEs such as polycondensation, polyaddition, ring-opening polymerization, and olefin metathesis polymerization. In this study, a series of linear PPEs has been prepared via one-step Michael addition polymerization. Subsequently, camptothecin (CPT) derivatives containing disulfide bonds and azido groups were linked onto the side chain of the PPE through Cu(I)-catalyzed azidealkyne cyclo-addition "click" chemistry to yield a reduction-responsive polymeric prodrug P(EAEP-PPA)-g-ss-CPT. The chemical structures were characterized by nuclear magnetic resonance spectroscopy, gel permeation chromatography, Fourier transform infrared, ultraviolet-visible spectrophotometer, and high performance liquid chromatograph analyses, respectively. The amphiphilic prodrug could self-assemble into micelles in aqueous solution. The average particle size and morphology of the prodrug micelles were measured by dynamic light scattering and transmission electron microscopy, respectively. The results of size change under different conditions indicate that the micelles possess a favorable stability in physiological conditions and can be degraded in reductive medium. Moreover, the studies of in vitro drug release behavior confirm the reduction-responsive degradation of the prodrug micelles. A methyl thiazolyl tetrazolium assay verifies the good biocompatibility of P(EAEP-PPA) not only for normal cells, but also for tumor cells. The results of cytotoxicity and the intracellular uptake about prodrug micelles further demonstrate that the prodrug micelles can efficiently release CPT into 4T1 or HepG2 cells to inhibit the cell proliferation. All these results show that the polyphosphoester-based prodrug can be used for triggered drug delivery system in cancer treatment.

  16. Relay cross metathesis reactions of vinylphosphonates.

    PubMed

    Malla, Raj K; Ridenour, Jeremy N; Spilling, Christopher D

    2014-01-01

    Dimethyl (β-substituted) vinylphosphonates do not readily undergo cross metathesis reactions with Grubbs catalyst and terminal alkenes. However, the corresponding mono- or diallyl vinylphosphonate esters undergo facile cross metathesis reactions. The improved reactivity is attributed to a relay step in the cross metathesis reaction mechanism.

  17. Olefin metathesis in nano-sized systems

    PubMed Central

    Diallo, Abdou K; Gatard, Sylvain; Liang, Liyuan; Ornelas, Cátia; Martinez, Victor; Méry, Denise; Ruiz, Jaime

    2011-01-01

    Summary The interplay between olefin metathesis and dendrimers and other nano systems is addressed in this mini review mostly based on the authors’ own contributions over the last decade. Two subjects are presented and discussed: (i) The catalysis of olefin metathesis by dendritic nano-catalysts via either covalent attachment (ROMP) or, more usefully, dendrimer encapsulation – ring closing metathesis (RCM), cross metathesis (CM), enyne metathesis reactions (EYM) – for reactions in water without a co-solvent and (ii) construction and functionalization of dendrimers by CM reactions. PMID:21286399

  18. Borane catalysed ring opening and closing cascades of furans leading to silicon functionalized synthetic intermediates

    PubMed Central

    Hazra, Chinmoy K.; Gandhamsetty, Narasimhulu; Park, Sehoon; Chang, Sukbok

    2016-01-01

    The conversion of renewable biomass resources to synthetically valuable chemicals is highly desirable, but remains a formidable challenge in regards to the substrate scope and reaction conditions. Here we present the development of tris(pentafluorophenyl)borane–catalysed conversion of furans via ring-opening and closing cascade processes to afford silicon-functionalized synthetic chemicals under transition metal-free conditions. The furan ring-opening with hydrosilanes is highly efficient (TON up to 2,000) and atom-economical without forming any byproduct to give rise to α-silyloxy-(Z)-alkenyl silanes. Additional equivalents of silane smoothly induce a subsequent B(C6F5)3-catalysed cyclization of initially formed olefinic silane compounds to produce anti-(2-alkyl)cyclopropyl silanes, another versatile synthon being potentially applicable in the synthesis of natural products and pharmacophores. PMID:27892459

  19. Borane catalysed ring opening and closing cascades of furans leading to silicon functionalized synthetic intermediates

    NASA Astrophysics Data System (ADS)

    Hazra, Chinmoy K.; Gandhamsetty, Narasimhulu; Park, Sehoon; Chang, Sukbok

    2016-11-01

    The conversion of renewable biomass resources to synthetically valuable chemicals is highly desirable, but remains a formidable challenge in regards to the substrate scope and reaction conditions. Here we present the development of tris(pentafluorophenyl)borane-catalysed conversion of furans via ring-opening and closing cascade processes to afford silicon-functionalized synthetic chemicals under transition metal-free conditions. The furan ring-opening with hydrosilanes is highly efficient (TON up to 2,000) and atom-economical without forming any byproduct to give rise to α-silyloxy-(Z)-alkenyl silanes. Additional equivalents of silane smoothly induce a subsequent B(C6F5)3-catalysed cyclization of initially formed olefinic silane compounds to produce anti-(2-alkyl)cyclopropyl silanes, another versatile synthon being potentially applicable in the synthesis of natural products and pharmacophores.

  20. Iridium-catalyzed asymmetric ring-opening reactions of oxabicyclic alkenes with secondary amine nucleophiles

    PubMed Central

    Hu, Ping; Long, Yuhua; Wu, Yujuan; Zeng, Heping; Wang, Hui; Zuo, Xiongjun

    2009-01-01

    Summary Iridium-catalyzed asymmetric ring-opening reactions of oxabicyclic alkenes with various aliphatic and aromatic secondary amines are reported for the first time. The reaction gave the corresponding trans-1,2-dihydronaphthalenol derivatives in good yields with moderate enantioselectivities in the presence of 2.5 mol % [Ir(COD)Cl]2 and 5 mol % bisphosphine ligand (S)-p-Tol-BINAP. The trans-configuration of 3f was confirmed by X-ray crystallography. PMID:20126558

  1. Pyridine ring opening at room temperature at a rhenium tricarbonyl bipyridine complex.

    PubMed

    Huertos, Miguel A; Pérez, Julio; Riera, Lucía

    2008-04-30

    Pyridine ring opening occurs in the reaction of [Re(CO)3(MeIm)(bipy)]OTf with KN(SiMe3)2 followed by double methylation with methyl trifluoromethanesulfonate. Analogues of the neutral product of the initial deprotonation and of the product of the first methylation were isolated by using mesitylimidazole (MesIm) in place of methylimidazole (MeIm) and/or 1,10-phenanthroline (phen) instead of 2,2'-bipyridine (bipy).

  2. The ring-opening reaction of chromenes: a photochemical mode-dependent transformation.

    PubMed

    Migani, Annapaola; Gentili, Pier Luigi; Negri, Fabrizia; Olivucci, Massimo; Romani, Aldo; Favaro, Gianna; Becker, Ralph S

    2005-10-06

    The efficiency of the photochemical ring-opening of chromenes (or benzopyrans) depends on the vibronic transition selected by the chosen excitation wavelength. In the present work, ab initio CASPT2//CASSCF calculations are used to determine the excited-state ring-opening reaction coordinate for 2H-chromene (C) and 2,2-diethyl-2H-chromene (DEC) and provide an explanation for such an unusual mode-dependent behavior. It is shown that excited-state relaxation and decay occur via a multimodal and barrierless (or nearly barrierless) reaction coordinate. In particular, the relaxation out of the Franck-Condon involves a combination of in-plane skeletal stretching and out-of-plane modes, while the second part of the reaction coordinate is dominated exclusively by a different out-of-plane mode. Population of this last mode is shown to be preparatory with respect to both C-O bond breaking and decay via an S(1)/S(0) conical intersection. The observed mode-dependent ring-opening efficiency is explained by showing that the vibrational mode corresponding to the most efficient vibronic transition has the largest projection onto the out-of-plane mode of the reaction coordinate. To support the computationally derived mechanism, we provide experimental evidence that the photochemical ring-opening reaction of 2,2-dimethyl-7,8-benzo(2H)chromene, that similarly to DEC exhibits a mode-dependent photoreaction, has a low ( approximately 1 kcal mol(-1)) activation energy barrier.

  3. Nitrenes, diradicals, and ylides. Ring expansion and ring opening in 2-quinazolylnitrenes.

    PubMed

    Kvaskoff, David; Bednarek, Pawel; George, Lisa; Waich, Kerstin; Wentrup, Curt

    2006-05-26

    Tetrazolo[1,5-a]quinazoline (9) is converted to 2-azidoquinazoline (10) on sublimation at 200 degrees C and above, and the azide-tetrazole equilibrium is governed by entropy. 2-Quinazolylnitrenes 11 and 27 and/or their ring expansion products 14 and 29 can undergo type I (ylidic) and type II (diradicaloid) ring opening. Argon matrix photolysis of 9/10 affords 2-quinazolylnitrene (11), which has been characterized by ESR, UV, and IR spectroscopy. A minor amount of a second nitrene, formed by rearrangement or ring opening, is also observed. A diradical (19) is formed rapidly by type II ring opening and characterized by ESR spectroscopy; it decays thermally at 15 K with a half-life of ca. 47 min, in agreement with its calculated facile intersystem crossing (19T --> 19OSS) followed by facile cyclization/rearrangement to 1-cyanoindazole (21) (calculated activation barrier 1-2 kcal/mol) and N-cyanoanthranilonitrile (22). 21and 22 are the isolated end products of photolysis. 21 is also the end product of flash vacuum thermolysis. An excellent linear correlation between the zero-field splitting parameter D (cm(-1)) and the spin density rho on the nitrene N calculated at the B3LYP/EPRIII level is reported (R2 = 0.993 for over 100 nitrenes). Matrix photolysis of 3-phenyltetrazolo[1,5-a]quinazoline (25) affords the benzotriazacycloheptatetraene 29, which can be photochemically interconverted with the type I ring opening product 2-isocyano-alpha-diazo-alpha-phenyltoluene (33) as determined by IR and UV spectroscopy. The corresponding carbene 37, obtained by photolysis of 33, was detected by matrix ESR spectroscopy.

  4. Structural disorder and transformation in crystal growth: direct observation of ring-opening isomerization in a metal–organic solid solution

    PubMed Central

    Jiang, Ji-Jun; He, Jian-Rong; Lü, Xing-Qiang; Wang, Da-Wei; Li, Guo-Bi; Su, Cheng-Yong

    2014-01-01

    A rare example is reported in which discrete Ag2 L 2 ring and (AgL)∞ chain motifs [L = N,N′-bis(3-imidazol-1-yl-propyl)-pyromellitic diimide] co-crystallize in the same crystal lattice with varying ratios and degrees of disorder. Crystal structures obtained from representative crystals reveal compatible packing arrangements of the cyclic and polymeric isomers within the crystal lattice, which enables them to co-exist within a crystalline solid solution. A feasible pathway for transformation between the isomers is suggested via facile rotation of the coordinating imidazolyl groups. This chemical system could provide a chance for direct observation of ring-opening isomerization at the crystal surface. Mass spectrometry and 1H NMR titration show a dynamic equilibrium between cyclic and oligomeric species in solution, and a potential crystallization process is suggested involving alignment of precursors directed by aromatic stacking interactions between pyromellitic diimide units, followed by ring-opening isomerization at the interface between the solid and the solution. Both cyclic and oligomeric species can act as precursors, with interconversion between them being facile due to a low energy barrier for rotation of the imidazole rings. Thermogravimetric analysis and variable-temperature powder X-ray diffraction indicate a transition to a different crystalline phase around 120°C, which is associated with loss of solvent from the crystal lattice. PMID:25295173

  5. Structural disorder and transformation in crystal growth: direct observation of ring-opening isomerization in a metal-organic solid solution.

    PubMed

    Jiang, Ji-Jun; He, Jian-Rong; Lü, Xing-Qiang; Wang, Da-Wei; Li, Guo-Bi; Su, Cheng-Yong

    2014-09-01

    A rare example is reported in which discrete Ag2 L 2 ring and (AgL)∞ chain motifs [L = N,N'-bis(3-imidazol-1-yl-propyl)-pyromellitic diimide] co-crystallize in the same crystal lattice with varying ratios and degrees of disorder. Crystal structures obtained from representative crystals reveal compatible packing arrangements of the cyclic and polymeric isomers within the crystal lattice, which enables them to co-exist within a crystalline solid solution. A feasible pathway for transformation between the isomers is suggested via facile rotation of the coordinating imidazolyl groups. This chemical system could provide a chance for direct observation of ring-opening isomerization at the crystal surface. Mass spectrometry and (1)H NMR titration show a dynamic equilibrium between cyclic and oligomeric species in solution, and a potential crystallization process is suggested involving alignment of precursors directed by aromatic stacking interactions between pyromellitic diimide units, followed by ring-opening isomerization at the interface between the solid and the solution. Both cyclic and oligomeric species can act as precursors, with interconversion between them being facile due to a low energy barrier for rotation of the imidazole rings. Thermogravimetric analysis and variable-temperature powder X-ray diffraction indicate a transition to a different crystalline phase around 120°C, which is associated with loss of solvent from the crystal lattice.

  6. Ring Opening of Naphthenic Molecules Over Metal Containing Mesoporous Y Zeolite Catalyst.

    PubMed

    Lee, You-Jin; Kim, Eun Sang; Kim, Tae-Wan; Kim, Chul-Ung; Jeong, Kwang-Eun; Lee, Chang-Ha; Jeong, Soon-Yong

    2015-07-01

    Mesoporous Y zeolite (Meso-Y) with a uniform mesopore was synthesized via pseudomorphic syn- thesis. The Meso-Y supported Ni-W catalyst (NiW/Meso-Y) was introduced as a catalyst for the selective ring opening of naphthenic rings. The catalytic test for the ring opening of naphthalene as a model compound of multi-ring aromatics was performed using a batch-type reaction system with both sulfided 20 wt% NiW/Meso-Y and NiW/Y catalysts under different reaction conditions. The catalytic results reveal that the Meso-Y supported NiW catalyst experiences a naphthalene conversion similar to the NiW/Y catalyst, but the NiW/Meso-Y catalyst has higher product yields for BTEX (benzene, toluene, ethyl benzene, and xylene) and the middle distillate than those of the NiW/Y catalyst at a low reaction temperature. These results suggest that the mesoporosity of the NiW/Meso-Y catalyst is more advantageous for the ring opening reaction of multi-ring aromatics due to the easier access for the bulky molecules compared to the NiW/Y catalyst.

  7. Formation of ring-opened and rearranged products of guanine: mechanisms and biological significance.

    PubMed

    Jena, N R; Mishra, P C

    2012-07-01

    DNA damage by endogenous and exogenous agents is a serious concern, as the damaged products can affect genome integrity severely. Damage to DNA may arise from various factors such as DNA base modifications, strand break, inter- and intrastrand crosslinks, and DNA-protein crosslinks. Among these factors, DNA base modification is a common and important form of DNA damage that has been implicated in mutagenesis, carcinogenesis, and many other pathological conditions. Among the four DNA bases, guanine (G) has the smallest oxidation potential, because of which it is frequently modified by reactive species, giving rise to a plethora of lethal lesions. Similarly, 8-oxo-7,8-dihydroguanine (8-oxoG), an oxidatively damaged guanine lesion, also undergoes various degradation reactions giving rise to several mutagenic species. The various products formed from reactions of G or 8-oxoG with different reactive species are mainly 2,6-diamino-4-oxo-5-formamidopyrimidine, 2,5-diamino-4H-imidazolone, 2,2,4-triamino-5-(2H)-oxazolone, 5-guanidino-4-nitroimidazole, guanidinohydantoin, spiroiminodihydantoin, cyanuric acid, parabanic acid, oxaluric acid, and urea, among others. These products are formed from either ring opening or ring opening and subsequent rearrangement. The main aim of this review is to provide a comprehensive overview of various possible reactions and the mechanisms involved, after which these ring-opened and rearranged products of guanine would be formed in DNA. The biological significance of oxidatively damaged products of G is also discussed.

  8. "Ring opening-ring closure" strategy for the synthesis of aryl-C-glycosides.

    PubMed

    Liu, Chen-Fu; Xiong, De-Cai; Ye, Xin-Shan

    2014-05-16

    A new "ring-opening-ring closure" strategy for the synthesis of aryl-C-glycosides was described. This strategy exploited the nickel-catalyzed regioselective β-O elimination of glycals by reactions with various aryl boronic acids or potassium aryltrifluoroborates to yield the ring-opened products, which underwent the Lewis acid, protonic acid, PhSeCl, or NBS mediated ring closure reactions to afford diverse aryl-C-glycosides. After Lewis acids and protonic acids were screened, it was found that, starting from the ring-opened substrates, the Ph3PHBr or Sc(OTf)3 mediated ring closure reaction provided α- or β-preferred aryl-C-Δ(2,3)-glycosides, respectively. Furthermore, β-D-phenyl-C-glycosides were successfully prepared via the PhSeCl-mediated cyclization reaction, whereas the α-D-phenyl-C-glycoside was obtained via the NBS-mediated cyclization reaction. After removal of the 2-substituted functionalities by Bu3SnH/AIBN, the synthesis of 2-deoxy-aryl-C-glycosides was ultimately realized in a stereoselective manner.

  9. Mass Spectral Profile for Rapid Differentiating Beta-Lactams from Their Ring-Opened Impurities.

    PubMed

    Wang, Hecheng; Huang, Haiwei; Cao, Jin; Chui, Dehua; Xiao, Shengyuan

    2015-01-01

    High performance liquid chromatography tandem mass spectrometry (HPLC MS) has been widely used for β-lactam antibiotics determination. However, its application to identify impurities of these frequently used drugs is not sufficient at present. In this job, characteristic profiles of the collision induced dissociation (CID) spectra of both β-lactams and ring-opened β-lactams were extracted from the MS data of six β-lactam antibiotics and their forty-five impurities, and were confirmed by the MS data reported in the literature. These characteristics have been successfully applied to rapid differentiation of β-lactam and ring-opened β-lactam impurities in cefixime, cefdinir, and cefaclor. However, these characteristic profiles can only be obtained under low activating voltage. They did not display in the high energy activated CID spectra. Diagnostic fragmentations for determining the localization of double bond and substituents on the thiazine ring and the side chain were also observed. In addition, several characteristic fragmentations are hopeful to be used to differentiate the configurations of C-2 on the thiazine ring of ring-opened impurities, which is generally disadvantageous of mass spectrometry. Taken together, forty-five impurities were identified from the capsules of cefixime, cefdinir, and cefaclor.

  10. Mass Spectral Profile for Rapid Differentiating Beta-Lactams from Their Ring-Opened Impurities

    PubMed Central

    Wang, Hecheng; Huang, Haiwei; Cao, Jin; Chui, Dehua

    2015-01-01

    High performance liquid chromatography tandem mass spectrometry (HPLC MS) has been widely used for β-lactam antibiotics determination. However, its application to identify impurities of these frequently used drugs is not sufficient at present. In this job, characteristic profiles of the collision induced dissociation (CID) spectra of both β-lactams and ring-opened β-lactams were extracted from the MS data of six β-lactam antibiotics and their forty-five impurities, and were confirmed by the MS data reported in the literature. These characteristics have been successfully applied to rapid differentiation of β-lactam and ring-opened β-lactam impurities in cefixime, cefdinir, and cefaclor. However, these characteristic profiles can only be obtained under low activating voltage. They did not display in the high energy activated CID spectra. Diagnostic fragmentations for determining the localization of double bond and substituents on the thiazine ring and the side chain were also observed. In addition, several characteristic fragmentations are hopeful to be used to differentiate the configurations of C-2 on the thiazine ring of ring-opened impurities, which is generally disadvantageous of mass spectrometry. Taken together, forty-five impurities were identified from the capsules of cefixime, cefdinir, and cefaclor. PMID:26090434

  11. A single-ring OpenPET enabling PET imaging during radiotherapy.

    PubMed

    Tashima, Hideaki; Yamaya, Taiga; Yoshida, Eiji; Kinouchi, Shoko; Watanabe, Mitsuo; Tanaka, Eiichi

    2012-07-21

    We develop an OpenPET system which can provide an accessible open space to the patient during PET scanning. Our first-generation OpenPET geometry which we called dual-ring OpenPET consisted of two separated detector rings and it could extend its axial field of view (FOV) therefore enabling imaging the gap region in addition to the in-ring region. However, applications such as dose verification by in-beam PET measurement during particle therapy and real-time tumor tracking by PET require sensitivity focused onto the gap rather than on the wide FOV. In this paper, we propose a second-generation OpenPET geometry, single-ring OpenPET, which can provide an accessible and observable open space with higher sensitivity and a reduced number of detectors than the earlier one. The proposed geometry has a cylinder shape cut at a slant angle, in which the shape of each cut end becomes an ellipse. We provided a theoretical analysis for sensitivity of the proposed geometry, compared with the dual-ring OpenPET and a geometry where the conventional PET was positioned at a slant angle against the patient bed to form an accessible open space, which we called a slant PET. The central sensitivity depends on the solid angle of these geometries. As a result, we found that the single-ring OpenPET has a sensitivity 1.2 times higher than the dual-ring OpenPET and 1.3 times higher than the slant PET when designed for a 600 mm bed width with 300 mm accessible open space and about 200 detector blocks, each with a front area of 2500 mm². In addition, numerical simulation was carried out to show the imaging property of the proposed geometry realized with the ellipsoidal rings and these results indicate that the depth-of-interaction detector can provide uniform resolution even when the detectors are arranged in an ellipsoidal ring.

  12. A single-ring OpenPET enabling PET imaging during radiotherapy

    NASA Astrophysics Data System (ADS)

    Tashima, Hideaki; Yamaya, Taiga; Yoshida, Eiji; Kinouchi, Shoko; Watanabe, Mitsuo; Tanaka, Eiichi

    2012-07-01

    We develop an OpenPET system which can provide an accessible open space to the patient during PET scanning. Our first-generation OpenPET geometry which we called dual-ring OpenPET consisted of two separated detector rings and it could extend its axial field of view (FOV) therefore enabling imaging the gap region in addition to the in-ring region. However, applications such as dose verification by in-beam PET measurement during particle therapy and real-time tumor tracking by PET require sensitivity focused onto the gap rather than on the wide FOV. In this paper, we propose a second-generation OpenPET geometry, single-ring OpenPET, which can provide an accessible and observable open space with higher sensitivity and a reduced number of detectors than the earlier one. The proposed geometry has a cylinder shape cut at a slant angle, in which the shape of each cut end becomes an ellipse. We provided a theoretical analysis for sensitivity of the proposed geometry, compared with the dual-ring OpenPET and a geometry where the conventional PET was positioned at a slant angle against the patient bed to form an accessible open space, which we called a slant PET. The central sensitivity depends on the solid angle of these geometries. As a result, we found that the single-ring OpenPET has a sensitivity 1.2 times higher than the dual-ring OpenPET and 1.3 times higher than the slant PET when designed for a 600 mm bed width with 300 mm accessible open space and about 200 detector blocks, each with a front area of 2500 mm2. In addition, numerical simulation was carried out to show the imaging property of the proposed geometry realized with the ellipsoidal rings and these results indicate that the depth-of-interaction detector can provide uniform resolution even when the detectors are arranged in an ellipsoidal ring.

  13. Polymerization of Plant Oils in Carbon Dioxide Medium

    USDA-ARS?s Scientific Manuscript database

    Lewis acid catalyst, boron trifluoride diethyl etherate (BF3•OEt2), catalyzed polymerization of epoxidized soybean oil (ESO) in liquid carbon dioxide was conducted in an effort to develop useful biodegradable polymers. The ring-opening polymerization was employed at mild conditions, such as at room...

  14. Organometallic chemistry: A new metathesis

    NASA Astrophysics Data System (ADS)

    Hennessy, Elisabeth T.; Jacobsen, Eric N.

    2016-08-01

    Carbonyls and alkenes, two of the most common functional groups in organic chemistry, generally do not react with one another. Now, a simple Lewis acid has been shown to catalyse metathesis between alkenes and ketones in a new carbonyl olefination reaction.

  15. Methods for suppressing isomerization of olefin metathesis products

    DOEpatents

    Firth, Bruce E.; Kirk, Sharon E.; Gavaskar, Vasudeo S.

    2015-09-22

    A method for suppressing isomerization of an olefin metathesis product produced in a metathesis reaction includes adding an isomerization suppression agent to a mixture that includes the olefin metathesis product and residual metathesis catalyst from the metathesis reaction under conditions that are sufficient to passivate at least a portion of the residual metathesis catalyst. The isomerization suppression agent is phosphorous acid, a phosphorous acid ester, phosphinic acid, a phosphinic acid ester or combinations thereof. Methods of refining natural oils are described.

  16. Methods for suppressing isomerization of olefin metathesis products

    DOEpatents

    Firth, Bruce E.; Kirk, Sharon E.

    2015-10-27

    A method for suppressing isomerization of an olefin metathesis product produced in a metathesis reaction includes adding an isomerization suppression agent that includes nitric acid to a mixture that includes the olefin metathesis product and residual metathesis catalyst from the metathesis reaction under conditions that are sufficient to passivate at least a portion of the residual metathesis catalyst. Methods of refining a natural oil are described.

  17. Tandem ring-opening decarboxylation of cyclopropane hemimalonates with sodium azide: a short route to γ-aminobutyric acid esters.

    PubMed

    Emmett, Michael R; Grover, Huck K; Kerr, Michael A

    2012-08-03

    Cyclopropane hemimalonates, when treated with sodium azide, undergo a tandem ring-opening decarboxylation to produce γ-azidobutyric acids in good yields. These adducts were hydrogenated to form γ-aminobutyric acid (GABA) methyl esters.

  18. Strained to the Limit: When a Cyclobutyl Moiety Becomes a Thermodynamic Sink in a Protolytic Ring Opening of Photogenerated Oxetanes

    PubMed Central

    Valiulin, Roman A.; Arisco, Teresa M.; Kutateladze, Andrei G.

    2010-01-01

    Strained polycyclic oxetanes generated photochemically from the Diels-Alder adducts of cyclic dienes and enones undergo deep skeletal rearrangements under protolytic ring-opening conditions offering expeditious access to chlorohydrins and other products of unique skeletal topology. PMID:20608636

  19. Nucleophilic ring opening of bridging thietane ligands in trirhenium carbonyl cluster complexes

    SciTech Connect

    Adams, R.D.; Cortopassi, J.E.; Falloon, S.B.

    1992-11-01

    The reactions of 3,3-dimethylthietane, SCH{sub 2}CMe{sub 2}CH{sub 2} (3,3-DMT), and thietane, SCH{sub 2}CH{sub 2}CH{sub 2}, with Re{sub 3}(CO){sub 10}[{mu}-SCH{sub 2}CH{sub 2}CH{sub 2}]({mu}-H){sub 3}, 2b. Compound 2a was characterized crystallographically and was found to consist of a trirhenium cluster with three bridging hydride ligands and a bridging thietane ligand coordinated through its sulfur atom. 2a and 2b react with halide ions by ring-opening additions to the 3,3-DMT ligand to yield the complex anions [Re{sub 3}(CO){sub 10}({mu}-SCH{sub 2}CMe{sub 2}CH{sub 2}x)({mu}-h){sub 3}]{sup -} 3A-6A, X = F (71%), Cl(71%), Br(84%), I(87%) and [Re{sub 3}(CO){sub 10}({mu}-SCH{sub 2}CH{sub 2}CH{sub 2}Cl)({mu}-H){sub 3}]{sup -}, 4b (67%). Similarly, addition of NMe{sub 3} to 2a and 2b yielded the ring-opened zwitterions Re{sub 3}(CO){sub 10}({mu}-SCH{sub 2}CMe{sub 2}CH{sub 2}NMe{sub 3})({mu}-H){sub 3}, 7 a crystographically. They are zwitterions positively charged at the nitrogen atoms and negatively charged on the trirhenium clusters. Complex 7b was also obtained in a 48% yield from the reaction of Re{sub 3}(C){sub 12}({mu}-H){sub 3} with Me{sub 3}NO in the presence of thietane, but the corresponding reaction using 3,3-DMT yielded only 2a and Re{sub 3}(CO){sub 11}(SCH{sub 2}CMe{sub 2}CH{sub 2})({mu}-H){sub 3}, 8. Attempts to obtain a ring-opening addition to 2a by reaction with PMe{sub 2}Ph yielded only Re{sub 3}(CO){sub 10}(PMe{sub 2}PH){sub 2}({mu}-H){sub 3} by ligand substitution. Attempts to obtain ring opening addition to 8 by reaction with I{sup -} yielded only [Re{sub 3}(CO){sub 11}I({mu}-H){sub 3}]{sup -} by ligand substitution. 20 refs., 3 figs., 10 tabs.

  20. Ring-opening of unsymmetrical 1,2-dioxines using cobalt(II) salen complexes.

    PubMed

    Greatrex, Ben W; Taylor, Dennis K

    2005-01-21

    The regioselectivity of the metal-catalyzed ring opening of unsymmetrical 1,2-dioxines to cis-gamma-hydroxyenones was investigated using two different Co(II) salen complexes. Regioselectivity was determined by direct examination of the enone ratios and by derivitization with a stabilized phosphorus ylide. The steric influence of the substituents on the 1,2-dioxine was the primary influence on regioselectivity. Temperature played little role; however, solvent and selection of Co(II) complex could be used to mildly influence the outcome of the rearrangement for selected substrates. The origins of the selectivity for the reaction are discussed.

  1. From N-alkylimidazole ligands at a rhenium center: ring opening or formation of NHC complexes.

    PubMed

    Huertos, Miguel A; Pérez, Julio; Riera, Lucía; Menéndez-Velázquez, Amador

    2008-10-15

    Cationic rhenium tricarbonyl complexes with three N-alkylimidazole ligands undergo deprotonation of the central CH group upon reaction with 1 equiv of KN(SiMe3)2. For the tris(N-methylimidazole) complex, the metal fragment shifts from N to C, leaving an NHC complex with a nonsubstituted N atom. For compounds with at least one N-mesitylimidazole ligand, the intramolecular attack of the deprotonated carbon onto the central carbon of an N-mesitylimidazole ligand results in ring opening of the latter.

  2. An Oxidopyrylium Cyclization/Ring-Opening Route to Polysubstituted α-Hydroxytropolones

    PubMed Central

    Meck, Christine; Mohd, Noushad; Murelli, Ryan P.

    2012-01-01

    α-Hydroxytropolones are a class of molecules with therapeutic potential against several human diseases. However, structure-activity relationship studies on these molecules have been limited due to a scarcity of efficient synthetic methods to access them. It is demonstrated herein that α-hydroxytropolones can be generated through a BCl3-mediated ring-opening/aromatization/demethylation process on 8-oxabicyclo[3.2.1]octenes. Used in conjunction with an improved method based on established oxidopyrylium dipolar cycloadditions, several polysubstituted α-hydroxytropolones can be accessed in 3 steps from readily available α-hydroxy-γ-pyrones. PMID:23167954

  3. Palladium-catalyzed ring-opening reactions of cyclopropanated 7-oxabenzonorbornadiene with alcohols

    PubMed Central

    Tait, Katrina; Alrifai, Oday; Boutin, Rebecca; Haner, Jamie

    2016-01-01

    Summary Palladium-catalyzed ring-opening reactions of cyclopropanated 7-oxabenzonorbornadiene derivatives using alcohol nucleophiles were investigated. The optimal conditions were found to be 10 mol % PdCl2(CH3CN)2 in methanol, offering yields up to 92%. The reaction was successful using primary, secondary and tertiary alcohol nucleophiles and was compatible with a variety of substituents on cyclopropanated oxabenzonorbornadiene. With unsymmetrical C1-substituted cyclopropanated 7-oxabenzonorbornadienes, the regioselectivity of the reaction was excellent, forming only one regioisomer in all cases. PMID:27829926

  4. Synthesis of doped graphene nanoribbons from molecular and polymeric precursors

    NASA Astrophysics Data System (ADS)

    Cloke, Ryan Randal

    As electronic devices continue to shrink and energy problems continue to grow, nanoscale materials are becoming increasingly important. Graphene is a material with exceptional promise to complement silicon in next-generation electronics because of its extraordinary charge carrier mobility, while also finding a role in cutting-edge energy solutions due to its high surface area and conductivity. Improving on this material even further by reducing the width of graphene to nanoscale dimensions with atomically-precise dopant patterns is the subject of this thesis. Nanometer-wide strips of graphene, known as graphene nanoribbons (GNRs), offer the advantages of semiconducting behavior, combined with more accessible surface area compared to bulk graphene (Chapter 1). Additionally, it is demonstrated that GNRs can be doped with atomic precision, allowing for intricate modulation of the electronic properties of this material, which was studied by STM, STS, and nc-AFM (Chapter 2). Controlled growth of GNRs on surfaces is still an outstanding challenge within the field, and to this end, a variety of porphyrin-GNR template materials were synthesized (Chapter 3). The GNRs obtained in this work were also synthesized in solution, and it was shown that these materials possess excellent properties for applications in hydrogen storage, carbon dioxide reduction, and Li-ion batteries (Chapter 4). A prerequisite for solution-synthesized GNRs, conjugated aromatic polymers are an important class of materials in their own right. Therefore, Ring-Opening Alkyne Metathesis Polymerization was developed using conjugated, strained diynes (Chapter 5). The resulting conjugated polymers were explored both for their own materials properties due to a remarkable self-assembly process that was discovered, and also as precursors to GNRs (Chapter 6). This work advances the fundamental understanding of carbon-based nanostructures, as well as the large-scale production of GNRs for next-generation energy

  5. The effect of supported MoO(X) structures on the reaction pathways of propene formation in the metathesis of ethylene and 2-butene.

    PubMed

    Hahn, T; Kondratenko, E V; Linke, D

    2014-08-21

    The kind of surface MoOX structures on Al2O3-SiO2 was found to determine propene selectivity in the metathesis of ethylene and 2-butene. Compared to isolated tetrahedral MoOX species, their polymerized octahedral counterparts show significantly lower activity for isomerisation of 2- to 1-butene thus hindering non-selective metathesis of these butenes. In addition, they reveal higher ability to engage ethylene in propene formation.

  6. The photochemical ring opening reaction of chromene as seen by transient absorption and fluorescence spectroscopy.

    PubMed

    Herzog, Teja T; Ryseck, Gerald; Ploetz, Evelyn; Cordes, Thorben

    2013-07-01

    In this paper we investigate the photochromic ring-opening reaction of 2,2-diphenyl-5,6-benzo(2H)chromene. In particular, we study the uncertainties and contradictions in various published reaction models using a combination of transient absorption and fluorescence spectroscopy with femtosecond time resolution. We propose a simplified reaction scheme which is in good agreement with theoretical studies. Here, photoexcitation populates a Franck-Condon state, whose fast vibrational wave packet motion, vibrational relaxation, bond-alternation and/or solvent rearrangement processes occur on the sub-picosecond timescale. Our data suggest that the resulting excited state minimum with picosecond lifetime still features structural characteristics of the closed form. Subsequently, the ring-opened photoproducts are formed in a concerted step from the excited state. The velocity of the photoreaction hence only depends on the time that the molecule needs to reach the transition region between the ground and excited states where the crucial bond breakage occurs.

  7. Reactive and unreactive pathways in a photochemical ring opening reaction from 2D femtosecond stimulated Raman.

    PubMed

    Valley, David T; Hoffman, David P; Mathies, Richard A

    2015-04-14

    Two-dimensional femtosecond stimulated Raman spectroscopy (2D-FSRS) is used to probe the structural evolution of a modified cyclohexadiene as it undergoes a photoinduced ring opening reaction. Analysis of the excited state stimulated Raman vibrational data reveals oscillations of the center frequencies and amplitudes of 21 high frequency modes. These oscillations in vibrational properties are due to anharmonic couplings between the high frequency finger print modes and the impulsively driven low frequency molecular distortions in the excited state. The largest anharmonic couplings, with intrinsic oscillation magnitudes of up to 40 cm(-1), are observed between the 467 cm(-1) C-C bend and the 1333 cm(-1) C-C stretch with the 191 cm(-1) methyl wag, all of which are centered on the reactive cyclohexadiene moiety. Conversely, motions located on the periphery - the 993 cm(-1) phenyl bend, the 1389 cm(-1) methyl bend and 1580 cm(-1) phenyl C-C stretch - are coupled with the 104 cm(-1) asymmetric bend. These couplings reveal two key energetic pathways: one leading to formation of the ring-opened product and the other reversion back to the ground state. This work is also important because it presents a new powerful method for measuring anharmonicities of potential energy surfaces and determining their role in chemical reactivity.

  8. Catalytic σ-Bond Metathesis

    NASA Astrophysics Data System (ADS)

    Reznichenko, Alexander L.; Hultzsch, Kai C.

    This account summarizes information on recently reported applications of organo-rare-earth metal complexes in various catalytic transformations of small molecules. The σ-bond metathesis at d0rare-earth metal centers plays a pivotal role in carbon-carbon and carbon-heteroatom bond forming processes. Relevant mechanistic details are discussed and the focus of the review lies in practical applications of organo-rare-earth metal complexes.

  9. Microwave-Assisted Olefin Metathesis

    NASA Astrophysics Data System (ADS)

    Nicks, François; Borguet, Yannick; Sauvage, Xavier; Bicchielli, Dario; Delfosse, Sébastien; Delaude, Lionel; Demonceau, Albert

    Since the first reports on the use of microwave irradiation to accelerate organic chemical transformations, a plethora of papers have been published in this field. In most examples, microwave heating has been shown to dramatically reduce reaction times, increase product yields, and enhance product purity by reducing unwanted side reactions compared to conventional heating methods. The present contribution aims at illustrating the advantages of this technology in olefin metathesis and, when data are available, at comparing microwave-heated and conventionally heated experiments

  10. Catalytic behaviour in the ring-opening polymerisation of organoaluminiums supported by bulky heteroscorpionate ligands.

    PubMed

    Castro-Osma, Jose A; Alonso-Moreno, Carlos; Lara-Sánchez, Agustín; Otero, Antonio; Fernández-Baeza, Juan; Sánchez-Barba, Luis F; Rodríguez, Ana M

    2015-07-21

    A series of alkyl organoaluminium complexes based on bulky heteroscorpionate ligands were designed as catalysts for the ring-opening polymerisation of cyclic esters. Thus, the treatment of AlX3 (X = Me, Et) with bulky acetamide or thioacetamide heteroscorpionate ligands nbptamH (1) [nbptamH = N-naphthyl-2,2-bis(3,5-dimethylpyrazol-1-yl)thioacetamide], fbpamH (2) [fbpamH = N-fluorenyl-2,2-bis(3,5-dimethylpyrazol-1-yl)acetamide], ptbptamH (3) [ptbptamH = N-phenyl-2,2-bis(3,5-di-tert-butylpyrazol-1-yl)thioacetamide], ntbptamH (4) [ntbptamH = N-naphthyl-2,2-bis(3,5-di-tert-butylpyrazol-1-yl)thioacetamide], ptbpamH (5) [ptbpamH = N-phenyl-2,2-bis(3,5-di-tert-butylpyrazol-1-yl)acetamide] and (S)-mtbpamH (6) [(S)-mtbpamH = (S)-(−)-N-α-methylbenzyl-2,2-bis(3,5-di-tert-butylpyrazol-1-yl)acetamide] for 1 hour at 0 °C afforded the dialkyl aluminium complexes [AlX2{κ(2)-nbptam}] (X = Me 7, Et 8), [AlX2{κ(2)-fbpam}] (X = Me 9, Et 10), [AlX2{κ(2)-ptbptam}] (X = Me 11, Et 12), [AlX2{κ(2)-ntbptam}] (X = Me 13, Et 14), [AlX2{κ2(-)ptbpam}] (X = Me 15, Et 16) and [AlX2{κ(2)-(S)-mtbpam}] (X = Me 17, Et 18). The structures of the complexes were determined by spectroscopic methods and the X-ray crystal structure of 14 was also established. The alkyl-containing aluminium complexes 7–18 can act as efficient single-component initiators for the ring-opening polymerisation of ε-caprolactone and rac-lactide. The polymerisations are living, as evidenced by the narrow polydispersities of the isolated polymers and the linear nature of the number average molecular weight versus conversion plot. Finally, a comparative study of ring-opening polymerisation for new bulky heteroscorpionate aluminium initiators and the less congested aluminium analogues is reported.

  11. Mechanical analysis of the ring opening test applied to human ascending aortas.

    PubMed

    García-Herrera, Claudio M; Bustos, Claudio A; Celentano, Diego J; Ortega, Roberto

    2016-12-01

    This work presents experiments, modelling and numerical simulation aimed at describing the mechanical response of human ascending aortas in the ring opening test. The objective is to quantify, from the opening angles measured in the test, the residual stress distribution along the artery wall and, afterwards, how this stress pattern changes when the artery is subjected to standard physiological pressures. The cases studied correspond to four groups including both healthy and pathological arteries. The tissues are characterized via tensile test measurements that enable to derive the material parameters of two constitutive models adopted in the present analysis. Overall, the numerical results obtained for all groups were found to be a useful data that allow to estimate the residual stress and their influence on the vessels under normal and hypertension physiological conditions.

  12. Concerted Ring Opening and Cycloaddition of Chiral Epoxy Enolsilanes with Dienes.

    PubMed

    Krenske, Elizabeth H; Lam, Sarah; Ng, Jerome P L; Lo, Brian; Lam, Sze Kui; Chiu, Pauline; Houk, Kendall N

    2015-06-15

    Silyl-triflate-catalyzed (4+3) cycloadditions of epoxy enolsilanes with dienes provide a mild and chemoselective synthetic route to seven-membered carbocycles. Epoxy enolsilanes containing a terminal enolsilane and a single stereocenter undergo cycloaddition with almost complete conservation of enantiomeric purity, a finding that argues against the involvement of oxyallyl cation intermediates which have been previously proposed for these types of reactions. Reported are theoretical and experimental investigations of the cycloaddition mechanism. The major enantiomers of the cycloadducts are derived from S(N)2-like reactions of the silylated epoxide with the diene, in which stereospecific ring opening and formation of the two new C-C bonds occur in a single step. Calculations predict, and experiments confirm, that the observed small losses of enantiomeric purity are traced to a triflate-mediated double S(N)2 cycloaddition pathway.

  13. Iridium-catalyzed asymmetric ring-opening of oxabenzonorbornadienes with phenols.

    PubMed

    Cheng, Hanchao; Yang, Dingqiao

    2012-11-02

    A novel iridium-catalyzed asymmetric ring-opening (ARO) reaction of oxabenzonorbornadienes with a variety of phenols was reported, which afforded the corresponding trans-2-phenoxy-1,2-dihydronaphthalen-1-ol products in high yields with moderate to excellent enantioselectivities (up to 98% ee) under mild conditions. The trans products are formed via the enantioselective cleavage of a bridgehead carbon-oxygen bond in 1 followed by S(N)2 nucleophilic attack by phenols. The effects of various bisphosphine ligands, Ag (I) salts, ammonium halides, bases, and solvents on the yield and enantioselectivity of the reaction were also investigated. The trans-configuration of the product 2a was confirmed by X-ray crystal structure analysis. A possible mechanism for the present catalytic reaction was proposed.

  14. Synthesis of a digermane-containing tricylic nonadecadienedione incorporating an equivalent of ring-opened THF.

    PubMed

    Gottfried, Amy C; Wang, Jia; Wilson, Erin E; Beck, Larry W; Banaszak Holl, Mark M; Kampf, Jeff W

    2004-11-29

    The combination of 2 equiv of bis[bis(trimethylsilyl)amide]germylene (5) with 2 equiv of 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD) in tetrahydrofuran (THF) results in the ring-opening of 1 equiv of THF to form 2,2,8,8-tetrakis(1,1,1,3,3,3-hexamethyl-disilazan-2-yl)-5,16-diphenyl-7,9,14-trioxa-1,3,5,16,18,19-hexaaza-2,8-digerma-tricyclo[13.2.1.13,6]nonadeca-6(19),15(18)-diene-4,17-dione (6). This fast and nearly quantitative reaction builds a 15-membered ring from five different molecules. The new ring, structurally assigned by X-ray crystallography, contains a flexible methylene chain that moves rapidly on the NMR time scale.

  15. Zirconium(IV)-Catalyzed Ring Opening of on-DNA Epoxides in Water.

    PubMed

    Fan, Lijun; Davie, Christopher P

    2017-05-04

    DNA-encoded library technology (ELT) has spurred wide interest in the pharmaceutical industry as a powerful tool for hit and lead generation. In recent years a number of "DNA-compatible" chemical modifications have been published and used to synthesize vastly diverse screening libraries. Herein we report a newly developed, zirconium tetrakis(dodecyl sulfate) [Zr(DS)4 ] catalyzed ring-opening of on-DNA epoxides in water with amines, including anilines. Subsequent cyclization of the resulting on-DNA β-amino alcohols leads to a variety of biologically interesting, nonaromatic heterocycles. Under these conditions, a library of 137 million on-DNA β-amino alcohols and their cyclization products was assembled. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. TDDFT-MD Study on Dynamics in Photoinduced Ring Opening of Benzene

    NASA Astrophysics Data System (ADS)

    Tateyama, Yoshitaka; Miyamoto, Yoshiyuki; Oyama, Norihisa; Ohno, Takahisa

    2004-03-01

    Coupled dynamics of ions and electrons in the excited states of molecular and solid benzene is investigated on the femtosecond scale by the efficient simulation scheme recently developed for the time-dependent density functional theory. Within the π arrow π excitations, any out-of-plane motion of ions is not induced in the molecular system basically. In the solid, however, we found that large swing of the C-H bonds and subsequent twist of the carbon ring takes place, leading to sp^3-like bonding of carbon ions. This swing-to-twist motion presents a plausible mechanism underlying the photoinduced ring opening in solid benzene experimentally observed under pressure. This research is partially supported by ACT-JST, and also by FSIS and Special Coordination Funds of Ministry of Education, Culture, Sports, Science and Technology of Japanese Government.

  17. Creation of localized spins in graphene by ring-opening of epoxy derived hydroxyl

    PubMed Central

    Chen, Jie; Zhang, Weili; Sun, Yuanyuan; Zheng, Yongping; Tang, Nujiang; Du, Youwei

    2016-01-01

    Creation of high-density localized spins in the basal plane of graphene sheet by introduction of sp3-type defects is considered to be a potential route for the realization of high-magnetization graphene. Theoretical and experimental studies confirmed that hydroxyl can be an effective sp3-type candidate for inducing robust magnetic moment. However, the artificial generation of hydroxyl groups for creating high-density spins on the basal plane of graphene sheet is very scarce. Here we demonstrate that high-content hydroxyl groups can be generated on the basal plane of graphene oxide (GO) sheet by ring opening of epoxy groups. We show that by introduction of 10.74 at.% hydroxyl groups, the density of localized spins of GO can be significantly increased from 0.4 to 5.17 μB/1000 C. Thus, this study provided an effective method to obtain graphene with high-density localized spins. PMID:27225991

  18. Semiclassical dynamic simulation of photon induced ring-opening of cyclohexadiene to hexatriene

    NASA Astrophysics Data System (ADS)

    Li, Anyang; Yuan, Shuai; Dou, Yusheng; Wang, Yubin; Wen, Zhenyi

    2009-08-01

    A dynamical picture and the detailed changes in the structure for the ring opening reaction of cyclohexadiene (CHD) to form hexatriene (HT) are studied by a semiclassical electron radiation-ion dynamics (SERID) simulation. Following the simulated trajectory, the potential energy curves (PECs) of three lowest singlet states (S 0, S 1 and S 2) have been calculated at the CASSCF/MRPT2 level with 6-31G* basis sets. Two non-adiabatic state-to-state transitions are found at 112 fs and 129 fs, which confirms the mechanism suggested in the Ref. [M. Garavelli, C.S. Page, P. Celani, M. Olivucci, W.E. Schmid, S.A. Trushin, W. Fuss, J. Phys. Chem. A 105 (2001) 4458].

  19. Iridium-catalyzed asymmetric ring-opening of azabicyclic alkenes with alcohols.

    PubMed

    Yang, Dingqiao; Xia, Jiuyun; Long, Yuhua; Zeng, Zhongyi; Zuo, Xiongjun; Wang, Sanyong; Li, Chunrong

    2013-08-07

    A novel asymmetric ring-opening reaction of N-substituted azabenzonorbornadienes with a wide variety of substituted benzyl alcohols and the addition reaction of N-substituted azabenzonorbornadienes with thiols are reported, affording the corresponding 1,2-trans-alkoxyamino products in moderate yields with excellent enantioselectivities (up to 94% ee) and the corresponding thiol addition products in high yields with lower enantiomeric excesses (ee) in the presence of iridium catalyst, respectively. The effects of ligands, catalyst loading, solvents and additives, and temperature were also investigated. The anti-configuration of the product 3c was confirmed by X-ray crystal structure analysis. A possible mechanism for the present catalytic reaction is proposed.

  20. A cascade reaction: ring-opening insertion of dioxaphospholane into lutetium alkyl bonds.

    PubMed

    Johnson, Kevin R D; Hayes, Paul G

    2014-02-14

    Geometrically constrained dioxaphospholane rings were incorporated into a bis(phosphinimine)carbazole ligand (HL) in an effort to generate an ancillary ligand system that is capable of supporting reactive lutetium alkyl functionalities and resistant to cyclometalation reactivity. This new ligand was used to prepare a lutetium dialkyl species, LLu(CH2SiMe3)2; however, the complex exhibited low thermal stability at ambient temperature. This dialkyl compound was found to be highly susceptible to a cascading inter- and intramolecular reaction that resulted in the sole formation of an asymmetric bimetallic tetraalkoxide complex. The product of this reaction, generated by the ring-opening insertion of dioxaphospholane moieties into lutetium-carbon bonds, was characterized by multinuclear NMR spectroscopy and single crystal X-ray diffraction.

  1. Prediction of enhanced solvent-induced enantioselectivity for a ring opening with a bifurcating reaction path

    SciTech Connect

    Carpenter, Barry K.; Harvey, Jeremy N.; Glowacki, David R.

    2014-12-11

    Classical molecular dynamics simulations are reported for the deazetisation and ring opening of meso-2,3-difluoro-2,3-dimethyldiazocyclopropane in three solvents: CHCl3, CHFClBr and CH3CH(OH)CF3 (TFIPA). In this study, the achiral reactant leads to enantiomeric allene products, and the question addressed in the study is whether either of the chiral, enantiomerically pure solvents can induce significant enantiomeric excess in the products. The direct dynamics calculations use an empirical valence bond potential for the solute, with empirical parameters optimised against M06-2X/cc-pVTZ density functional results. The results reveal that the exothermic N2 loss and ring opening promote transient strong solvent–solute interactions within the first ~100 fs of the reaction. Because of the bifurcating reaction path, these interactions occur at time when the “decision” about which enantiomer of the product to form has yet to be made (at least for many of the trajectories). Hence, it is possible in principle that the solvent could exert a larger-than-normal influence on the course of the reaction. In fact, the results reveal no such effect for CHFClBr but do predict that TFIPA should induce 15.2 ± 2.1% enantiomeric excess. This is roughly an order of magnitude larger than solvent-induced enantiomeric excesses found experimentally in reactions where the conversion of reactant(s) to enantiomeric products occur over separate transition states.

  2. Nonlinear optical signatures of ultraviolet light-induced ring opening in α-terpinene

    NASA Astrophysics Data System (ADS)

    West, Brantley A.; Molesky, Brian P.; Montoni, Nicholas P.; Moran, Andrew M.

    2013-02-01

    Photoinduced electrocyclic ring opening reactions in conjugated cylcoalkenes are among the most elementary processes in organic chemistry. One prototypical ring opening reaction transforms cyclohexadiene into hexatriene. It is known that a sequence of sub-100 fs internal conversion transitions precedes bond breaking in cyclohexadiene and some of its derivatives. However, these excited state dynamics have never been directly monitored in solution because of insufficient time resolution. Here we aim to uncover the extraordinary photophysics behind related ultrafast internal conversion processes in a derivative of cyclohexadiene, α-terpinene (α-TP), solvated in cyclohexane. Transient absorption anisotropy experiments conducted with 20 fs laser pulses at 267 nm expose non-exponential depopulation kinetics for the ππ* electronic state of α-TP. Our data show that population transfer rapidly accelerates within the first 100 fs after photoexcitation. In addition, recurrences in two-dimensional photon echo (2DPE) line shapes reveal strong vibronic coupling in a normal mode near 523 cm-1, which involves torsions of the C=C bonds and hydrogen out-of-plane (HOOP) wagging on a vinyl group. With the support of several experiments, we hypothesize that the excited state wavepacket in α-TP undergoes several recurrences in the C=C stretching coordinate before displacement along the C=C torsion/vinyl HOOP coordinate finally sets it free from the Franck-Condon region of the potential energy surface. The unconfined wavepacket departs the ππ* electronic state by way of a conical intersection with a lower energy excited state. The present observations are made possible by recent improvements to both the time resolution and detection sensitivity of our experimental setup. This work demonstrates that it is now possible to acquire 2DPE signals in the deep ultraviolet, which are comparable with high-quality measurements in the visible spectral region. These technical developments

  3. Prediction of enhanced solvent-induced enantioselectivity for a ring opening with a bifurcating reaction path

    DOE PAGES

    Carpenter, Barry K.; Harvey, Jeremy N.; Glowacki, David R.

    2014-12-11

    Classical molecular dynamics simulations are reported for the deazetisation and ring opening of meso-2,3-difluoro-2,3-dimethyldiazocyclopropane in three solvents: CHCl3, CHFClBr and CH3CH(OH)CF3 (TFIPA). In this study, the achiral reactant leads to enantiomeric allene products, and the question addressed in the study is whether either of the chiral, enantiomerically pure solvents can induce significant enantiomeric excess in the products. The direct dynamics calculations use an empirical valence bond potential for the solute, with empirical parameters optimised against M06-2X/cc-pVTZ density functional results. The results reveal that the exothermic N2 loss and ring opening promote transient strong solvent–solute interactions within the first ~100 fsmore » of the reaction. Because of the bifurcating reaction path, these interactions occur at time when the “decision” about which enantiomer of the product to form has yet to be made (at least for many of the trajectories). Hence, it is possible in principle that the solvent could exert a larger-than-normal influence on the course of the reaction. In fact, the results reveal no such effect for CHFClBr but do predict that TFIPA should induce 15.2 ± 2.1% enantiomeric excess. This is roughly an order of magnitude larger than solvent-induced enantiomeric excesses found experimentally in reactions where the conversion of reactant(s) to enantiomeric products occur over separate transition states.« less

  4. Ruthenium-based olefin metathesis catalysts bearing pH-responsive ligands: External control of catalyst solubility and activity

    NASA Astrophysics Data System (ADS)

    Balof, Shawna Lynn

    2011-12-01

    Sixteen novel, Ru-based olefin metathesis catalysts bearing pH responsive ligands were synthesized. The pH-responsive groups employed with these catalysts included dimethylamino (NMe2) modified NHC ligands as well as N-donor dimethylaminopyridine (DMAP) and 3-(o-pyridyl)propylidene ligands. These pH-responsive ligands provided the means by which the solubility and/or activity profiles of the catalysts produced could be controlled via acid addition. The main goal of this dissertation was to design catalyst systems capable of performing ring opening metathesis (ROMP) and ring closing metathesis (RCM) reactions in both organic and aqueous media. In an effort to quickly gain access to new catalyst structures, a template synthesis for functionalized NHC ligand precursors was designed, in addition to other strategies, to obtain ligand precursors with ancillary NMe2 groups. Kinetic studies for the catalysts produced from these precursors showed external control of catalyst solubility was afforded via protonation of the NMe2 groups of their NHC ligands. Additionally, this protonation afforded external control of catalyst propagation rates for several catalysts. This is the first known independent external control for the propagation rates of ROMP catalysts. The incorporation of pH-responsive N-donor ligands into catalyst structures also provided the means for the external control of metathesis activity, as the protonation of these ligands resulted in an increased initiation rate based on their fast and irreversible dissociation from the metal center. The enhanced external control makes these catalysts applicable to a wide range of applications, some of which have been explored by us and/or through collaboration. Three of the catalysts designed showed remarkable metathesis activity in aqueous media. These catalysts displayed comparable RCM activity in aqueous media to a class of water-soluble catalysts reported by Grubbs et al., considered to be the most active catalyst for

  5. Catalytic, Cascade Ring-Opening Benzannulations of 2,3-Dihydrofuran O,O- and N,O-Acetals.

    PubMed

    Aponte-Guzmán, Joel; Phun, Lien H; Cavitt, Marchello A; Taylor, J Evans; Davy, Jack C; France, Stefan

    2016-07-18

    An Al(OTf)3 -catalyzed intramolecular cascade ring-opening benzannulation of 2,3-dihydrofuran O,O- and N,O-acetals is described. The cascade sequence involves the dihydrofuran ring-opening by acetal hydrolysis, an intramolecular Prins-type cyclization, and aromatization to generate an array of benzo-fused (hetero)aromatic systems in up to 95 % yield. This method represents the first example of dihydrofuran acetal usage in benzannulation reactions. The approach provides excellent regiocontrol based on the choice of alkenes used to form the requisite dihydrofuran acetals. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  6. Catalytic asymmetric ring-opening of meso-aziridines with malonates under heterodinuclear rare earth metal Schiff base catalysis.

    PubMed

    Xu, Yingjie; Lin, Luqing; Kanai, Motomu; Matsunaga, Shigeki; Shibasaki, Masakatsu

    2011-04-20

    Catalytic asymmetric ring-opening of meso-aziridines with malonates is described. The combined use of two rare earth metal sources with different properties promoted the desired ring-opening reaction. A 1:1:1 mixture of a heterobimetallic La(O-iPr)(3)/Yb(OTf)(3)/Schiff base 1a (0.25-10 mol %) efficiently promoted the reaction of five-, six-, and seven-membered ring cyclic meso-aziridines as well as acyclic meso-aziridines with dimethyl, diethyl, and dibenzyl malonates, giving chiral cyclic and acyclic γ-amino esters in 99-63% yield and >99.5-97% ee.

  7. Stereospecific Synthesis of 2-Iminothiazolidines via Domino Ring-Opening Cyclization of Activated Aziridines with Aryl- and Alkyl Isothiocyanates.

    PubMed

    Bhattacharyya, Aditya; Kavitha, C V; Ghorai, Manas K

    2016-08-05

    Lewis acid catalyzed domino ring-opening cyclization of activated aziridines with aryl and alkyl isothiocyanates has been accomplished leading to the formation of a wide variety of highly substituted and functionalized 2-iminothiazolidines with excellent diastereo- and enantiospecificity (de, ee up to >99%). The reaction proceeds via a Lewis acid catalyzed SN2-type ring-opening of the activated aziridine followed by a concomitant 5-exo-dig cyclization in a domino fashion to furnish the 2-iminothiazolidine derivative in excellent yields (up to 99%).

  8. A femtosecond stimulated Raman spectroscopic study on the oxazine ring opening dynamics of structurally-modified indolobenzoxazines

    NASA Astrophysics Data System (ADS)

    Redeckas, Kipras; Toliautas, Stepas; Steponavičiūtė, Rasa; Šačkus, Algirdas; Sulskus, Juozas; Vengris, Mikas

    2016-06-01

    Steady-state and time-resolved femtosecond stimulated Raman scattering spectroscopic methods were applied to elucidate the photodynamics and the oxazine ring opening contingency in phenyl-substituted indolobenzoxazine systems. Using wavelength- and pulse duration-tunable multi-pulse techniques, we have measured the (static) stimulated Raman spectra of the chemically ring-opened indolobenzoxazines, and the (dynamic) femto-to-nanosecond time- and wavenumber-resolved spectra of their photo-generated species. The two experimental realizations show a notable vibronic disparity, thereby indicating the structural difference between the chemically bond-cleaved and the UV excitation produced species.

  9. Bridged bis(amidinate) ytterbium alkoxide and phenoxide: syntheses, structures, and their high activity for controlled polymerization of L-lactide and epsilon-caprolactone.

    PubMed

    Wang, Junfeng; Yao, Yingming; Zhang, Yong; Shen, Qi

    2009-01-19

    Bridged bis(amidinate) ytterbium alkoxide and phenoxide with diverse molecular structures were synthesized in high yields and confirmed by X-ray crystal structural analysis. The reaction of LYbCl(THF)(2) (L = Me(3)SiNC(Ph)N(CH(2))(3)NC(Ph)NSiMe(3)) with 1 equiv of NaOAr (ArO = 2,6-diisopropylphenoxo) afforded the mononuclear complex LYb(OAr)DME 1 with a seven-coordinated ytterbium atom surrounded by one chelating bis(amidinate) ligand, one phenoxo group, and one DME (dimethoxyethane) molecule. The same reaction with 1 equiv of NaO(i)Pr yielded the binuclear complex Yb(mu(2)-L)(2)(mu(2)-O(i)Pr)(2)Yb, 2, with two equivalent six-coordinate metal centers connected by two linked bis(amidinate)s and two O(i)Pr bridges formed via a ligand redistribution reaction that occurred during the metathesis reaction. Both 1 and 2 initiated the ring-opening polymerization of L-lactide, as well as epsilon-caprolactone (epsilon-CL), in a controlled manner with high reactivity, as indicated by a linear relationship between M(n) and conversion and by narrow molecular weight distributions (PDI = 1.15-1.25) up to 100% conversion. The differences in catalytic performance between complexes 1 and 2 are discussed.

  10. Candle and candle wax containing metathesis and metathesis-like products

    DOEpatents

    Murphy, Timothy A; Tupy, Michael J; Abraham, Timothy W; Shafer, Andy

    2014-04-01

    A wax comprises a metathesis product and/or a product that resembles, at least in part, a product which may be formed from a metathesis reaction. The wax may be used to form articles, for example, candles (container candles, votive candles, and/or a pillar candles), crayons, fire logs, or tarts. The wax commonly includes other components in addition to the metathesis product.

  11. Candle and candle wax containing metathesis and metathesis-like products

    DOEpatents

    Murphy, Timothy A; Tupy, Michael J; Abraham, Timothy W; Shafer, Andy

    2014-12-16

    A wax comprises a metathesis product and/or a product that resembles, at least in part, a product which may be formed from a metathesis reaction. The wax may be used to form articles for example, candles (container candles, votive candles, and/or a pillar candles), crayons, fire logs or tarts. The wax commonly includes other components in addition to the metathesis product.

  12. Heterofunctional Glycopolypeptides by Combination of Thiol-Ene Chemistry and NCA Polymerization.

    PubMed

    Krannig, Kai-Steffen; Schlaad, Helmut

    2016-01-01

    Glycopolypeptides are prepared either by the polymerization of glycosylated amino acid N-carboxyanhydrides (NCAs) or by the post-polymerization functionalization of polypeptides with suitable functional groups. Here we present a method for the in-situ functionalization and (co-) polymerization of allylglycine N-carboxyanhydride in a facile one-pot procedure, combining radical thiol-ene photochemistry and nucleophilic ring-opening polymerization techniques, to yield well-defined heterofunctional glycopolypeptides.

  13. Flavylium based dual photochromism: addressing cis-trans isomerization and ring opening-closure by different light inputs.

    PubMed

    Gago, Sandra; Basílio, Nuno; Moro, Artur J; Pina, Fernando

    2015-04-30

    The multistate system of 4',7-dihydroxy-3-methoxyflavylium is constituted by a multiequilibrium involving trans-chalcone, cis-chalcone, hemiketal, flavylium cation and quinoidal base. This system possesses two independently addressable inter-connected photochromic systems based on the cis-trans isomerization and ring opening-closure of the hemiketal.

  14. Phase transfer reagent promoted tandem ring-opening and ring-closing reactions of unique 3-(1-alkynyl) chromones.

    PubMed

    Liu, Yang; Jin, Shiyu; Huang, Liping; Hu, Youhong

    2015-05-01

    A phase transfer reagent promoted tandem ring-opening and ring-closing reaction of 3-(1-alkynyl) chromones has been developed. This process remarkably generates functionalized 3-acyl-2-substituted chromones. Interestingly, when 3-(hepta-1,6-diyn-1-yl)chromone derivatives are applied, a novel tetracyclic chromone scaffold can be obtained by a further intramolecular 4 + 2 cyclization.

  15. Distinguishing and quantifying the torquoselectivity in competitive ring-opening reactions using the stress tensor and QTAIM.

    PubMed

    Guo, Huan; Morales-Bayuelo, Alejandro; Xu, Tianlv; Momen, Roya; Wang, Lingling; Yang, Ping; Kirk, Steven R; Jenkins, Samantha

    2016-12-05

    Currently the theories to explain and predict the classification of the electronic reorganization due to the torquoselectivity of a ring-opening reaction cannot accommodate the directional character of the reaction pathway; the torquoselectivity is a type of stereoselectivity and therefore is dependent on the pathway. Therefore, in this investigation we introduced new measures from quantum theory of atoms in molecules and the stress tensor to clearly distinguish and quantify the transition states of the inward (TSIC) and outward (TSOC) conrotations of competitive ring-opening reactions of 3-(trifluoromethyl)cyclobut-1-ene and 1-cyano-1-methylcyclobutene. We find the metallicity ξ(rb ) of the ring-opening bond does not occur exactly at the transition state in agreement with transition state theory. The vector-based stress tensor response βσ was used to distinguish the effect of the CN, CH3 , and CF3 groups on the TSIC and TSOC paths that was consistent with the ellipticity ε, the total local energy density H(rb ) and the stress tensor stiffness Sσ . We determine the directional properties of the TSIC and TSOC ring-opening reactions by constructing a stress tensor UσTS space with trajectories TσTS (s) with length l in real space, longer l correlated with the lowest density functional theory-evaluated total energy barrier and hence will be more thermodynamically favored. © 2016 Wiley Periodicals, Inc.

  16. A specific nucleophilic ring-opening reaction of aziridines as a unique platform for the construction of hydrogen polysulfides sensors.

    PubMed

    Chen, Wei; Rosser, Ethan W; Zhang, Di; Shi, Wen; Li, Yilin; Dong, Wen-Ji; Ma, Huimin; Hu, Dehong; Xian, Ming

    2015-06-05

    A hydrogen polysulfide mediated aziridine ring-opening reaction was discovered. Based on this reaction, a novel H2S(n)-specific chemosensor (AP) was developed. AP showed high sensitivity and selectivity for H2S(n). Notably, the fluorescent turn-on product (1) exhibited excellent two-photon photophysical properties, a large Stokes shift, and high solid state luminescent efficiency.

  17. Bismuth(III) trifluoromethanesulfonate catalyzed ring opening reaction of mono epoxy oleochemicals to form keto and diketo derivatives

    USDA-ARS?s Scientific Manuscript database

    Using a catalytic system, methyl oleate is transformed into long chain keto and diketo derivatives via an epoxide route. Methyl 9(10)-oxooctadecanoate and methyl 9,10-dioxooctadecanoate were made by a ring opening reaction of epoxidized methyl oleate using bismuth triflate catalyst. Lower reaction t...

  18. Ring opening of nonactivated 2-(1-aminoalkyl) aziridines: unusual regio- and stereoselective C-2 and C-3 cleavage.

    PubMed

    Concellón, José M; Riego, Estela

    2003-08-08

    We have studied the ring opening of nonactivated amino aziridines 1 by water under acidic conditions. Depending on the acid used, amino aziridines are cleaved at C-3 or C-2 with high regioselectivity, and total stereoselectivity, affording chiral 2,3-diaminoalkan-1-ols 3 or 1,3-diaminoalkan-2-ols 4 in high yield.

  19. Ring opening and carbonylation of 3,3-dimethylthietane ligands in ruthenium carbonyl cluster complexes

    SciTech Connect

    Adams, R.D.; Belinski, J.A.; Yamamoto, J.H.

    1992-10-01

    When heated to 97{degrees}C, the complex Ru{sub 4}(CO){sub 12}[{mu}-SCH{sub 2}CMe{sub 2}CH{sub 2}]2 (1) was transformed into two new hexaruthenium cluster complexes, Ru{sub 6}(CO){sub 13}({mu}{sub 3}-SCH{sub 2}CMe{sub 2}CH{sub 2}){sub 4} (2) and Ru{sub 6}(CO){sub 12}({mu}-SCH{sub 2}CMe{sub 2}CH{sub 2})({mu}{sub 3}-SCH{sub 2}CMe{sub 2}CH{sub 2}){sub 3}[{mu}{sub 3}-SCH{sub 2}C(Me)(CH{sub 2})CH{sub 2}] ({mu}-H) (3), that contain four and five ring-opened 3,3-dimethylthietane (3,3-DMT) ligands, respectively. In compound 3 one of the ring-opened DMT ligands has also undergone a CH activation on one of the methyl groups. Compound 2 reacts with additional 3,3-DMT at 97{degrees}C to form 3 in 18% yield. When treated with CO at 95{degrees}C (500 psi), compound 2 yielded 4,4-dimethylthiobutyrolactone and Ru{sub 3}(CO){sub 12}. It was also found that the complex Os{sub 3}(CO){sub 11-}(SCH{sub 2}CMe{sub 2}CH{sub 2}C{double_bond}O) (4) yields 4,4-dimethylthiobutyrolactone when treated with CO at 120{degrees}C (1200 psi). Crystal data for 2: space group P2{sub 1}/n, {alpha} = 22.652 (7) A, {beta} = 11.712 (2) A, c = 19.965 (6) A, {Beta} = 115.75 (2){degrees} Z = 4, 3665 reflections, R = 0.021. Crystal data for 3: space group P2{sub 1}/c, {alpha} = 17.332 (8) A, {Beta} = 14.668 (9) A, c = 19.823 (9) A, {Beta} = 91.27 (4){degrees}, Z = 4, 1875 reflections, R = 0.050. 13 refs., 2 figs., 13 refs.

  20. Ring-opening photochemistry in cyclohexadiene derivatives: Ultrafast dynamics in solution and model membranes

    NASA Astrophysics Data System (ADS)

    Arruda, Brenden C.

    The ultrafast dynamics of molecules in condensed phases is an area of research that has the possibility to inform the design of molecules for functional nano-devices as well as improve on understanding of biological processes. Presented in this thesis are experiments probing the excited and ground state dynamics of molecules based on the 1,3-cyclohexadiene (CHD) chromophore. The reversible photochemistry of these molecules is applicable to the study of photo-switching systems under consideration for molecular memory devices as well as the photobiological synthesis of Vitamin D3. The full reaction mechanism for a number of CHD derivatives is deduced from ultrafast broadband transient absorption spectroscopy and supporting density functional calculations. Steric groups on the cyclohexadiene backbone can affect both the excited state properties as well as the dynamic approach to equilibrium for the hexatriene photoproducts following excitation of CHD. The photoreaction was characterized in multiple solvent environments with a range of viscosity, polarity, hydrogen-bonding capacity, and packing density. The conformational dynamics of the photoproducts depend on the substitution pattern and solvent. The alpha-phellandrene photoproduct relaxes to a fully trans form much like hexatriene, while alpha-terpinene and 7-dehydrocholesterol photoproducts are limited to certain conformations by steric clashes. The solvent affects the relaxation timescales differently for each photoproduct, but all of the dynamics occur within 5 - 10 ps. The ring opening of DHC that occurs in the biological synthesis of Vitamin D3 is also examined in a liposomal model for the cell membrane. In this anisotropic environment, the excited state dynamics are significantly lengthened to ~ 11 -- 50 ps depending on the liposome properties. This suggests significant interaction between DHC and the lipids that affects the ring-opening reaction coordinate. The excited state and photoproduct conformational

  1. Synthesis of branched dithiotrisaccharides via ring-opening reaction of sugar thiiranes.

    PubMed

    Repetto, Evangelina; Manzano, Verónica E; Uhrig, María Laura; Varela, Oscar

    2012-01-06

    Satisfactory procedures are described for the synthesis of 5,6- and 3,4-thiirane derivatives from the respective hexofuranose or hexopyranose epoxide precursors. The controlled ring-opening reaction of thiiranes by 1-thioaldoses was successfully accomplished to afford, regio- and stereoselectively, β-S-(1→4)-3,4-dithiodisaccharides. For instance, the regioselective attack of per-O-acetyl-1-thioglucose (16) to C-4 of 2-propyl 2,6-di-O-acetyl-3,4-epithio-α-D-galactopyranoside (14) gave the derivative of Glcp-β-S-(1→4)-3,4-dithioGlcp-O-iPr (17). This thiodisaccharide was accompanied by the (1→3)-disulfide 18, formed between 16 and 17, and the symmetric (3→3)-disulfide 19, which resulted from the oxidative dimerization of 17. However, the S-acetyl derivative of 17 could be obtained in good yield (62%) by LiAlH(4) reduction of the crude mixture 17-19, followed by acetylation. The same sequence of reactions starting from 14 and the 1-thiolate of Galp afforded the per-O,S-acetyl derivative of Galp-β-S-(1→4)-3,4-dithio-α-D-Glcp-O-iPr (23), which was selectively S-deacetylated to give 25. The dithiosaccharides 17 and 25 are 3,4-di-S-analogues of derivatives of the natural disaccharides cellobiose and lactose, respectively. The ring-opening reaction of 5,6-epithiohexofuranoses of D-galacto (8) or L-altro (11) configuration with 1-thioaldoses was also regio- and stereoselective to give the respective β-S-(1→6)-linked 5,6-dithiodisaccharides 26 or 29 in excellent yields. Glycosylation of the free thiol group of 17, 25, or 26, using trichloroacetimidates as glycosyl donors, led to the corresponding branched dithiotrisaccharides. Some of them are sulfur analogues of derivatives of branched trisaccharides found in natural polysaccharides.

  2. Theoretical investigations on the hydrolysis pathway of tin verdoheme complexes: elucidation of tin's ring opening inhibition role.

    PubMed

    Davari, Mahdi D; Bahrami, Homayoon; Zahedi, Mansour; Safari, Nasser

    2009-11-01

    In order to obtain a better molecular understanding of inhibitory role of tin metal in the verdoheme ring opening process, hydrolysis of three possibly six, five, and four coordinate verdoheme complexes of tin(IV) and (II) have been studied using DFT method. The results of calculations indicate that, in excellent accord with experimental reports, hydrolysis of different possibly coordinated tin(IV) and (II) verdohemes does not lead to the opening of the macrocycle. Contrary to iron and zinc verdohemes, in five and four coordinate verdoheme complexes of tin(IV) and (II), formation of open ring helical complexes of tin are unfavorable both thermodynamically and kinetically. In these pathways, coordination of hydroxide nucleophile to tin metal due to the highly charged, exclusive oxophilicity nature of the Sn center, and high affinity of Sn to increase coordination state are proposed responsible as inhibiting roles of tin via the ring opening. While, in saturated six coordinate tin(IV) and (II) verdoheme complexes the ring opening of tin verdohemes is possible thermodynamically, but it is not predicted to occur from a kinetics point of view. In the six coordinate pathway, tin plays no coordination role and direct addition of hydroxide nucleophile to the positive oxo-carbon centers and formation of closed ring hydroxy compounds is proposed for preventing the verdoheme ring opening. These key points and findings have been corroborated by the results obtained from atomic charge analysis, geometrical parameters, and molecular orbital calculations. In addition, the results of inhibiting ring opening reaction of tin verdoheme complexes could support the great interest of tin porphyrin analogues as pharmacologic means of chemoprevention of neonatal jaundice by the competitive inhibitory action of tin porphyrins on heme oxygenase.

  3. Detailed kinetic study of the ring opening of cycloalkanes by CBS-QB3 calculations.

    PubMed

    Sirjean, B; Glaude, P A; Ruiz-Lopez, M F; Fournet, R

    2006-11-23

    This work reports a theoretical study of the gas-phase unimolecular decomposition of cyclobutane, cyclopentane and cyclohexane by means of quantum chemical calculations. A biradical mechanism has been envisaged for each cycloalkane, and the main routes for the decomposition of the biradicals formed have been investigated at the CBS-QB3 level of theory. Thermochemical data(DeltaHf(o), S(o), Cp(o)) for all the involved species have been obtained by means of isodesmic reactions. The contribution of hindered rotors has also been included. Activation barriers of each reaction have been analyzed to assess the energetically most favorable pathways for the decomposition of biradicals. Rate constants have been derived for all elementary reactions using transition-state theory at 1 atm and temperatures ranging from 600 to 2000 K. Global rate constant for the decomposition of the cyclic alkanes in molecular products have been calculated. Comparison between calculated and experimental results allowed us to validate the theoretical approach. An important result is that the rotational barriers between the conformers, which are usually neglected, are of importance in decomposition rate of the largest biradicals. Ring strain energies (RSE) in transition states for ring opening have been estimated and show that the main part of RSE contained in the cyclic reactants is removed upon the activation process.

  4. Polymers from sugars: cyclic monomer synthesis, ring-opening polymerisation, material properties and applications.

    PubMed

    Gregory, Georgina L; López-Vidal, Eva M; Buchard, Antoine

    2017-02-14

    Plastics are ubiquitous in modern society. However, the reliance on fossil fuels and the environmental persistence of most polymers make them unsustainable. Scientists are facing the challenge of developing cost-effective and performance-competitive polymers from renewable resources. Carbohydrates are a renewable feedstock with tremendous potential: sugars are widely available, environmentally benign and are likely to impart biocompatibility and degradability properties to polymers due to their high oxygen content. Sugars are also a feedstock with great structurally diversity and functionalisation potential that can enable fine tuning of the resulting polymer properties. In recent years, Ring-Opening Polymerisation (ROP) has emerged as the method of choice for the controlled polymerisation of renewable cyclic monomers, in particular lactones and cyclic carbonates, to allow the precise synthesis of complex polymer architectures and address commodity and specialist applications. This feature article gives an overview of sugar-based polymers that can be made by ROP. In particular, recent advances in the synthetic routes towards monomers that preserve the original carbohydrate core structure are presented. The performances of various homogeneous catalysts and the properties of the resultant polymers are given, and future opportunities highlighted for the development of both the materials and catalysts.

  5. Improvement of physicochemical characteristics of monoepoxide linoleic acid ring opening for biolubricant base oil.

    PubMed

    Salimon, Jumat; Salih, Nadia; Abdullah, Bashar Mudhaffar

    2011-01-01

    For environmental reasons, a new class of environmentally acceptable and renewable biolubricant based on vegetable oils is available. In this study, oxirane ring opening reaction of monoepoxide linoleic acid (MEOA) was done by nucleophilic addition of oleic acid (OA) with using p-toluene sulfonic acid (PTSA) as a catalyst for synthesis of 9(12)-hydroxy-10(13)-oleoxy-12(9)-octadecanoic acid (HYOOA) and the physicochemical properties of the resulted HYOOA are reported to be used as biolubricant base oils. Optimum conditions of the experiment using D-optimal design to obtain high yield% of HYOOA and lowest OOC% were predicted at OA/MEOA ratio of 0.30 : 1 (w/w), PTSA/MEOA ratio of 0.50 : 1 (w/w), reaction temperature at 110°C, and reaction time at 4.5 h. The results showed that an increase in the chain length of the midchain ester resulted in the decrease of pour point (PP) -51°C, increase of viscosity index (VI) up to 153, and improvement in oxidative stability (OT) to 180.94°C.

  6. Alkyl peroxides reveal the ring opening mechanism of verdoheme catalyzed by heme oxygenase.

    PubMed

    Matsui, Toshitaka; Omori, Kohei; Jin, Hiromichi; Ikeda-Saito, Masao

    2008-04-02

    Heme oxygenase (HO) catalyzes heme catabolism through three successive oxygenation steps where the substrate heme itself activates O2. Although a rate-determining step of the HO catalysis is considered as third oxygenation, the verdoheme degradation mechanism has been the least understood in the HO catalysis. In order to discriminate three possible pathways proposed for the verdoheme ring-opening, we have examined reactions of the verdoheme-HO-1 complex with alkyl peroxides, namely MeOOH. Under reducing conditions, the MeOOH reaction afforded two novel products whose absorption spectra are similar to but slightly different from that of biliverdin. HPLC, ESI-MS, and NMR analysis show that these products are 1- and 19-methoxy-deoxy-biliverdins. The addition of a methoxy group at one end of the linear tetrapyrrole unambiguously indicates transient formation of the Fe-OOMe intermediate and rearrangement of its terminal methoxy group to the alpha-pyrrole carbon. The corresponding OH transfer of the Fe-OOH species is highly probable in the H2O2-dependent verdoheme degradation and is likely to be the case in the O2-dependent reaction catalyzed by HO as well.

  7. Dinuclear Zinc Salen Catalysts for the Ring Opening Copolymerization of Epoxides and Carbon Dioxide or Anhydrides.

    PubMed

    Thevenon, Arnaud; Garden, Jennifer A; White, Andrew J P; Williams, Charlotte K

    2015-12-21

    A series of four dizinc complexes coordinated by salen or salan ligands, derived from ortho-vanillin and bearing (±)-trans-1,2-diaminocyclohexane (L1) or 2,2-dimethyl-1,3-propanediamine (L2) backbones, is reported. The complexes are characterized using a combination of X-ray crystallography, multinuclear NMR, DOSY, and MALDI-TOF spectroscopies, and elemental analysis. The stability of the dinuclear complexes depends on the ligand structure, with the most stable complexes having imine substituents. The complexes are tested as catalysts for the ring-opening copolymerization (ROCOP) of CO2/cyclohexene oxide (CHO) and phthalic anhydride (PA)/CHO. All complexes are active, and the structure/activity relationships reveal that the complex having both L2 and imine substituents displays the highest activity. In the ROCOP of CO2/CHO its activity is equivalent to other metal salen catalysts (TOF = 44 h(-1) at a catalyst loading of 0.1 mol %, 30 bar of CO2, and 80 °C), while for the ROCOP of PA/CHO, its activity is slightly higher than other metal salen catalysts (TOF = 198 h(-1) at a catalyst loading of 1 mol % and 100 °C). Poly(ester-block-carbonate) polymers are also afforded using the most active catalyst by the one-pot terpolymerization of PA/CHO/CO2.

  8. Grafting of Ring-Opened Cyclopropylamine Thin Films on Silicon (100) Hydride via UV Photoionization.

    PubMed

    Tung, J; Ching, J Y; Ng, Y M; Tew, L S; Khung, Y L

    2017-08-31

    The grafting of cyclopropylamine onto a silicon (100) hydride (Si-H) surface via a ring-opening mechanism using UV photoionization is described here. In brief, radicals generated from the Si-H surface upon UV irradiation were found to behave in classical hydrogen abstraction theory manner by which the distal amine group was first hydrogen abstracted and the radical propagated down to the cyclopropane moiety. This subsequently liberated the strained bonds of the cyclopropane group and initiated the surface grafting process, producing a thin film approximately 10-15 nm in height. Contact angle measurements also showed that such photoionization irradiation had yielded an extremely hydrophilic surface (∼21.3°) and X-ray photoelectron spectroscopy also confirmed the coupling was through the Si-C linkage. However, when the surface underwent high-temperature hydrosilylation (>160 °C), the reaction proceeded predominantly through the nucleophilic NH2 group to form a Si-N linkage to the surface. This rendered the surface hydrophobic and hence suggested that the Si-H homolysis model may not be the main process. To the best of our knowledge, this was the first attempt reported in the literature to use photoionization to directly graft cyclopropylamine onto a silicon surface and in due course generate a highly rich NH-terminated surface that was found to be highly bioactive in promoting cell viability on the basis of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide studies.

  9. Improvement of Physicochemical Characteristics of Monoepoxide Linoleic Acid Ring Opening for Biolubricant Base Oil

    PubMed Central

    Salimon, Jumat; Salih, Nadia; Abdullah, Bashar Mudhaffar

    2011-01-01

    For environmental reasons, a new class of environmentally acceptable and renewable biolubricant based on vegetable oils is available. In this study, oxirane ring opening reaction of monoepoxide linoleic acid (MEOA) was done by nucleophilic addition of oleic acid (OA) with using p-toluene sulfonic acid (PTSA) as a catalyst for synthesis of 9(12)-hydroxy-10(13)-oleoxy-12(9)-octadecanoic acid (HYOOA) and the physicochemical properties of the resulted HYOOA are reported to be used as biolubricant base oils. Optimum conditions of the experiment using D-optimal design to obtain high yield% of HYOOA and lowest OOC% were predicted at OA/MEOA ratio of 0.30 : 1 (w/w), PTSA/MEOA ratio of 0.50 : 1 (w/w), reaction temperature at 110°C, and reaction time at 4.5 h. The results showed that an increase in the chain length of the midchain ester resulted in the decrease of pour point (PP) −51°C, increase of viscosity index (VI) up to 153, and improvement in oxidative stability (OT) to 180.94°C. PMID:22131799

  10. Ring-opening reactions of cyclic acetals and 1,3-oxazolidines with halosilane equivalents.

    PubMed

    Iwata, Arihiro; Tang, Heqing; Kunai, Atsutaka; Ohshita, Joji; Yamamoto, Yasushi; Matui, Chinami

    2002-07-26

    Reactions of acetal and 1,3-oxazolidine rings were examined using two kinds of iodosilane equivalent reagents, a 1:2 mixture of Me3SiNEt2 and MeI (reagent 1a) and a 1:1 mixture of Et3SiH and MeI containing a catalytic amount of PdCl2 (reagent 1b). In the reactions of alkanone ethylene acetals with reagent 1a, a C-O bond in the acetal ring readily cleaved to give 2-(trimethylsiloxy)ethyl enol ethers. Similarly, the C-O bond of 1,3-oxazolidine rings cleaved to give ring-opened imine or enamine derivatives. The reactions of aromatic ketone ethylene acetals and cyclohexanone trimethylene acetal led to deprotection of the acetal unit to liberate free ketones. With reagent 1b, cycloalkanone ethylene acetal afforded a dimeric product with 2-iodoethyl alkenoate moieties, while aromatic ketone ethylene or trimethylene acetals produced deprotected ketones.

  11. Polymerization of euphorbia oil in carbon dioxide media

    USDA-ARS?s Scientific Manuscript database

    Boron trifluoride diethyl etherate (BF3•OEt2), Lewis acid, catalyzed ring-opening polymerization of euphorbia oil (EO), a natural epoxy oil, was conducted in carbon dioxide. The resulting polymers (RPEO) were characterized by FTIR, 1H-NMR, 13C-NMR, solid state 13C-NMR spectroscopies, differential sc...

  12. Metathesis of alkanes and related reactions.

    PubMed

    Basset, Jean-Marie; Copéret, Christophe; Soulivong, Daravong; Taoufik, Mostafa; Cazat, Jean Thivolle

    2010-02-16

    The transformation of alkanes remains a difficult challenge because of the relative inertness of the C-H and C-C bonds. The rewards for asserting synthetic control over unfunctionalized, saturated hydrocarbons are considerable, however, because converting short alkanes into longer chain analogues is usually a value-adding process. Alkane metathesis is a novel catalytic and direct transformation of two molecules of a given alkane into its lower and higher homologues; moreover, the process proceeds at relatively low temperature (ambient conditions or higher). It was discovered through the use of a silica-supported tantalum hydride, ([triple bond]SiO)(2)TaH, a multifunctional catalyst with a single site of action. This reaction completes the story of the metathesis reactions discovered over the past 40 years: olefin metathesis, alkyne metathesis, and ene-yne cyclizations. In this Account, we examine the fundamental mechanistic aspects of alkane metathesis as well as the novel reactions that have been derived from its study. The silica-supported tantalum hydride catalyst was developed as the result of systematic and meticulous studies of the interaction between oxide supports and organometallic complexes, a field of study denoted surface organometallic chemistry (SOMC). A careful examination of this surface-supported tantalum hydride led to the later discovery of alumina-supported tungsten hydride, W(H)(3)/Al(2)O(3), which proved to be an even better catalyst for alkane metathesis. Supported tantalum and tungsten hydrides are highly unsaturated, electron-deficient species that are very reactive toward the C-H and C-C bonds of alkanes. They show a great versatility in various other reactions, such as cross-metathesis between methane and alkanes, cross-metathesis between toluene and ethane, or even methane nonoxidative coupling. Moreover, tungsten hydride exhibits a specific ability in the transformation of isobutane into 2,3-dimethylbutane as well as in the metathesis

  13. Alkyne metathesis on the rise.

    PubMed

    Fürstner, Alois

    2013-03-04

    The early years of alkyne metathesis were marked by a somewhat ironic state of affairs: the proposed mechanism was swiftly validated and more than one effective catalyst became available shortly after the discovery of this transformation; surprisingly, however, the impact on synthesis remained very limited for a long period of time. Recent advances, however, suggest that this situation is about to change: the remarkable activity, functional-group tolerance, and reliability of the latest generation of catalysts open the door for highly advanced applications. The resulting (cyclo)alkynes are amenable to numerous postmetathetic transformations, which diversify the product portfolio and bring many different structural motifs into reach. Since the catalysts have also evolved from the glovebox to the benchtop, there should be little barrier left for a wider use of this reaction in organic synthesis.

  14. Group 1 and group 2 metal complexes supported by a bidentate bulky iminopyrrolyl ligand: synthesis, structural diversity, and ε-caprolactone polymerization study.

    PubMed

    Kottalanka, Ravi K; Harinath, A; Rej, Supriya; Panda, Tarun K

    2015-12-14

    We report here a series of alkali and alkaline earth metal complexes, each with a bulky iminopyrrolyl ligand [2-(Ph3CN=CH)C4H3NH] (1-H) moiety in their coordination sphere, synthesized using either alkane elimination or silylamine elimination methods or the salt metathesis route. The lithium salt of molecular composition [Li(2-(Ph3CN=CH)C4H3N)(THF)2] (2) was prepared using the alkane elimination method, and the silylamine elimination method was used to synthesize the dimeric sodium and tetra-nuclear potassium salts of composition [(2-(Ph3CN=CH)C4H3N)Na(THF)]2 (3) and [(2-(Ph3CN=CH)C4H3N)K(THF)0.5]4 (4) respectively. The magnesium complex of composition [(THF)2Mg(CH2Ph){2-(Ph3CN=CH)C4H3N}] (5) was synthesized through the alkane elimination method, in which [Mg(CH2Ph)2(OEt2)2] was treated with the bulky iminopyrrole ligand 1-H in 1 : 1 molar ratio, whereas the bis(iminopyrrolyl)magnesium complex [(THF)2Mg{2-(Ph3CN=CH)C4H3N}2] (6) was isolated using the salt metathesis route. The heavier alkaline earth metal complexes of the general formula {(THF)nM(2-(Ph3CN=CH)C4H3N)2} [M = Ca (7), Sr (8), and n = 2; M = Ba (9), n = 3] were prepared in pure form using two synthetic methods: in the first method, the bulky iminopyrrole ligand 1-H was directly treated with the alkaline earth metal precursor [M{N(SiMe3)2}2(THF)n] (where M = Ca, Sr and Ba) in 2 : 1 molar ratio in THF solvent at ambient temperature. The complexes 7-9 were also obtained using the salt metathesis reaction, which involves the treatment of the potassium salt (4) with the corresponding metal diiodides MI2 (M = Ca, Sr and Ba) in 2 : 1 molar ratio in THF solvent. The molecular structures of all the metal complexes (1-H, 2-9) in the solid state were established through single-crystal X-ray diffraction analysis. The complexes 5-9 were tested as catalysts for the ring-opening polymerization of ε-caprolactone. High activity was observed in the heavier alkaline earth metal complexes 7-9, with a very

  15. Biotransformation of two β-secretase inhibitors including ring opening and contraction of a pyrimidine ring.

    PubMed

    Lindgren, Anders; Eklund, Göran; Turek, Dominika; Malmquist, Jonas; Swahn, Britt-Marie; Holenz, Jörg; von Berg, Stefan; Karlström, Sofia; Bueters, Tjerk

    2013-05-01

    Recently, the discovery of the aminoisoindoles as potent and selective inhibitors of β-secretase was reported, including the close structural analogs compound (S)-1-pyridin-4-yl-4-fluoro-1-(3-(pyrimidin-5-yl)phenyl)-1H-isoindol-3-amine [(S)-25] and (S)-1-(2-(difluoromethyl)pyridin-4-yl)-4-fluoro-1-(3-(pyrimidin-5-yl)phenyl)-1H-isoindol-3-amine hemifumarate (AZD3839), the latter being recently progressed to the clinic. The biotransformation of (S)-25 was investigated in vitro and in vivo in rat, rabbit, and human and compared with AZD3839 to further understand the metabolic fate of these compounds. In vitro, CYP3A4 was the major responsible enzyme and metabolized both compounds to a large extent in the commonly shared pyridine and pyrimidine rings. The main proposed metabolic pathways in various in vitro systems were N-oxidation of the pyridine and/or pyrimidine ring and conversion to 4-pyrimidone and pyrimidine-2,4-dione. Both compounds were extensively metabolized, and more than 90% was excreted in feces after intravenous administration of radiolabeled compound to the rat. Here, the main pathways were N-oxidation of the pyridine and/or pyrimidine ring and a ring contraction of the pyrimidine ring into an imidazole ring. Ring-contracted metabolites accounted for 25% of the total metabolism in the rat for (S)-25, whereas the contribution was much smaller for AZD3839. This metabolic pathway was not foreseen on the basis of the obtained in vitro data. In conclusion, we discovered an unusual metabolic pathway of aryl-pyrimidine-containing compounds by a ring-opening reaction followed by elimination of a carbon atom and a ring closure to form an imidazole ring.

  16. Evidence for concerted ring opening and C-Br bond breaking in UV-excited bromocyclopropane

    NASA Astrophysics Data System (ADS)

    Pandit, Shubhrangshu; Preston, Thomas J.; King, Simon J.; Vallance, Claire; Orr-Ewing, Andrew J.

    2016-06-01

    Photodissociation of gaseous bromocyclopropane via its A-band continuum has been studied at excitation wavelengths ranging from 230 nm to 267 nm. Velocity-map images of ground-state bromine atoms (Br), spin-orbit excited bromine atoms (Br∗), and C3H5 hydrocarbon radicals reveal the kinetic energies of these various photofragments. Both Br and Br∗ atoms are predominantly generated via repulsive excited electronic states in a prompt photodissociation process in which the hydrocarbon co-fragment is a cyclopropyl radical. However, the images obtained at the mass of the hydrocarbon radical fragment identify a channel with total kinetic energy greater than that deduced from the Br and Br∗ images, and with a kinetic energy distribution that exceeds the energetic limit for Br + cyclopropyl radical products. The velocity-map images of these C3H5 fragments have lower angular anisotropies than measured for Br and Br∗, indicating molecular restructuring during dissociation. The high kinetic energy C3H5 signals are assigned to allyl radicals generated by a minor photochemical pathway which involves concerted C-Br bond dissociation and cyclopropyl ring-opening following single ultraviolet (UV)-photon absorption. Slow photofragments also contribute to the velocity map images obtained at the C3H5 radical mass, but the corresponding slow Br atoms are not observed. These features in the images are attributed to C3H5+ from the photodissociation of the C3H5Br+ molecular cation following two-photon ionization of the parent compound. This assignment is confirmed by 118-nm vacuum ultraviolet ionization studies that prepare the molecular cation in its ground electronic state prior to UV photodissociation.

  17. Alkene Metathesis and Renewable Materials: Selective Transformations of Plant Oils

    NASA Astrophysics Data System (ADS)

    Malacea, Raluca; Dixneuf, Pierre H.

    The olefin metathesis of natural oils and fats and their derivatives is the basis of clean catalytic reactions relevant to green chemistry processes and the production of generate useful chemicals from renewable raw materials. Three variants of alkene metathesis: self-metathesis, ethenolysis and cross-metathesis applied to plant oil derivatives will show new routes to fine chemicals, bifunctional products, polymer precursours and industry intermediates.

  18. (Iminophosphoranyl)(thiophosphoranyl)methane rare-earth borohydride complexes: synthesis, structures and polymerization catalysis.

    PubMed

    Schmid, Matthias; Oña-Burgos, Pascual; Guillaume, Sophie M; Roesky, Peter W

    2015-07-21

    The (iminophosphoranyl)(thiophosphoranyl)methanide {CH(PPh2=NSiMe3)(PPh2=S)}(-) ligand has been used for the synthesis of divalent and trivalent rare-earth borohydride complexes. The salt metathesis of the potassium reagent [K{CH(PPh2=NSiMe3)(PPh2=S)}]2 with [Yb(BH4)2(THF)2] resulted in the divalent monoborohydride ytterbium complex [{CH(PPh2=NSiMe3)(PPh2=S)}Yb(BH4)(THF)2]. The 2D (31)P/(171)Yb HMQC-NMR spectrum clearly showed the coupling between both nuclei. The trivalent bisborohydrides [{CH(PPh2=NSiMe3)(PPh2=S)}Ln(BH4)2(THF)] (Ln = Y, Sm, Tb, Dy, Er, Yb and Lu) were obtained by reaction of [K{CH(PPh2=NSiMe3)(PPh2=S)}]2 with [Ln(BH4)3(THF)3]. All new compounds were characterized by single X-ray diffraction. The divalent and trivalent compounds were next used as initiators in the ring-opening polymerization (ROP) of ε-caprolactone (CL) and trimethylene carbonate (TMC). All complexes afforded a generally well-controlled ROP of both of these cyclic esters. High molar mass poly(ε-caprolactone) diols (Mn,NMR < 101,300 g mol(-1), ĐM = 1.44), and α,ω-dihydroxy and α-hydroxy,ω-formate telechelic poly(trimethylene carbonate)s (Mn,NMR < 20,000 g mol(-1), ĐM = 1.61) were thus synthesized under mild operating conditions.

  19. Free energy surface for Brønsted acid-catalyzed glucose ring-opening in aqueous solution.

    PubMed

    Qian, Xianghong

    2013-10-03

    Car-Parrinello-based molecular dynamics coupled with metadynamics simulations were used to determine the mechanism and associated free energy surface for opening the ring structure of cyclic glucopyranose in acidic aqueous solutions. The ring-opening process is initiated by the protonation of the ring oxygen atom and the breakage of the C1-O5 bond. The barrier for this process is about 25 kcal/mol, in good agreement with experimental measurements. Moreover, the glucose cyclic conformation is found to be more stable than the open chain form. The barrier for proton-catalyzed ring-opening in aqueous solution appears to be largely solvent induced due to the high affinity of water molecules for protons.

  20. Tandem synthesis of pyrroloacridones via [3 + 2] alkyne annulation/ring-opening with concomitant intramolecular aldol condensation.

    PubMed

    Verma, Akhilesh K; Kotla, Siva K Reddy; Aggarwal, Trapti; Kumar, Sonu; Nimesh, Hemlata; Tiwari, Rakesh K

    2013-06-07

    An efficient cascade strategy for the direct synthesis of pyrrolo[3,2,1-de]acridones 4a-v, 5a-h from iodo-pyranoquinolines 2a-i by the palladium-catalyzed regioselective [3 + 2] alkyne annulation/ring-opening followed by intramolecular aldol condensation under microwave irradiation is described. The chemistry involves the in situ formation of pyrroloquinolines Y, via palladium-catalyzed selective [3 + 2] annulation of iodopyranoquinolines and internal akynes with ring-opening and successive intramolecular cross-aldol condensation. Both the symmetrical and unsymmetrical internal alkynes were reacted smoothly to provide the desired pyrroloacridones in good yields. This methodology provides the facile conversion of easily accessble iodopyranoquinoline into highly functionalized biologically important pyrroloacridones in a single process.

  1. Efficient asymmetric synthesis of N-protected-β-aryloxyamino acids via regioselective ring opening of serine sulfamidate carboxylic acid.

    PubMed

    Malhotra, Rajesh; Dey, Tushar K; Dutta, Swarup; Basu, Sourav; Hajra, Saumen

    2014-09-07

    First regioselective ring opening of serine derived cyclic sulfamidate by hard nucleophiles like ArONa is developed, where β-elimination of serine sulfamidate ester by stronger nucleophiles is overcome by reversal of the electronic effect of the carboxylate anion. This method provides easy and direct access to a variety of N-Boc- and N-PMB protected β-aryloxy-α-amino acids with complete retention of enantiopurity in moderate to high yields.

  2. Direct observation of ring-opening dynamics in strong-field ionized selenophene using femtosecond inner-shell absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Lackner, Florian; Chatterley, Adam S.; Pemmaraju, C. D.; Closser, Kristina D.; Prendergast, David; Neumark, Daniel M.; Leone, Stephen R.; Gessner, Oliver

    2016-12-01

    Femtosecond extreme ultraviolet transient absorption spectroscopy is used to explore strong-field ionization induced dynamics in selenophene (C4H4Se). The dynamics are monitored in real-time from the viewpoint of the Se atom by recording the temporal evolution of element-specific spectral features near the Se 3d inner-shell absorption edge (˜58 eV). The interpretation of the experimental results is supported by first-principles time-dependent density functional theory calculations. The experiments simultaneously capture the instantaneous population of stable molecular ions, the emergence and decay of excited cation states, and the appearance of atomic fragments. The experiments reveal, in particular, insight into the strong-field induced ring-opening dynamics in the selenophene cation, which are traced by the emergence of non-cyclic molecules as well as the liberation of Se+ ions within an overall time scale of approximately 170 fs. We propose that both products may be associated with dynamics on the same electronic surfaces but with different degrees of vibrational excitation. The time-dependent inner-shell absorption features provide direct evidence for a complex relaxation mechanism that may be approximated by a two-step model, whereby the initially prepared, excited cyclic cation decays within τ1 = 80 ± 30 fs into a transient molecular species, which then gives rise to the emergence of bare Se+ and ring-open cations within an additional τ2 = 80 ± 30 fs. The combined experimental and theoretical results suggest a close relationship between σ* excited cation states and the observed ring-opening reactions. The findings demonstrate that the combination of femtosecond time-resolved core-level spectroscopy with ab initio estimates of spectroscopic signatures provide new insights into complex, ultrafast photochemical reactions such as ring-opening dynamics in organic molecules in real-time and with simultaneous sensitivity for electronic and structural

  3. Ring-opening copolymerization of maleic anhydride with epoxides: a chain-growth approach to unsaturated polyesters.

    PubMed

    DiCiccio, Angela M; Coates, Geoffrey W

    2011-07-20

    We report the ring-opening copolymerization of maleic anhydride with a variety of epoxides catalyzed by a chromium(III) salen complex. Quantitative isomerization of the cis-maleate form of all polymers affords the trans-fumarate analogues. Addition of chain transfer reagents yields low M(n), narrow PDI polymer samples. This method provides access to a range of new unsaturated polyesters with versatile functionality, as well as the first synthesis of high molecular weight poly(propylene fumarate).

  4. Concise formal synthesis of (-)-salinosporamide A (marizomib) using a regio- and stereoselective epoxidation and reductive oxirane ring-opening strategy.

    PubMed

    Ling, Taotao; Potts, Barbara C; Macherla, Venkat R

    2010-06-04

    Expedient access to a highly functionalized 2-pyrrolidinone (8), the gamma-lactam core of 20S proteasome inhibitor (-)-salinosporamide A (marizomib; NPI-0052; 1), using a regio- and stereoselective epoxide formation/reductive oxirane ring-opening strategy is presented. Notably, the sequential construction of the C-4, C-3, and C-2 stereocenters of 1 in a completely stereocontrolled fashion is a key feature of streamlining the synthesis of intermediate 12. A related strategy is also discussed.

  5. Unexpected lateral-lithiation-induced alkylative ring opening of tetrahydrofurans in deep eutectic solvents: synthesis of functionalised primary alcohols.

    PubMed

    Sassone, Francesca C; Perna, Filippo M; Salomone, Antonio; Florio, Saverio; Capriati, Vito

    2015-06-11

    o-Tolyl-substituted tetrahydrofurans undergo highly regioselective ring opening with the concomitant formation of new C-C bonds as the result of a lateral lithiation reaction. This reaction provides a new method for the synthesis of functionalised primary alcohols and can be run directly in protic eutectic mixtures as benign reaction media at 0 °C and under air, competitively with protonolysis.

  6. Organometallic polymerization catalysts

    SciTech Connect

    Waymouth, R.M.

    1993-12-31

    Well-defined transition metal catalysts have resulted in exciting new opportunities in polymer synthesis. The stereochemistry of vinyl polymers can be rationally controlled with choice of the appropriate catalysts. Studies with optically active catalyst precursors have revealed considerable information on the absolute stereochemistry of olefin polymerization and have led to the synthesis of novel chiral polyolefins. The development of homogeneous olefin metathesis catalysts has also led to a variety of well-defined new polymer structures with controlled molecular weight and molecular weight distribution. Recent advances in understanding the mechanisms and stereochemistry of homogeneous transition metal catalyzed polymerization will be discussed. The ability to control polymer structure through catalyst design presents exciting opportunities in the synthesis of {open_quotes}tailor-made{close_quotes} macromolecules.

  7. Fluoride-Triggered Ring-Opening of Photochromic Diarylpyrans into Merocyanine Dyes: Naked-Eye Sensing in Subppm Levels.

    PubMed

    Mukhopadhyay, Arindam; Maka, Vijay Kumar; Moorthy, Jarugu Narasimha

    2016-09-02

    The fluoride-mediated desilylation reaction has been exploited, for the first time, to trigger ring-opening of photochromic diarylbenzo-/naphthopyrans into highly colored anionic merocyanine dyes with high molar absorptivities to permit naked-eye sensing. The absorption spectral shifts, i.e., differences in the absorption maxima of colorless and colored forms, observed for a rationally designed set of silyloxy-substituted diarylpyrans subsequent to fluoride-induced ring opening are remarkably high (330-480 nm), and are unknown for any colorimetric probe. In particular, the disilyloxy-substituted diphenylnaphthopyran and its analog, in which the diphenyl groups are fused in the form of fluorene, allows "naked-eye" detection of fluoride in subppm levels (<1.0 ppm) in THF as well as in DMSO-H2O. The sensing is specific for fluoride among various other anions. This approach for colorimetric sensing of fluoride by ring-opening of the otherwise photochromic benzo-/naphthopyrans is heretofore unprecedented.

  8. Solvent-free acid-catalyzed ring-opening of epoxidized oleochemicals using stearates/stearic acid, and its applications.

    PubMed

    Ahn, Byung-Jun Kollbe; Kraft, Stefan; Sun, Xiuzhi Susan

    2012-03-07

    Toxic solvent and strong acid catalysts causing environmental issues have been mainly used for ring-opening of epoxidized oleochemicals. Here, we demonstrated that magnesium stearate (Mg-stearate) was a high efficient catalyst for solvent-free ring-opening of epoxidized methyl oleate, a model compound of midchain epoxide. Mg-stearate resulted in the highest yield (95%) and conversion rate (99%) toward midchain alkoxyesters under the same conditions (160 °C, 12 h) superior to other fatty acid derivatives such as a Lewis acid (lithium and sodium stearate) and Brønsted acid (stearic acid). Based on this chemical study, we synthesized biogrease and thermoplastic using epoxidized soybean oil (ESO) and Mg-stearate via one-pot, solvent-free, and purification-free process. Mg-stearate played a significant role as a reactant for epoxide ring-opening and as a thickener when excess loading rate was used; viscosity increased from 1800 to 4500 Pa·s at 25 °C when ESO:Mg-stearate increased from 1:1 equiv to 1:2, then behaved like thermoplastics (T(g) = -27 °C, T(m) = 90 °C) with 1:4.

  9. Hydrolases in Polymer Chemistry: Chemoenzymatic Approaches to Polymeric Materials

    NASA Astrophysics Data System (ADS)

    Heise, Andreas; Palmans, Anja R. A.

    Lipases show high activity in the polymerization of a range of monomers using ring-opening polymerization and polycondensation. The range of polymer structures from this enzymatic polymerization can be further increased by combination with chemical methods. This paper reviews the developments of the last 5-8 years in chemoenzymatic strategies towards polymeric materials. Special emphasis is on the synthesis of polymer architectures like block and graft copolymers and polymer networks. Moreover, the combination of chemical and enzymatic catalysis for the synthesis of unique chiral polymers is highlighted.

  10. Direct valorisation of waste cocoa butter triglycerides via catalytic epoxidation, ring-opening and polymerisation.

    PubMed

    Plaza, Dorota D; Strobel, Vinzent; Heer, Parminder Kaur Ks; Sellars, Andrew B; Hoong, Seng-Soi; Clark, Andrew J; Lapkin, Alexei A

    2017-09-01

    Development of circular economy requires significant advances in the technologies for valorisation of waste, as waste becomes new feedstock. Food waste is a particularly important feedstock, containing large variation of complex chemical functionality. Although most food waste sources are complex mixtures, waste from food processing, no longer suitable for the human food chain, may also represent relatively clean materials. One such material requiring valorisation is cocoa butter. Epoxidation of a triglyceride from a food waste source, processing waste cocoa butter, into the corresponding triglyceride epoxide was carried out using a modified Ishii-Venturello catalyst in batch and continuous flow reactors. The batch reactor achieved higher yields due to the significant decomposition of hydrogen peroxide in the laminar flow tubular reactor. Integral and differential models describing the reaction and the phase transfer kinetics were developed for the epoxidation of cocoa butter and the model parameters were estimated. Ring-opening of the epoxidised cocoa butter was undertaken to provide polyols of varying molecular weight (Mw = 2000-84 000 Da), hydroxyl value (27-60 mg KOH g(-1)) and acid value (1-173 mg KOH g(-1)), using either aqueous ortho-phosphoric acid (H 3 PO 4) or boron trifluoride diethyl etherate (BF 3·OEt2)-mediated oligomerisation in bulk, using hexane or tetrahydrofuran (THF) as solvents. The thermal and tensile properties of the polyurethanes obtained from the reaction of these polyols with 4,4'-methylene diphenyl diisocyanate (MDI) are described. The paper presents a complete valorisation scheme for a food manufacturing industry waste stream, starting from the initial chemical transformation, developing a process model for the design of a scaled-up process, and leading to synthesis of the final product, in this case a polymer. This work describes aspects of optimisation of the conversion route, focusing on clean synthesis and also demonstrates the

  11. Rhodium-catalyzed ring-opening reactions of a 3-aza-2-oxabicyclo[2.2.1]hept-5-ene with arylboronic acids.

    PubMed

    Machin, Ben P; Ballantine, Melissa; Mandel, Jérémie; Blanchard, Nicolas; Tam, William

    2009-10-02

    Rhodium-catalyzed ring-opening reactions of a 3-aza-2-oxabicyclo[2.2.1]hept-5-ene with arylboronic acids were investigated. The use of [RhCl(COD)](2), (+/-)-BINAP, and NaHCO(3) in MeOH at 60 degrees C was found to be the optimized conditions for the ring-opening reactions to give the 1,2-ring-opened products. Various arylboronic acids were examined, and low to moderate yields were obtained and stereoselectivities (trans/cis) from 50:50 to 100:0 were observed.

  12. I. Diamino telechelic polybutadienes: Synthesis, characterization and melt coupling. II. Poly(epsilon-caprolactone-beta-poly(ethylene glycol) polymeric nanoparticles for drug delivery. III. Zirconia based cellulosic HPLC chiral stationary phase for enantioseparations

    NASA Astrophysics Data System (ADS)

    Ji, Shengxiang

    This thesis is comprised of three parts under the theme of functional specialty polymers. The first project involves the synthesis, characterization, and melt coupling of diamino telechelic polybutadienes. The second part describes the preparation of PCL-PEG polymeric nanoparticles for drug delivery. The third project focuses on the preparation of cellulosic HPLC chiral stationary phases for enantioseparations. Styrene-butadiene-styrene (SBS) block copolymers (BCPs) are difficult to process due to high order-disorder transition temperature and high viscosity. An attractive strategy for approaching this problem is the use of reactive coupling between diamino telechelic PB (TPB) and anhydride-terminated polystyrene (PS-anh) to generate SBS BCPs during melt processing. Diamino TPBs were synthesized by ring-opening metathesis polymerization of 1,5-cyclooctadiene using 1,8-dicyano-4-octene as a chain transfer agent, followed by lithium aluminum hydride reduction. A 19F NMR method was developed to quantify the primary amine functionality for TPBs. Melt coupling of diamino TPB and PS-anh at 180 °C resulted in formation of SBS triblock copolymers, which was confirmed by SAXS. Maleimide terminated poly(epsilon-caprolactone)- b-poly(ethylene glycol) (PCL-PEG-MAL) nanoparticles are of special interest in biomedical applications. However, the synthesis of PCL-PEG-MAL with high maleimide functionality is difficult. Carboxylic acid functionalized poly(epsilon-caprolactone)s (PCL-COOHs) with narrow polydispersity were prepared by ring-opening polymerization of epsilon-caprolactone. Three PCL-PEG-OHs were, synthesized by coupling of excess HO-PEG-OH with different molecular weight PCL-COCls, The hydroxyl end-groups were transferred to maleimide groups to give PCL-PEG-MALs. Nanoparticles with maleimide functionality were prepared by impingement mixing. Particle sizes and size distributions were determined by dynamic light scattering. The amount of accessible maleimide on the

  13. Recent Applications of Alkene Metathesis in Fine Chemical Synthesis

    NASA Astrophysics Data System (ADS)

    Bicchielli, Dario; Borguet, Yannick; Delaude, Lionel; Demonceau, Albert; Dragutan, Ileana; Dragutan, Valerian; Jossifov, Christo; Kalinova, Radostina; Nicks, François; Sauvage, Xavier

    During the last decade or so, the emergence of the metathesis reaction in organic synthesis has revolutionised the strategies used for the construction of complex molecular structures. Olefin metathesis is indeed particularly suited for the construction of small open-chain molecules and macrocycles using crossmetathesis and ring-closing metathesis, respectively. These reactions serve, inter alia, as key steps in the synthesis of various agrochemicals and pharmaceuticals such as macrocyclic peptides, cyclic sulfonamides, novel macrolides, or insect pheromones. The present chapter is aiming at illustrating the great synthetic potential of metathesis reactions. Shortcomings, such as the control of olefin geometry and the unpredictable effect of substituents on the reacting olefins, will also be addressed. Examples to be presented include epothilones, amphidinolides, spirofungin A, and archazolid. Synthetic approaches involving silicon-tethered ring-closing metathesis, relay ring-closing metathesis, sequential reactions, domino as well as tandem metathesis reactions will also be illustrated.

  14. Tunable mechano-responsive organogels by ring-opening copolymerizations of N-carboxyanhydrides.

    PubMed

    Fan, Jingwei; Zou, Jiong; He, Xun; Zhang, Fuwu; Zhang, Shiyi; Raymond, Jeffery E; Wooley, Karen L

    2014-01-01

    The simple copolymerization of N-carboxyanhydride (NCA) monomers is utilized to generate copolypeptides having a combination of α-helix and β-sheet sub-structures that, when grown from a solvophilic synthetic polymer block segment, are capable of driving mechano-responsive supramolecular sol-to-gel-to-sol and sol-to-gel-to-gel transitions reversibly, which allow also for injection-based processing and self-healing behaviors. A new type of polypeptide-based organogelator, methoxy poly(ethylene glycol)-block-poly(γ-benzyl-l-glutamate-co-glycine) (mPEG-b-P(BLG-co-Gly)), is facilely synthesized by statistical ring-opening copolymerizations (ROPs) of γ-benzyl-l-glutamate (BLG) and glycine (Gly) NCAs initiated by mPEG-amine. These systems exhibit tunable secondary structures and result in sonication stimulus responsiveness of the organogels with the polypeptide segment variation, controlled by varying the ratio of BLG NCA to Gly NCA during the copolymerizations. Attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) studies indicate the α-helical component decreases while the β-sheet content increases systematically with a higher mole fraction of Gly in the polypeptide segment. The supramolecular assembly of β-sheet nanofibrils, having a tunable width over the range of 10.4 - 14.5 nm with varied BLG to Gly ratio, are characterized by transmission electron microscopy (TEM). The further self-assembly of these nanostructures into 3-D gel networks within N,N-dimethylformamide (DMF) occurs at low critical gelation concentrations (CGC) (lowest ca. 0.6 wt %). Increased BLG to Gly ratios lead to an increase of the α-helical component in the secondary structures of the polypeptide segments, resulting in wider and more flexible nanofibrils. The presence of α-helical component in the polymers enhances the stability of the organogels against sonication, and instantaneous gel-to-gel transitions are observed as in situ reconstruction of networks

  15. Aromatic Metamorphosis of Dibenzofurans into Triphenylenes Starting with Nickel-Catalyzed Ring-Opening C-O Arylation.

    PubMed

    Kurata, Yuto; Otsuka, Shinya; Fukui, Norihito; Nogi, Keisuke; Yorimitsu, Hideki; Osuka, Atsuhiro

    2017-02-28

    A new class of aromatic metamorphosis has been developed in which dibenzofurans were converted into triphenylenes. This transformation is composed of three successive operations: (1) nickel-catalyzed ring-opening C-O bond arylation with arylmagnesium bromides, (2) trifluoromethanesulfonylation (triflation) of the resulting hydroxy moiety with Tf2O, and (3) palladium-catalyzed or photoinduced ring closure. In the last ring-closing step, the photoinduced process has proven to be more productive than the palladium-catalyzed one. By employing π-extended dinaphthofuran as the substrate, dorsally benzo-fused [5]helicene was obtained in a satisfactory yield.

  16. Asymmetric synthesis of 2,3-dihydropyrroles by ring-opening/cyclization of cyclopropyl ketones using primary amines.

    PubMed

    Xia, Yong; Liu, Xiaohua; Zheng, Haifeng; Lin, Lili; Feng, Xiaoming

    2015-01-02

    The asymmetric ring-opening/cyclization of cyclopropyl ketones with primary amine nucleophiles was catalyzed by a chiral N,N'-dioxide/scandium(III) complex through a kinetic resolution process. A broad range of cyclopropyl ketones and primary amines are suitable substrates of this reaction. The corresponding products were afforded in excellent enantioselectivities and yields (up to 97 % ee and 98 % yield) under mild reaction conditions. This method provides a promising access to chiral 2,3-dihydropyrroles as well as an effective procedure for the kinetic resolution of 2-substituted cyclopropyl ketones. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  17. Cooperative activation in ring-opening hydrolysis of epoxides by Co-salen complexes: A first principle study

    NASA Astrophysics Data System (ADS)

    Sun, Keju; Li, Wei-Xue; Feng, Zhaochi; Li, Can

    2009-03-01

    Density functional theory calculations were used to study the cooperative activations of the epoxide ring-opening hydrolysis catalyzed by the Co-salen complexes. We find that the activation energies of the reactions with two Co-salen catalysts are significantly lower than that of single catalyst. The cooperation effect comes not only from the simultaneous activation of both reactants but also from the cooperative charge transfer during the reactions. The transition states analysis indicates that the preferential reaction pathway is a SN 2 reaction, which explains the second order kinetic dependence on the concentration of the catalysts found in the experiments.

  18. Metal-Free Synthesis of N-Aryl Amides using Organocatalytic Ring-Opening Aminolysis of Lactones.

    PubMed

    Guo, Wusheng; Gómez, José Enrique; Martínez-Rodríguez, Luis; Bandeira, Nuno A G; Bo, Carles; Kleij, Arjan W

    2017-04-05

    Catalytic ring-opening of bio-sourced non-strained lactones with aromatic amines can offer a straightforward, 100 % atom-economical, and sustainable pathway towards relevant N-aryl amide scaffolds. Herein, the first general, metal-free, and highly efficient N-aryl amide formation is reported from poorly reactive aromatic amines and non-strained lactones under mild operating conditions using an organic bicyclic guanidine catalyst. This protocol has high application potential as exemplified by the formal syntheses of drug-relevant molecules.

  19. Acyclic diene metathesis with a monomer from renewable resources: control of molecular weight and one-step preparation of block copolymers.

    PubMed

    Rybak, Anastasiya; Meier, Michael A R

    2008-01-01

    The preparation of a long-chain aliphatic alpha,omega-diene from plant oil derivatives and its subsequent polymerization through acyclic diene metathesis (ADMET) is described. The ADMET bulk polymerization of the thus-obtained monomer, undecyl undecenoate, was investigated and optimized by applying ruthenium-based metathesis catalysts from Grubbs and Hoveyda-Grubbs, leading to high-molecular-weight polyesters. Moreover, by applying different amounts of methyl 10-undecenoate as a chain stopper in this ADMET step growth polymerization, the molecular weight of the resulting polyester could be tuned in a range from approximately 10 to 45 kDa. Finally, the application of a poly(ethylene glycol) methyl ether acrylate as the chain stopper led to the preparation of ABA triblock copolymers in a one-step, one-pot procedure.

  20. A novel multistep mechanism for the stereocontrolled ring opening of hindered sulfamidates: mild, green, and efficient reactivity with alcohols.

    PubMed

    Jiménez-Osés, Gonzalo; Avenoza, Alberto; Busto, Jesús H; Rodríguez, Fernando; Peregrina, Jesús M

    2009-09-28

    Cyclic hindered sulfamidates exhibited an outstanding performance in their ring-opening reactions with alcohols and in the absence of any external activator. The mechanism of this unprecedented transformation was thoroughly studied both experimentally and theoretically. As a result, a nontrivial stepwise pathway involving solvent-induced conversion of the sulfamidates to activated aziridinium and then to oxazolinium cations, which are finally opened at their 5-position with inversion of configuration, is proposed. The presence of the SO(3) moiety in the sulfamidate was revealed as a "built-in activator". In fact, the spontaneous SO(3) cleavage takes place under the reaction conditions and avoids the subsequent step of hydrolysis after the ring opening of the sulfamidates. This is another important improvement of this methodology with respect to the standard basic conditions, allowing a greater compatibility with other functional groups. Furthermore, the carbamate group plays a key role in this mechanism. Briefly, a highly chemoselective and stereoespecific formal solvolysis of hindered sulfamidates with alcohols without further activation is described. This reaction takes place exclusively at the quaternary center with inversion of configuration, providing a new straightforward synthetic route to O-substituted alpha-methylisoserines.

  1. β-Lactam Ring Opening: A Useful Entry to Amino Acids and Relevant Nitrogen-Containing Compounds

    NASA Astrophysics Data System (ADS)

    Palomo, C.; Oiarbide, M.

    The main strategies for the ring opening of β-lactams by chemical means are described. The discovery of each approach is put into context, sometimes in connection to processes occurring in biological systems, and the synthetic opportunities each approach offers are shown. Thus, this β-lactam route affords a number of synthetically relevant building-blocks, including α-amino acids, β-amino acids, their derived peptides, and other nitrogen containing heterocycles and open chain molecules. The content, which encompases references to initial work, further major development, and the most relevant recent literature contributions, is categorized according to the ring bond cleavaged (N 1-C 2, C 2-C 3, C 3 -C 4 , N 1-C 4), to finish with ring opening strategies leading to large heterocyclic compounds. Within each category, distinction has been made according to the type of nucleophilic agent employed, principally O-, N-, and C-nucleophiles. Also, a variety of applications of the strategy to the synthesis of interesting target compounds are shown.

  2. 2-quinoxalinylnitrenes and 4-quinazolinylnitrenes: rearrangement to cyclic and acyclic carbodiimides and ring-opening to nitrile ylides.

    PubMed

    Kvaskoff, David; Vosswinkel, Michael; Wentrup, Curt

    2011-04-13

    This work was undertaken with the aim to obtain direct evidence for the interrelationships between hetarylnitrenes, their ring-expanded cyclic carbodiimide isomers, and ring-opened nitrile ylides. Tetrazolo[1,5-a]quinoxaline 11T and tetrazolo[5.1-c]quinazoline 13T undergo valence tautomerization to the corresponding azides 11A and 13A on mild flash vacuum thermolysis (FVT). Photolysis in Ar matrixes at ca. 15 K affords the triplet nitrenes 12 and 14, identified by ESR, UV, and IR spectroscopy. The nitrenes are converted photochemically to the seven-membered ring carbodiimide 15 followed by the open-chain carbodiimide 22. The 3-methoxy- and 3-chloro-2-quinoxalinylnitrenes 24 yield the ring-expanded carbodiimides 26 very cleanly on matrix photolysis, whereas FVT affords N-cyanobenzimidazoles 28. The ring-opened nitrile ylides 36 and 49 are identified as intermediates in the photolyses of 2-phenyl-4-quinazolinylnitrene 32 and 7-nitro-2-phenyl-4- quinazolinylnitrene 47. In these systems, a photochemically reversible interconversion of the seven-membered ring carbodiimides 35 and 48 and the nitrile ylides 36 and 49 is established. Recyclization of open-chain nitrile ylides is identified as an important mechanism of formation of ring contraction products (N-cyanobenzimidazoles). © 2011 American Chemical Society

  3. Cyclopropenimine superbases: Competitive initiation processes in lactide polymerization

    SciTech Connect

    Stukenbroeker, Tyler S.; Bandar, Jeffrey S.; Zhang, Xiangyi; Lambert, Tristan H.; Waymouth, Robert M.

    2015-07-30

    Cyclopropenimine superbases were employed in this study to catalyze the ring-opening polymerization of lactide. Polymerization occurred readily in the presence and absence of alcohol initiators. Polymerizations in the absence of alcohol initiators revealed a competitive initiation mechanism involving deprotonation of lactide by the cyclopropenimine to generate an enolate. NMR and MALDI-TOF analysis of the poly(lactides) generated from cyclopropenimines in the absence of alcohol initiators showed acylated lactide and hydroxyl end groups. Finally, model studies and comparative experiments with guanidine and phosphazene catalysts revealed the subtle influence of the nature of the superbase on competitive initiation processes.

  4. Supported neodymium catalysts for isoprene and rac-β-butyrolactone polymerization: modulation of reactivity by controlled grafting.

    PubMed

    Terrier, Michael; Brulé, Emilie; Vitorino, Marta J; Ajellal, Noureddine; Robert, Carine; Gauvin, Régis M; Thomas, Christophe M

    2011-01-17

    A series of hybrid materials, bearing neodymium silylamide initiating groups, have been shown to mediate isoprene polymerization when combined with alkyl aluminum activators [methylaluminoxane, AlEt(2)Cl, Al(iBu)(3)]. The surface species nature and relative distribution were correlated with isoprene polymerization activity and selectivity. This approach to stereocontrol modulation has been extended to racemic β-butyrolactone isoselective ring opening polymerization.

  5. Replacing tin in lactide polymerization: design of highly active germanium-based catalysts.

    PubMed

    Guo, Jia; Haquette, Pierre; Martin, Juliette; Salim, Karine; Thomas, Christophe M

    2013-12-16

    Most germane: Hexacoordinate germanium(IV) species exhibit unprecedented activities, yet controlled behavior, as initiators for the ring-opening polymerization of rac-lactide to form polylactide polymers. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  6. Polymerization of euphorbia oil with Lewis acid in carbon dioxide media

    USDA-ARS?s Scientific Manuscript database

    Boron trifluoride diethyl etherate (BF3-OEt2) Lewis acid catalyzed ring-opening polymerization of euphorbia oil (EO), a natural epoxy oil, in liquid carbon dioxide was conducted in an effort to develop useful vegetable oil based polymers. The resulting polymers (RPEO) were characterized by FTIR, 1H-...

  7. Methods of making organic compounds by metathesis

    DOEpatents

    Abraham, Timothy W.; Kaido, Hiroki; Lee, Choon Woo; Pederson, Richard L.; Schrodi, Yann; Tupy, Michael John

    2015-09-01

    Described are methods of making organic compounds by metathesis chemistry. The methods of the invention are particularly useful for making industrially-important organic compounds beginning with starting compositions derived from renewable feedstocks, such as natural oils. The methods make use of a cross-metathesis step with an olefin compound to produce functionalized alkene intermediates having a pre-determined double bond position. Once isolated, the functionalized alkene intermediate can be self-metathesized or cross-metathesized (e.g., with a second functionalized alkene) to produce the desired organic compound or a precursor thereto. The method may be used to make bifunctional organic compounds, such as diacids, diesters, dicarboxylate salts, acid/esters, acid/amines, acid/alcohols, acid/aldehydes, acid/ketones, acid/halides, acid/nitriles, ester/amines, ester/alcohols, ester/aldehydes, ester/ketones, ester/halides, ester/nitriles, and the like.

  8. Sulfated Carbon Quantum Dots as Efficient Visible-Light Switchable Acid Catalysts for Room-Temperature Ring-Opening Reactions.

    PubMed

    Li, Haitao; Sun, Chenghua; Ali, Muataz; Zhou, Fengling; Zhang, Xinyi; MacFarlane, Douglas R

    2015-07-13

    Acid catalytic processes play a classic and important role in modern organic synthesis. How well the acid can be controlled often plays the key role in the controllable synthesis of the products with high conversion yield and selectivity. The preparation of a novel, photo-switchable solid-acid catalyst based on carbon quantum dots is described. The carbon quantum dots are decorated with small amounts of hydrogensulfate groups and thus exhibit a photogenerated acidity that produces a highly efficient acid catalysis of the ring opening of epoxides with methanol and other primary alcohols. This reversible, light-switchable acidity is shown to be due to photoexcitation and charge separation in the carbon quantum dots, which create an electron withdrawing effect from the acidic groups. The catalyst is easily separated by filtration, and we demonstrate multiple cycles of its recovery and reuse. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. Ring opening of donor-acceptor cyclopropanes with the azide ion: a tool for construction of N-heterocycles.

    PubMed

    Ivanov, Konstantin L; Villemson, Elena V; Budynina, Ekaterina M; Ivanova, Olga A; Trushkov, Igor V; Melnikov, Mikhail Ya

    2015-03-23

    A general method for ring opening of various donor-acceptor cyclopropanes with the azide ion through an SN 2-like reaction has been developed. This highly regioselective and stereospecific process proceeds through nucleophilic attack on the more-substituted C2 atom of a cyclopropane with complete inversion of configuration at this center. Results of DFT calculations support the SN 2 mechanism and demonstrate good qualitative correlation between the relative experimental reactivity of cyclopropanes and the calculated energy barriers. The reaction provides a straightforward approach to a variety of polyfunctional azides in up to 91 % yield. The high synthetic utility of these azides and the possibilities of their involvement in diversity-oriented synthesis were demonstrated by the developed multipath strategy of their transformations into five-, six-, and seven-membered N-heterocycles, as well as complex annulated compounds, including natural products and medicines such as (-)-nicotine and atorvastatin.

  10. Stereocontrolled ring-opening of a hindered sulfamidate with nitrogen-containing aromatic heterocycles: synthesis of chiral quaternary imidazole derivatives.

    PubMed

    Mata, Lara; Jiménez-Osés, Gonzalo; Avenoza, Alberto; Busto, Jesús H; Peregrina, Jesús M

    2011-05-20

    This paper explores the role of a hindered cyclic sulfamidate derived from α-methylisoserine as an electrophile in a nucleophilic displacement reaction with nitrogen-containing aromatic heterocycles. Several imidazoles and pyrazole were tested as nucleophiles in the absence of an additional base to give the corresponding ring-opening compounds. We show that the process takes place by inversion of the configuration of the quaternary electrophilic center, retaining the enantiomeric excess of the starting sulfamidate. This reaction opens the way to obtain important quaternary imidazole derivatives such as an innovative type of bis-amino acid related to histidinoalanine and a novel α,α-disubstituted β-amino acid (β(2,2)-amino acid).

  11. A unique Pd-catalysed Heck arylation as a remote trigger for cyclopropane selective ring-opening.

    PubMed

    Singh, Sukhdev; Bruffaerts, Jeffrey; Vasseur, Alexandre; Marek, Ilan

    2017-02-07

    Combining functionalization at a distant position from a reactive site with the creation of several consecutive stereogenic centres, including the formation of a quaternary carbon stereocentre, in acyclic system represents a pinnacle in organic synthesis. Here we report the regioselective Heck arylation of terminal olefins as a distant trigger for the ring-opening of cyclopropanes. This Pd-catalysed unfolding of the strained cycle, driving force of the chain-walking process, remarkably proved its efficiency and versatility, as the reaction proceeded regardless of the molecular distance between the initiation (double bond) and termination (alcohol) sites. Moreover, employing stereodefined polysubstituted cyclopropane vaults allowed to access sophisticated stereoenriched acyclic scaffolds in good yields. Conceptually, we demonstrated that merging catalytically a chain walking process with a selective C-C bond cleavage represents a powerful approach to construct linear skeleton possessing two stereogenic centres.

  12. A unique Pd-catalysed Heck arylation as a remote trigger for cyclopropane selective ring-opening

    NASA Astrophysics Data System (ADS)

    Singh, Sukhdev; Bruffaerts, Jeffrey; Vasseur, Alexandre; Marek, Ilan

    2017-02-01

    Combining functionalization at a distant position from a reactive site with the creation of several consecutive stereogenic centres, including the formation of a quaternary carbon stereocentre, in acyclic system represents a pinnacle in organic synthesis. Here we report the regioselective Heck arylation of terminal olefins as a distant trigger for the ring-opening of cyclopropanes. This Pd-catalysed unfolding of the strained cycle, driving force of the chain-walking process, remarkably proved its efficiency and versatility, as the reaction proceeded regardless of the molecular distance between the initiation (double bond) and termination (alcohol) sites. Moreover, employing stereodefined polysubstituted cyclopropane vaults allowed to access sophisticated stereoenriched acyclic scaffolds in good yields. Conceptually, we demonstrated that merging catalytically a chain walking process with a selective C-C bond cleavage represents a powerful approach to construct linear skeleton possessing two stereogenic centres.

  13. A Specific Nucleophilic Ring-Opening Reaction of Aziridines as a Unique Platform for the Construction of Hydrogen Polysulfides Sensors

    DOE PAGES

    Chen, Wei; Rosser, Ethan W.; Zhang, Di; ...

    2015-05-11

    Hydrogen polysulfides (H2Sn, n>1) have been recently suggested to be the actual signalling molecules that involved in sulfur-related redox biology. However the exact mechanisms of H2Sn are still poorly understood and a major hurdle in this field is the lack of reliable and convenient methods for H2Sn detection. In this work we report a unique ring-opening reaction of N-sulfonylaziridine by Na2S2 under mild conditions. Based on this reaction a novel H2Sn-specific fluorescent probe (AP) was developed. The probe showed high sensitivity and selectivity for H2Sn. Notably, the fluorescent turn-on product, i.e. compound 1, exhibited excellent two-photon photophysical properties and amore » large Stokes shift. Moreover, the high solid state luminescent efficiency of compound 1 makes it a potential candidate for organic emitters and solid-state lighting devices.« less

  14. A unique Pd-catalysed Heck arylation as a remote trigger for cyclopropane selective ring-opening

    PubMed Central

    Singh, Sukhdev; Bruffaerts, Jeffrey; Vasseur, Alexandre; Marek, Ilan

    2017-01-01

    Combining functionalization at a distant position from a reactive site with the creation of several consecutive stereogenic centres, including the formation of a quaternary carbon stereocentre, in acyclic system represents a pinnacle in organic synthesis. Here we report the regioselective Heck arylation of terminal olefins as a distant trigger for the ring-opening of cyclopropanes. This Pd-catalysed unfolding of the strained cycle, driving force of the chain-walking process, remarkably proved its efficiency and versatility, as the reaction proceeded regardless of the molecular distance between the initiation (double bond) and termination (alcohol) sites. Moreover, employing stereodefined polysubstituted cyclopropane vaults allowed to access sophisticated stereoenriched acyclic scaffolds in good yields. Conceptually, we demonstrated that merging catalytically a chain walking process with a selective C–C bond cleavage represents a powerful approach to construct linear skeleton possessing two stereogenic centres. PMID:28169276

  15. Exceptionally active yttrium-salen complexes for the catalyzed ring opening of epoxides by TMSCN and TMSN(3).

    PubMed

    Saha, Biswajit; Lin, Mei-Huey; RajanBabu, T V

    2007-11-09

    Halide or alkoxide free yttrium-salen complexes are excellent catalysts for the ring opening of epoxides mediated by TMSCN and TMSN3. Substrate to catalyst ratios up to 10000 have been realized in these potentially useful reactions, which can be run under solvent-free conditions. Even though the enantioselectivities for the TMSCN-mediated reaction remains modest (best 77% ee), these studies with a highly tunable ligand system may provide further impetus for work in this important area of catalysis. Even though attempts to isolate a Y-cyanide complex, which was detected by in situ IR spectroscopy, failed, a related dimeric hydroxide complex was isolated. A kinetic study using in situ IR spectroscopy did not provide conclusive data to assign an order with respect to Y in this reaction.

  16. Mechanism, reactivity, and regioselectivity in rhodium-catalyzed asymmetric ring-opening reactions of oxabicyclic alkenes: a DFT Investigation

    NASA Astrophysics Data System (ADS)

    Qi, Zheng-Hang; Zhang, Yi; Gao, Yun; Zhang, Ye; Wang, Xing-Wang; Wang, Yong

    2017-01-01

    The origin of the enantio- and regioselectivity of ring-opening reaction of oxabicyclic alkenes catalyzed by rhodium/Josiphos has been examined using M06-2X density functional theory(DFT). DFT calculations predict a 98% ee for the enantioselectivity and only the 1,2-trans product as one regio- and diastereomer, in excellent agreement with experimental results. The solvent tetrahydrofuran(THF) plays a key role in assisting nucleophilic attack. Orbital composition analysis of the LUMO and the NPA atomic charge calculations were conducted to probe the origins of the regioselectivity. The orbital composition analysis reveals two potential electrophilic sites of the Rh-π-allyl intermediate M3 and the NPA atomic charges demonstrate that Cα carries more positive charges than Cγ, which suggests that Cα is the electrophilic site.

  17. N-Substituted and ring opened saccharin derivatives selectively inhibit transmembrane, tumor-associated carbonic anhydrases IX and XII.

    PubMed

    Ivanova, Jekaterīna; Carta, Fabrizio; Vullo, Daniela; Leitans, Janis; Kazaks, Andris; Tars, Kaspars; Žalubovskis, Raivis; Supuran, Claudiu T

    2017-07-01

    A series of N-substituted saccharins incorporating aryl, alkyl and alkynyl moieties, as well as some ring opened derivatives were prepared and investigated as inhibitors of the metalloenzyme carbonic anhydrase (CA, EC 4.2.1.1). The widespread cytosolic isoforms CA I and II were not inhibited by these sulfonamides whereas transmembrane, tumor-associated ones were effectively inhibited, with KIs in the range of 22.1-481nM for CA IX and of 3.9-245nM for hCA XII. Although the inhibition mechanism of these tertiary/secondary sulfonamides is unknown for the moment, the good efficacy and especially selectivity for the inhibition of the tumor-associated over the cytosolic, widespread isoforms, make these derivatives of considerable interest as enzyme inhibitors with various pharmacologic applications. Copyright © 2017 Elsevier Ltd. All rights reserved.

  18. Mechanism, reactivity, and regioselectivity in rhodium-catalyzed asymmetric ring-opening reactions of oxabicyclic alkenes: a DFT Investigation

    PubMed Central

    Qi, Zheng-Hang; Zhang, Yi; Gao, Yun; Zhang, Ye; Wang, Xing-Wang; Wang, Yong

    2017-01-01

    The origin of the enantio- and regioselectivity of ring-opening reaction of oxabicyclic alkenes catalyzed by rhodium/Josiphos has been examined using M06-2X density functional theory(DFT). DFT calculations predict a 98% ee for the enantioselectivity and only the 1,2-trans product as one regio- and diastereomer, in excellent agreement with experimental results. The solvent tetrahydrofuran(THF) plays a key role in assisting nucleophilic attack. Orbital composition analysis of the LUMO and the NPA atomic charge calculations were conducted to probe the origins of the regioselectivity. The orbital composition analysis reveals two potential electrophilic sites of the Rh–π-allyl intermediate M3 and the NPA atomic charges demonstrate that Cα carries more positive charges than Cγ, which suggests that Cα is the electrophilic site. PMID:28074930

  19. Analyzing torquoselectivity in electrocyclic ring opening reactions of trans-3,4-dimethylcyclobutene and 3-formylcyclobutene through electronic structure principles.

    PubMed

    Morales-Bayuelo, Alejandro; Pan, Sudip; Caballero, Julio; Chattaraj, Pratim K

    2015-09-21

    The validity of maximum hardness, minimum electrophilicity and minimum polarizability principles is assessed to explain the phenomenon of torquoselectivity (inward and outward preference) in the conrotatory ring opening reactions of trans-3,4-dimethylcyclobutene into Z,Z- and E,E-butadienes and 3-formylcyclobutene into E- and Z-2,4-pentadienals. The hardness, average polarizability and electrophilicity profiles are computed along the intrinsic reaction coordinate and divided into three relevant stages. The transition states involved in the unfavorable inward conrotation of trans-3,4-dimethylcyclobutene and in the unfavorable outward conrotation of 3-formylcyclobutene are found to be higher in energy, softer, more electrophilic and more polarizable than the transition states corresponding to the torquoselective outward and inward conrotations, respectively. These observations are in conformity with the maximum hardness, minimum electrophilicity and minimum polarizability principles. The sharp changes in the local reactivity descriptors are also observed around the transition states in their respective profiles.

  20. Permanganate oxidation of diclofenac: The pH-dependent reaction kinetics and a ring-opening mechanism.

    PubMed

    Cheng, Hanyang; Song, Dean; Liu, Huijuan; Qu, Jiuhui

    2015-10-01

    In this work, the fate of diclofenac (DCF) during permanganate (Mn(VII)) oxidation was investigated at environmentally relevant pH conditions (from 5 to 9). The batch experiments showed that the kinetics of the Mn(VII)/DCF reaction follows a second-order rate law with an apparent rate constant of 1.57±0.02 M(-1) s(-1) at pH 7 and 20 °C. The half-value of DCF was calculated to be 37.5 min, when the concentration of Mn(VII) (0.4 mM) was 20-fold excess of DCF. The pH-dependence of the reaction kinetics was investigated, and the DCF reactivity with Mn(VII) was found to decrease with increasing pH. The second-order rate constants were then quantitatively described by incorporating the species distribution of DCF. A lower reactivity of the anionic DCF (DCF(-)) in comparison with its neutral counterpart (DCF(0)) was most likely attributable to the interaction between the ionized carboxylate group and amine nitrogen position, which can reduce the nucleophilicity of amine nitrogen by inductive and resonance effects. Moreover, a range of degradation products and the corresponding structures were proposed on the basis of the LC-Q-TOF-MS analysis. A detailed ring-opening reaction mechanism was proposed as follows: Mn(VII) acts as an electrophile to attack the amine moiety, leading to the formation of the primary intermediate products 2,6-dichloroaniline and 5-hydroxy-diclofenac, which can be further transformed. The further degradation proceeded through a multistep process including ring-opening, decarboxylation, hydroxylation, and cyclation reactions.

  1. Low-Temperature Molecular Layer Deposition Using Monofunctional Aromatic Precursors and Ozone-Based Ring-Opening Reactions.

    PubMed

    Svärd, Laura; Putkonen, Matti; Kenttä, Eija; Sajavaara, Timo; Krahl, Fabian; Karppinen, Maarit; Van de Kerckhove, Kevin; Detavernier, Christophe; Simell, Pekka

    2017-09-26

    Molecular layer deposition (MLD) is an increasingly used deposition technique for producing thin coatings consisting of purely organic or hybrid inorganic-organic materials. When organic materials are prepared, low deposition temperatures are often required to avoid decomposition, thus causing problems with low vapor pressure precursors. Monofunctional compounds have higher vapor pressures than traditional bi- or trifunctional MLD precursors, but do not offer the required functional groups for continuing the MLD growth in subsequent deposition cycles. In this study, we have used high vapor pressure monofunctional aromatic precursors in combination with ozone-triggered ring-opening reactions to achieve sustained sequential growth. MLD depositions were carried out by using three different aromatic precursors in an ABC sequence, namely with TMA + phenol + O3, TMA + 3-(trifluoromethyl)phenol + O3, and TMA + 2-fluoro-4-(trifluoromethyl)benzaldehyde + O3. Furthermore, the effect of hydrogen peroxide as a fourth step was evaluated for all studied processes resulting in a four-precursor ABCD sequence. According to the characterization results by ellipsometry, infrared spectroscopy, and X-ray reflectivity, self-limiting MLD processes could be obtained between 75 and 150 °C with each of the three aromatic precursors. In all cases, the GPC (growth per cycle) decreased with increasing temperature. In situ infrared spectroscopy indicated that ring-opening reactions occurred in each ABC sequence. Compositional analysis using time-of-flight elastic recoil detection indicated that fluorine could be incorporated into the film when 3-(trifluoromethyl)phenol and 2-fluoro-4-(trifluoromethyl)benzaldehyde were used as precursors.

  2. Fe@Fe2O3 promoted electrochemical mineralization of atrazine via a triazinon ring opening mechanism.

    PubMed

    Ding, Xing; Wang, Shengyao; Shen, Wanqiu; Mu, Yi; Wang, Li; Chen, Hao; Zhang, Lizhi

    2017-04-01

    In this study, an electrochemical/electro-Fenton oxidation (EC/EF) system was designed to degrade atrazine, by utilizing boron-doped diamond (BDD) and Fe@Fe2O3 core-shell nanowires loaded active carbon fiber (Fe@Fe2O3/ACF) as the anode and the cathode, respectively. This EC/EF system exhibited much higher degradation rate, decholorination and mineralization efficiency of atrazine than the electrochemical (EC) and electrochemical/traditional electro-Fenton (EC/TEF) oxidation counterpart systems without Fe@Fe2O3 core-shell nanowires. Active species trapping experiment revealed that Fe@Fe2O3 could activate molecular oxygen to produce more OH through Fenton reaction, which favored the atrazine degradation. High performance liquid chromatography, high performance liquid chromatography-mass spectrometry and gas chromatography-mass spectrometry were applied to probe the decomposition and mineralization of atrazine during this novel EC/EF process, which revealed that two intermediates of triazinons (the isomerization of hydroxylated atrazine) were generated during the electrochemical/electro-Fenton oxidation of atrazine in the presence of Fe@Fe2O3 core-shell nanowires. The experimental and theoretical calculation results suggested that atrazine might be degraded via a triazinon ring opening mechanism, while the presence of Fe@Fe2O3 notably accelerated the decholorination process, and produced more hydroxylated products to promote the generation of trazinons and the subsequent ring cleavage as well as the final complete mineralization. This work provides a deep insight into the triazine ring opening mechanism and the design of efficient electrochemical advanced oxidation technologies (EAOTs) for persistent organic pollutant removal. Copyright © 2017 Elsevier Ltd. All rights reserved.

  3. Structural effects on the beta-scission reaction of alkoxyl radicals. Direct measurement of the absolute rate constants for ring opening of benzocycloalken-1-oxyl radicals.

    PubMed

    Bietti, Massimo; Lanzalunga, Osvaldo; Salamone, Michela

    2005-02-18

    [reaction: see text] The absolute rate constants for beta-scission of a series of benzocycloalken-1-oxyl radicals and of the 2-(4-methylphenyl)-2-butoxyl radical have been measured directly by laser flash photolysis. The benzocycloalken-1-oxyl radicals undergo ring opening with rates which parallel the ring strain of the corresponding cycloalkanes. In the 1-X-indan-1-oxyl radical series, ring opening is observed when X = H, Me, whereas exclusive C-X bond cleavage occurs when X = Et. The factors governing the fragmentation regioselectivity are discussed.

  4. One-Pot Acid-Catalyzed Ring-Opening/Cyclization/Oxidation of Aziridines with N-Tosylhydrazones: Access to 1,2,4-Triazines.

    PubMed

    Crespin, Lorène; Biancalana, Lorenzo; Morack, Tobias; Blakemore, David C; Ley, Steven V

    2017-03-03

    A new, three-step, telescoped reaction sequence for the regioselective conversion of N-tosyl hydrazones and aziridines to 3,6-disubstituted and 3,5,6-trisubstituted 1,2,4-triazines is described. The process involves an efficient nucleophilic ring opening of the aziridine, giving access to a wide range of aminohydrazones, isolated with excellent yields. A "one-pot" procedure, combining the ring opening with a cyclization and an oxidation step, allows the preparation of diversified triazines in good yields.

  5. Intramolecular monomer-on-monomer (MoM) Mitsunobu cyclization for the synthesis of benzofused thiadiazepine-dioxides.

    PubMed

    Maity, Pradip K; Kainz, Quirin M; Faisal, Saqib; Rolfe, Alan; Samarakoon, Thiwanka B; Basha, Fatima Z; Reiser, Oliver; Hanson, Paul R

    2011-12-14

    The utilization of a monomer-on-monomer (MoM) intramolecular Mitsunobu cyclization reaction employing norbornenyl-tagged (Nb-tagged) reagents is reported for the synthesis of benzofused thiadiazepine-dioxides. Facile purification was achieved via ring-opening metathesis (ROM) polymerization initiated by one of three metathesis catalyst methods: (i) free metathesis catalyst, (ii) surface-initiated catalyst-armed silica, or (iii) surface-initiated catalyst-armed Co/C magnetic nanoparticles.

  6. FeCl3 mediated synthesis of substituted indenones by a formal [2+2] cycloaddition/ring opening cascade of o-keto-cinnamates.

    PubMed

    Dethe, Dattatraya H; Murhade, Ganesh M

    2015-07-11

    A novel FeCl3 mediated formal [2+2] cycloaddition/ring opening cascade of o-keto-cinnamates was developed for the synthesis of indenones. The reaction tolerates a broad range of functional groups, including bromide, chloride, amide, acid and ester groups.

  7. Enantioselective ring-opening reaction of meso-epoxides with ArSeH catalyzed by heterometallic Ti-Ga-Salen system.

    PubMed

    Yang, Minghua; Zhu, Chengjian; Yuan, Fang; Huang, Yijun; Pan, Yi

    2005-05-12

    The first example of enantioselective ring-opening reaction of meso-epoxides with aryl selenols to give optically active beta-arylseleno alcohol in up to 97% ee was realized, using a chiral Ti-Ga-Salen heterometallic catalyst. A strong synergistic effect of different Lewis acids in the system was exhibited in the catalytic process.

  8. Silver(I)-catalyzed dual activation of propargylic alcohol and aziridine/azetidine: triggering ring-opening and endo-selective ring-closing in a cascade.

    PubMed

    Bera, Milan; Roy, Sujit

    2009-11-20

    [Ag(COD)(2)]PF(6) catalyzes the reaction between propargyl alcohols and N-tosylaziridines/azetidines leading to a diverse range of N,O-heterocycles, namely, oxazines, oxazepines, and oxazocines via ring-opening and ring-closing in a cascade.

  9. Dicationic ring opening reactions of trans-2-phenylcyclopropylamine•HCl: electrophilic cleavage of the distal (C2-C3) bond of cyclopropanes

    PubMed Central

    Lill, Sten O. Nilsson; Naredla, Rajasekhar Reddy; Zielinski, Matthew E.; Knoecer, Larecia; Klumpp, Douglas A.

    2013-01-01

    Electrophilic ring opening of trans-2-phenylcyclopropylamine•HCl occurs at the distal (C2-C3) bond. This is consistent with weakening of the distal bond by the σ-withdrawing ammonium group and charge-charge repulsive effects in the transition state. PMID:23941589

  10. The edaravone and 3-n-butylphthalide ring-opening derivative 10b effectively attenuates cerebral ischemia injury in rats

    PubMed Central

    Hua, Kai; Sheng, Xiao; Li, Ting-ting; Wang, Lin-na; Zhang, Yi-hua; Huang, Zhang-jian; Ji, Hui

    2015-01-01

    Aim: Compound 10b is a hybrid molecule of edaravone and a ring-opening derivative of 3-n-butylphthalide (NBP). The aim of this study was to examine the effects of compound 10b on brain damage in rats after focal cerebral ischemia. Methods: SD rats were subjected to 2-h-middle cerebral artery occlusion (MCAO). At the onset of reperfusion, the rats were orally treated with NBP (60 mg/kg), edaravone (3 mg/kg), NBP (60 mg/kg)+edaravone (3 mg/kg), or compound 10b (70, 140 mg/kg). The infarct volume, motor behavior deficits, brain water content, histopathological alterations, and activity of GSH, SOD, and MDA were analyzed 24 h after reperfusion. The levels of relevant proteins in the ipsilateral striatum were examined using immunoblotting. Results: Administration of compound 10b (70 or 140 mg/kg) significantly reduced the infarct volume and neurological deficits in MCAO rats. The neuroprotective effects of compound 10b were more pronounced compared to NBP, edaravone or NBP+edaravone. Furthermore, compound 10b significantly upregulated the protein levels of the cytoprotective molecules Bcl-2, HO-1, Nrf2, Trx, P-NF-κB p65, and IκB-α, while decreasing the expression of Bax, caspase 3, caspase 9, Txnip, NF-κB p65, and P-IκB-α. Conclusion: Oral administration of compound 10b effectively attenuates rat cerebral ischemia injury. PMID:26073328

  11. Near ultraviolet photochemistry of 2-bromo- and 2-iodothiophene: Revealing photoinduced ring opening in the gas phase?

    NASA Astrophysics Data System (ADS)

    Marchetti, Barbara; Karsili, Tolga N. V.; Kelly, Orla; Kapetanopoulos, Panos; Ashfold, Michael N. R.

    2015-06-01

    Velocity map imaging methods, with a new and improved ion optics design, have been used to explore the near ultraviolet photodissociation dynamics of gas phase 2-bromo- and 2-iodothiophene molecules. In both cases, the ground (X) and spin-orbit excited (X*) (where X = Br, I) atom products formed at the longest excitation wavelengths are found to recoil with fast, anisotropic velocity distributions, consistent with prompt C-X bond fission following excitation via a transition whose dipole moment is aligned parallel to the breaking bond. Upon tuning to shorter wavelengths, this fast component fades and is progressively replaced by a slower, isotropic recoil distribution. Complementary electronic structure calculations provide a plausible explanation for this switch in fragmentation behaviour—namely, the opening of a rival C-S bond extension pathway to a region of conical intersection with the ground state potential energy surface. The resulting ground state molecules are formed with more than sufficient internal energy to sample the configuration space associated with several parent isomers and to dissociate to yield X atom products in tandem with both cyclic and ring-opened partner fragments.

  12. Studies Dealing with the Cycloaddition/Ring Opening/Elimination Sequence of 2-Amino-Substituted Isobenzofurans.

    PubMed

    Padwa, Albert; Kappe, C. Oliver; Cochran, John E.; Snyder, James P.

    1997-05-02

    The alpha-thiocarbocation generated from the Pummerer reaction of an o-amido-substituted sulfoxide is intercepted by the adjacent amido carbonyl group to produce a 2-amino-substituted isobenzofuran as a transient intermediate. In the presence of an electron-deficient dienophile, the reactive isobenzofuran undergoes a Diels-Alder cycloaddition followed by ring opening to furnish a vinylogous C-acyliminium ion that readily aromatizes. The one-pot intramolecular cascade process only occurs either if the olefinic tether is activated by an ester or if a carbonyl group is located adjacent to the nitrogen atom of the 2-amino-substituted isobenzofuran. To examine the amine vs amide influence on the course of intramolecular cycloaddition, density functional theory (DFT) calculations have been carried out for both ground and transition states. The results strongly suggest that the amide-substituted isobenzofurans are destabilized by steric effects between the aromatic ring and the nitrogen-containing side chain. Raising of the ground-state amide energies thereby reduces the activation energy for internal cycloaddition and leads to Diels-Alder adducts more rapidly than for the corresponding amines. Amide tethers emerge as remote-site promoters of intramolecular cycloaddition for tandem processes yielding products with multiple fused rings.

  13. Near ultraviolet photochemistry of 2-bromo- and 2-iodothiophene: Revealing photoinduced ring opening in the gas phase?

    SciTech Connect

    Marchetti, Barbara; Karsili, Tolga N. V.; Ashfold, Michael N. R.; Kelly, Orla; Kapetanopoulos, Panos

    2015-06-14

    Velocity map imaging methods, with a new and improved ion optics design, have been used to explore the near ultraviolet photodissociation dynamics of gas phase 2-bromo- and 2-iodothiophene molecules. In both cases, the ground (X) and spin-orbit excited (X*) (where X = Br, I) atom products formed at the longest excitation wavelengths are found to recoil with fast, anisotropic velocity distributions, consistent with prompt C–X bond fission following excitation via a transition whose dipole moment is aligned parallel to the breaking bond. Upon tuning to shorter wavelengths, this fast component fades and is progressively replaced by a slower, isotropic recoil distribution. Complementary electronic structure calculations provide a plausible explanation for this switch in fragmentation behaviour—namely, the opening of a rival C–S bond extension pathway to a region of conical intersection with the ground state potential energy surface. The resulting ground state molecules are formed with more than sufficient internal energy to sample the configuration space associated with several parent isomers and to dissociate to yield X atom products in tandem with both cyclic and ring-opened partner fragments.

  14. Catalytic oxidative ring opening of THF promoted by a carboxylate-bridged diiron complex, triarylphosphines, and dioxygen.

    PubMed

    Moreira, Rayane F; Tshuva, Edit Y; Lippard, Stephen J

    2004-07-12

    The catalytic oxidation of triphenylphosphine in the presence of dioxygen by the diiron(II) complex [Fe(2)(micro-O(2)CAr(Tol))(2)(Me(3)TACN)(2)(MeCN)(2)](OTf)(2) (1), where (-)O(2)CAr(Tol) = 2,6-di(p-tolyl)benzoate and Me(3)TACN = 1,4,7-trimethyl-1,4,7-triazacyclononane, has been investigated. The corresponding diiron(III) complex, [Fe(2)(micro-O)(micro-O(2)CAr(Tol))(2)(Me(3)TACN)(2)](OTf)(2) (2), the only detectable iron-containing species during the course of the reaction, can itself promote the reaction. Phosphine oxidation is coupled to the catalytic oxidation of THF solvent to afford, selectively, the C-C bond-cleavage product 3-hydroxypropylformate, an unprecedented transformation. After consumption of the phosphine, solvent oxidation continues but results in the products 2-hydroperoxytetrahydrofuran, butyrolactone, and butyrolactol. The similarities of the reaction pathways observed in the presence and absence of catalyst, as well as (18)O labeling, solvent dependence, and radical probe experiments, provide evidence that the oxidation is initiated by a metal-centered H-atom abstraction from THF. A mechanism for catalysis is proposed that accounts for the coupled oxidation of the phosphine and the THF ring-opening reaction.

  15. A Specific Nucleophilic Ring-Opening Reaction of Aziridines as a Unique Platform for the Construction of Hydrogen Polysulfides Sensors

    SciTech Connect

    Chen, Wei; Rosser, Ethan W.; Zhang, Di; Shi, Wen; Li, Yilin; Dong, Wen-Ji; Ma, Huimin; Hu, Dehong; Xian, Ming

    2015-05-11

    Hydrogen polysulfides (H2Sn, n>1) have been recently suggested to be the actual signalling molecules that involved in sulfur-related redox biology. However the exact mechanisms of H2Sn are still poorly understood and a major hurdle in this field is the lack of reliable and convenient methods for H2Sn detection. In this work we report a unique ring-opening reaction of N-sulfonylaziridine by Na2S2 under mild conditions. Based on this reaction a novel H2Sn-specific fluorescent probe (AP) was developed. The probe showed high sensitivity and selectivity for H2Sn. Notably, the fluorescent turn-on product, i.e. compound 1, exhibited excellent two-photon photophysical properties and a large Stokes shift. Moreover, the high solid state luminescent efficiency of compound 1 makes it a potential candidate for organic emitters and solid-state lighting devices.

  16. An alkyne metathesis-based route toortho-dehydrobenzannulenes

    SciTech Connect

    Miljanic, Ognjen S.; Vollhardt, Peter C.; Whitener, Glenn D.

    2002-11-07

    An application of alkyne metathesis to 1,2-di(prop-1-ynyl)arenes, producing dehydrobenzannulenes, is described. An efficient method for selective Sonogashira couplings of bromoiodoarenes under conditions of microwave irradiation is also reported.

  17. Synthetic, mechanistic, and computational investigations of nitrile-alkyne cross-metathesis.

    PubMed

    Geyer, Andrea M; Wiedner, Eric S; Gary, J Brannon; Gdula, Robyn L; Kuhlmann, Nicola C; Johnson, Marc J A; Dunietz, Barry D; Kampf, Jeff W

    2008-07-16

    The terminal nitride complexes NW(OC(CF 3) 2Me) 3(DME) ( 1-DME), [Li(DME) 2][NW(OC(CF 3) 2Me) 4] ( 2), and [NW(OCMe 2CF 3) 3] 3 ( 3) were prepared in good yield by salt elimination from [NWCl 3] 4. X-ray structures revealed that 1-DME and 2 are monomeric in the solid state. All three complexes catalyze the cross-metathesis of 3-hexyne with assorted nitriles to form propionitrile and the corresponding alkyne. Propylidyne and substituted benzylidyne complexes RCW(OC(CF 3) 2Me) 3 were isolated in good yield upon reaction of 1-DME with 3-hexyne or 1-aryl-1-butyne. The corresponding reactions failed for 3. Instead, EtCW(OC(CF 3)Me 2) 3 ( 6) was prepared via the reaction of W 2(OC(CF 3)Me 2) 6 with 3-hexyne at 95 degrees C. Benzylidyne complexes of the form ArCW(OC(CF 3)Me 2) 3 (Ar = aryl) then were prepared by treatment of 6 with the appropriate symmetrical alkyne ArCCAr. Three coupled cycles for the interconversion of 1-DME with the corresponding propylidyne and benzylidyne complexes via [2 + 2] cycloaddition-cycloreversion were examined for reversibility. Stoichiometric reactions revealed that both nitrile-alkyne cross-metathesis (NACM) cycles as well as the alkyne cross-metathesis (ACM) cycle operated reversibly in this system. With catalyst 3, depending on the aryl group used, at least one step in one of the NACM cycles was irreversible. In general, catalyst 1-DME afforded more rapid reaction than did 3 under comparable conditions. However, 3 displayed a slightly improved tolerance of polar functional groups than did 1-DME. For both 1-DME and 3, ACM is more rapid than NACM under typical conditions. Alkyne polymerization (AP) is a competing reaction with both 1-DME and 3. It can be suppressed but not entirely eliminated via manipulation of the catalyst concentration. As AP selectively removes 3-hexyne from the system, tandem NACM-ACM-AP can be used to prepare symmetrically substituted alkynes with good selectivity, including an arylene-ethynylene macrocycle

  18. Synthesis and characterization of polymeric materials derived from 2,5-diketopiperazines and pyroglutamic acid

    NASA Astrophysics Data System (ADS)

    Parrish, Dennis Arch

    The research presented in this dissertation describes the investigation of 2,5-diketopiperazines (DKPs) as property modifiers for addition polymers and the self association behavior of pyroglutamic acid derivatives. The first project involved the copolymerization of methyl methacrylate and styrene with DKP-based methacrylate monomers. Low incorporations of serine- and aspartame-based DKPs in the copolymer resulted in dramatic increases in the glass transition temperature (Ts). The research presented in Chapter II focuses on the ring-opening reactions of pyroglutamic diketopiperazine (pyDKP). The original intent was to synthesize polymers containing backbone DKPs through ring-opening polymerization of the five-membered rings. However, it was discovered that regioselective ring-opening occurs at the six-membered ring to give pyroglutamic acid derivatives. Since this reaction had not been reported previously, the focus of research was altered to investigate the scope and limitations of the new reaction. The ring-opening reactions of pyDKP with diamines to give bispyroglutamides is described in Chapter IV. While these materials are not polymeric, they display polymeric behavior. It was found that multi-functional pyroglutamides display Tgs during thermal analysis, exhibit high thermal stability, and form melt-drawn fibers. In contrast, the materials have low solution viscosities and are freely soluble in water, ethanol, and chloroform. This behavior is attributed to non-covalent supramolecular associations. The final part of this dissertation involved the investigation of thermoreversible organic solvent gelators. The ring-opening reaction of pyDKP with long alkyl amines unexpectedly gelled the reaction solvent. A series of analogous gelators were synthesized, and the minimum concentration required for gelation in various solvents was determined. It was found that the nature of the solvent, alkyl chain length, and optical activity of the gelator determined gelator

  19. Examining the wake structure in Saturn's rings from microwave observations over varying ring opening angles and wavelengths

    NASA Astrophysics Data System (ADS)

    Dunn, David E.; de Pater, Imke; Molnar, Lawrence A.

    2007-12-01

    Over the last 15 to 20 years several high quality, high resolution data have been taken with the very large array (VLA). These data exhibit a wide range of ring opening angles ( |B|=0 to 26°) and wavelengths ( λ=0.7 to 20 cm). At these wavelengths the primary flux from the rings is scattered saturnian thermal emission, with a small contribution coming from the ring particles' own thermal emission. Much of the data do show signs of asymmetries due to wakes either on the ansae or the portion of the rings which occult the planet. As in previous work, we use our Monte Carlo radiative transfer code including idealized wakes [Dunn, D.E., Molnar, L.A., Fix, J.D., 2002. Icarus 160, 132-160; Dunn, D.E., Molnar, L.A., Niehof, J.T., de Pater, I., Lissauer, J.L., 2004. Icarus 171, 183-198] to model the relative contributions of the scattered and thermal radiation emanating from the rings and compare the results to that seen in the data. Although the models do give satisfactory fits to all of our data, we find that no single model can simulate the data at all different |B| and λ. We find that one model works best for moderate and low |B| and another one at higher |B|. The main difference between these models is the ratio of the wake width to their separation. We similarly find that the 2 cm data require higher density wakes than the longer wavelength data, perhaps caused by a preponderance of somewhat smaller ring material in the wakes. We further find evidence for an increase in the physical temperature of the rings with increasing |B|. Continuous observations are required to determine whether the above results regarding variations in wake parameters with |B| and λ are indeed caused by these parameters, or instead by changes over time.

  20. Photoisomerization among ring-open merocyanines. I. Reaction dynamics and wave-packet oscillations induced by tunable femtosecond pulses

    NASA Astrophysics Data System (ADS)

    Ruetzel, Stefan; Diekmann, Meike; Nuernberger, Patrick; Walter, Christof; Engels, Bernd; Brixner, Tobias

    2014-06-01

    Upon ultraviolet excitation, photochromic spiropyran compounds can be converted by a ring-opening reaction into merocyanine molecules, which in turn can form several isomers differing by cis and trans configurations in the methine bridge. Whereas the spiropyran-merocyanine conversion reaction of the nitro-substituted indolinobenzopyran 6-nitro-1',3',3'-trimethylspiro[2H-1-benzopyran-2,2'-indoline] (6-nitro BIPS) has been studied extensively in theory and experiments, little is known about photoisomerization among the merocyanine isomers. In this article, we employ femtosecond transient absorption spectroscopy with variable excitation wavelengths to investigate the excited-state dynamics of the merocyanine in acetonitrile at room temperature, where exclusively the trans-trans-cis (TTC) and trans-trans-trans (TTT) isomers contribute. No photochemical ring-closure pathways exist for the two isomers. Instead, we found that (18±4)% of excited TTC isomers undergo an ultrafast excited-state cis→trans photoisomerization to TTT within 200 fs, while the excited-state lifetime of TTC molecules that do not isomerize is 35 ps. No photoisomerization was detected for the TTT isomer, which relaxes to the ground state with a lifetime of roughly 160 ps. Moreover, signal oscillations at 170 cm-1 and 360 cm-1 were observed, which can be ascribed to excited-state wave-packet dynamics occurring in the course of the TTC→TTT isomerization. The results of high-level time-dependent density functional theory in conjunction with polarizable continuum models are presented in the subsequent article [C. Walter, S. Ruetzel, M. Diekmann, P. Nuernberger, T. Brixner, and B. Engels, J. Chem. Phys. 140, 224311 (2014)].

  1. 2-Pyridylnitrene and 3-pyridazylcarbene and their relationship via ring-expansion, ring-opening, ring-contraction, and fragmentation.

    PubMed

    Kvaskoff, David; Bednarek, Pawel; Wentrup, Curt

    2010-03-05

    Photolysis of triazolo[1,5-b]pyridazine 8 isolated in Ar matrix generates diazomethylpyridazines 9Z and 9E and diazopentenynes 11Z and 11E as detected by IR spectroscopy. ESR spectroscopy detected the 3-pydidazylcarbene 10 as well as pent-2-en-3-yn-1-ylidene 12 formed by loss of one and two molecules of N(2), respectively. Further photolysis caused rearrangement of the carbenes to 1,2-pentadien-4-yne 13 and 3-ethynylcyclopropene 14. Flash vacuum thermolysis (FVT) of 8 at 400-500 degrees C with Ar matrix isolation of the products yielded 13, 14, and 1,4-pentadiyne 15. At higher temperatures, glutacononitriles 27Z and 27E were formed as well together with minor amounts of 2- and 3-cyanopyrroles 28 and 29. Tetrazolo[1,5-a]pyridine/2-azidopyridine 22T/22A yields 2-pyridylnitrene 19 as well as the novel open-chain cyanodienylnitrene 23 and the ring-expanded 1,3-diazacyclohepta-1,2,4,6-tetraene 21 on short wavelength photolysis. Nitrenes 19 and 23 were detected by ESR spectroscopy, and cumulene 21 by IR and UV spectroscopy. FVT of 22T/22A also affords 2-pyridylnitrene 19 and diazacycloheptatetraene 21, as well as glutacononitriles 27Z,E and 2- and 3-cyanopyrroles 28 and 29. Photolysis of 21 above 300 nm yields the novel spiroazirene 25, identified by its matrix IR spectrum. The reaction pathways connecting the four carbenes (10Z,E and 12Z,E) and three nitrenes (19, 23EZ, and 23ZZ) in their open-shell singlet and triplet states are elucidated with the aid of theoretical calculations at DFT, CASSCF, and CASPT2 levels. Three possible mechanisms of ring-contraction in arylnitrenes are identified: (i) via ring-opening to dienylnitrenes, (ii) concerted ring-contraction, and (iii) via spiroazirenes 25, whereby (i) is the energetically most favorable.

  2. Nonproductive events in ring-closing metathesis using ruthenium catalysts.

    PubMed

    Stewart, Ian C; Keitz, Benjamin K; Kuhn, Kevin M; Thomas, Renee M; Grubbs, Robert H

    2010-06-30

    The relative TONs of productive and nonproductive metathesis reactions of diethyl diallylmalonate are compared for eight different ruthenium-based catalysts. Nonproductive cross metathesis is proposed to involve a chain-carrying ruthenium methylidene. A second more-challenging substrate (dimethyl allylmethylallylmalonate) that forms a trisubstituted olefin product is used to further delineate the effect of catalyst structure on the relative efficiencies of these processes. A steric model is proposed to explain the observed trends.

  3. Polymeric micelles for acyclovir drug delivery.

    PubMed

    Sawdon, Alicia J; Peng, Ching-An

    2014-10-01

    Polymeric prodrug micelles for delivery of acyclovir (ACV) were synthesized. First, ACV was used directly to initiate ring-opening polymerization of ɛ-caprolactone to form ACV-polycaprolactone (ACV-PCL). Through conjugation of hydrophobic ACV-PCL with hydrophilic methoxy poly(ethylene glycol) (MPEG) or chitosan, polymeric micelles for drug delivery were formed. (1)H NMR, FTIR, and gel permeation chromatography were employed to show successful conjugation of MPEG or chitosan to hydrophobic ACV-PCL. Through dynamic light scattering, zeta potential analysis, transmission electron microscopy, and critical micelle concentration (CMC), the synthesized ACV-tagged polymeric micelles were characterized. It was found that the average size of the polymeric micelles was under 200nm and the CMCs of ACV-PCL-MPEG and ACV-PCL-chitosan were 2.0mgL(-1) and 6.6mgL(-1), respectively. The drug release kinetics of ACV was investigated and cytotoxicity assay demonstrates that ACV-tagged polymeric micelles were non-toxic.

  4. Polymeric Micelles for Acyclovir Drug Delivery

    PubMed Central

    Sawdon, Alicia J.; Peng, Ching-An

    2014-01-01

    Polymeric prodrug micelles for delivery of acyclovir (ACV) were synthesized. First, ACV was used directly to initiate ring-opening polymerization of ε-caprolactone to form ACV-polycaprolactone (ACV-PCL). Through conjugation of hydrophobic ACV-PCL with hydrophilic methoxy poly(ethylene glycol) (MPEG) or chitosan, polymeric micelles for drug delivery were formed. 1H NMR, FTIR, and gel permeation chromatography were employed to show successful conjugation of MPEG or chitosan to hydrophobic ACV-PCL. Through dynamic light scattering, zeta potential analysis, transmission electron microscopy, and critical micelle concentration (CMC), the synthesized ACV-tagged polymeric micelles were characterized. It was found that the average size of the polymeric micelles was under 200 nm and the CMCs of ACV-PCLMPEG and ACV-PCL-chitosan were 2.0 mg L−1 and 6.6 mg L−1, respectively. The drug release kinetics of ACV was investigated and cytotoxicity assay demonstrates that ACV-tagged polymeric micelles were non-toxic. PMID:25193154

  5. Iron(III)-catalysed carbonyl-olefin metathesis

    NASA Astrophysics Data System (ADS)

    Ludwig, Jacob R.; Zimmerman, Paul M.; Gianino, Joseph B.; Schindler, Corinna S.

    2016-05-01

    The olefin metathesis reaction of two unsaturated substrates is one of the most powerful carbon-carbon-bond-forming reactions in organic chemistry. Specifically, the catalytic olefin metathesis reaction has led to profound developments in the synthesis of molecules relevant to the petroleum, materials, agricultural and pharmaceutical industries. These reactions are characterized by their use of discrete metal alkylidene catalysts that operate via a well-established mechanism. While the corresponding carbonyl-olefin metathesis reaction can also be used to construct carbon-carbon bonds, currently available methods are scarce and severely hampered by either harsh reaction conditions or the required use of stoichiometric transition metals as reagents. To date, no general protocol for catalytic carbonyl-olefin metathesis has been reported. Here we demonstrate a catalytic carbonyl-olefin ring-closing metathesis reaction that uses iron, an Earth-abundant and environmentally benign transition metal, as a catalyst. This transformation accommodates a variety of substrates and is distinguished by its operational simplicity, mild reaction conditions, high functional-group tolerance, and amenability to gram-scale synthesis. We anticipate that these characteristics, coupled with the efficiency of this reaction, will allow for further advances in areas that have historically been enhanced by olefin metathesis.

  6. Research Update: A hafnium-based metal-organic framework as a catalyst for regioselective ring-opening of epoxides with a mild hydride source

    SciTech Connect

    Stephenson, Casey J.; Hassan Beyzavi, M.; Klet, Rachel C.; Hupp, Joseph T. E-mail: o-farha@northwestern.edu; Farha, Omar K. E-mail: o-farha@northwestern.edu

    2014-12-01

    Reaction of styrene oxide with sodium cyanoborohydride and a catalytic amount of Hf-NU-1000 yields the anti-Markovnikov product, 2-phenylethanol, with over 98% regioselectivity. On the other hand, propylene oxide is ring opened in a Markovnikov fashion to form 2-propanol with 95% regioselectivity. Both styrene oxide and propylene oxide failed to react with sodium cyanoborohydride without the addition of Hf-NU-1000 indicative of the crucial role of Hf-NU-1000 as a catalyst in this reaction. To the best of our knowledge, this is the first report of the use of a metal-organic framework material as a catalyst for ring-opening of epoxides with hydrides.

  7. LITHIUM CHLORIDE AS CATALYST FOR THE RING-OPENING POLYMERIZATION OF LACTIDE IN THE PRESENCE OF HYDROXYL-CONTAINING COMPOUNDS. (R826123)

    EPA Science Inventory

    The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...

  8. LITHIUM CHLORIDE AS CATALYST FOR THE RING-OPENING POLYMERIZATION OF LACTIDE IN THE PRESENCE OF HYDROXYL-CONTAINING COMPOUNDS. (R826123)

    EPA Science Inventory

    The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...

  9. Composite Materials with Improved Properties in Compression. Appendix 5. Synthesis and Anionic Ring Opening Polymerization of 1-Germa-1,1-dimethyl(3,4,c) thienocyclopentane

    DTIC Science & Technology

    1990-05-09

    Include Security Classification) (U) COMPOSITE MATERIALS WITH IMPROVED PROPERTIES IN COMPRESSION 12. PERSONAL AUTHOR(S) Stephen Q. Zhou and William P...properties. For example, they have been found to be photoactive. They undergoyhotobleaching b as well as to have thermochromic properties. , Most...been considerable interest in conjugated polythiophene which can be converted to high1l con- ducting materials by treatment with oxidative dopants

  10. One-pot synthesis of 2-amino-4(3H)-quinazolinones via ring-opening of isatoic anhydride and palladium-catalyzed oxidative isocyanide-insertion.

    PubMed

    Ji, Fei; Lv, Mei-Fang; Yi, Wen-Bin; Cai, Chun

    2014-08-14

    An efficient and practical two-step process has been developed for the synthesis of 2-amino-4(3H)-quinazolinones via ring-opening of isatoic anhydride and palladium-catalyzed oxidative isocyanide-insertion in one pot. This regioselective procedure could construct a wide range of 2-amino-4(3H)-quinazolinones in moderate to excellent yields. Furthermore, the methodology also had distinct advantages of easily accessible starting materials and operational simplicity.

  11. A new chiral Fe(III)-salen grafted mesoporous catalyst for enantioselective asymmetric ring opening of racemic epoxides at room temperature under solvent-free conditions.

    PubMed

    Roy, Susmita; Bhanja, Piyali; Safikul Islam, Sk; Bhaumik, Asim; Islam, Sk Manirul

    2016-01-31

    We have designed a new mesoporous SBA-15 supported chiral Fe(III)-salen material (Fe@SBSAL) having high BET surface area and porosity. The material showed excellent catalytic efficiency in regio- and enantioselective (ee > 99%) asymmetric ring opening (ARO) of racemic meso- and terminal-epoxides with various anilines at room temperature under solvent-free conditions within 1-3 h reaction time.

  12. The Effect of K and Acidity of NiW-Loaded HY Zeolite Catalyst for Selective Ring Opening of 1-Methylnaphthalene.

    PubMed

    Lee, You-Jin; Kim, Eun-Sang; Kim, Jeong-Rang; Kim, Joo-Wan; Kim, Tae-Wan; Chae, Ho-Jeong; Kim, Chul-Ung; Lee, Chang-Ha; Jeong, Soon-Yong

    2016-05-01

    Bi-functional catalysts were prepared using HY zeolites with various SiO2/Al2O3 ratios for acidic function, NiW for metallic function, and K for acidity control. 1-Methylnaphthalene was selected as a model compound for multi-ring aromatics in heavy oil, and its selective ring opening reaction was investigated using the prepared bi-functional catalysts with different levels of acidity in a fixed bed reactor system. In NiW/HY catalysts without K addition, the acidity decreased with the SiO2/Al2O3 mole ratio of the HY zeolite. Ni1.1W1.1/HY(12) catalyst showed the highest acidity but slightly lower yields for the selective ring opening than Ni1.1W1.1/HY(30) catalyst. The acidity of the catalyst seemed to play an important role as the active site for the selective ring opening of 1-methylnaphthalene but there should be some optimum catalyst acidity for the reaction. Catalyst acidity could be controlled between Ni1.1W1.1/HY(12) and Ni1.1W1.1/HY(30) by adding a moderate amount of K to Ni1.1W1.1/HY(12) catalyst. K0.3Ni1.1W1.1/HY(12) catalyst should have the optimum acidity for the selective ring opening. The addition of a moderate amount of K to the NiW/HY catalyst must improve the catalytic performance due to the optimization of catalyst acidity.

  13. Asymmetric Ring-Opening Reactions of Aza- and Oxa-bicyclic Alkenes with Boronic Acids Using a Palladium/Zinc Co-catalytic System.

    PubMed

    Zhang, Wei; Chen, Jingchao; Zeng, Guangzhi; Yang, Fan; Xu, Jianbin; Sun, Weiqing; Shinde, Madhuri Vikas; Fan, Baomin

    2017-03-03

    The asymmetric ring opening reactions of bicyclic alkenes with boronic acids were accomplished by using a highly active palladium/zinc co-catalytic system that was suitable for both azabenzonorbornadienes and oxabenzonorbornadienes, which were transformed to the corresponding chiral hydronaphthalene products in high yields (up to 99%) and high optical purities (up to 98% ee). The reaction protocol is general and mild and displays good functional group tolerance.

  14. Indium-Catalyzed Amide Allylation of N-Carbonyl Imides: Formation of Azaspiro-γ-lactones via Ring Opening-Reclosure.

    PubMed

    Sengoku, Tetsuya; Murata, Yusuke; Aso, Yuwa; Kawakami, Ai; Inuzuka, Toshiyasu; Sakamoto, Masami; Takahashi, Masaki; Yoda, Hidemi

    2015-12-04

    A novel and facile synthesis of azaspiro-γ-lactones with a methylene-lactam framework from N-carbonyl imides is described. Mechanistic investigations provide evidence for a two-step reaction process involving ZnCl(2)-promoted addition of β-amido allylindium species followed by an unexpectedly molecular-sieves-mediated ring opening-reclosure concomitantly with the loss of an N-carbonyl unit.

  15. A Synthetic Route to Chiral 1,4-Disubstituted Tetrahydro-β-Carbolines via Domino Ring-Opening Cyclization of Activated Aziridines with 2-Vinylindoles.

    PubMed

    Sayyad, Masthanvali; Wani, Imtiyaz Ahmad; Babu, Raja; Nanaji, Yerramsetti; Ghorai, Manas K

    2017-03-03

    A simple and efficient strategy for the synthesis of various 1,4-disubstituted tetrahydro-β-carbolines with excellent stereoselectivity (de, ee up to >99%) via domino ring opening cyclization (DROC) of activated aziridines with 2-vinylindoles is described. The reaction proceeds through LiClO4-catalyzed Friedel-Crafts-type alkylation of 2-vinylindoles with activated aziridines followed by an intramolecular aza-Michael reaction in a domino fashion.

  16. A Stereoselective Route to Tetrahydrobenzoxazepines and Tetrahydrobenzodiazepines via Ring-Opening and Aza-Michael Addition of Activated Aziridines with 2-Hydroxyphenyl and 2-Aminophenyl Acrylates.

    PubMed

    Shahi, Chandan Kumar; Bhattacharyya, Aditya; Nanaji, Yerramsetti; Ghorai, Manas K

    2017-01-06

    A simple and efficient synthetic route to 2,3,4,5-tetrahydrobenzoxazepines and -benzodiazepines bearing easily functionalizable appendages has been developed by ring-opening of activated aziridines with 2-hydroxyphenyl acrylates and 2-aminophenyl acrylate, respectively, and subsequent intramolecular C-N bond formation through palladium-catalyzed aza-Michael reaction. The straightforward synthetic approach delivers the desired molecular scaffolds in high yields (up to 82%) with excellent stereoselectivity (ee up to 94%).

  17. Metathesis depolymerization for removable surfactant templates.

    SciTech Connect

    Zifer, Thomas; Wheeler, David Roger; Rahimian, Kamayar; McElhanon, James Ross; Long, Timothy Michael; Jamison, Gregory Marks; Loy, Douglas Anson; Kline, Steven R.; Simmons, Blake Alexander

    2005-03-01

    Current methodologies for the production of meso- and nanoporous materials include the use of a surfactant to produce a self-assembled template around which the material is formed. However, post-production surfactant removal often requires centrifugation, calcination, and/or solvent washing which can damage the initially formed material architecture(s). Surfactants that can be disassembled into easily removable fragments following material preparation would minimize processing damage to the material structure, facilitating formation of templated hybrid architectures. Herein, we describe the design and synthesis of novel cationic and anionic surfactants with regularly spaced unsaturation in their hydrophobic hydrocarbon tails and the first application of ring closing metathesis depolymerization to surfactant degradation resulting in the mild, facile decomposition of these new compounds to produce relatively volatile nonsurface active remnants.

  18. Synthetic and theoretical investigation on the one-pot halogenation of β-amino alcohols and nucleophilic ring opening of aziridinium ions.

    PubMed

    Chen, Yunwei; Sun, Xiang; Wu, Ningjie; Li, Jingbai; Jin, Shengnan; Zhong, Yongliang; Liu, Zirui; Rogachev, Andrey; Chong, Hyun-Soon

    2016-01-21

    Aziridinium ions are useful reactive intermediates for the synthesis of enantiomerically enriched building blocks. However, N,N-dialkyl aziridinium ions are relatively underutilized in the synthesis of optically active molecules as compared to other three-membered ring cogeners, aziridines and epoxides. The characterization of both optically active aziridinium ions and secondary β-halo amines as the precursor molecules of aziridinium ions has been scarcely reported and is often unclear. In this paper, we report for the first time the preparation and experimental and theoretical characterization of optically active aziridinium ions and secondary β-halo amines. Optically active secondary N,N-substituted β-halo amines were efficiently synthesized from N,N-substituted alaninol via formation and ring opening at the more hindered carbon of aziridinium ions by halides. Optically active β-halo amines and aziridinium ions were characterized by NMR and computational analyses. The structure of an optically active β-chloro amine was confirmed via X-ray crystallographic analysis. The aziridinium ions derived from N,N-dibenzyl alaniol remained stable only for several hours, which was long enough for analyses of NMR and optical activity. The stereospecific ring opening of aziridinium ions by halides was computationally studied using DFT and highly-accurate DLPNO-CCSD(T) methods. The highly regioselective and stereoselective ring opening of aziridinium ions was applied for efficient one-pot conversion of β-alaninols to enantiomerically enriched β-amino alcohols, β-amino nitriles, and vicinal diamine derivatives.

  19. Enzyme-regulated topology of a cyclic peptide brush polymer for tuning assembly.

    PubMed

    Wang, Zhao; Li, Yiwen; Huang, Yuran; Thompson, Matthew P; LeGuyader, Clare L M; Sahu, Swagat; Gianneschi, Nathan C

    2015-12-14

    Norbornenyl cyclic elastin-like peptides were polymerized via ring opening metathesis polymerization (ROMP) to generate thermally responsive brush polymers. The thermally-responsive nature of the materials could be attenuated by the addition of a proteolytic enzyme that causes the cyclic peptide side chains to be linearized.

  20. On the reaction mechanism of tirapazamine reduction chemistry: unimolecular N-OH homolysis, stepwise dehydration, or triazene ring-opening.

    PubMed

    Yin, Jian; Glaser, Rainer; Gates, Kent S

    2012-03-19

    reactions of the spin-trap molecules with 2-4 concomitant with triazene ring-opening.

  1. Polymeric microspheres

    DOEpatents

    Walt, David R.; Mandal, Tarun K.; Fleming, Michael S.

    2004-04-13

    The invention features core-shell microsphere compositions, hollow polymeric microspheres, and methods for making the microspheres. The microspheres are characterized as having a polymeric shell with consistent shell thickness.

  2. Stereoretentive Olefin Metathesis: An Avenue to Kinetic Selectivity.

    PubMed

    Montgomery, T Patrick; Ahmed, Tonia S; Grubbs, Robert H

    2017-09-04

    Olefin metathesis is an incredibly valuable transformation that has gained widespread use in both academic and industrial settings. Lately, stereoretentive olefin metathesis has garnered much attention as a method for the selective generation of both E- and Z-olefins. Early studies employing ill-defined catalysts showed evidence for retention of the stereochemistry of the starting olefins at low conversion. However, thermodynamic ratios E/Z were reached as the reaction proceeded to equilibrium. Recent studies in olefin metathesis have focused on the synthesis of catalysts that can overcome the inherent thermodynamic preference of an olefin, providing synthetically useful quantities of a kinetically favored olefin isomer. These reports have led to the development of stereoretentive catalysts that not only generate Z-olefins selectively, but also kinetically produce E-olefins, a previously unmet challenge in olefin metathesis. Advancements in stereoretentive olefin metathesis using tungsten, ruthenium, and molybdenum catalysts are presented. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. Real-time propagation time-dependent density functional theory study on the ring-opening transformation of the photoexcited crystalline benzene

    NASA Astrophysics Data System (ADS)

    Tateyama, Yoshitaka; Oyama, Norihisa; Ohno, Takahisa; Miyamoto, Yoshiyuki

    2006-03-01

    Mechanism of the ring-opening transformation in the photoexcited crystalline benzene is investigated on the femtosecond scale by a computational method based on the real-time propagation (RTP) time-dependent density functional theory (TDDFT). The excited-state dynamics of the benzene molecule is also examined not only for the distinction between the intrinsic properties of molecule and the intermolecular interaction but for the first validation using the vibration frequencies for the RTP-TDDFT approach. It is found that the vibration frequencies of the excited and ground states in the molecule are well reproduced. This demonstrates that the present method of time evolution using the Suzuki-Trotter-type split operator technique starting with the Franck-Condon state approximated by the occupation change of the Kohn-Sham orbitals is adequately accurate. For the crystalline benzene, we carried out the RTP-TDDFT simulations for two typical pressures. At both pressures, large swing of the C-H bonds and subsequent twist of the carbon ring occurs, leading to tetrahedral (sp3-like) C-H bonding. The ν4 and ν16 out-of-plane vibration modes of the benzene molecule are found mostly responsible for these motions, which is different from the mechanism proposed for the thermal ring-opening transformation occurring at higher pressure. Comparing the results between different pressures, we conclude that a certain increase of the intermolecular interaction is necessary to make seeds of the ring opening (e.g., radical site formation and breaking of the molecular character) even with the photoexcitation, while the hydrogen migration to fix them requires more free volume, which is consistent with the experimental observation that the transformation substantially proceeds on the decompression.

  4. Biaryl synthesis by ring-opening Friedel-Crafts arylation of 1,4-epoxy-1,4-dihydronaphthalenes catalyzed by iron trichloride.

    PubMed

    Sawama, Yoshinari; Asai, Shota; Kawajiri, Takahiro; Monguchi, Yasunari; Sajiki, Hironao

    2015-01-26

    Biaryl and heterobiaryl compounds are important frameworks across a range of fields including pharmaceutical and functional material chemistries. We have accomplished the efficient synthesis of various naphthalene-linked arenes and heteroarenes as biaryls and heterobiaryls by the FeCl3 -catalyzed Friedel-Crafts reactions accompanied by the ring-opening of the 1,4-epoxy moiety of 1,4-epoxy-1,4-dihydronaphthalenes. Especially, it is noteworthy that 1-silylated substrates were regioselectively transformed to the 3-aryl-1-silylnaphthalenes and the double Friedel-Crafts reactions using thiophene derivatives could directly produce the corresponding bis-naphthlated thiophene derivatives.

  5. Microwave irradiation: synthesis and characterization of α-ketoamide and bis (α-ketoamide) derivatives via the ring opening of N-acetylisatin

    PubMed Central

    2014-01-01

    Background The carbonyl group at position 2 of N-acetylisatin behaves as an amide which is more susceptible to nucleophilic attack via ring-opening in the presence of nucleophiles. Because of this behavior, in the present work we describe the microwave synthesis of a series of α-ketoamide and bis-(α-ketoamide) derivatives via the facile ring-opening of N-acylisatin with different amines and diamines. The microwave irradiation afforded the product in less reaction time, higher yield and purity. Reaction of N-acylisatin with methanol under microwave irradiation afforded the α-phenylglyoxyl methyl ester derivatives with excellent yields and purities. Aminolysis of the ester derivatives with piperidine and morpholine afforded the same α-ketoamide derivatives obtained from direct aminolysis of N-acylisatin. The structures of the synthesized compounds were confirmed by FT-IR, NMR, X-ray and elemental analysis. Results Reaction of N-acetylisatin and N-propoionylsatin with different amines and diamines afforded a series of α-ketoamide and bis-(α-ketoamide) derivatives respectively via the ring opening of N-acylisatins. The reaction was performed under conventional condition as well as microwave irradiation. The microwave irradiation afforded the product in less reaction time, higher yield and purity. Reaction of N-acylisatin with methanol under microwave irradiation afforded the α-phenylglyoxyl methyl ester derivatives in excellent yields and purities as observed from their spectral data. A plausible mechanism involves nucleophilic attack by methanol at C2 carbonyl carbon of N-acetylisatin and subsequent ring opening to generate the α-ketoester. Aminolysis of α-ketoester with amine afforded the same α-ketoamide which is obtained by direct aminolysis of N-acylisatin. The IR, NMR spectra, microanalyses, and single crystal X-ray diffraction confirmed the structures of the synthesized compounds. Conclusions In conclusion, we have demonstrated that microwave

  6. Reactivity of NHC Alane Adducts towards N-Heterocyclic Carbenes and Cyclic (Alkyl)(amino)carbenes: Ring Expansion, Ring Opening, and Al-H Bond Activation.

    PubMed

    Schneider, Heidi; Hock, Andreas; Bertermann, Rüdiger; Radius, Udo

    2017-09-07

    The synthesis of mono-NHC alane adducts of the type (NHC)⋅AlH3 (NHC=Me2 Im (1), Me2 Im(Me) (2), iPr2 Im (3 and [D3 ]-3), iPr2 Im(Me) (4), Dipp2 Im (10); Im=imidazolin-2-ylidene, Dipp=2,6-diisopropylphenyl) and (NHC)⋅AliBu2 H (NHC=iPr2 Im (11), Dipp2 Im (12)) as well as their reactivity towards different types of carbenes is presented. Although the mono-NHC adducts remained stable at elevated temperatures, ring expansion occurred when (iPr2 Im)⋅AlH3 (3) was treated with a second equivalent of the carbene iPr2 Im to give (iPr2 Im)⋅AlH(RER-iPr2 ImH2 ) (6). In 6, {(iPr2 Im}AlH} is inserted into the NHC ring. In contrast, ring opening was observed with the sterically more demanding Dipp2 Im with the formation of (iPr2 Im)⋅AlH2 (ROR-Dipp2 ImH2 )H2 Al⋅(iPr2 Im) (9). In 9, two {(iPr2 Im)⋅AlH2 } moieties stabilize the ring-opened Dipp2 Im. If two hydridic sites are blocked, the adducts are stable with respect to further ring expansion or ring opening, as exemplified by the adducts (iPr2 Im)⋅AliBu2 H (11) and (Dipp2 Im)⋅AliBu2 H (12). The adducts (NHC)⋅AlH3 and (iPr2 Im)⋅AliBu2 H reacted with cAAC(Me) by insertion of the carbene carbon atom into the Al-H bond to give (NHC)⋅AlH2 /iBu2 (cAAC(Me) H) (13-18) instead of ligand substitution, ring-expansion, or ring-opened products. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. Enhancement of strong-field multiple ionization in the vicinity of the conical intersection in 1,3-cyclohexadiene ring opening

    SciTech Connect

    Petrovic, Vladimir S. Kim, Jaehee; Schorb, Sebastian; White, James; Cryan, James P.; Zipp, Lucas; Glownia, J. Michael; Broege, Douglas; Miyabe, Shungo; Tao, Hongli; Martinez, Todd; Bucksbaum, Philip H.

    2013-11-14

    Nonradiative energy dissipation in electronically excited polyatomic molecules proceeds through conical intersections, loci of degeneracy between electronic states. We observe a marked enhancement of laser-induced double ionization in the vicinity of a conical intersection during a non-radiative transition. We measured double ionization by detecting the kinetic energy of ions released by laser-induced strong-field fragmentation during the ring-opening transition between 1,3-cyclohexadiene and 1,3,5-hexatriene. The enhancement of the double ionization correlates with the conical intersection between the HOMO and LUMO orbitals.

  8. Ring-Opening of the γ-OH-PdG Adduct Promotes Error-Free Bypass by the Sulfolobus solfataricus DNA Polymerase Dpo4

    PubMed Central

    2013-01-01

    Acrolein, a mutagenic aldehyde, reacts with deoxyguanosine (dG) to form 3-(2′-deoxy-β-d-erythro-pentofuranosyl)-5,6,7,8-tetrahydro-8-hydroxypyrimido[1,2-a] purin-10(3H)-one (γ-OH-PdG). When placed opposite deoxycytosine (dC) in DNA, γ-OH-PdG undergoes ring-opening to the N2-(3-oxopropyl)-dG. Ring-opening of the adduct has been hypothesized to facilitate nonmutagenic bypass, particularly by DNA polymerases of the Y family. This study examined the bypass of γ-OH-PdG by Sulfolobus solfataricus Dpo4, the prototypic Y-family DNA polymerase, using templates that contained the adduct in either the 5′-CXG-3′ or the 5′-TXG-3′ sequence context. Although γ-OH-PdG partially blocked Dpo4-catalyzed DNA synthesis, full primer extension was observed, and the majority of bypass products were error-free. Conversion of the adduct into an irreversibly ring-opened derivative prior to reaction facilitated bypass and further improved the fidelity. Structures of ternary Dpo4·DNA·dNTP complexes were determined with primers that either were positioned immediately upstream of the lesion (preinsertion complexes) or had a 3′-terminal dC opposite the lesion (postinsertion complexes); the incoming nucleotides, either dGTP or dATP, were complementary to the template 5′-neighbor nucleotide. In both postinsertion complexes, the adduct existed as ring-opened species, and the resulting base-pair featured Watson–Crick hydrogen bonding. The incoming nucleotide paired with the 5′-neighbor template, while the primer 3′-hydroxyl was positioned to facilitate extension. In contrast, γ-OH-PdG was in the ring-closed form in both preinsertion complexes, and the overall structure did not favor catalysis. These data provide insights into γ-OH-PdG chemistry during replication bypass by the Dpo4 DNA polymerase and may explain why γ-OH-PdG-induced mutations due to primer–template misalignment are uncommon. PMID:23947567

  9. 3-Pyridylnitrene, 2- and 4-pyrimidinylcarbenes, 3-quinolylnitrenes, and 4-quinazolinylcarbenes. Interconversion, ring expansion to diazacycloheptatetraenes, ring opening to nitrile ylides, and ring contraction to cyanopyrroles and cyanoindoles

    PubMed Central

    Lan, Nguyen Mong; Lukosch, Adelheid; Bednarek, Pawel; Kvaskoff, David

    2013-01-01

    Summary Precursors of 3-pyridylnitrene and 2- and 4-pyrimidinylcarbenes all afford mixtures of 2- and 3-cyanopyrroles on flash vacuum thermolysis, but 3-cyanopyrroles are the first-formed products. 3-Quinolylnitrenes and 4-quinazolinylcarbenes similarly afford 3-cyanoindoles. 2-Pyrimidinylcarbenes rearrange to 3-pyridylnitrenes, but 4-pyrimidinylcarbenes and 4-quinazolinylcarbenes do not necessarily rearrange to the corresponding 3-pyridylnitrenes or 3-quinolylnitrenes. The ring contraction reactions are interpreted in terms of ring opening of either the nitrenes or the diazacycloheptatetraenes to nitrile ylides. PMID:23766786

  10. Fe(OTf)3 versus Bi(OTf)3 as mild catalysts in epoxide oxidative ring-opening, urea α-diketone condensation, and glycoluril diether synthesis.

    PubMed

    Mandadapu, Vijaybabu; Wu, Feng; Day, Anthony I

    2014-03-07

    The salt Fe(OTf)3 has been shown to function as an effective catalyst in three different reactions, epoxide oxidative ring-opening to an α-hydroxy ketone, urea α-diketone condensation to form glycolurils, and glycoluril diether synthesis by formaldehyde condensation. In each of these reactions, Fe(OTf)3 was compared to Bi(OTf)3, a viable alternative catalyst with few or no prior examples of this type. Differences and advantages are highlighted but in most cases yields were generally high, and both catalysts outperformed conventional acid catalyzed methods.

  11. Regioselective palladium-catalyzed ring-opening reactions of C1-substituted oxabicyclo[2,2,1]hepta-2,5-diene-2,3-dicarboxylates

    PubMed Central

    Edmunds, Michael; Raheem, Mohammed Abdul; Boutin, Rebecca; Tait, Katrina

    2016-01-01

    Summary Palladium-catalyzed ring-opening reactions of C1 substituted 7-oxanorbornadiene derivatives with aryl iodides were investigated. The optimal conditions for this reaction were found to be PdCl2(PPh3)2, ZnCl2, Et3N and Zn in THF. Both steric and electronic factors played a role in the outcome of the reaction as increasing the steric bulk on the bridgehead carbon decreased the yield. These reactions were found to be highly regioselective, giving only one of the two possible regioisomers in all cases. A diverse collection of novel, highly substituted biphenyl derivatives were obtained. PMID:26977182

  12. Modular, One-Pot, Sequential Aziridine Ring Opening-S(N)Ar Strategy to 7-, 10-, and 11-Membered Benzo-Fused Sultams.

    PubMed

    Loh, Joanna K; Asad, Naeem; Samarakoon, Thiwanka B; Hanson, Paul R

    2015-10-16

    The generation of common and stereochemically rich medium-sized benzo-fused sultams via complementary pairing of heretofore-unknown (o-fluoroaryl)sulfonyl aziridine building blocks with an array of amino alcohols/amines in a modular one-pot, sequential protocol using an aziridine ring opening and intramolecular nucleophilic aromatic substitution is reported. The strategy employs a variety of amino alcohols/amines and proceeds with 6 + 4/6 + 5 and 6 + 1 cycloetherification pathways in a highly chemo- and regioselective fashion to obtain skeletally and structurally diverse, polycyclic, 10- to 11- and 7-membered benzo-fused sultams for broad-scale screening.

  13. Novel thermal and microwave-assisted facile route to naphthalen-2(1H)-ones via an oxidative alkoxylation-ring-opening protocol.

    PubMed

    Dolka, Chrysanthi; Van Hecke, Kristof; Van Meervelt, Luc; Tsoungas, Petros G; Van der Eycken, Erik V; Varvounis, George

    2009-07-16

    Several novel 1,1-disubstituted-8-hydroxynaphthalen-2(1H)-ones have been efficiently synthesized via a two-step sequence from 2-hydroxy-1-naphthaldehyde oxime. The methodology involves oxidative ring closure and alkoxylation to 3a-alkoxynaphtho[1,8-de][1,2]oxazin-4(3aH)-ones, followed by thermal ring-opening. Both thermal and microwave irradiation conditions were used. A novel one-pot reaction of oxime to 8-isopropoxynaphthalene-1,7-diol using microwave irradiation is also reported.

  14. Decomposition Pathways of Z-Selective Ruthenium Metathesis Catalysts

    PubMed Central

    Herbert, Myles B.; Lan, Yu; Keitz, Benjamin K.; Liu, Peng; Endo, Koji; Day, Michael W.; Houk, K. N.; Grubbs, Robert H.

    2012-01-01

    The decomposition of a Z-selective ruthenium metathesis catalyst and structurally similar analogs has been investigated utilizing X-ray crystallography and density functional theory. Isolated X-ray crystal structures suggest that recently reported C-H activated catalysts undergo decomposition via insertion of the alkylidene moiety into the chelating ruthenium-carbon bond followed by hydride elimination, which is supported by theoretical calculations. The resulting ruthenium hydride intermediates have been implicated in previously observed olefin migration, and thus lead to unwanted byproducts in cross metathesis reactions. Preventing these decomposition modes will be essential in the design of more active and selective Z-selective catalysts. PMID:22500642

  15. Refining of plant oils to chemicals by olefin metathesis.

    PubMed

    Chikkali, Samir; Mecking, Stefan

    2012-06-11

    Plant oils are attractive substrates for the chemical industry. Their scope for the production of chemicals can be expanded by sophisticated catalytic conversions. Olefin metathesis is an example, which also illustrates generic issues of "biorefining" to chemicals. Utilization on a large scale requires high catalyst activities, which influences the choice of the metathesis reaction. The mixture of different fatty acids composing a technical-grade plant oil substrate gives rise to a range of products. This decisively determines possible process schemes, and potentially provides novel chemicals and intermediates not employed to date.

  16. Building Indenylidene-Ruthenium Catalysts for Metathesis Transformations

    NASA Astrophysics Data System (ADS)

    Clavier, Hervé; Nolan, Steven P.

    Ruthenium-mediated olefin metathesis has emerged as an indispensable tool in organic synthesis for the formation carbon-carbon double bonds, attested by the large number of applications for natural product synthesis. Among the numerous catalysts developed to mediate olefin metathesis transformations, ruthenium-indenylidene complexes are robust and powerful pre-catalysts. The discovery of this catalyst category was slightly muddled due to a first mis-assignment of the compound structure. This report provides an overview of the synthetic routes for the construction of the indenylidene pattern in ruthenium complexes. The parameters relating to the indenylidene moiety construction will be discussed as well as the mechanism of this formation

  17. Thermal properties of ruthenium alkylidene-polymerized dicyclopentadiene

    PubMed Central

    Vidavsky, Yuval; Navon, Yotam; Ginzburg, Yakov; Gottlieb, Moshe

    2015-01-01

    Summary Differential scanning calorimetry (DSC) analysis of ring opening methatesis polymerization (ROMP) derived polydicyclopentadiene (PDCPD) revealed an unexpected thermal behavior. A recurring exothermic signal can be observed in the DSC analysis after an elapsed time period. This exothermic signal was found to be proportional to the resting period and was accompanied by a constant increase in the glass-transition temperature. We hypothesize that a relaxation mechanism within the cross-linked scaffold, together with a long-lived stable ruthenium alkylidene species are responsible for the observed phenomenon. PMID:26425203

  18. Suicide Inhibition of Cytochrome P450 Enzymes by Cyclopropylamines via a Ring-Opening Mechanism: Proton-Coupled Electron Transfer Makes a Difference

    PubMed Central

    Zhang, Xiaoqian; Li, Xiao-Xi; Liu, Yufang; Wang, Yong

    2017-01-01

    N-benzyl-N-cyclopropylamine (BCA) has been attracting great interests for decades for its partial suicide inactivation role to cytochrome P450 (P450) via a ring-opening mechanism besides acting as a role of normal substrates. Understanding the mechanism of such partial inactivation is vital to the clinical drug design. Thus, density functional theoretical (DFT) calculations were carried out on such P450-catalyzed reactions, not only on the metabolic pathway, but on the ring-opening inactivation one. Our theoretical results demonstrated that, in the metabolic pathway, besides the normal carbinolamine, an unexpected enamine was formed via the dual hydrogen abstraction (DHA) process, in which the competition between rotation of the H-abstracted substrate radical and the rotation of hydroxyl group of the protonated Cpd II moiety plays a significant role in product branch; In the inactivation pathway, the well-noted single electron transfer (SET) mechanism-involved process was invalidated for its high energy barrier, a proton-coupled electron transfer [PCET(ET)] mechanism plays a role. Our results are consistent with other related theoretical works on heteroatom-hydrogen (X-H, X = O, N) activation and revealed new features. The revealed mechanisms will play a positive role in relative drug design. PMID:28197402

  19. Multi-level Quantum Mechanics and Molecular Mechanics Study of Ring Opening Process of Guanine Damage by Hydroxyl Radical in Aqueous Solution.

    PubMed

    Liu, Peng; Wang, Qiong; Niu, Meixing; Wang, Dunyou

    2017-08-10

    Combining multi-level quantum mechanics theories and molecular mechanics with an explicit water model, we investigated the ring opening process of guanine damage by hydroxyl radical in aqueous solution. The detailed, atomic-level ring-opening mechanism along the reaction pathway was revealed in aqueous solution at the CCSD(T)/MM levels of theory. The potentials of mean force in aqueous solution were calculated at both the DFT/MM and CCSD(T)/MM levels of the theory. Our study found that the aqueous solution has a significant effect on this reaction in solution. In particular, by comparing the geometries of the stationary points between in gas phase and in aqueous solution, we found that the aqueous solution has a tremendous impact on the torsion angles much more than on the bond lengths and bending angles. Our calculated free-energy barrier height 31.6 kcal/mol at the CCSD(T)/MM level of theory agrees well with the one obtained based on gas-phase reaction profile and free energies of solvation. In addition, the reaction path in gas phase was also mapped using multi-level quantum mechanics theories, which shows a reaction barrier at 19.2 kcal/mol at the CCSD(T) level of theory, agreeing very well with a recent ab initio calculation result at 20.8 kcal/mol.

  20. Suicide Inhibition of Cytochrome P450 Enzymes by Cyclopropylamines via a Ring-opening Mechanism: Proton-Coupled Electron Transfer Makes a Difference

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaoqian; Li, Xiao-Xi; Liu, Yufang; Wang, Yong

    2017-01-01

    N-benzyl-N-cyclopropylamine (BCA) has been attracting great interests for decades for its partial suicide inactivation role to cytochrome P450 (P450) via a ring-opening mechanism besides acting as a role of normal substrates. Understanding the mechanism of such partial inactivation is vital to the clinical drug design. Thus, density functional theoretical (DFT) calculations were carried out on such P450-catalyzed reactions, not only on the metabolic pathway, but on the ring-opening inactivation one. Our theoretical results demonstrated that, in the metabolic pathway, besides the normal carbinolamine, an unexpected enamine was formed via the dual hydrogen abstraction (DHA) process, in which the competition between rotation of the H-abstracted substrate radical and the rotation of hydroxyl group of the protonated Cpd II moiety plays a significant role in product branch; In the inactivation pathway, the well-noted single electron transfer (SET) mechanism-involved process was invalidated for its high energy barrier, a proton-coupled electron transfer (PCET(ET)) mechanism plays a role. Our results are consistent with other related theoretical works on heteroatom-hydrogen (X-H, X = O, N) activation and revealed new features. The revealed mechanisms will play a positive role in relative drug design.

  1. Pseudomonas aeruginosa Cif defines a distinct class of α/β epoxide hydrolases utilizing a His/Tyr ring-opening pair

    PubMed Central

    Bahl, Christopher D.; Madden, Dean R.

    2012-01-01

    The Gram-negative bacterium Pseudomonas aeruginosa is an opportunistic pathogen that secretes a multitude of virulence factors during the course of infection. Among these is Cif, an epoxide hydrolase (EH) that reduces the functional localization of the cystic fibrosis transmembrane conductance regulator in epithelial cells. In addition to being the first reported EH virulence factor, Cif possesses unique sequence deviations from canonical EH motifs. Foremost among these is the substitution of a histidine for the second epoxide ring-opening tyrosine in the active site. To test the functional equivalence of the Tyr and His side chains at this position, we have generated the mutant Cif-H177Y. Structural analysis confirms that both the WT His and mutant Tyr side chains can be accommodated without large-scale conformational changes. However, the Tyr mutation is functionally inactive. Based on a detailed analysis of the structure of the Tyr mutant, it appears that Cif's main-chain conformation imposes a functional requirement for a His at this position. Comparison with canonical EH structures reveals additional conformational differences, which are coupled to divergent sequence characteristics. When used to probe the genomes of other opportunistic pathogens, these sequence-structure criteria uncover candidate sequences that appear to form a distinct subfamily of Cif-like epoxide hydrolases characterized by a conserved His/Tyr ring-opening pair. PMID:21933119

  2. Pseudomonas aeruginosa Cif defines a distinct class of α/β epoxide hydrolases utilizing a His/Tyr ring-opening pair.

    PubMed

    Bahl, Christopher D; Madden, Dean R

    2012-02-01

    The Gram-negative bacterium Pseudomonas aeruginosa is an opportunistic pathogen that secretes a multitude of virulence factors during the course of infection. Among these is Cif, an epoxide hydrolase (EH) that reduces the functional localization of the cystic fibrosis transmembrane conductance regulator in epithelial cells. In addition to being the first reported EH virulence factor, Cif possesses unique sequence deviations from canonical EH motifs. Foremost among these is the substitution of a histidine for the first epoxide ring-opening tyrosine in the active site. To test the functional equivalence of Tyr and His side chains at this position, we have generated the mutant Cif-H177Y. Structural analysis confirms that both the WT His and mutant Tyr side chains can be accommodated without large-scale conformational changes. However, the Tyr mutant is functionally inactive. Based on a detailed analysis of the structure of the Tyr mutant, it appears that Cif's main-chain conformation imposes a functional requirement for a His at this position. Comparison with canonical EH structures reveals additional conformational differences, which are coupled to divergent sequence characteristics. When used to probe the genomes of other opportunistic pathogens, these sequence-structure criteria uncover candidate sequences that appear to form a distinct subfamily of Cif-like epoxide hydrolases characterized by a conserved His/Tyr ring-opening pair.

  3. Suicide Inhibition of Cytochrome P450 Enzymes by Cyclopropylamines via a Ring-Opening Mechanism: Proton-Coupled Electron Transfer Makes a Difference.

    PubMed

    Zhang, Xiaoqian; Li, Xiao-Xi; Liu, Yufang; Wang, Yong

    2017-01-01

    N-benzyl-N-cyclopropylamine (BCA) has been attracting great interests for decades for its partial suicide inactivation role to cytochrome P450 (P450) via a ring-opening mechanism besides acting as a role of normal substrates. Understanding the mechanism of such partial inactivation is vital to the clinical drug design. Thus, density functional theoretical (DFT) calculations were carried out on such P450-catalyzed reactions, not only on the metabolic pathway, but on the ring-opening inactivation one. Our theoretical results demonstrated that, in the metabolic pathway, besides the normal carbinolamine, an unexpected enamine was formed via the dual hydrogen abstraction (DHA) process, in which the competition between rotation of the H-abstracted substrate radical and the rotation of hydroxyl group of the protonated Cpd II moiety plays a significant role in product branch; In the inactivation pathway, the well-noted single electron transfer (SET) mechanism-involved process was invalidated for its high energy barrier, a proton-coupled electron transfer [PCET(ET)] mechanism plays a role. Our results are consistent with other related theoretical works on heteroatom-hydrogen (X-H, X = O, N) activation and revealed new features. The revealed mechanisms will play a positive role in relative drug design.

  4. Organocatalytic enantioselective cascade Michael-alkylation reactions: synthesis of chiral cyclopropanes and investigation of unexpected organocatalyzed stereoselective ring opening of cyclopropanes.

    PubMed

    Xie, Hexin; Zu, Liansuo; Li, Hao; Wang, Jian; Wang, Wei

    2007-09-05

    The development of efficient methods for the facile construction of important molecular architectures is a central goal in organic synthesis. An unprecedented organocatalytic asymmetric cascade Michael-alkylation reaction of alpha,beta-unsaturated aldehydes with bromomalonates has been developed. The process, efficiently catalyzed by chiral diphenylprolinol TMS ether in the presence of base 2,6-lutidine, serves as a powerful approach to the preparation of synthetically and biologically important cyclopropanes in high levels of enantio- and diastereoselectivities. Remarkably, the power of the cascade process is fueled by its high efficiency of the production of two new C-C bonds, two new stereogenic centers, and one quaternary carbon center in one single operation, which otherwise is difficult to achieve by traditional strategies. Moreover, the beauty of the cascade process is further underscored by the nature of the product formation depending on the reaction conditions. With the alternation of base from 2,6-lutidine (1.1 equiv), which is effective for the cyclopropanations, to NaOAc (4.0 equiv), the spontaneous ring-opening of cyclopropanes takes place to lead to stereoselective (E) alpha-substituted malonate alpha,beta-unsaturated aldehydes. A possible reaction mechanism, which involves a Michael-alkylation-retro-Michael pathway, is proposed and verified by experimental studies. This investigation represents the first example of an organocatalyst-promoted ring opening of the cyclopropanes, whereas such reactions have been intensively explored by Lewis acid-based catalysis.

  5. Increased functionality of methyl oleate using alkene metathesis

    USDA-ARS?s Scientific Manuscript database

    A series of alkene cross metathesis reactions were performed using a homogeneous ruthenium based catalyst. Using this technology, a variety of functional groups can be incorporated into the biobased starting material, methyl oleate. Trans-stilbene, styrene, methyl cinnamate and hexen-3-ol were all s...

  6. Ruthenium olefin metathesis catalysts featuring unsymmetrical N-heterocyclic carbenes.

    PubMed

    Paradiso, Veronica; Bertolasi, Valerio; Costabile, Chiara; Grisi, Fabia

    2016-01-14

    New ruthenium Grubbs' and Hoveyda-Grubbs' second generation catalysts bearing N-alkyl/N-isopropylphenyl N-heterocyclic carbene (NHC) ligands with syn or anti backbone configuration were obtained and compared in model olefin metathesis reactions. Different catalytic efficiencies were observed depending on the size of the N-alkyl group (methyl or cyclohexyl) and on the backbone configuration. The presence of an N-cyclohexyl substituent determined the most significant reactivity differences between catalysts with syn or anti phenyl groups on the backbone. In particular, anti catalysts proved highly efficient, especially in the ring-closing metathesis (RCM) of encumbered diolefins, while syn catalysts showed low efficiency in the RCM of less hindered diolefins. This peculiar behavior, rationalized through DFT studies, was found to be related to the high propensity of these catalysts to give nonproductive metathesis events. Enantiopure anti catalysts were also tested in asymmetric metathesis reactions, where moderate enantioselectivities were observed. The steric and electronic properties of unsymmetrical NHCs with the N-cyclohexyl group were then evaluated using the corresponding rhodium complexes. While steric factors proved unimportant for both syn and anti NHCs, a major electron-donating character was found for the unsymmetrical NHC with anti phenyl substituents on the backbone.

  7. Recent advances in the development of alkyne metathesis catalysts

    PubMed Central

    Wu, Xian

    2011-01-01

    Summary The number of well-defined molybdenum and tungsten alkylidyne complexes that are able to catalyze alkyne metathesis reactions efficiently has been significantly expanded in recent years.The latest developments in this field featuring highly active imidazolin-2-iminato- and silanolate–alkylidyne complexes are outlined in this review. PMID:21286398

  8. Synthesis of cyclic sulfones by ring-closing metathesis.

    PubMed

    Yao, Qingwei

    2002-02-07

    A general and highly efficient synthesis of cyclic sulfones based on ring-closing metathesis has been developed. The synthetic utility of the resulting cyclic sulfones was demonstrated by their participation in stereoselective Diels-Alder reactions and transformation to cyclic dienes by the Ramberg-Bäcklund reaction.

  9. Yttrium phosphasalen initiators for rac-lactide polymerization: excellent rates and high iso-selectivities.

    PubMed

    Bakewell, Clare; Cao, Thi-Phuong-Anh; Long, Nicholas; Le Goff, Xavier F; Auffrant, Audrey; Williams, Charlotte K

    2012-12-26

    Highly active yttrium phosphasalen initiators for the stereocontrolled ring-opening polymerization of rac-lactide are reported. The initiators are coordinated by a new class of ancillary ligand: an iminophosphorane derivative of the popular "salen" ligand, termed "phosphasalen". Changing the phosphasalen structure enables access to high iso-selectivities (P(i) = 0.84) or hetero-selectivities (P(s) = 0.87). The initiators also show very high rates, excellent polymerization control, and tolerance to low loadings; furthermore, no chiral auxiliaries/ligands are needed for the stereocontrol. The combination of such high rates with high iso-selectivities is very unusual.

  10. Effect of the nature of the substituent in N-alkylimidazole ligands on the outcome of deprotonation: ring opening versus the formation of N-heterocyclic carbene complexes.

    PubMed

    Huertos, Miguel A; Pérez, Julio; Riera, Lucía; Díaz, Jesús; López, Ramón

    2010-07-26

    Complexes [Re(CO)(3)(N-RIm)(3)]OTf (N-RIm=N-alkylimidazole, OTf=trifluoromethanesulfonate; 1a-d) have been straightforwardly synthesised from [Re(OTf)(CO)(5)] and the appropriate N-alkylimidazole. The reaction of compounds 1a-d with the strong base KN(SiMe(3))(2) led to deprotonation of a central C-H group of an imidazole ligand, thus affording very highly reactive derivatives. The latter can evolve through two different pathways, depending on the nature of the substituents of the imidazole ligands. Compound 1a contains three N-MeIm ligands, and its product 2a features a C-bound imidazol-2-yl ligand. When 2a is treated with HOTf or MeOTf, rhenium N-heterocyclic carbenes (NHCs) 3a or 4a are afforded as a result of the protonation or methylation, respectively, of the non-coordinated N atom. The reaction of 2a with [AuCl(PPh(3))] led to the heterobimetallic compound 5, in which the N-heterocyclic ligand is once again N-bound to the Re atom and C-coordinated to the gold fragment. For compounds 1b-d, with at least one N-arylimidazole ligand, deprotonation led to an unprecedented reactivity pattern: the carbanion generated by the deprotonation of the C2-H group of an imidazole ligand attacks a central C-H group of a neighbouring N-RIm ligand, thus affording the product of C-C coupling and ring-opening of the imidazole moiety that has been attacked (2c, d). The new complexes featured an amido-type N atom that can be protonated or methylated, thus obtaining compounds 3c, d or 4c, d, respectively. The latter reaction forces a change in the disposition of the olefinic unit generated by the ring-opening of the N-RIm ligand from a cisoid to a transoid geometry. Theoretical calculations help to rationalise the experimental observation of ring-opening (when at least one of the substituents of the imidazole ligands is an aryl group) or tautomerisation of the N-heterocyclic ligand to afford the imidazol-2-yl product.

  11. Enantioselective synthesis of 5-epi-citreoviral using ruthenium-catalyzed asymmetric ring-closing metathesis.

    PubMed

    Funk, Timothy W

    2009-11-05

    Chiral ruthenium olefin metathesis catalysts can perform asymmetric ring-closing reactions in > or = 90% ee with low catalyst loadings. To illustrate the practicality of these reactions and the products they form, an enantioselective total synthesis of 5-epi-citreoviral was completed by using an asymmetric ring-closing olefin metathesis reaction as a key step early in the synthesis. All of the stereocenters in the final compound were set by using the chiral center generated by asymmetric olefin metathesis.

  12. Ru-Based Z-Selective Metathesis Catalysts with Modified Cyclometalated Carbene Ligands†

    PubMed Central

    Bronner, Sarah M.; Herbert, Myles B.; Patel, Paresma R.; Marx, Vanessa M.; Grubbs, Robert H.

    2014-01-01

    A series of cyclometalated Z-selective ruthenium olefin metathesis catalysts with alterations to the N-heterocyclic carbene (NHC) ligand were prepared. X-Ray crystal structures of several new catalysts were obtained, elucidating the structural features of this class of cyclometalated complexes. The metathesis activity of each stable complex was evaluated, and one catalyst, bearing geminal dimethyl backbone substitution, was found to be comparable to our best Z-selective metathesis catalyst to date. PMID:25346842

  13. Facile solvothermal synthesis of abnormal growth of one-dimensional ZnO nanostructures by ring-opening reaction of polyvinylpyrrolidone

    NASA Astrophysics Data System (ADS)

    Xu, G.; Wang, X. L.; Liu, G. Z.

    2015-02-01

    Abnormal growth of one-dimensional (1-D) ZnO nanostructures (NSs) have been accomplished with the assistance of polyvinylpyrrolidone (PVP) under a super high alkaline alcoholic solvothermal condition. The products were characterized by transmission electron microscopy (TEM), thermogravimetric analysis (TGA), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and proton nuclear magnetic resonance (1H NMR) spectroscopy. The effect of synthetic conditions, such as reaction temperature and the addition of PVP, on the morphologies of ZnO products were investigated. The results show that PVP molecules had the significant role in the transformation of morphologies of ZnO NSs ranging from nanorods, nanoparticles to pyramids, as well as flower-like assembly features. The possible growth mechanism of ZnO pyramids was proposed based on ring-opening reaction of PVP.

  14. Ring-opening reactions of 1,4-diazabicyclo[2.2.2]octane (DABCO) derived quaternary ammonium salts with phenols and related nucleophiles.

    PubMed

    Maraš, Nenad; Polanc, Slovenko; Kočevar, Marijan

    2012-02-14

    1,4-Diazabicyclo[2.2.2]octane (DABCO) has been evaluated as a starting material for the synthesis of 1-alkyl-4-(2-phenoxyethyl)piperazines and related derivatives. We found that 1-alkyl-1,4-diazabicyclo[2.2.2]octan-1-ium salts, resulting from the alkylation of DABCO, efficiently react with a variety of nucleophiles in polyethyleneglycol (PEG) or diglyme at high temperatures to give piperazine products resulting from the nucleophilic ring-opening reaction. The benzylation side reaction was found to be relevant with softer nucleophiles when using 1-benzyl-1,4-diazabicyclo[2.2.2]octan-1-ium salts, while other types of alkylations were not observed. One-pot methodologies allow for the synthesis of piperazines directly from primary alcohols, alkyl halides or sulfonates, using phenols, or other nucleophile sources, and DABCO.

  15. Regiocontrolled ring opening of monoprotected 2,3-epoxy-1,4-diols using alkynyl aluminum reagents. Synthesis of differentially monoprotected alkynyl triol derivatives.

    PubMed

    Prieto, José A; Torres, Jaileen Rentas; Rodríguez-Berrios, Raul

    The regioselectivity of the epoxide ring opening reaction of cis and trans TIPS-monoprotected 2,3-epoxy-1,4-diols with diethylalkynyl aluminum reagents was studied. Alane and alanate conditions in toluene or dichloromethane were explored. The alkynyl attack at the C2 epoxide carbon was favored for both, the alane and alanate conditions in toluene, while in dichloromethane the C3 attack was preferred. The best regioselectivities were obtained using the alanate conditions in toluene. This methodology provides access to differentially monoprotected alkynyl triols with high diastereoselectivity. These compounds are useful building bocks for polypropionate synthesis and are precursors for the introduction of the hydroxymethyl moiety found in some polyketide systems.

  16. ROMP Synthesis of Iron-Containing Organometallic Polymers.

    PubMed

    Dragutan, Ileana; Dragutan, Valerian; Filip, Petru; Simionescu, Bogdan C; Demonceau, Albert

    2016-02-06

    The paper overviews iron-containing polymers prepared by controlled "living" ring-opening metathesis polymerization (ROMP). Developments in the design and synthesis of this class of organometallic polymers are highlighted, pinpointing methodologies and newest trends in advanced applications of hybrid materials based on polymers functionalized with iron motifs.

  17. Ionomers and methods of making same and uses thereof

    SciTech Connect

    Coates, Geoffrey W.; Kostalik, IV, Henry A.; Clark, Timothy J.; Robertson, Nicholas J.

    2016-11-15

    Ionomers comprising ionic groups such as, for example, tetraalkylammonium groups and methods of making such ionomers. For example, the ionomers can be produced by ring opening metathesis polymerization of alkene-containing monomers with tetraalkylammonium groups and, optionally, alkene-containing monomers without tetraalkylammonium groups. The ionomers can be used in applications such as, for example, fuel cell applications.

  18. Beyond catalyst deactivation: cross-metathesis involving olefins containing N-heteroaromatics

    PubMed Central

    Lafaye, Kevin; Bosset, Cyril; Nicolas, Lionel

    2015-01-01

    Summary Alkenes containing N-heteroaromatics are known to be poor partners in cross-metathesis reactions, probably due to catalyst deactivation caused by the presence of a nitrogen atom. However, some examples of ring-closing and cross-metathesis involving alkenes that incorporate N-heteroaromatics can be found in the literature. In addition, recent mechanistic studies have focused on the rationalization of nitrogen-induced catalysts deactivation. The purpose of this mini-review is to give a brief overview of successful metathesis reactions involving olefins containing N-heteroaromatics in order to delineate some guidelines for the use of these challenging substrates in metathesis reactions. PMID:26664645

  19. Computational study of productive and non-productive cycles in fluoroalkene metathesis.

    PubMed

    Rybáčková, Markéta; Hošek, Jan; Šimůnek, Ondřej; Kolaříková, Viola; Kvíčala, Jaroslav

    2015-01-01

    A detailed DFT study of the mechanism of metathesis of fluoroethene, 1-fluoroethene, 1,1-difluoroethene, cis- and trans-1,2-difluoroethene, tetrafluoroethene and chlorotrifluoroethene catalysed with the Hoveyda-Grubbs 2(nd) generation catalyst was performed. It revealed that a successful metathesis of hydrofluoroethenes is hampered by a high preference for a non-productive catalytic cycle proceeding through a ruthenacyclobutane intermediate bearing fluorines in positions 2 and 4. Moreover, the calculations showed that the cross-metathesis of perfluoro- or perhaloalkenes should be a feasible process and that the metathesis is not very sensitive to stereochemical issues.

  20. Computational study of productive and non-productive cycles in fluoroalkene metathesis

    PubMed Central

    Rybáčková, Markéta; Hošek, Jan; Šimůnek, Ondřej; Kolaříková, Viola

    2015-01-01

    Summary A detailed DFT study of the mechanism of metathesis of fluoroethene, 1-fluoroethene, 1,1-difluoroethene, cis- and trans-1,2-difluoroethene, tetrafluoroethene and chlorotrifluoroethene catalysed with the Hoveyda–Grubbs 2nd generation catalyst was performed. It revealed that a successful metathesis of hydrofluoroethenes is hampered by a high preference for a non-productive catalytic cycle proceeding through a ruthenacyclobutane intermediate bearing fluorines in positions 2 and 4. Moreover, the calculations showed that the cross-metathesis of perfluoro- or perhaloalkenes should be a feasible process and that the metathesis is not very sensitive to stereochemical issues. PMID:26664636

  1. Polymerization initated at sidewalls of carbon nanotubes

    NASA Technical Reports Server (NTRS)

    Tour, James M. (Inventor); Hudson, Jared L. (Inventor); Krishnamoorti, Ramanan (Inventor); Yurekli, Koray (Inventor); Mitchell, Cynthia A. (Inventor)

    2011-01-01

    The present invention is directed to aryl halide (such as aryl bromide) functionalized carbon nanotubes that can be utilized in anionic polymerization processes to form polymer-carbon nanotube materials with improved dispersion ability in polymer matrices. In this process the aryl halide is reacted with an alkyllithium species or is reacted with a metal to replace the aryl-bromine bond with an aryl-lithium or aryl-metal bond, respectively. It has further been discovered that other functionalized carbon nanotubes, after deprotonation with a deprotonation agent, can similarly be utilized in anionic polymerization processes to form polymer-carbon nanotube materials. Additionally or alternatively, a ring opening polymerization process can be performed. The resultant materials can be used by themselves due to their enhanced strength and reinforcement ability when compared to their unbound polymer analogs. Additionally, these materials can also be blended with pre-formed polymers to establish compatibility and enhanced dispersion of nanotubes in otherwise hard to disperse matrices resulting in significantly improved material properties. The resultant polymer-carbon nanotube materials can also be used in drug delivery processes due to their improved dispersion ability and biodegradability, and can also be used for scaffolding to promote cellular growth of tissue.

  2. Differential reactivity of purified bioactive coffee furans, cafestol and kahweol, with acidic nitrite: product characterization and factors controlling nitrosation versus ring-opening pathways.

    PubMed

    De Lucia, Maria; Panzella, Lucia; Melck, Dominique; Giudicianni, Italo; Motta, Andrea; Napolitano, Alessandra; d'Ischia, Marco

    2009-12-01

    Cafestol and kahweol, coffee-specific furan diterpenes, are believed to cause various physiological effects in human subjects, including an increase in cholesterol and plasma triacylglycerol levels as well as cancer chemopreventive effects. Despite the increasing interest in these compounds raised by the diverse range of biological activities, their reaction behavior and degradation pathways under physiologically relevant conditions remain uncharted. Herein, we report a detailed investigation of the structural modifications suffered by cafestol and kahweol in the presence of acidic nitrite under conditions mimicking those occurring in the stomach during digestion as well as by action of other oxidants. Prior to the chemical study, an isolation procedure for kahweol from green coffee beans was developed based on Soxhlet extraction followed by preparative HPLC. Preliminary experiments showed that kahweol is much more reactive than cafestol toward nitrite at pH 3, as evidenced by inhibition experiments with the 2,3-diaminonaphthalene assay as well as by product analysis in coffee extracts. When exposed to equimolar nitrite in phosphate buffer, pH 3, kahweol gave as a main product the ring-opened dicarbonyl derivative 1. Under more forcing conditions, cafestol reacted as well to give a main nitrogenous product identified as the 1-hydroxy-2-pyrrolinone 2. It is concluded that the conjugated double bond in kahweol is a critical structural element, increasing the susceptibility of the furan ring to protonation rather than nitrosation and favoring ring-opening routes driven by the irreversible oxidation steps. These results offer a useful background to assess the effects of coffee-specific lipids in association with abnormally high nitrite levels from the diet.

  3. Theoretical investigation of the conrotatory ring opening oc cyclobutene and 1,2-dihydro-1,2-diazacyclobutadienes with ab initio and density functional Gaussian-type-orbital approach

    SciTech Connect

    Jursic, B.S.; Zdravkovski, Z.

    1995-10-15

    The theoretical study of the thermally allowed conrotatory opening of cyclobutene (1) and cis- (2) and trans-1,2-dihydro-1,2-diazacyclobutadiene (3) were performed with ab initio and density functional calculations. The reactants and the transition states were fully optimized by using the 6-31 + G** basis set with RHF, MP2, SVWN, and BLYP methods. The calculated activation barriers for the ring opening of 1 with both MP2 and SVWN incorporating ZPVE correction give extraordinary agreement with the experimental value. The predicted activation energies for 2 and 3 are lower than in the case of the cyclobutene ring opening. Of the two 1,2-dihydro-1,2-diazacyclobutadiene isomers, the trans isomer has a lower activation barrier. The structural and energy differences and the trend among these compounds are interpreted in terms of orbital overlap and steric interactions in the course of the conrotatory ring opening. 18 refs., 11 tabs.

  4. Molybdenum chloride catalysts for Z-selective olefin metathesis reactions

    NASA Astrophysics Data System (ADS)

    Koh, Ming Joo; Nguyen, Thach T.; Lam, Jonathan K.; Torker, Sebastian; Hyvl, Jakub; Schrock, Richard R.; Hoveyda, Amir H.

    2017-01-01

    The development of catalyst-controlled stereoselective olefin metathesis processes has been a pivotal recent advance in chemistry. The incorporation of appropriate ligands within complexes based on molybdenum, tungsten and ruthenium has led to reactivity and selectivity levels that were previously inaccessible. Here we show that molybdenum monoaryloxide chloride complexes furnish higher-energy (Z) isomers of trifluoromethyl-substituted alkenes through cross-metathesis reactions with the commercially available, inexpensive and typically inert Z-1,1,1,4,4,4-hexafluoro-2-butene. Furthermore, otherwise inefficient and non-stereoselective transformations with Z-1,2-dichloroethene and 1,2-dibromoethene can be effected with substantially improved efficiency and Z selectivity. The use of such molybdenum monoaryloxide chloride complexes enables the synthesis of representative biologically active molecules and trifluoromethyl analogues of medicinally relevant compounds. The origins of the activity and selectivity levels observed, which contradict previously proposed principles, are elucidated with the aid of density functional theory calculations.

  5. Molybdenum chloride catalysts for Z-selective olefin metathesis reactions.

    PubMed

    Koh, Ming Joo; Nguyen, Thach T; Lam, Jonathan K; Torker, Sebastian; Hyvl, Jakub; Schrock, Richard R; Hoveyda, Amir H

    2017-02-02

    The development of catalyst-controlled stereoselective olefin metathesis processes has been a pivotal recent advance in chemistry. The incorporation of appropriate ligands within complexes based on molybdenum, tungsten and ruthenium has led to reactivity and selectivity levels that were previously inaccessible. Here we show that molybdenum monoaryloxide chloride complexes furnish higher-energy (Z) isomers of trifluoromethyl-substituted alkenes through cross-metathesis reactions with the commercially available, inexpensive and typically inert Z-1,1,1,4,4,4-hexafluoro-2-butene. Furthermore, otherwise inefficient and non-stereoselective transformations with Z-1,2-dichloroethene and 1,2-dibromoethene can be effected with substantially improved efficiency and Z selectivity. The use of such molybdenum monoaryloxide chloride complexes enables the synthesis of representative biologically active molecules and trifluoromethyl analogues of medicinally relevant compounds. The origins of the activity and selectivity levels observed, which contradict previously proposed principles, are elucidated with the aid of density functional theory calculations.

  6. Self-Assembly of Disorazole C1 through a One-Pot Alkyne Metathesis Homodimerization Strategy**

    PubMed Central

    Ralston, Kevin J; Ramstadius, H Clinton; Brewster, Richard C; Niblock, Helen S; Hulme, Alison N

    2015-01-01

    Alkyne metathesis is increasingly explored as a reliable method to close macrocyclic rings, but there are no prior examples of an alkyne-metathesis-based homodimerization approach to natural products. In this approach to the cytotoxic C2-symmetric marine-derived bis(lactone) disorazole C1, a highly convergent, modular strategy is employed featuring cyclization through an ambitious one-pot alkyne cross-metathesis/ring-closing metathesis self-assembly process. PMID:25926364

  7. Heterobimetallic s-block hydrides by σ-bond metathesis.

    PubMed

    Liptrot, David J; Hill, Michael S; Mahon, Mary F

    2014-08-04

    Reactions between PhSiH3 and alkali-metal diamidoalkylmagnesiates ([M{N(SiMe3)2}2MgBu], M = Li, Na, K) provide either selective alkyl metathesis or the formation of polyhydride aggregates contingent upon the identity of the Group 1 metal. In the case of [M{N(SiMe3)2}2MgBu], this reactivity results in a structurally unprecedented dodecametallic decahydride cluster species.

  8. Metathesis process for preparing an alpha, omega-functionalized olefin

    DOEpatents

    Burdett, Kenneth A.; Mokhtarzadeh, Morteza; Timmers, Francis J.

    2010-10-12

    A cross-metathesis process for preparing an .alpha.,.omega.-functionalized olefin, such as methyl 9-decenoate, and an .alpha.-olefin having three or more carbon atoms, such as 1-decene. The process involves contacting in a first reaction zone an .alpha.-functionalized internal olefin, such as methyl oleate, and an .alpha.-olefinic monomer having three or more carbon atoms, such as 1-decene, with a first metathesis catalyst to prepare an effluent stream containing the .alpha.,.omega.-functionalized olefin, such as methyl 9-decenoate, an unfunctionalized internal olefin, such as 9-octadecene, unconverted reactant olefins, and optionally, an .alpha.,.omega.-difunctionalized internal olefinic dimer, such as dimethyl 9-octadecen-1,18-dioate; separating said effluent streams; then contacting in a second reaction zone the unfunctionalized internal olefin with ethylene in the presence of a second metathesis catalyst to obtain a second product effluent containing the .alpha.-olefinic monomer having three or more carbon atoms; and cycling a portion of the .alpha.-olefinic monomer stream(s) to the first zone.

  9. Non-steady-state living polymerization: a new route to control cationic ring-opening polymerization (CROP) of oxetane via an activation chain end (ACE) mechanism at ambient temperature.

    PubMed

    Bouchékif, Hassen; Philbin, Marcia I; Colclough, Eamon; Amass, Allan J

    2005-08-14

    Well-defined polyoxetane with low polydispersivity has been synthesized via a novel living polymerisation process using 3-phenoxypropyl 1,4-dioxanium hexafluoroantimonate (3-PPD) as a model of a living "monomeric polyoxetane" initiator, in 1,4-dioxane at 35 degrees C.

  10. Epoxide Activated Anionic Polymerization: Application to the Synthesis of (Co)Polyethers with Controlled Structure and Tuned Properties

    NASA Astrophysics Data System (ADS)

    Labbe, Amelie; Rejsek, Virginie; Carlotti, Stephane; Deffieux, Alain

    A ring opening polymerization process allowing the fast and controlled anionic polymerization of epoxide monomers is described and applied to the synthesis of (co)polyethers with novel structure and composition. The approach is based on the simultaneous formation of complexes between an organometallic Lewis acid additive with both the anionic initiator and the monomer. In conjunction with the use of tetraalkylammonium or phosphonium salts as initiators, the addition of such additive allows the synthesis of polyethers and block copolyethers with controlled molar masses and narrow polydispersities, in hydrocarbon media, at low temperature, and in short reaction times. The low nucleophilic character of the propagating species involved in the polymerization avoids transfer to monomer, a side reaction which is often predominant in conventional anionic polymerizations. This also allows the controlled polymerization of functional epoxides such as glycidyl methacrylate and epichlorohydrin. Properties and potential applications of these new polyethers and copolyethers are also reported.

  11. Reduction in Syllable Onsets in the Acquisition of Polish: Deletion, Coalescence, Metathesis and Gemination

    ERIC Educational Resources Information Center

    Lukaszewicz, Beata

    2007-01-01

    This paper focuses on four strategies of onset reduction employed by a single child (4;0-4;4) acquiring Polish: deletion, coalescence, metathesis, and gemination. Deletion and coalescence occur in word-initial onsets while metathesis and gemination are restricted to word-medial position. The data, which constitute an intriguing "conspiracy" case…

  12. Iron(III)-Catalyzed Ring-Closing Carbonyl-Olefin Metathesis.

    PubMed

    Saá, Carlos

    2016-09-05

    Recent developments in catalytic carbonyl-olefin metathesis are summarized in this Highlight. Schindler and co-workers have reported that the environmentally benign FeCl3 catalyst promotes ring-closing carbonyl-olefin metathesis (RCCOM) in high yield under very mild conditions. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. Reduction in Syllable Onsets in the Acquisition of Polish: Deletion, Coalescence, Metathesis and Gemination

    ERIC Educational Resources Information Center

    Lukaszewicz, Beata

    2007-01-01

    This paper focuses on four strategies of onset reduction employed by a single child (4;0-4;4) acquiring Polish: deletion, coalescence, metathesis, and gemination. Deletion and coalescence occur in word-initial onsets while metathesis and gemination are restricted to word-medial position. The data, which constitute an intriguing "conspiracy" case…

  14. Imino phenoxide complexes of niobium and tantalum as catalysts for the polymerization of lactides, ε-caprolactone and ethylene.

    PubMed

    Saha, Tanmoy Kumar; Mandal, Mrinmay; Thunga, Madhubabu; Chakraborty, Debashis; Ramkumar, Venkatachalam

    2013-07-28

    Imino phenoxide complexes of Nb and Ta show precise control towards the solvent free ring-opening polymerization of lactides (LA) and ε-caprolactone (CL). There is a close proximity between the observed number average molecular weight (M(n)) and theoretical molecular weight and the molecular weight distributions (MWDs) were found to be narrow. Analysis of low molecular weight oligomers of LA synthesized from these compounds revealed that the ligand is incorporated as one of the end terminal groups in the polymer chain. In addition, these complexes were realized to be precatalysts for the polymerization of ethylene.

  15. Polymeric nanoparticles

    PubMed Central

    Bolhassani, Azam; Javanzad, Shabnam; Saleh, Tayebeh; Hashemi, Mehrdad; Aghasadeghi, Mohammad Reza; Sadat, Seyed Mehdi

    2014-01-01

    Nanocarriers with various compositions and biological properties have been extensively applied for in vitro/in vivo drug and gene delivery. The family of nanocarriers includes polymeric nanoparticles, lipid-based carriers (liposomes/micelles), dendrimers, carbon nanotubes, and gold nanoparticles (nanoshells/nanocages). Among different delivery systems, polymeric carriers have several properties such as: easy to synthesize, inexpensive, biocompatible, biodegradable, non-immunogenic, non-toxic, and water soluble. In addition, cationic polymers seem to produce more stable complexes led to a more protection during cellular trafficking than cationic lipids. Nanoparticles often show significant adjuvant effects in vaccine delivery since they may be easily taken up by antigen presenting cells (APCs). Natural polymers such as polysaccharides and synthetic polymers have demonstrated great potential to form vaccine nanoparticles. The development of new adjuvants or delivery systems for DNA and protein immunization is an expanding research field. This review describes polymeric carriers especially PLGA, chitosan, and PEI as vaccine delivery systems. PMID:24128651

  16. Synthesis of terminal alkenes from internal alkenes and ethylene via olefin metathesis

    DOEpatents

    Schrodi, Yann

    2013-07-09

    This invention relates generally to olefin metathesis, and more particularly relates to the synthesis of terminal alkenes from internal alkenes using a cross-metathesis reaction catalyzed by a selected olefin metathesis catalyst. In one embodiment of the invention, for example, a method is provided for synthesizing a terminal olefin, the method comprising contacting an olefinic substrate comprised of at least one internal olefin with ethylene, in the presence of a metathesis catalyst, wherein the catalyst is present in an amount that is less than about 1000 ppm relative to the olefinic substrate, and wherein the metathesis catalyst has the structure of formula (II) ##STR00001## wherein the various substituents are as defined herein. The invention has utility, for example, in the fields of catalysis, organic synthesis, and industrial chemistry.

  17. Synthesis of terminal alkenes from internal alkenes and ethylene via olefin metathesis

    DOEpatents

    Schrodi, Yann [Agoura Hills, CA

    2011-11-29

    This invention relates generally to olefin metathesis, and more particularly relates to the synthesis of terminal alkenes from internal alkenes using a cross-metathesis reaction catalyzed by a selected olefin metathesis catalyst. In one embodiment of the invention, for example, a method is provided for synthesizing a terminal olefin, the method comprising contacting an olefinic substrate comprised of at least one internal olefin with ethylene, in the presence of a metathesis catalyst, wherein the catalyst is present in an amount that is less than about 1000 ppm relative to the olefinic substrate, and wherein the metathesis catalyst has the structure of formula (II) ##STR00001## wherein the various substituents are as defined herein. The invention has utility, for example, in the fields of catalysis, organic synthesis, and industrial chemistry.

  18. Synthesis of terminal alkenes from internal alkenes and ethylene via olefin metathesis

    DOEpatents

    Schrodi, Yann

    2015-09-22

    This invention relates generally to olefin metathesis, and more particularly relates to the synthesis of terminal alkenes from internal alkenes using a cross-metathesis reaction catalyzed by a selected olefin metathesis catalyst. In one embodiment of the invention, for example, a method is provided for synthesizing a terminal olefin, the method comprising contacting an olefinic substrate comprised of at least one internal olefin with ethylene, in the presence of a metathesis catalyst, wherein the catalyst is present in an amount that is less than about 1000 ppm relative to the olefinic substrate, and wherein the metathesis catalyst has the structure of formula (II) ##STR00001## wherein the various substituents are as defined herein. The invention has utility, for example, in the fields of catalysis, organic synthesis, and industrial chemistry.

  19. Synthesis of terminal alkenes from internal alkenes and ethylene via olefin metathesis

    DOEpatents

    Schrodi, Yann

    2016-02-09

    This invention relates generally to olefin metathesis, and more particularly relates to the synthesis of terminal alkenes from internal alkenes using a cross-metathesis reaction catalyzed by a selected olefin metathesis catalyst. In one embodiment of the invention, for example, a method is provided for synthesizing a terminal olefin, the method comprising contacting an olefinic substrate comprised of at least one internal olefin with ethylene, in the presence of a metathesis catalyst, wherein the catalyst is present in an amount that is less than about 1000 ppm relative to the olefinic substrate, and wherein the metathesis catalyst has the structure of formula (II) ##STR00001## wherein the various substituents are as defined herein. The invention has utility, for example, in the fields of catalysis, organic synthesis, and industrial chemistry.

  20. Reactivity of methacrylates in insertion polymerization.

    PubMed

    Rünzi, Thomas; Guironnet, Damien; Göttker-Schnetmann, Inigo; Mecking, Stefan

    2010-11-24

    Polymerization of ethylene by complexes [{(P^O)PdMe(L)}] (P^O = κ(2)-(P,O)-2-(2-MeOC(6)H(4))(2)PC(6)H(4)SO(3))) affords homopolyethylene free of any methyl methacrylate (MMA)-derived units, even in the presence of substantial concentrations of MMA. In stoichiometric studies, reactive {(P^O)Pd(Me)L} fragments generated by halide abstraction from [({(P^O)Pd(Me)Cl}μ-Na)(2)] insert MMA in a 1,2- as well as 2,1-mode. The 1,2-insertion product forms a stable five-membered chelate by coordination of the carbonyl group. Thermodynamic parameters for MMA insertion are ΔH(++) = 69.0(3.1) kJ mol(-1) and ΔS(++) = -103(10) J mol(-1) K(-1) (total average for 1,2- and 2,1-insertion), in comparison to ΔH(++) = 48.5(3.0) kJ mol(-1) and ΔS(++) = -138(7) J mol(-1) K(-1) for methyl acrylate (MA) insertion. These data agree with an observed at least 10(2)-fold preference for MA incorporation vs MMA incorporation (not detected) under polymerization conditions. Copolymerization of ethylene with a bifunctional acrylate-methacrylate monomer yields linear polyethylenes with intact methacrylate substituents. Post-polymerization modification of the latter was exemplified by free-radical thiol addition and by cross-metathesis.

  1. Kunststoffe (Polymere)

    NASA Astrophysics Data System (ADS)

    Weißbach, Wolfgang

    Polymere bestehen aus Riesen- oder Makromolekülen, die durch chemische Reaktionen aus einfachen, niedermolekularen Verbindungen entstehen, den Monomeren. Ausgangsstoffe sind überwiegend Kohlenwasserstoffe (KW), die größte Gruppe der C-Verbindungen. Sie müssen reaktionsfähige Stellen besitzen, das sind OH-Gruppen oder Dopppelbindungen.

  2. Protonation of metal-bound ?-hydroxycarboxylate ligand and implication for the role of homocitrate in nitrogenase: Computational study of the oxy-bidentate chelate ring opening

    NASA Astrophysics Data System (ADS)

    Cao, Zexing; Jin, Xi; Zhou, Zhaohui; Zhang, Qianer

    Protonation of the metal-bound oxy-bidentate ligand in the model complexes of [(HS)3(NH3)M(OCH2COO)]q (M = Mo, Fe, V, Co; q = -2, -1) in the gas phase and in solutions of water and acetonitrile has been explored by the density functional approach. Calculations show that protonation of the carboxyl oxygen can open the ?-hydroxycarboxylate chelate ring ligated to a transition-metal center under specific oxidation and spin states. The feasibility of the chelate ring opening by protonation depends on the electronic nature of the metal site in tune with conversion of a six-coordinate with a five-coordinate metal atom. Such selective dissociation of the metal-bound chelate ligand manipulates the availability of an empty site at the metal center and significantly affects reactivity of the metal-mediated chemical processes. Protonation changes the stability of species with different spin multiplicities and impels spin transition at the metal center in dissociation of the oxy-bidentate ligand. Solvent environments of water and acetonitrile play an important role in stabilizing the negatively charged species.

  3. 3,4,5,6-tetramethylphenanthrene 9,10-oxide: a step on the way to the transition state for nucleophilic ring opening of arene oxides

    SciTech Connect

    Darnow, J.N.; Armstrong, R.N.

    1987-05-01

    Force field calculations (MM2) and studies of the parent hydrocarbons suggest that 3,4,5,6-tetramethylphenanthrene 9,10-oxide (TMPO) should exist as two kinetically stable enantiomers. Stereoelectronic considerations indicate that the axial chirality of each enantiomer should direct nucleophilic attack to the diastereotopic oxirane carbon that most closely approaches the geometry of the transition state. The two enantiomers of TMPO can be synthesized from the chiral hydrocarbons by direct oxidation. The half-life for racemization of TMPO is 30 min at 25/sup 0/C. The two enantiomers are found to be substrates for glutathione (GSH) transferase and epoxide hydrolase. Isozyme 4-4 of GSH transferase which normally catalyzes addition of GSH to oxirane carbons of R absolute configuration, catalyzes addition to the oxirane carbon of S configuration in the M-isomer of TMPO and of R configuration in the P-isomer. Analogous results are obtained with the epoxide hydrolase catalyzed addition of water. The results suggest that TMPO should be an interesting stereochemical probe of both spontaneous and enzyme catalyzed ring opening reactions of arene oxides.

  4. Formation of dinuclear, macrocyclic, and chain structures from HgI(2) and a semirigid benzimidazole-based bridging ligand: an example of ring-opening supramolecular isomerism.

    PubMed

    Su, Cheng-Yong; Goforth, Andrea M; Smith, Mark D; zur Loye, Hans-Conrad

    2003-09-08

    The reactions of HgI(2) with the semirigid ditopic ligand 1,3-bis(benzimidazol-1-ylmethyl)-2,4,6-trimethylbenzene (bbimms) afforded three new complexes, [Hg(2)(mu-I)(2)I(2)(bbimms)] (1), [Hg(2)I(4)(bbimms)(2)] (2), and catena-poly[HgI(2)(bbimms)] (3). The ligand and all complexes have been structurally characterized by single-crystal X-ray diffraction. 1 is a triply bridged dinuclear complex comprised of two Hg(II) ions, one bridging ligand, two bridging I(-) anions, and two terminal I(-) anions. 2 is a dinuclear metallamacrocycle comprised of two Hg(II) ions, two bridging ligands, and four terminal I(-) anions, while 3 is a helical chain with the repeating unit of HgI(2)(bbimms). 2 and 3 can be classified as supramolecular isomers, and both are related to the triply bridged precursor 1 via the addition of one more ligand in a ring-opening process.

  5. Ring-opening insertion of a substituted dithiazole-3-thione into the Re-Re bond in a dirhenium carbonyl complex

    SciTech Connect

    Adams, R.D.; Huang, M.

    1996-04-16

    The reaction of the complex Re{sub 2}(CO){sub 9}(NCMe) with 5-((ethoxycarbonyl)amino)-1,2,4-dithiazole-3-thione (1) has yielded the series of complexes Re(CO){sub 4}[{mu}-S{sub 2}CNC(N(H)CO{sub 2}Et)S]Re(CO){sub 5} (2; 8% yield), Re(CO){sub 4}[{mu}-S{sub 2}CNC(NHCO{sub 2}Et)S]Re(CO){sub 4} (3; 14% yield), and Re(CO){sub 4}[{mu}-S{sub 2}CNHC(NCO{sub 2}Et)S]Re(CO){sub 4} (4; 27% yield) by the ring-opening insertion of 1 into the rhenium-rhenium bond of Re{sub 2}(CO){sub 9}(NCMe). The sulfur-sulfur bond in 1 was also cleaved. Two mononuclear rhenium complexes, Re(CO){sub 4}[S{sub 2}CNHCSNH(CO{sub 2}Et)] (5; 14% yield) and Re(CO){sub 4}[SCNC(NHCO{sub 2}Et)SCSN] (6; 6% yield), were also isolated and characterized. Compounds 3 and 4 are isomers that exist in an equilibrium at room temperature. The isomerization of 3 to 4 and vice versa is catalyzed by the presence of pyridine. Each of the complexes 2-6 as well as the starting material 1 was characterized by a single-crystal X-ray diffraction analysis. 16 refs., 6 figs., 3 tabs.

  6. Reaction pathways by quantum Monte Carlo: insight on the torsion barrier of 1,3-butadiene, and the conrotatory ring opening of cyclobutene.

    PubMed

    Barborini, Matteo; Guidoni, Leonardo

    2012-12-14

    Quantum Monte Carlo (QMC) methods are used to investigate the intramolecular reaction pathways of 1,3-butadiene. The ground state geometries of the three conformers s-trans, s-cis, and gauche, as well as the cyclobutene structure are fully optimised at the variational Monte Carlo (VMC) level, obtaining an excellent agreement with the experimental results and other quantum chemistry high level calculations. Transition state geometries are also estimated at the VMC level for the s-trans to gauche torsion barrier of 1,3-butadiene and for the conrotatory ring opening of cyclobutene to the gauche-1,3-butadiene conformer. The energies of the conformers and the reaction barriers are calculated at both variational and diffusional Monte Carlo levels providing a precise picture of the potential energy surface of 1,3-butadiene and supporting one of the two model profiles recently obtained by Raman spectroscopy [Boopalachandran et al., J. Phys. Chem. A 115, 8920 (2011)]. Considering the good scaling of QMC techniques with the system's size, our results also demonstrate how variational Monte Carlo calculations can be applied in the future to properly investigate the reaction pathways of large and correlated molecular systems.

  7. Cross metathesis for the synthesis of novel C-sialosides.

    PubMed

    Meinke, Sebastian; Thiem, Joachim

    2008-07-21

    Cross metathesis of both anomers of C-allyl sialoside (3alpha/3beta) with styrene catalyzed by the second generation Grubbs or Hoveyda-Grubbs catalysts gave the corresponding aryl derivatives (4alpha/4beta) in virtually quantitative yields. The products were hydrogenated to model compounds 5alpha/5beta. Similarly, reaction of the alpha-anomer 3alpha with galactose derivative 8 gave the olefin-linked disaccharide mimetic 9. Following hydrogenation and deprotection, the ethylene-bridged Neu5Acalpha(2-->6)Gal analogue 11 could be obtained.

  8. Enhanced Olefin Cross Metathesis Reactions: The Copper Iodide Effect

    PubMed Central

    Voigtritter, Karl; Ghorai, Subir

    2011-01-01

    Copper iodide has been shown to be an effective co-catalyst for the olefin cross metathesis reaction. In particular, it has both a catalyst stabilizing effect due to iodide ion, as well as copper(I)-based phosphine-scavenging properties that apply to use of the Grubbs-2 catalyst. A variety of Michael acceptors and olefinic partners can be cross-coupled under mild conditions in refluxing diethyl ether that avoid chlorinated solvents. This effect has also been applied to chemistry in water at room temperature using the new surfactant TPGS-750-M. PMID:21528868

  9. Highly Z-Selective Metathesis Homocoupling of Terminal Olefins

    PubMed Central

    Jiang, Annie J.; Zhao, Yu; Schrock, Richard R.; Hoveyda, Amir H.

    2009-01-01

    Mo and W MonoAryloxide-Pyrrolide (MAP) olefin metathesis catalysts can couple terminal olefins to give as high as >98% Z-products in moderate to high yields with as little as 0.2% catalyst. Results are reported for 1-hexene, 1-octene, allylbenzene, allyltrimethylsilane, methyl-10-undecenoate, methyl-9-decenoate, allylB(pinacolate), allylOBenzyl, allylNHTosyl, and allylNHPh. It is proposed that high Z-selectivity is achieved because a large aryloxide only allows metallacyclobutanes to form that contain adjacent cis substituents and because isomerization of Z-product to E-product can be slow in that same steric environment. PMID:19919135

  10. Synthesis of functional poly(disubstituted acetylene)s through the post-polymerization modification route.

    PubMed

    Gao, Yuan; Wang, Xiao; Sun, Jing Zhi; Tang, Ben Zhong

    2015-04-01

    We report the recent progress in the preparation of functional poly(disubstituted acetylene)s (PDSAs) through post-polymerization modification routes. The metathesis polymerization of disubstituted acetylene monomers activated by Mo/W-Sn complex catalysts, which do not tolerate highly polar functionalities, was assumed to be a key step in the polymer synthetic procedures. We and other groups have explored several approaches to prepare PDSAs with latent reactive functionalities, which are inactive to Mo/W-Sn complex catalysts but can be used as highly reactive sites for post-polymerization modification. Click chemistry, Michael-type addition reactions, the use of activated esters and other strategies are demonstrated by recently published examples. These works indicate that post-polymerization modification is an efficient route to the synthesis of various functional PDSAs.

  11. Aromatizing olefin metathesis by ligand isolation inside a metal-organic framework.

    PubMed

    Vermeulen, Nicolaas A; Karagiaridi, Olga; Sarjeant, Amy A; Stern, Charlotte L; Hupp, Joseph T; Farha, Omar K; Stoddart, J Fraser

    2013-10-09

    The aromatizing ring-closing metathesis has been shown to take place inside an extended porous framework. Employing a combination of solvent-assisted linker exchange and postsynthesis modification using olefin metathesis, the noninterpenetrated SALEM-14 was formed and converted catalytically into PAH-MOF-1 with polycyclic aromatic hydrocarbon (PAH) pillars. The metal-organic framework in SALEM-14 prevents "intermolecular" olefin metathesis from occurring between the pillars in the presence of the first generation Hoveyda-Grubbs catalyst, while favoring the production of a PAH, which can be released from the framework under acidic conditions in dimethylsulfoxide.

  12. Olefin Metathesis in Homogeneous Aqueous Media Catalyzed by Conventional Ruthenium Catalysts

    PubMed Central

    Binder, Joseph B.; Blank, Jacqueline J.; Raines, Ronald T.

    2008-01-01

    Olefin metathesis in aqueous solvents is sought for applications in green chemistry and with the hydrophilic substrates of chemical biology, such as proteins and polysaccharides. Most demonstrations of metathesis in water, however, utilize exotic complexes. We have examined the performance of conventional catalysts in homogeneous water–organic mixtures, finding that the second-generation Hoveyda–Grubbs catalyst has extraordinary efficiency in aqueous dimethoxyethane and aqueous acetone. High (71–95%) conversions are achieved for ring-closing and cross metathesis of a variety of substrates in these solvent systems. PMID:17949009

  13. Washout rate in rat brain irradiated by a 11C beam after acetazolamide loading using a small single-ring OpenPET prototype

    NASA Astrophysics Data System (ADS)

    Hirano, Yoshiyuki; Takuwa, Hiroyuki; Yoshida, Eiji; Nishikido, Fumihiko; Nakajima, Yasunori; Wakizaka, Hidekatsu; Yamaya, Taiga

    2016-03-01

    In dose verification techniques of particle therapies based on in-beam positron emission tomography (PET), the causes of washout of positron emitters by physiological effects should be clarified to correct washout for accurate verification. As well, the quantitative washout rate has a potential usefulness as a diagnostic index which should be explored. Therefore, we measured washout rates of rat brain after vasodilator acetazolamide loading to investigate the possible effects of blood flow on washout. Six rat brains were irradiated by a radioisotope 11C beam and time activity curves on the whole brains were obtained with a small single-ring OpenPET prototype. Then, washout rates were calculated with the Mizuno model, where two washout rates (k 2m and k 2s ) were assumed, and a two-compartment model including efflux from tissue to blood (k 2) and influx (k 3) and efflux (k 4) between the two tissue compartments. Before the irradiations, we used laser-Doppler flowmetry to confirm that acetazolamide increased cerebral blood flow (CBF) of a rat. We compared means of k 2m , k 2s and k 2, k 3 and k 4 without acetazolamide loading (Rest) and with acetazolamide loading (ACZ). For all k values, ACZ values were lower than Rest values. In other words, though CBF increased, washout rates were decreased. This may be attributed to the implanted 11C reacting to form 11CO2. Because acetazolamide increased the concentration of CO2 in brain, suppressed diffusion of 11CO2 and decomposition of 11CO2 into ions were prevented.

  14. Enzymes Involved in the Aerobic Bacterial Degradation of N-Heteroaromatic Compounds: Molybdenum Hydroxylases and Ring-Opening 2,4-Dioxygenases

    NASA Astrophysics Data System (ADS)

    Fetzner, S.

    Many N-heteroaromatic compounds are utilized by micro-organisms as a source of carbon (and nitrogen) and energy. The aerobic bacterial degradation of these growth substrates frequently involves several hydroxylation steps and subsequent dioxygenolytic cleavage of (di)hydroxy-substituted heteroaromatic intermediates to aliphatic metabolites which finally are channeled into central metabolic pathways. As a rule, the initial bacterial hydroxylation of a N-heteroaromatic compound is catalyzed by a molybdenum hydroxylase, which uses a water molecule as source of the incorporated oxygen. The enzyme's redox-active centers - the active site molybdenum ion coordinated to a distinct pyranopterin cofactor, two different [2Fe2S] centers, and in most cases, flavin adenine dinucleotide - transfer electrons from the N-heterocyclic substrate to an electron acceptor, which for many molybdenum hydroxylases is still unknown. Ring-opening 2,4-dioxygenases involved in the bacterial degradation of quinaldine and 1H-4-oxoquinoline catalyze the cleavage of two carbon-carbon bonds with concomitant formation of carbon monoxide. Since they contain neither a metal center nor an organic cofactor, and since they do not show any sequence similarity to known oxygenases, these unique dioxygenases form a separate enzyme family. Quite surprisingly, however, they appear to be structurally and mechanistically related to enzymes of the α/β hydrolase fold superfamily. Microbial enzymes are a great resource for biotechnological applications. Microbial strains or their enzymes may be used for degradative (bioremediation) or synthetic (biotransformation) purposes. Modern bioremediation or biotransformation strategies may even involve microbial catalysts or strains designed by protein engineering or pathway engineering. Prerequisite for developing such modern tools of biotechnology is a comprehensive understanding of microbial metabolic pathways, of the structure and function of enzymes, and of the

  15. Biodegradable Multiamine Polymeric Vector for siRNA Delivery.

    PubMed

    Yuan, Yuanyuan; Gong, Faming; Cao, Yang; Chen, Weicai; Cheng, Du; Shuai, Xintao

    2015-04-01

    The gene silencing activity of small interfering RNA (siRNA) has led to their use as tools for target validation and as potential therapeutics for a variety of diseases. A major challenge is the development of vectors with high delivery efficiency and low toxicity. Although poly(ethylenimine) (PEI) has been regarded as the most promising polymeric vector for nucleic acid delivery, the nonbiodegradable structure greatly hinders its clinical application. In the present study, a diblock copolymer, PEG-PAsp(DIP-DETA), of poly(ethylene glycol) (PEG) and poly(L-aspartic acid) (PAsp) randomly grafted with pH-sensitive 2-(diisopropylamino)ethylamine (DIP) and diethylenetriamine (DETA) groups was synthesized via ring-opening polymerization and aminolysis reaction. Similar to polyethylenimine (PEI), the copolymer possesses a multiamine structure that not only allows effective siRNA complexation at neutral pH but also facilitates lysosomal release of siRNA via a proton buffering effect. Moreover, the poly(L-aspartic acid) backbone renders the vector biodegradability, which is not achievable with PEI. This novel polymeric vector can mediate effective intracellular siRNA delivery in various cancer cells. Consequently, the delivery of BCL-2 siRNA resulted in target gene silencing, inducing apoptosis and inhibiting the growth of cancer cells. These results show the potential of this non-PEI based polymeric vector with proton buffering capacity and biodegradability for siRNA delivery in cancer therapy.

  16. Synthesis of nanosized silicon particles by a rapid metathesis reaction

    SciTech Connect

    Won, C.W.; Nersisyan, H.H.; Won, H.I.; Lee, H.H.

    2009-11-15

    A solid-state rapid metathesis reaction was performed in a bed of sodium silicofluoride (Na{sub 2}SiF{sub 6}) and sodium azide (NaN{sub 3}) powders diluted with sodium fluoride (NaF), to produce silicon nanoparticles. After a local ignition of Na{sub 2}SiF{sub 6}+4NaN{sub 3}+kNaF mixture (here k is mole number of NaF), the reaction proceeded in a self-sustaining combustion mode developing high temperatures (950-1000 deg. C) on very short time scales (a few seconds). Silicon nanoparticles prepared by the combustion process was easily separated from the salt byproducts by simple washing with distilled water. The structural and morphological studies on the nanoparticles were carried out using X-ray diffractometer (XRD) and field emission scanning electron microscope (FESEM). The mean size of silicon particles calculated from the FESEM image was about 37.75 nm. FESEM analysis also shows that the final purified product contains a noticeable amount of silicon fibers, dendrites and blocks, along with nanoparticles. The mechanism of Si nanostructures formation is discussed and a simple model for interpretation of experimental results is proposed. - Graphical abstract: Silicon nanoparticles 37.75 nm in mean diameter was obtained by rapid metathesis reaction performed in Na{sub 2}SiF{sub 6}+4NaN{sub 3} powder bed diluted with NaF.

  17. Highly efficient molybdenum-based catalysts for enantioselective alkene metathesis

    PubMed Central

    Malcolmson, Steven J.; Meek, Simon J.; Sattely, Elizabeth S.; Schrock, Richard R.; Hoveyda, Amir H.

    2009-01-01

    Discovery of efficient catalysts is one of the most compelling objectives of modern chemistry. Chiral catalysts are in particularly high demand, as they facilitate synthesis of enantiomerically enriched small molecules that are critical to developments in medicine, biology and materials science1. Especially noteworthy are catalysts that promote—with otherwise inaccessible efficiency and selectivity levels—reactions demonstrated to be of great utility in chemical synthesis. Here we report a class of chiral catalysts that initiate alkene metathesis1 with very high efficiency and enantioselectivity. Such attributes arise from structural fluxionality of the chiral catalysts and the central role that enhanced electronic factors have in the catalytic cycle. The new catalysts have a stereogenic metal centre and carry only monodentate ligands; the molybdenum-based complexes are prepared stereoselectively by a ligand exchange process involving an enantiomerically pure aryloxide, a class of ligands scarcely used in enantioselective catalysis2,3. We demonstrate the application of the new catalysts in an enantioselective synthesis of the Aspidosperma alkaloid, quebrachamine, through an alkene metathesis reaction that cannot be promoted by any of the previously reported chiral catalysts. PMID:19011612

  18. Primary products and mechanistic considerations in alkane metathesis.

    PubMed

    Basset, Jean Marie; Copéret, Christophe; Lefort, Laurent; Maunders, Barry M; Maury, Olivier; Le Roux, Erwan; Saggio, Guillaume; Soignier, Sophie; Soulivong, Daravong; Sunley, Glenn J; Taoufik, Mostafa; Thivolle-Cazat, Jean

    2005-06-22

    Alkane metathesis, a reaction catalyzed by the silica-supported tantalum hydride [(SiO)2Ta-H], 1, which transforms acyclic alkanes into their higher and lower homologues, was reported in 1997. New studies conducted in a continuous flow reactor in the case of propane indicate that, by varying the contact time, hydrogen and olefins are primary products. This crucial observation, as well as the known properties of tantalum alkyls to perform alpha-H or beta-H eliminations, supports the proposition of a new mechanism involving metallacyclobutane intermediates just like in olefin metathesis. The observed selectivities for linear and branched Cn+1 and Cn+2 products as well as the linear/branched ratio can be well-explained on the basis of the minimization of steric interactions between 1,2- or 1,3-substituents in the various tantallacyclobutane intermediates or during their formation. Hydrogen plays a specific role in the cleavage of metal alkyls to complete the catalytic cycle.

  19. Organocatalytic condensation-ring opening-annulation cascade reactions between N-Bocindolin-2-ones/benzofuran-2(3H)-ones and salicylaldehydes for synthesis of 3-arylcoumarins.

    PubMed

    Cheng, Yuyu; Zhang, Pengfei; Jia, Yanwen; Fang, Zhiqiang; Li, Pengfei

    2017-09-20

    An organocatalytic cascade synthesis of 3-arylcoumarins has been developed. Mediated by 1,8-diazabicyclo[5,4,0]-undec-7-ene or tetramethylguanidine, a number of 3-arylcoumarins were obtained in good to excellent yields via condensation-ring opening-annulation between N-Bocindolin-2-ones/benzofuran-2(3H)-ones and salicylaldehydes. This method was featured by a broad scope of reactants, mild conditions, and simple operation.

  20. Healing efficiency of epoxy-based materials for structural application

    NASA Astrophysics Data System (ADS)

    Raimondo, Marialuigia; Guadagno, Liberata

    2012-07-01

    This paper describes a self-healing composite exhibiting high levels of healing efficiency under working conditions typical of aeronautic applications. The self-healing material is composed of a thermosetting epoxy matrix in which a catalyst of Ring Opening Metathesis Polymerization (ROMP) and nanocapsules are dispersed. The nanocapsules contain a monomer able to polymerize via ROMP. The preliminary results demonstrate an efficient self-repair function which is also active at very low temperatures.

  1. α-Alkylidene-γ-butyrolactone Formation via Bi(OTf)3-Catalyzed, Dehydrative, Ring-Opening Cyclizations of Cyclopropyl Carbinols: Understanding Substituent Effects and Predicting E/Z Selectivity.

    PubMed

    Sandridge, Matthew J; McLarney, Brett D; Williams, Corey W; France, Stefan

    2017-09-06

    A Bi(OTf)3-catalyzed ring-opening cyclization of (hetero)aryl cyclopropyl carbinols to form α-alkylidene-γ-butyrolactones (ABLs) is reported. This transformation represents different chemoselectivity from previous reports that demonstrated formation of (hetero)aryl-fused cyclohexa-1,3-dienes upon acid-promoted cyclopropyl carbinol ring opening. ABLs are obtained in up to 89% yield with a general preference for the E-isomers. Mechanistically, Bi(OTf)3 serves as a stable and easy to handle precursor to TfOH. TfOH then catalyzes the formation of cyclopropyl carbinyl cations, which undergo ring opening, intramolecular trapping by the neighboring ester group, subsequent hydrolysis, and loss of methanol resulting in the formation of the ABLs. The nature and relative positioning of the substituents on both the carbinol and the cyclopropane determine both chemo- and stereoselective outcomes. Carbinol substituents determine the extent of cyclopropyl carbinyl cation formation. The cyclopropane donor substituents determine the overall reaction chemoselectivity. Weakly stabilizing or electron-poor donor groups provide better yields of the ABL products. In contrast, copious amounts of competing products are observed with highly stabilizing cyclopropane donor substituents. Finally, a predictive model for E/Z-selectivity was developed using DFT calculations.

  2. Biokompatible Polymere

    NASA Astrophysics Data System (ADS)

    Ha, Suk-Woo; Wintermantel, Erich; Maier, Gerhard

    Der klinische Einsatz von synthetischen Polymeren begann in den 60-er Jahren in Form von Einwegartikeln, wie beispielsweise Spritzen und Kathetern, vor allem aufgrund der Tatsache, dass Infektionen infolge nicht ausreichender Sterilität der wiederverwendbaren Artikel aus Glas und metallischen Werkstoffen durch den Einsatz von sterilen Einwegartikeln signifikant reduziert werden konnten [1]. Die Einführung der medizinischen Einwegartikel aus Polymeren erfolgte somit nicht nur aus ökonomischen, sondern auch aus hygienischen Gründen. Wegen der steigenden Anzahl synthetischer Polymere und dem zunehmenden Bedarf an ärztlicher Versorgung reicht die Anwendung von Polymeren in der Medizin von preisgünstigen Einwegartikeln, die nur kurzzeitig intrakorporal eingesetzt werden, bis hin zu Implantaten, welche über eine längere Zeit grossen Beanspruchungen im menschlichen Körper ausgesetzt sind. Die steigende Verbreitung von klinisch eingesetzten Polymeren ist auf ihre einfache und preisgünstige Verarbeitbarkeit in eine Vielzahl von Formen und Geometrien sowie auf ihr breites Eigenschaftsspektrum zurückzuführen. Polymere werden daher in fast allen medizinischen Bereichen eingesetzt.

  3. Concise Syntheses of Insect Pheromones Using Z-Selective Cross Metathesis**

    PubMed Central

    Herbert, Myles B.; Marx, Vanessa M.; Pederson, Richard L.; Grubbs, Robert H.

    2013-01-01

    The shortest synthetic routes to nine cis-pheromones containing a variety of functionality, including an unconjugated (E,Z) diene, are reported. These lepidopteran pheromones are used extensively for pest control, and were easily prepared using ruthenium-based Z-selective cross metathesis, highlighting the advantages of this method over less efficient ways to form Z-olefins. Important insight into the mechanism of Z-selective metathesis was uncovered during experimentation and subsequently explored. PMID:23055437

  4. Cationic ruthenium alkylidene catalysts bearing phosphine ligands.

    PubMed

    Endo, Koji; Grubbs, Robert H

    2016-02-28

    The discovery of highly active catalysts and the success of ionic liquid immobilized systems have accelerated attention to a new class of cationic metathesis catalysts. We herein report the facile syntheses of cationic ruthenium catalysts bearing bulky phosphine ligands. Simple ligand exchange using silver(i) salts of non-coordinating or weakly coordinating anions provided either PPh3 or chelating Ph2P(CH2)nPPh2 (n = 2 or 3) ligated cationic catalysts. The structures of these newly reported catalysts feature unique geometries caused by ligation of the bulky phosphine ligands. Their activities and selectivities in standard metathesis reactions were also investigated. These cationic ruthenium alkylidene catalysts reported here showed moderate activity and very similar stereoselectivity when compared to the second generation ruthenium dichloride catalyst in ring-closing metathesis, cross metathesis, and ring-opening metathesis polymerization assays.

  5. Self‐Assembly of Disorazole C1 through a One‐Pot Alkyne Metathesis Homodimerization Strategy†

    PubMed Central

    Ralston, Kevin J.; Ramstadius, H. Clinton; Brewster, Richard C.; Niblock, Helen S.

    2015-01-01

    Abstract Alkyne metathesis is increasingly explored as a reliable method to close macrocyclic rings, but there are no prior examples of an alkyne‐metathesis‐based homodimerization approach to natural products. In this approach to the cytotoxic C2‐symmetric marine‐derived bis(lactone) disorazole C1, a highly convergent, modular strategy is employed featuring cyclization through an ambitious one‐pot alkyne cross‐metathesis/ring‐closing metathesis self‐assembly process. PMID:27346897

  6. Z-Selective Olefin Metathesis on Peptides: Investigation of Side-Chain Influence, Preorganization, and Guidelines in Substrate Selection

    PubMed Central

    2015-01-01

    Olefin metathesis has emerged as a promising strategy for modulating the stability and activity of biologically relevant compounds; however, the ability to control olefin geometry in the product remains a challenge. Recent advances in the design of cyclometalated ruthenium catalysts has led to new strategies for achieving such control with high fidelity and Z selectivity, but the scope and limitations of these catalysts on substrates bearing multiple functionalities, including peptides, remained unexplored. Herein, we report an assessment of various factors that contribute to both productive and nonproductive Z-selective metathesis on peptides. The influence of sterics, side-chain identity, and preorganization through peptide secondary structure are explored by homodimerization, cross metathesis, and ring-closing metathesis. Our results indicate that the amino acid side chain and identity of the olefin profoundly influence the activity of cyclometalated ruthenium catalysts in Z-selective metathesis. The criteria set forth for achieving high conversion and Z selectivity are highlighted by cross metathesis and ring-closing metathesis on diverse peptide substrates. The principles outlined in this report are important not only for expanding the scope of Z-selective olefin metathesis to peptides but also for applying stereoselective olefin metathesis in general synthetic endeavors. PMID:25102124

  7. Synthesis of Catenane Structures via Ring-Closing Metathesis.

    PubMed

    Weck, Marcus; Mohr, Bernhard; Sauvage, Jean-Pierre; Grubbs, Robert H.

    1999-07-23

    This study presents a detailed description of a synthetic strategy to obtain catenane architectures through ring-closing metathesis. The approach is based on phenanthroline-based ligands containing terminal olefinic units that were designed to coordinate in a tetrahedral arrangement around a copper atom. Treatment of the assembled copper complexes with ruthenium catalyst 1 resulted in [2]catenates in high yields of 88-92%. Demetalation produced the corresponding [2]catenand in nearly quantitative yields. Hydrogenation of the catenates with Crabtree's catalyst and subsequent demetalation yielded fully saturated catenands. The presently described procedure makes [2]catenanes very accessible since the synthetic route consists of six steps (Schemes 2 and 4) from commercially available 1,10-phenanthroline, the overall yield being 51%.

  8. High-performance vitrimers from commodity thermoplastics through dioxaborolane metathesis.

    PubMed

    Röttger, Max; Domenech, Trystan; van der Weegen, Rob; Breuillac, Antoine; Nicolaÿ, Renaud; Leibler, Ludwik

    2017-04-07

    Windmills, cars, and dental restoration demand polymer materials and composites that are easy to process, assemble, and recycle while exhibiting outstanding mechanical, thermal, and chemical resistance. Vitrimers, which are polymer networks able to shuffle chemical bonds through exchange reactions, could address these demands if they were prepared from existing plastics and processed with fast production rates and current equipment. We report the metathesis of dioxaborolanes, which is rapid and thermally robust, and use it to prepare vitrimers from polymers as different as poly(methyl methacrylate), polystyrene, and high-density polyethylene that, although permanently cross-linked, can be processed multiple times by means of extrusion or injection molding. They show superior chemical resistance and dimensional stability and can be efficiently assembled. The strategy is applicable to polymers with backbones made of carbon-carbon single bonds.

  9. High-performance vitrimers from commodity thermoplastics through dioxaborolane metathesis

    NASA Astrophysics Data System (ADS)

    Röttger, Max; Domenech, Trystan; van der Weegen, Rob; Breuillac, Antoine; Nicolaÿ, Renaud; Leibler, Ludwik

    2017-04-01

    Windmills, cars, and dental restoration demand polymer materials and composites that are easy to process, assemble, and recycle while exhibiting outstanding mechanical, thermal, and chemical resistance. Vitrimers, which are polymer networks able to shuffle chemical bonds through exchange reactions, could address these demands if they were prepared from existing plastics and processed with fast production rates and current equipment. We report the metathesis of dioxaborolanes, which is rapid and thermally robust, and use it to prepare vitrimers from polymers as different as poly(methyl methacrylate), polystyrene, and high-density polyethylene that, although permanently cross-linked, can be processed multiple times by means of extrusion or injection molding. They show superior chemical resistance and dimensional stability and can be efficiently assembled. The strategy is applicable to polymers with backbones made of carbon-carbon single bonds.

  10. Directed evolution of artificial metalloenzymes for in vivo metathesis

    NASA Astrophysics Data System (ADS)

    Jeschek, Markus; Reuter, Raphael; Heinisch, Tillmann; Trindler, Christian; Klehr, Juliane; Panke, Sven; Ward, Thomas R.

    2016-09-01

    The field of biocatalysis has advanced from harnessing natural enzymes to using directed evolution to obtain new biocatalysts with tailor-made functions. Several tools have recently been developed to expand the natural enzymatic repertoire with abiotic reactions. For example, artificial metalloenzymes, which combine the versatile reaction scope of transition metals with the beneficial catalytic features of enzymes, offer an attractive means to engineer new reactions. Three complementary strategies exist: repurposing natural metalloenzymes for abiotic transformations; in silico metalloenzyme (re-)design; and incorporation of abiotic cofactors into proteins. The third strategy offers the opportunity to design a wide variety of artificial metalloenzymes for non-natural reactions. However, many metal cofactors are inhibited by cellular components and therefore require purification of the scaffold protein. This limits the throughput of genetic optimization schemes applied to artificial metalloenzymes and their applicability in vivo to expand natural metabolism. Here we report the compartmentalization and in vivo evolution of an artificial metalloenzyme for olefin metathesis, which represents an archetypal organometallic reaction without equivalent in nature. Building on previous work on an artificial metallohydrolase, we exploit the periplasm of Escherichia coli as a reaction compartment for the ‘metathase’ because it offers an auspicious environment for artificial metalloenzymes, mainly owing to low concentrations of inhibitors such as glutathione, which has recently been identified as a major inhibitor. This strategy facilitated the assembly of a functional metathase in vivo and its directed evolution with substantially increased throughput compared to conventional approaches that rely on purified protein variants. The evolved metathase compares favourably with commercial catalysts, shows activity for different metathesis substrates and can be further evolved in

  11. Directed evolution of artificial metalloenzymes for in vivo metathesis.

    PubMed

    Jeschek, Markus; Reuter, Raphael; Heinisch, Tillmann; Trindler, Christian; Klehr, Juliane; Panke, Sven; Ward, Thomas R

    2016-09-29

    The field of biocatalysis has advanced from harnessing natural enzymes to using directed evolution to obtain new biocatalysts with tailor-made functions. Several tools have recently been developed to expand the natural enzymatic repertoire with abiotic reactions. For example, artificial metalloenzymes, which combine the versatile reaction scope of transition metals with the beneficial catalytic features of enzymes, offer an attractive means to engineer new reactions. Three complementary strategies exist: repurposing natural metalloenzymes for abiotic transformations; in silico metalloenzyme (re-)design; and incorporation of abiotic cofactors into proteins. The third strategy offers the opportunity to design a wide variety of artificial metalloenzymes for non-natural reactions. However, many metal cofactors are inhibited by cellular components and therefore require purification of the scaffold protein. This limits the throughput of genetic optimization schemes applied to artificial metalloenzymes and their applicability in vivo to expand natural metabolism. Here we report the compartmentalization and in vivo evolution of an artificial metalloenzyme for olefin metathesis, which represents an archetypal organometallic reaction without equivalent in nature. Building on previous work on an artificial metallohydrolase, we exploit the periplasm of Escherichia coli as a reaction compartment for the 'metathase' because it offers an auspicious environment for artificial metalloenzymes, mainly owing to low concentrations of inhibitors such as glutathione, which has recently been identified as a major inhibitor. This strategy facilitated the assembly of a functional metathase in vivo and its directed evolution with substantially increased throughput compared to conventional approaches that rely on purified protein variants. The evolved metathase compares favourably with commercial catalysts, shows activity for different metathesis substrates and can be further evolved in

  12. New developments of polysaccharide synthesis via enzymatic polymerization

    PubMed Central

    Kobayashi, Shiro

    2007-01-01

    This review focuses on the in vitro synthesis of polysaccharides, the method of which is “enzymatic polymerization” mainly developed by our group. Polysaccharides are formed by repeated glycosylation reactions between a glycosyl donor and a glycosyl acceptor. A hydrolysis enzyme was found very efficient as catalyst, where the monomer is designed based on the new concept of a “transition-state analogue substrate” (TSAS); sugar fluoride monomers for polycondensation and sugar oxazoline monomers for ring-opening polyaddition. Enzymatic polymerization enabled the first in vitro synthesis of natural polysaccharides such as cellulose, xylan, chitin, hyaluronan and chondroitin, and also of unnatural polysaccharides such as a cellulose–chitin hybrid, a hyaluronan–chondroitin hybrid, and others. Supercatalysis of hyaluronidase was disclosed as unusual enzymatic multi-catalyst functions. Mutant enzymes were very useful for synthetic and mechanistic studies. In situ observations of enzymatic polymerization by SEM, TEM, and combined SAS methods revealed mechanisms of the polymerization and of the self-assembling of high-order molecular structure formed by elongating polysaccharide molecules. PMID:24367148

  13. Amphiphilic Cellulose Ethers Designed for Amorphous Solid Dispersion via Olefin Cross-Metathesis.

    PubMed

    Dong, Yifan; Mosquera-Giraldo, Laura I; Taylor, Lynne S; Edgar, Kevin J

    2016-02-08

    The design of cellulose ether-based amphiphiles has been difficult and limited because of the harsh conditions typically required for appending ether moieties to cellulose. Olefin cross-metathesis recently has been shown to be a valuable approach for appending a variety of functional groups to cellulose ethers and esters, provided that an olefin handle for metathesis can be attached. This synthetic pathway gives access to these functional derivatives under very mild conditions and at high efficiency. Modification of ethyl cellulose by metathesis to prepare useful derivatives, for example, for solubility and bioavailability enhancement of drugs by amorphous solid dispersion (ASD), has been limited by the low DS(OH) of commercial ethyl cellulose derivatives. This is problematic because ethyl cellulose is otherwise a very attractive substrate for synthesis of amphiphilic derivatives by olefin metathesis. Herein we explore two methods for opening up this design space for ether-based amphiphiles, for example, permitting synthesis of more hydrophilic derivatives. One approach is to start with the more hydrophilic commercial methyl cellulose, which contains much higher DS(OH) and therefore is better suited for introduction of high DS of olefin metathesis "handles". In another approach, we explored a homogeneous one-pot synthesis methodology from cellulose, where controlled DS of ethyl groups was introduced at the same time as the ω-unsaturated alkyl groups, thereby permitting complete control of DS(OH), DS(Et), and ultimately DS of the functional group added by metathesis. We describe the functionalized derivatives available by these successful approaches. In addition, we explore new methods for reduction of the unsaturation in initial metathesis products to provide robust methods for enhancing product stability against further radical-catalyzed reactions. We demonstrate initial evidence that the products show strong promise as amphiphilic matrix polymers for amorphous

  14. Nobel Chemistry in the Laboratory: Synthesis of a Ruthenium Catalyst for Ring-Closing Olefin Metathesis--An Experiment for the Advanced Inorganic or Organic Laboratory

    ERIC Educational Resources Information Center

    Greco, George E.

    2007-01-01

    An experiment for the upper-level undergraduate laboratory is described in which students synthesize a ruthenium olefin metathesis catalyst, then use the catalyst to carry out the ring-closing metathesis of diethyl diallylmalonate. The olefin metathesis reaction was the subject of the 2005 Nobel Prize in chemistry. The catalyst chosen for this…

  15. Nobel Chemistry in the Laboratory: Synthesis of a Ruthenium Catalyst for Ring-Closing Olefin Metathesis--An Experiment for the Advanced Inorganic or Organic Laboratory

    ERIC Educational Resources Information Center

    Greco, George E.

    2007-01-01

    An experiment for the upper-level undergraduate laboratory is described in which students synthesize a ruthenium olefin metathesis catalyst, then use the catalyst to carry out the ring-closing metathesis of diethyl diallylmalonate. The olefin metathesis reaction was the subject of the 2005 Nobel Prize in chemistry. The catalyst chosen for this…

  16. Gallium and indium complexes containing the bis(imino)phenoxide ligand: synthesis, structural characterization and polymerization studies.

    PubMed

    Ghosh, Swarup; Gowda, Ravikumar R; Jagan, Rajamony; Chakraborty, Debashis

    2015-06-14

    A series of gallium and indium complexes containing a bis(imino)phenolate ligand framework were synthesized and completely characterized with different spectroscopic techniques. The molecular structures of a few complexes were determined using single crystal X-ray diffraction studies. These compounds were found to be extremely active towards the bulk ring opening polymerization (ROP) of lactides yielding polymers with high number average molecular weight (Mn) and controlled molecular weight distributions (MWDs). The neutral complexes produce isotactic enriched poly(lactic acid) (PLA) from rac-lactide (rac-LA) under melt conditions, whereas the ionic complex produces atactic PLA. The polymerizations are controlled, as evidenced by the narrow molecular distribution (MWDs) of the isolated polymers in addition to the linear nature of number average molecular weight (Mn) versus conversion plots with variations in monomer to catalyst ratios. The kinetic and mechanistic studies associated with these polymerizations have been performed.

  17. Sustainable, Stereoregular, and Optically Active Polyamides via Cationic Polymerization of ε-Lactams Derived from the Terpene β-Pinene.

    PubMed

    Winnacker, Malte; Sag, Jacob; Tischner, Andreas; Rieger, Bernhard

    2017-03-08

    A convenient synthesis of sustainable polyamides, which contain side groups and stereocenters, starting from the biobased small terpene β-pinene is reported. The polyamides, which are obtained via the pinene-based lactam via ring-opening polymerization, show excellent thermal properties, rendering this approach very interesting for the utilization of novel biobased and structurally significant high-performance polymers and materials. Polymer masses and yields are shown to be dependent on different parameters, and the stereoinformation of the lactam monomer can thus be transferred into the polymer chain. In addition, another lactam side product can also be transformed to polyamides.

  18. Multi input single output model predictive control of non-linear bio-polymerization process

    SciTech Connect

    Arumugasamy, Senthil Kumar; Ahmad, Z.

    2015-05-15

    This paper focuses on Multi Input Single Output (MISO) Model Predictive Control of bio-polymerization process in which mechanistic model is developed and linked with the feedforward neural network model to obtain a hybrid model (Mechanistic-FANN) of lipase-catalyzed ring-opening polymerization of ε-caprolactone (ε-CL) for Poly (ε-caprolactone) production. In this research, state space model was used, in which the input to the model were the reactor temperatures and reactor impeller speeds and the output were the molecular weight of polymer (M{sub n}) and polymer polydispersity index. State space model for MISO created using System identification tool box of Matlab™. This state space model is used in MISO MPC. Model predictive control (MPC) has been applied to predict the molecular weight of the biopolymer and consequently control the molecular weight of biopolymer. The result shows that MPC is able to track reference trajectory and give optimum movement of manipulated variable.

  19. Water soluble and heat resistant polymers by free radical polymerization of lactic acid-based monomers

    NASA Astrophysics Data System (ADS)

    Tanaka, Hitoshi; Kibayashi, Tatsuya; Niwa, Miki

    2013-08-01

    Tactic heat resistant polymer was prepared by free radical polymerization of lactic acid-based monomers, i.e. chiral 2-isopropyl-5-methylene-1,3-dioxolan-4-ones (1). The polymerization of 1 proceeded smoothly without ring-opening to give a polymer with high isotacticity (mm) of 29.7~100% and glass transition temperature (Tg) of 172~213°C. 1 also showed high reactivity in the copolymerization with styrene and methyl methacrylate, and the incorporation of 1 unit in the copolymer structure increased Tg of each polymer. In addition, hydrolysis of poly(1) produced a new type of water soluble poly(lactic acid), i.e. poly(α-hydroxy acrylate), and poly(α-hydroxy acrylate-co-divinyl benzene) hydrogel absorbed water as high as 1000 times of the original polymer weight.

  20. Multi input single output model predictive control of non-linear bio-polymerization process

    NASA Astrophysics Data System (ADS)

    Arumugasamy, Senthil Kumar; Ahmad, Z.

    2015-05-01

    This paper focuses on Multi Input Single Output (MISO) Model Predictive Control of bio-polymerization process in which mechanistic model is developed and linked with the feedforward neural network model to obtain a hybrid model (Mechanistic-FANN) of lipase-catalyzed ring-opening polymerization of ɛ-caprolactone (ɛ-CL) for Poly (ɛ-caprolactone) production. In this research, state space model was used, in which the input to the model were the reactor temperatures and reactor impeller speeds and the output were the molecular weight of polymer (Mn) and polymer polydispersity index. State space model for MISO created using System identification tool box of Matlab™. This state space model is used in MISO MPC. Model predictive control (MPC) has been applied to predict the molecular weight of the biopolymer and consequently control the molecular weight of biopolymer. The result shows that MPC is able to track reference trajectory and give optimum movement of manipulated variable.