A tremendous number of solvents, either as liquids or vapors, contaminate the environment on a daily basis worldwide. Olefin metathesis, which has been widely used as high-yielding protocols for ring-opening metathesis polymerization (ROMP), ring-closing metathesis (RCM), and isomerization reactions, is typically performed in toxic and volatile solvents such as dichloromethane. In this study, the results of our systematic experiments with the Grubbs G1, G2, and Hoveyda-Grubbs HG2 catalysts proved that benzotrifluoride (BTF) can replace dichloromethane (DCM) in these reactions, providing high yields and similar or even higher reaction rates in certain cases. The ROMP of norbornene resulted not only in high yields but also in polynorbornenes with a high molecular weight at low catalyst loadings. Ring-closing metathesis (RCM) experiments proved that, with the exception of the G1 catalyst, RCM occurs with similar high efficiencies in BTF as in DCM. It was found that isomerization of (Z)-but-2-ene-1,4-diyl diacetate with the G2 and HG2 catalysts proceeds at significantly higher initial rates in BTF than in DCM, leading to rapid isomerization with high yields in a short time. Overall, BTF is a suitable solvent for olefin metathesis, such as polymer syntheses by ROMP and the ring-closing and isomerization reactions. 相似文献
A series of 2,4,6‐trimethylbenzylidyne tungsten and molybdenum complexes was prepared from the tribromides mer‐[MesCMBr3(dme)] ( 9a , M=W; 9b , M=Mo, dme=1,2‐dimethoxyethane). Successive reaction of complexes 9 with lithium or potassium hexafluoro‐tert‐butoxide and lithium 1,3‐di‐tert‐butylimidazolin‐2‐imide, (Imt‐BuN)Li, afforded the imidazolin‐2‐iminato complexes [MesCM{OC(CF3)2Me}2(Imt‐BuN)] ( 10a , M=W; 10b , M=Mo), whereas the reactions of 9 with three equivalents of LiOSi(O‐t‐Bu)3 or KOC(CF3)3 gave [MesCM{OSi(O‐t‐Bu)3}3] ( 11a , M=W; 11b , M=Mo) and [MesCM{OC(CF3)3}3] ( 12a , M=W; 12b , M=Mo), respectively. For comparison, the benzylidyne complex [PhCMo{OSi(O‐t‐Bu)3}3] ( 7b ) was also prepared, and its molecular structure together with those of 10a , 10b , 11b , 12a and 12b were established by X‐ray diffraction analysis. Complexes 10 and 11 were employed as pre‐catalysts for the alkyne metathesis of the test substrate 3‐pentynyl benzyl ether ( 13 ) at low catalyst loadings (1 mol%) in the presence of molecular sieve (5 Å). Comparative studies of these 2,4,6‐trimethylbenzylidyne species (MesCM) with their benzylidyne analogues (PhCM) revealed that the increased steric bulk renders the former more stable and manageable in air in solid form for shorter periods of time, but at the expense of a slower initiation, which requires higher temperatures or longer reaction times.
Reported here are some results of rapid Ring Opening Metathesis Polymerization (ROMP) of norbornene-functional oligomeric siloxanes using a Ru-based catalytic system. The in situ formation of the active metal carbene catalyst by addition of a diazo compound to norbornene-functional siloxane containing the catalytic system, [(p-cymene)RuCl2]2/PCy3 allowed fast but controlled polymerization of the norbornene functionalities. Thus, in a solventless system, polymerization of a norbornene-functional siloxane, e.g., 1,1,1,2,3,3,3-heptamethyl-2-norbornen-5-yltrisiloxane, at 60°C with low catalyst levels (2 to 200 ppm) led to a colourless monolithic gel in less than 30 seconds. Besides being an efficient cross-linking technology, ROMP of suitable precursors may also be a source of novel silicone-organic materials. 相似文献
5,6-Dimethylenebicyclo[2.2.1]hept-2-ene ( I ) polymerizes in the presence of the two-component ring opening metathesis polymerization (ROMP) initiators WCl6/(CH3)4Sn and MoCl5/(CH3)4Sn. The product polymers were insoluble in all of many solvents investigated and are presumably cross-linked. The product polymers were investigated by IR and solid state 13C NMR spectroscopy, which established that the material consisted predominantly of poly(1,4-(2,3-dimethylene-cyclopentylene)vinylene) ( II ). A possible alternative route to II via thermal dehydrochlorination of poly(1,4-(2,3-bis(chloromethyl)cyclopentylene) vinylene) ( IV ) was also examined. 相似文献
Hg(II) halide complexes [HgCl2] 2L1 [L1 = N,N’-bis(3-pyridyl)bicyclo(2,2,2,)oct-7-ene-2,3,5,6-tetracarboxylic diamide), 1, [HgBr2(L1)]n, 2, [HgI2(L1)], 3, [Hg2X4(L2)2] [X = Cl, 4, Br, 5, and I, 6; L2 = N,N’-bis(4-pyridylmethyl)bicyclo(2,2,2,)oct-7-ene-2,3,5,6-tetracarboxylic diamide] and {[HgX2(L3)]⋅H2O}n [X = Cl, 7, Br, 8 and I, 9; L3 = 4,4′-oxybis(N-(pyridine-3-yl)benzamide)] are reported and structurally characterized using single-crystal X-ray diffraction analyses. The linear HgCl2 units of complex 1 are interlinked by the L1 ligands through Hg---N and Hg---O interactions, resulting in 1D supramolecular chains. Complex 2 shows 1D zigzag chains interlinked through the Br---Br interactions to form 1D looped supramolecular chains, while the mononuclear [HgI2L2] molecules of 3 are interlinked through Hg---O and I---I interactions, forming 2D supramolecular layers. Complexes 4–6 are isomorphous dinuclear metallocycles, and 7–9 form isomorphous 1D zigzag chains. The roles of the ligand type and the halide anion in determining the structural diversity of 1–9 is discussed and the luminescent properties of 7–9 evaluated. Complexes 7–9 manifest stability in aqueous environments. Moreover, complexes 7 and 8 show good sensing towards Fe3+ ions with low detection limits and good reusability up to five cycles, revealing that the Hg-X---Fe3+ (X = Cl and Br) interaction may have an important role in determining the quenching effect of 7 and 8. 相似文献
Poly(acrylamide-maleic acid) resin P(AAm-MA) was prepared by template polymerization. Polyacrylamide PAAm was used as a template for the polymerization of MA in an aqueous solution using gamma rays as the initiator. The effects on the capacity of P(AAm-MA), such as concentration of maleic acid and amount of template polymer, were investigated. P(AAm-MA) has been utilized as an adsorbent for the removal of Co(II) and Ni(II) ions from an aqueous solution. The effects of time of equilibrium, pH, temperatures, and dosage of the adsorbent on the removal of Co(II) and Ni(II) ions have been studied. The equilibrium data were analyzed using the Langmuir and Freundlich isotherm models. The equilibrium process was described well by the Langmuir isotherm model. 相似文献
Rubbery thermosets prepared by ROMP of a modified castor oil containing norbornene moieties and cyclooctene have been synthesized and characterized. The thermosets range from 55 to 85 wt.‐% oil and are flexible, slightly transparent and have a sand‐like hue. Increasing concentration of the modified castor oil in the feed ratio results in an increase in the extracted (unreacted or oligomeric) components in the final thermoset. Thermogravimetric analysis reveals that all of the specimens have temperatures of maximum degradation around 500 °C. DMA and TGA analysis on solvent‐extracted specimens show that the presence of the soluble fractions helps to plasticize the materials and give added thermal stability.
Phosphorescent copolymers bearing a covalently linked charged platinum(II) dye were prepared using ring-opening metathesis polymerisation (ROMP). Absorption, emission as well as dynamic light scattering measurements of these polyelectrolytes indicate the formation of red luminescent aggregates in solution with quantum yields up to 17% and luminescence decay times in the range of 250-300 ns. Neither the quantum yield nor lifetime of the luminescence is affected by the presence of oxygen. The resulting polymers are solution processible and exhibit good film-forming properties. In contrast, the mononuclear platinum species are poorly soluble and non-luminescent at room temperature in deaerated solution. 相似文献
We have analyzed the computational results for several elementary reactions of the ethylene polymerization process catalyzed
by an alternative (to the existing metallocene catalysts) “non-cyclopentadienyl” catalysts such as diimine-M(II) (where M
= Ni and Pd) and chelating bridged Ti- and Zr-complexes. The obtained data have been compared with those for the existing
zirconocene-based catalysts. In general, it was shown that: (i) the resting stage of the process is a metal-olefin-alkyl complex,
the olefin coordination energy of which is a few kcal/mol larger for diimine-M(II) systems than zirconocene or dialkoxide
systems; (ii) the rate-determining barrier is a migratory insertion barrier calculated from the metal-olefin-alkyl complex,
which is found to be a few kcal/mol larger for the diimine-M(II) system compared to the Cp2ZrCH
3+
catalyst. The presence of certain flexible bridging ligands X in the Ti-alkoxide complex, [Y(Ph)X(Ph)Y]TiCH
3+
, which are capable of donating electron density to the cationic metal center at various stages during the reaction makes
this barrier a few kcal/mol smaller for the dialkoxide than the Cp2ZrCH
3+
catalyst. It was shown that an increase in the metal-bridge interaction decreases the migratory insertion barrier and, consequently,
increases the catalytic activity of these complexes. Although the diimine-M(II) catalysts are less active than zirconocene-based
ones, the microstructure of the polymers produced by the former catalyst, which is found to be a function of temperature,
ethylene, steric bulkiness of the auxiliary ligands, and transition metal center, makes them attractive for practice. We also
have studied the mechanisms of several chain termination/transfer reactions, as well as the role of steric effects in the
studied elementary reactions. We have clearly demonstrated tremendous possibilities of the computational chemistry in solving
complex problems of the homogenous catalyst, and its high capability of predicting new and more active catalysts for different
commercially important processes including olefin polymerization reactions.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
Summary Random copolymerization of norbornene with styrene was studied by using a series of late metal catalysts/MAO. The precatalysts
used here are nickel complexes with b-ketoamine ligands based on pyrazolone derivatives. The copolymers obtained here suggest
that only one type of active species is present. Copolymers were characterized by 13C NMR, Gel permeation chromatography (GPC), thermogravimetric analysis (TGA) and FT-IR spectra. The analyses of the product
by 1H NMR and 13C NMR spectra gave the verification of “true” random vinyl addition copolymer. Varying the monomer feed ratio controlled the
composition of the copolymers. A copolymerization reactivity ratio (rNBE = 20.35 and rSty = 0.027) indicates a much higher reactivity of norbornene, which suggests a coordination polymerization mechanism. The solubility
and processability of the copolymers are improved relative to polynorbornene and the thermostability of the copolymers is
improved relative to polystyrene. 相似文献
Glass fiber biobased composites have been prepared by ROMP of a commercially available vegetable oil derivative possessing an unsaturated bicyclic moiety, and DCPD. The resins and the corresponding composites have been characterized thermophysically and mechanically. Higher DCPD content yields materials with higher glass transition temperatures. Glass fibers significantly improve the tensile modulus of the resin from 28.7 to 168 MPa. These biobased composites utilize only a limited amount of a petroleum‐based monomer, while employing substantial amounts of a renewable resource.
Bio‐based rubbers prepared by tandem cationic polymerization and ROMP using a norbornenyl‐modified linseed oil, Dilulin?, and a norbornene diester, NBDC, have been prepared and characterized. Increasing the concentration of the NBDC in the mixture results in a decrease in the glass transition temperature. The new bio‐based rubbers exhibit tensile test behavior ranging from relatively brittle (18% elongation) to moderately flexible (52% elongation) and with decreasing values of tensile stress with increasing NBDC content. Thermogravimetric analysis reveals that the bio‐based rubbers have maximum decomposition temperatures of over 450 °C with their thermal stability decreasing with increasing loadings of NBDC.