Showing papers on "Acyclic diene metathesis published in 2016"

FeCl3 -Catalyzed Ring-Closing Carbonyl-Olefin Metathesis.

Abstract: 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.

Universal Relationship between Conductivity and Solvation-Site Connectivity in Ether-Based Polymer Electrolytes

Abstract: We perform a joint experimental and computational study of ion transport properties in a systematic set of linear polyethers synthesized via acyclic diene metathesis (ADMET) polymerization. We measure ionic conductivity, σ, and glass transition temperature, Tg, in mixtures of polymer and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt. While Tg is known to be an important factor in the ionic conductivity of polymer electrolytes, recent work indicates that the number and proximity of lithium ion solvation sites in the polymer also play an important role, but this effect has yet to be systematically investigated. Here, adding aliphatic linkers to a poly(ethylene oxide) (PEO) backbone lowers Tg and dilutes the polar groups; both factors influence ionic conductivity. To isolate these effects, we introduce a two-step normalization scheme. In the first step, Vogel–Tammann–Fulcher (VTF) fits are used to calculate a temperature-dependent reduced conductivity, σr(T), which is defined as the conductivity o...

Catalyst Decomposition during Olefin Metathesis Yields Isomerization-Active Ruthenium Nanoparticles

Abstract: The second-generation Grubbs catalyst, RuCl2(H2IMes)(PCy3) (=CHPh) [GII; H2IMes=1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene, Cy=cyclohexyl], is shown to decompose during olefin metathesis to generate Ru nanoparticles (RuNPs). These RuNPs appear to contribute significantly to competing isomerization during metathesis. Larger, partially oxidized RuNPs are also observed in commercial GII, but these exhibit modest isomerization activity. Removal of RuNPs from the precatalyst does not prevent isomerization, because new, more reactive NPs are generated by catalyst decomposition during metathesis.

Photo- and Metallo-responsive N-Alkyl α-Bisimines as Orthogonally Addressable Main-Chain Functional Groups in Metathesis Polymers

Abstract: N-alkyl α-bisimines were employed as main-chain functional groups in acyclic diene metathesis (ADMET)-polymers, conferring dual responsiveness for the controlled switching of the polymeric particle shape with light and metal ions. Photochemical Z/E-isomerization leads to a significant and reversible change in hydrodynamic volume, thus introducing simple imines as novel photoswitches for light-responsive materials. Mild imine-directed CH activation by Pd(OAc)2 is demonstrated as a new single-chain nanoparticle (SCNP) folding process, enabling a controlled atom- and step-economic SCNP synthesis. The combination of light- and metallo-responsiveness in the same polymer provides the ability for orthogonal switching, a valuable tool for advanced functional material design.

Morphology and Thermal Properties of Precision Polymers: The Crystallization of Butyl Branched Polyethylene and Polyphosphoesters

Abstract: Chemical irregularities such as side chain branches or comonomers in an otherwise regular polymer influence its crystallization. In most polymer systems, these chemical defects are randomly distributed along the chain, and it is difficult to understand in detail their effect on crystallization. We have examined three precision polymers prepared by acyclic diene metathesis (ADMET) polymerization. This synthesis ensures exact placement of the chain defects; here they are all separated by 20 CH2 units. The polymers are two polyphosphoesters with a phosphate or phosphonate group in the main chain and one polyethylene with butyl branches. Although the alkyl part is identical for all three polymers, their thermal and crystal properties differ noticeably. By means of differential scanning calorimetry, X-ray scattering, and transmission electron microscopy, we characterize the lamellar crystals and correlate our findings to the observed difference in thermal behavior.

A Light-Activated Olefin Metathesis Catalyst Equipped with a Chromatic Orthogonal Self-Destruct Function.

Abstract: A sulfur-chelated photolatent ruthenium olefin metathesis catalyst has been equipped with supersilyl protecting groups on the N-heterocyclic carbene ligand. The silyl groups function as an irreversible chromatic kill switch, thus decomposing the catalyst when it is irradiated with 254 nm UV light. Therefore, different types of olefin metathesis reactions may be started by irradiation with 350 nm UV light and prevented by irradiation with shorter wavelengths. The possibility to induce and impede catalysis just by using light of different frequencies opens the pathway for stereolithographic applications and novel light-guided chemical sequences.

In-Chain Poly(phosphonate)s via Acyclic Diene Metathesis Polycondensation

Abstract: In-chain poly(phosphonate)s have been prepared via acyclic diene metathesis polymerization of three different monomers. Novel unsaturated phosphonate monomers with asymmetric structure have been developed. The monomers are accessible via a three-step synthesis that can be easily scaled up. This is the first report on poly(phosphonate)s by olefin metathesis where the stable carbon–phosphorus linkage is localized in the polymer backbone. This changes the nature of the degradation products compared to other poly(phosphoester)s. Polymers with molecular weights up to 31 000 g mol–1 can be achieved and have been characterized in detail NMR spectroscopy, size exclusion chromatography, thermogravimetry, and differential scanning calorimetry. They have been also compared to structural analogues polyphosphates with respect to crystallization (SAXS, WAXS) and their rheological behavior. Also, solution grown crystals were analyzed rendering some of the herein reported poly(phosphonate)s as interesting defect poly(eth...

Poly(phosphorodiamidate)s by Olefin Metathesis Polymerization with Precise Degradation.

Abstract: Degradable polymers are a currently growing field of research for biomedical and materials science applications. The majority of such compounds are based on polyesters and polyamides. In contrast, their phosphorus-containing counterparts are much less studied, in spite of their potential precise degradation profile and biocompatibility. Herein, the first library of poly(phosphorodiamidate)s (PPDAs) with two P−N bonds forming the polymer backbone and a pendant P−OR group is prepared through acyclic diene metathesis polymerization. They are designed to vary in their hydrophilicity and are compared with the structural analogues poly(phosphoester)s (PPEs) with respect to their thermal properties and degradation profiles. The degradation of PPDAs can be controlled precisely by the pH: under acidic conditions the P−N linkages in the polymer backbone are cleaved, whereas under basic conditions the pendant ester is cleaved selectively and almost no backbone degradation occurs. The PPDAs exhibit distinctively higher thermal stability (from thermogravimetric analysis (TGA)) and higher glass transition and/or melting temperatures (from differential scanning calorimetry (DSC)) compared with analogous PPEs. This renders this exotic class of phosphorus-containing polymers as highly promising for the development of future drug carriers or tissue engineering scaffolds.

Thermally Degradable Polyesters with Tunable Degradation Temperatures via Postpolymerization Modification and Intramolecular Cyclization

Abstract: We report the novel synthesis of thermally degradable polyesters through the postpolymerization modification of an unsaturated aliphatic polyester from maleic acid via Michael addition reaction with β-amino mercaptans. A high molecular weight polyester (P0) was synthesized by the acyclic diene metathesis (ADMET) polymerization of a diene monomer, di(10-undecenyl) maleate. Postpolymerization modification of P0 with three β-amino mercaptans (2-aminoethanethiol, l-cysteine methyl ester, and 2-(butylamino)ethanethiol) and 2-mercaptoethanol via the selective and quantitative thiol–Michael addition reaction with the maleate vinylic double bonds afforded four polyesters (P1–P4). All the polyesters were characterized by 1H NMR, GPC, and MALDI-TOF-MS, and their thermal properties were studied by thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). The three polymers with pendant amino groups (P1–P3) subjected to thermal-induced degradation in the solid state, the driving force of which i...

A Precision Ethylene-Styrene Copolymer with High Styrene Content from Ring-Opening Metathesis Polymerization of 4-Phenylcyclopentene.

Abstract: Ring-opening metathesis polymerization of 4-phenylcyclopentene is investigated for the first time under various conditions. Thermodynamic analysis reveals a polymerization enthalpy and entropy sufficient for high molar mass and conversions at lower temperatures. In one example, neat polymerization using Hoveyda-Grubbs second generation catalyst at -15 °C yields 81% conversion to poly(4-phenylcyclopentene) (P4PCP) with a number average molar mass of 151 kg mol(-1) and dispersity of 1.77. Quantitative homogeneous hydrogenation of P4PCP results in a precision ethylene-styrene copolymer (H2 -P4PCP) with a phenyl branch at every fifth carbon along the backbone. This equates to a perfectly alternating trimethylene-styrene sequence with 71.2% w/w styrene content that is inaccessible through molecular catalyst copolymerization strategies. Differential scanning calorimetry confirms P4PCP and H2 -P4PCP are amorphous materials with similar glass transition temperatures (Tg ) of 17 ± 2 °C. Both materials present well-defined styrenic analogs for application in specialty materials or composites where lower softening temperatures may be desired.

Synthesis and Crystallization Behavior of Equisequential ADMET Polyethylene Containing Arylene Ether Defects: Remarkable Effects of Substitution Position and Arylene Size

Abstract: A new series of polyethylene (PE) containing arylene ether units as defects in the main chain, which were precisely separated by 20 CH2 units, were synthesized via acyclic diene metathesis (ADMET) polymerization. The thermal stability, crystallization, and melting behaviors, crystal structure, and chain stacking were investigated with TGA, DSC, WAXD, and SAXS. It is found that the substitution position in the arylene units has a remarkable influence on the chain stacking and their location in the solid phase. The ortho-substituted phenylene units are excluded from the crystal phase, leading to a low melting temperature (Tm). In contrast, the para-substituted phenylene units can be included into the crystal, leading to a high Tm. The meta-substituted phenylene units can be partially included into the crystal, resulting in mixed crystal structures and an intermediate Tm. Such an effect of substitution position in precision PEs is different from that in poly(ethylene oxide) reported in the literature, which ...

NHC Backbone Configuration in Ruthenium-Catalyzed Olefin Metathesis.

Abstract: The catalytic properties of olefin metathesis ruthenium complexes bearing N-heterocyclic carbene ligands with stereogenic centers on the backbone are described. Differences in catalytic behavior depending on the backbone configurations of symmetrical and unsymmetrical NHCs are discussed. In addition, an overview on asymmetric olefin metathesis promoted by chiral catalysts bearing C₂-symmetric and C₁-symmetric NHCs is provided.

Tandem Olefin Metathesis/Oxidative Cyclization: Synthesis of Tetrahydrofuran Diols from Simple Olefins

Abstract: A tandem olefin metathesis/oxidative cyclization has been developed to synthesize 2,5-disubstituted tetrahydrofuran (THF) diols in a stereocontrolled fashion from simple olefin precursors. The ruthenium metathesis catalyst is converted into an oxidation catalyst in the second step and is thus responsible for both catalytic steps. The stereochemistry of the 1,5-diene intermediate can be controlled through the choice of catalyst and the type of metathesis conducted. This olefin stereochemistry then controls the THF diol stereochemistry through a highly stereospecific oxidative cyclization.

Synthesis of Novel Cyclic Olefin Polymer with High Glass Transition Temperature via Ring‐Opening Metathesis Polymerization

Abstract: Three norbornene derivatives containing bulky hydrocarbon groups (M1–M3) have been prepared and polymerized efficiently via ring-opening metathesis polymerization (ROMP) using different Grubbs catalysts (G1–G3) to afford polymers in high yield. Gel permeation chromatography curves show that all the obtained polymers exhibit unimodal distribution. Unsaturated moieties in the main chain of the obtained polymers are hydrogenated based on the chemistry of the reactive intermediate diimide (HNNH) in quantitative conversion, confirmed by 1H NMR measurement. All the polymers display relatively high thermal stability according to thermogravimetric analyses test. The results of differential scanning calorimetry measurement show that the cardo-like structure such as M2 and M3 is contributed to improve the Tg of cyclicolefin polymer materials. The highest Tg (up to 277 °C) of hydrogenated polymer H-PM3 is achieved, which is so far the highest value obtained by the ROMP approach, to the best of our knowledge. Furthermore, all the hydrogenated polymers show excellent transparency because of their amorphous structure.

Sequence Effects in Conjugated Donor-Acceptor Trimers and Polymers.

Abstract: To investigate the sequence effect on donor-acceptor conjugated oligomers and polymers, the trimeric isomers PBP and BPP, comprising dialkoxy phenylene vinylene (P), benzothiadiazole vinylene (B), and alkyl endgroups with terminal olefins, are synthesized. Sequence effects are evident in the optical/electrochemical properties and thermal properties. Absorption maxima for PBP and BPP differ by 41 nm and the electrochemical band gaps by 0.1 V. The molar emission intensity is five times greater in PBP than BPP. Both trimers are crystalline and the melting points differ by 17 °C. The PBP and BPP trimers are used as macromonomers in an acyclic diene metathesis polymerization to give PolyPBP and PolyBPP. The optical and electrochemical properties are similar to those of their trimer precursors-sequence effects are still evident. These results suggest that sequence is a tunable variable for electronic materials and that the polymerization of oligomeric sequences is a useful approach to introducing sequence into polymers.

Designing Sequence Selectivity into a Ring-Opening Metathesis Polymerization Catalyst.

Abstract: ConspectusThe development of a chemoselective catalyst for the sequence-selective copolymerization of two cycloolefins by ring-opening metathesis polymerization is described, starting with the mechanistic work that established the structure of the key metallacyclobutane intermediate. Experimental and computational investigations converged to a conclusion that the lowest energy metallacyclobutane intermediate in the ruthenium carbene-catalyzed metathesis reaction had the four-membered ring trans to the phosphine or NHC ligand. The trans-metallacyclobutane structure, for the case of a degenerate metathesis reaction catalyzed by a Grubbs first-generation complex, necessitated a rotation of the 3-fold symmetric tricyclohexylphosphine ligand, with respect to the 2-fold symmetric metallacyclobutane substructure. The degeneracy could be lifted by constraining the rotation. Lifting the degeneracy created the possibility of chemoselectivity. This mechanistic work led to a concept for the “tick-tock” catalyst for a...

Donor/Acceptor-Stabilized 1-Silaketene: Reversible [2+2] Cycloaddition with Pyridine and Evolution by an Olefin Metathesis Reaction.

Abstract: The reaction of silacyclopropylidene 1 with benzaldehyde generates a 1-silaketene complex 2 by a formal atomic silicon insertion into the C=O bond of the aldehyde. The highly reactive 1-silaketene 2 undergoes a reversible [2+2] cycloaddition with pyridine to give sila-β-lactam 3. Of particular interest, in the presence of 4-dimethylaminopyridine (DMAP), 1-silaketene complex 2 evolves through an intramolecular olefin metathesis reaction, generating a new 1-silaketene complex 8 and cis-stilbene. Theoretical studies suggest that the reaction proceeds through the formation of a transient silacyclobutanone, a four-membered-ring intermediate, similar to that proposed by Chauvin and co-workers for the transition-metal-based olefin metathesis.

Olefin Metathesis of Vinylgermanium Derivatives as Method for the Synthesis of Functionalized Cubic and Double-Decker Germasilsesquioxanes

Abstract: For the first time, olefin cross metathesis has been developed for vinylgermanium compounds. This paper also marks the first case of transition metal-catalyzed functionalization of heterosilsesquioxanes, which in our case are cubic vinylgermasilsesquioxanes and newly synthesized di(vinylgermyl)substituted double-decker silsesquioxane. These processes lead to a series of new molecular, unsaturated mono- and divinyl-substituted germasilsesquioxanes, which can be potentially applied as precursors for optoelectronics and for the synthesis of new advanced materials. Additionally, preliminary tests of metathetic copolymerization of divinylsubstituted double-decker digermasilsesquioxanes (DDSQ-2ViGe) with selected diolefins proved to be very promising and resulted in the synthesis of novel stereoregular trans-germasilsesquioxyl-vinylene-phenylene macromolecular derivatives. All newly obtained compounds were isolated and characterized by mass and spectroscopic methods.

Catalytic One-Pot Synthesis of End-Functionalized Poly(9,9′-di-n-octylfluorenevinylene)s by Acyclic Diene Metathesis (ADMET) Polymerization Using Ruthenium–Carbene Catalysts

Abstract: Synthesis of end-functionalized poly(9,9′-di-n-octylfluorenevinylene)s (EF-PFVs) has been achieved by (i) catalytic olefin metathesis of vinyl groups (chain ends) in once prepared PFVs by acyclic diene metathesis (ADMET) polymerization with 1,2-disubstituted (bifunctional) olefins (DOs) or (ii) one-pot synthesis by combined ADMET polymerization (of 2,7-divinyl-9,9-di-n-octhylfluorene, DVF) with end-functionalization/chain transfer using DOs in the presence of ruthenium catalyst, RuCl2(PCy3)(IMesH2)(CHPh) [Ru(1), Cy = cyclohexyl, IMesH2 = 1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene]. Efficient one-pot synthesis of a series of high molecular weight EF-PFVs has been achieved when DOs were added after a certain period of the ADMET polymerization.

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

Abstract: 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.

Structurally Diverse Poly(thienylene vinylene)s (PTVs) with Systematically Tunable Properties through Acyclic Diene Metathesis (ADMET) and Postpolymerization Modification

Abstract: Poly(thienylene vinylene)s (PTVs) are a unique class of low bandgap conjugated polymers that have received relatively little attention in organic electronic applications due to the limitations in conventional synthetic methodologies that are not capable to produce PTV structures beyond the rudimentary forms. We report here facile synthetic methods, combining acyclic diene metathesis (ADMET) and postpolymerization modification reactions, toward a series of structurally diverse PTVs. Specifically, halogen substituents including F, Cl, Br, and I, and conjugated thienyl groups bearing different substituents, have been installed onto every thiophene unit along the PTV backbones. While halogen substitution lowers both the HOMO and LUMO energy levels of the polymers, the overall optical properties are similar to the conventional unsubstituted PTVs. On the other hand, with increasing sizes of halogen atoms, the polymer crystallinity decreases caused by steric hindrance induced main-chain nonplanarity as suggested...

A Thermo- and Photo-Switchable Ruthenium Initiator For Olefin Metathesis

Abstract: A ruthenium carbene complex bearing azobenzene functionality is reported. The complex exists in the form of two isomers differing by the size of the chelate ring. Both isomers were isolated by applying kinetic or thermodynamic control during the synthesis and characterized by X-ray diffraction analysis. The isomerization of the complex was studied by UV/Vis spectroscopy. The stable isomer was tested as a catalyst in olefin metathesis. The complex was activated at about 100 °C to promote ring-closing and ring-opening polymerization metathesis reactions. The activation took place also at room temperature under middle ultraviolet radiation.