Nonconjugated Dienes Research Articles

(η5-C5Me4)SiMe2(NtertBu)]TiCl2 as Pre-Catalyst for the Copolymerisation of Ethylene with 5,7-Dimethylocta-1,6-diene and with 3,7-Dimethylocta-1,6-diene

[(η5-C5Me4)SiMe2(NtertBu)]TiCl2 was used as catalyst in the presence of methylaluminoxane (MAO) for the copolymerisation of ethylene with 5,7-dimethylocta-1,6-diene (5,7-DMO) and with 3,7-dimethylocta-1,6-diene (3,7-DMO), two linear non-conjugated dienes readily available from terpene feedstock. The effects of reaction temperature, Al/Ti mole ratio and diene concentration in feed on the polymerisation activity and on the incorporation rates of the diene were investigated. The structure of the polymer and the distribution of the comonomer along the chains were investigated through NMR and DSC.

Chirality Induction in Cyclopolymerization XVI. Synthesis of Optically Active Poly(methyl acrylate-co-dimethyl fumarate) by Radical Cyclopolymerization of Asymmetrical Nonconjugated Diene Having Chiral Pentanediol

The molecular design and synthesis of asymmetric bifunctional monomers, 3-(S)-acryloyloxy-1-(S)-methyl-butyl methyl fumarate (1a) and 3-(R)-acryloyloxy-1-(R)-methyl-butyl methyl fumarate (1b), have been carried out in terms of a novel method of producing optically active polymers based on cyclopolymerization. The polymerization of 1 proceeded via the cyclopolymerization mechanism to yield the cyclopolymer 2 with the extent cyclization of 0.87–0.96 when the monomer concentration ([M]) in the feed was 0.3 mol L-1 or less. The number-average molecular weight (Mn) decreased with a decrease in the [M] from 8300 to 3300 for polymer 2a and from 4200 to 2400 for polymer 2b. The specific rotation ([α]43523, c 1.0, CHCl3) of the resulting polymers changed from +19.3° to +33.4° for 2a and from -26.2° to -34.9° for 2b. In order to confirm the chirality induction, the chiral pentanediyl moiety was removed from polymer 2 by saponification, and the hydrolyzed polymer was treated with diazomethane to give poly(methyl acrylate-co-dimethyl fumarate) (3). The Mn was 2200–2600 for 3a and 2300–5700 for 3b, and the template-free polymers showed an optical activity with a specific rotation that ranged from -1.4° to -9.3° for 3a and from +7.5° to +8.8° for 3b. The CD spectra of 3a showed a positive Cotton effect whereas 3b showed a negative Cotton effect which is the mirror image of 3a. The optical activity of polymer 3 should be attributed to the threo-erythro sequence of the methyl acrylate and dimethyl fumarate units.

Synthesis of cyclic and multicyclic polyisoprenes

Cyclic polyisoprenes have been synthesized by reaction of α,ω-dilithiopolyisoprenes with dichlorodimethylsilane or 1,2-bis(isopropenyl-4-phenyl) ethane (BIPE). Using the dihalide compound, the effect of the solvent polarity on the coupling reaction is more pronounced in the case of α,ω-dilithiopolyisoprene than with monofunctional polyisoprenyllithium. The yield in cyclic compound falls from 88% in pure hexane down to 53% in the presence of 15 vol% of tetrahydrofurane (THF). Using the nonconjugated diene (BIPE) as linking agent the addition of THF is required but the formed cycle retains its living character and allows the synthesis of cycles having two arms (after addition of isoprene) and of a bicyclic structure after a second cyclization reaction.

Intramolecular epoxidation in unsaturated ketones and oxaziridines

The possibility of intramolecular epoxidation in acyclic unsaturated ketones (via dioxiranes) and oxaziridines (via oxaziridinium species) has been investigated. Treatment of several acyclic unsaturated ketones with Oxone® led to low levels of regio- and stereocontrol, suggesting that background epoxidation by Oxone® dominates. However, treatment of unsaturated oxaziridines with methyl trifluoromethanesulfonate led to intramolecular epoxidation. This process allowed regioselective epoxidation of a non-conjugated diene. It also proceeded with a high degree of stereocontrol consistent with a stereoelectronic preference for a spiro-transition state.

Transition Metal Complexes as Catalysts for the Homo- and Copolymerisation of Olefins and Non-Conjugated Dienes

The copolymerisation of ethylene with 5,7-dimethylocta-1,6-diene (5,7-DMO) was conducted in the presence of a series of catalytic systems, based on different transition metal derivatives associated with methylaluminoxane (MAO): a metallocene-based catalyst, Cp2ZrCl2 (1); a constrained geometry catalyst (Me4Cp)SiMe2(N-tert-Bu)TiCl2 (2); an iron-based catalyst, [(ArN=C(Me))2C5H3N]FeCl2 (3); and a Brookhart-type catalyst [Ar—N=C(An)C(An)=N—Ar]NiBr2 (Ar = 2-C6H4(t-Bu)) (4). The metallocene catalyst (1) and the constrained geometry catalyst (2) are able to incorporate 5,7-dimethylocta-1,6-diene (5,7-DMO) into polyethylene chains. Although (2) shows lower overall activities than Cp2ZrCl2, similar 5,7-DMO incorporation levels are obtained for much lower diene concentrations in the feed. The characteristics of the copolymers obtained with the two catalysts are compared. The iron catalyst (3) can only homopolymerise ethylene. However, the presence of 5,7-DMO in the feed does not significantly affect the polymerisation activity. On the contrary, with the Brookhart system (4), the presence of 5,7-DMO as well as any of the tested dienes (5-ethylidene-2-norbornene, 7-methyl-1,6-octadiene and 1,5-hexadiene) completely inhibits the polymerisation of olefins. A tentative mechanism, based on the chain migration mechanism proposed by Brookhart is suggested for the deactivation of the Ni catalyst.

Cuticular Hydrocarbons of <I>Kapala sulcifacies</I> (Hymenoptera: Eucharitidae) and Its Host, the Ponerine Ant <I>Ectatomma ruidum</I> (Hymenoptera: Formicidae)

Cuticular hydrocarbons from the ponerine ant Ectatomma ruidum Roger and a highly integrated eucharitid myrmecophile, Kapala sulcifacies (Cameron), associated with it, have been characterized. Ninety hydrocarbons were identified from the ant, 55 hydrocarbons from the female wasp and 54 hydrocarbons from the male wasp. The wasps and ants share 40 hydrocarbons. These shared 40 hydrocarbons represent 92.6% of their hydrocarbon composition for female Kapala, 84.3% for male Kapala and 67.7% for the ants. The wasps have a carbon number range of C27 to C35; the ants have a range of C23 to C35. Both species possess n-alkanes, C27 to C33 for the wasps, C23 to C34 for the ants. Both species also possess major quantities of Z-7- and Z-9 alkenes: C29 to C33 for the wasps; C23 to C35 for the ants. The female wasps possess a low amount of a conjugated C31 diene (neither the ants nor the male wasps possess this hydrocarbon), and the ants, but not the wasps, contain low quantities of nonconjugated dienes (carbon numbers of C23 to C29) with double bonds at Δ9, and Δ14. Both wasps and ants share homologous series of 3-, 5-, 10-, 11-, 12-, 13-, 15- and 17-methyl branched alkanes. Ants and wasps also share a homologous series of 3,7-dimethyl alkanes. Other internally branched dimethyl alkanes are found in both ants and wasps, but only 11, 15-DiMeC29 is shared. Wasps have 7, 15- and 10, 14-dimethyl alkanes while the ants have 15,19-dimethyl alkanes. Kapala sulcifacies and E. ruidum both possess hydrocarbons of the 5, X-, 11, X-, 12, X- and 13, X-DiMe series, but the compounds involved are not shared because they represent different compounds. Behavioral observations indicate that the ants accept the newly emerged adult parasitoids with no evidence of agonistic behavior for a period of time after adult eclosion. Nevertheless, the chemical deception is not completely efficient because young adult Kapala are soon ejected from the nest by transportation by their host. These transportations frequently occur after seizure at the base of the wasps’ characteristic scutellar spines, such structures allowing for easy transportation without injury for the parasite. Moreover, if no method of escaping the colony is provided, the ants ultimately attack the parasitoids. The substantial chemical overlap of the cuticular hydrocarbon profiles of the ants and wasps are discussed in the context of the social life of the colony.

Passivated Luminescent Porous Silicon

Freshly prepared porous silicon (PSi) surfaces have been modified with different organic molecules such as alkenes (1-decene, ethyl undecylenate) and nonconjugated dienes (1,7-octadiene) in a thermal process to yield organic monolayers covalently attached to the surface through Si-C bonds. These monolayers have been characterized using diffuse reflectance infrared Fourier transform, X-ray photoelectron, and Raman spectroscopies. Derivatized surfaces have shown a high stability in boiling aqueous and organic solvents, and in 49% HF and KOH (pH 13) solutions at room temperature. They protect the surface against oxidation when exposed to air at 100% humidity. The high passivation of the surface implies also photoluminescence (PL) stabilization. In fact, the modified surfaces retained their original PL, and the chemical process affected neither the peak position nor the intensity. The PL was preserved even after a steam treatment for several weeks, while the hydrogen-terminated porous layer was completely transformed into a transparent oxide. © 2001 The Electrochemical Society. All rights reserved.

Thermal Route for Chemical Modification and Photoluminescence Stabilization of Porous Silicon

This paper describes photoluminescence (PL) stabilization through chemical modification of freshly prepared porous silicon (PSi) surfaces. As-anodized PSi surfaces react with 1-alkenes, non-conjugated dienes and aldehydes at elevated temperatures to form organic monolayers covalently bonded to the surface. This thermal route is very general and tolerant of different functional groups. We have characterized these organic monolayers using diffuse reflectance infrared Fourier-transform (DRIFT), Auger and Raman spectroscopies. The PL intensity and peak energy of the as-anodized PSi is not affected by the chemical functionalization. Aging these derivatized PSi samples in ambient air has no effect on the PL. In fact, it is completely preserved even when they are steam treated for six weeks at 70 °C and 100% humidity. This treatment completely destroys the structural integrity of H-terminated PSi.

Core-electron spectroscopy of nonconjugated linear dienes chemisorbed onSi(001)−2×1with synchrotron radiation

The adsorption of two nonconjugated linear dienes, 1,7-octadiene and 1,4-pentadiene, on $\mathrm{Si}(001)\ensuremath{-}2\ifmmode\times\else\texttimes\fi{}1$ is studied using soft x-ray photoemission spectroscopy (XPS), C $1s$ near-edge x-ray absorption fine structure (NEXAFS) and core-decay spectroscopy. It is found that both dienes attach to the silicon surface via only one of their two $\mathrm{C}=\mathrm{C}$ bonds. This result, expected for the 1,4-pentadiene, is more surprising for 1,7-octadiene, as its length fits the distance separating two adjacent silicon dimer rows. The angular dependence of the C $1s$ absorption spectra indicates some ordering of the chemisorbed layer. C K-edge core-decay spectroscopy gives complementary information on the electronic structure, more specifically on the localization (versus delocalization) to the C $1s$ core hole of the electron promoted to an unoccupied level, which can be useful for the understanding of the transport properties of the grafted films. Independently of the molecule length, it is shown that the excited electron, promoted to a ${\ensuremath{\pi}}^{*}$ level, remains bound to the core hole, while it delocalizes when it is lifted to the ${\ensuremath{\sigma}}_{\mathrm{CH}}^{*}$ level (although this level lies below the ionization potential) and to higher-energy levels. The energy positions of NEXAFS resonances, in the chemisorbed case (characterized by the presence of a high-dielectric constant substrate) and in the condensed case (molecular solid) have been compared. We propose that resonance energies could be sensitive to final-state relaxation shifts when the promoted electron delocalizes before core-hole decay.

Pd(II)-dissolved in ionic liquids: a recyclable catalytic system for the selective biphasic hydrogenation of dienes to monoenes

Palladium acetylacetonate dissolved in 1-n-butyl-3-methylimidazolium tetrafluoroborate ionic liquid catalyses the selective two-phase hydrogenation of conjugated and non-conjugated (functionalized and non-functionalized) dienes into the respective monoenes. The system does not require the use of organic solvents, the products are removed by simple decantation or distillation and the recovered ionic catalytic solution can be reused several times without any significant changes in its catalytic activity and selectivity.

00/01289 Method and catalysts for the preparation of di-tertiary amines by the aminomethylation of nonconjugated dienes with synthesis gas and secondary amines

This paper presents an effecient method of modelling faulted rock using the multiregion boundary element method. The boundary element method is ideally suited for modelling problems in rock mechanics because of the requirement to descretize surfaces only. This contrasts with the volume discretization needed for the finite element method, finite difference method and the distinct element method. The disadvantage of the boundary element method is that the rock mass is assumed to be isotropic and elastic. However, it is possible to model the non-linear behaviour on fault planes by using the concept of multiple regions and by connecting these regions via non-linear springs or Goodman type joint elements. The disadvantage of this method has been that joint stiffnesses have to be specified and that a great number of iterations are needed because the stiffness coefficient of a spring may change very rapidly from a very high value (for example when a joint is in compression) to a very low value (when a joint is in tension). This paper describes a novel method for the treatment of faults with the boundary element method which eliminates the need to specify joint stiffness parameters and which is able to model signi fault movement with very few iterations. The numerical scheme makes very effecient use of computer resources because the non-linear iterations only involve degrees of freedom at the interfaces. Examples of applications of the new model to practical problems in mining and geological engineering are given.

Copolymers of vinyl epoxides with carbon monoxide

Highly functionalized alternating polyketones which possess epoxide groups in the side chains are synthesized by cationic palladium(II) complex catalyzed copolymerization of vinyl epoxides (non-conjugated diene monoepoxides) with carbon monoxide. Catalytic amounts of formic acid and 1,4-naphthoquinone promote the copolymerization significantly without effecting the epoxide group, with [Pd(L)(MeCN)2](BF4)2 (L = (R,R)-Me-DUPHOS) as the catalyst.

Copolymerization of ethylene and non-conjugated dienes with Cp 2ZrCl 2/MAO catalyst system: effect of polymerization temperature on the copolymer structure

Ethylene was copolymerized with linear, non-conjugated dienes by the metallocene catalyst system Cp 2ZrCl 2/MAO at several temperatures from 20 to 80°C. The dienes were 1,5-hexadiene (HD), 1,7-octadiene (OD) and 7-methyl-1,6-octadiene (MOD). Incorporation of the dienes was studied by 1 H and 13 C NMR and FTIR. Polymerization conditions had a dramatic effect on the degree of crosslinking of the product. At polymerization temperatures from 20 to 65°C the copolymers of ethylene and HD or OD were nearly totally crosslinked, whereas at 80°C the degree of crosslinking was consistently under 10%. When MOD was used as comonomer the degree of crosslinking did not increase above 40% even for copolymer produced at 20°C.

Characterization of comonomer distributions in ethylene/diene copolymers by13C-NMR, and using the segregation fractionation technique by DSC and DMTA

Ethylene and linear, nonconjugated dienes were copolymerized with the catalyst system Cp2ZrCl2/methylaluminoxane (MAO). The comonomer incorporation and the relationships between structure and properties were evaluated by NMR and by thermal techniques, especially the segregation fractionation technique (SFT) using DSC and dynamic mechanical thermal analysis (DMTA). The ethylene-1,5-hexadiene (HD) copolymers showed different behavior than the others and it was possible to incorporate as much as 7 mol % of the hexadiene comonomer into soluble polymer compared with only 2.4 mol % of the 1,7-octadiene (OD) and 7-methyl-1,6-octadiene (MOD). The melting endotherms of the HD copolymers obtained after segregation fractionation were very much like corresponding endotherms of high-density polyethylene (HDPE) and a population with nearly one lamellar thickness was postulated. This is in agreement with cyclic structure formation and absence of branching with crosslinking for these copolymers. The OD and MOD copolymers, on the other side, showed endotherms with several peaks indicating a distribution of the comonomers along the chain. Lamellar thickness distributions were calculated from the melting endotherms by using the Gibbs–Thomson equation. The DMTA measurements confirmed the absence of branches in the HD copolymers and the presence of branches in the OD and the MOD copolymers. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2379–2389, 1999

Soft-x-ray photoelectron, x-ray absorption, and autoionization spectroscopy of 1,5-cyclooctadiene onSi(001)−2×1

The adsorption of a nonconjugated diene, 1,5-cyclooctadiene, on $\mathrm{Si}(001)\ensuremath{-}2\ifmmode\times\else\texttimes\fi{}1$ is studied using valence-band and core-level soft-x-ray photoemission, near-edge x-ray absorption fine structure at the $\mathrm{C}1s$ edge, and autoionization spectroscopy. Core-level spectroscopies validate the bonding model for room-temperature adsorption proposed by Hovis and Hamers [J. Phys. Chem. B 101, 9581 (1997)]---based essentially on scanning tunneling microscopy (STM) and infrared spectroscopy experiments---where the diene attaches to the silicon surface via only one $\mathrm{C}\mathrm{=}\mathrm{C}$ bond. On the other hand, the complete quenching of the silicon surface states at saturation points to a coverage of one molecule per Si dimer, and not to a coverage of one molecule per two Si dimers, as the STM observation of locally $2\ifmmode\times\else\texttimes\fi{}2$ or $c(2\ifmmode\times\else\texttimes\fi{}4)$ ordered adsorption domains would suggest. The orientation of the free \ensuremath{\pi} orbital is deduced from the angular dependence of the $\mathrm{C}1s$ absorption spectra. This orientational order is lost after thermal annealings of the molecular film (610--680 K range), before the molecule decomposes (at \ensuremath{\sim}820 K). Valence-band spectra are taken at various photon energies (between 22 and 170 eV) to investigate the nature of the adsorbate-derived molecular levels resulting from the formation of the molecular film at 300 K. Valence-band spectra recorded at photon energies near the $\mathrm{C}1s$ edge show that an electron promoted to the lowest unoccupied molecular orbital (${\mathrm{\ensuremath{\pi}}}^{\mathrm{*}}$) of the chemisorbed molecule remains localized to the core-hole site, as both participator and spectator decay channels are observed.

Scanning Tunneling Microscopy of Organic Molecules and Monolayers on Silicon and Germanium (001) Surfaces

High-resolution scanning tunneling microscopy has been used to investigate the adsorption of a variety of unsaturated organic molecules on the (001) surface of silicon and germanium. Results are presented for a number of prototypical alkenes, conjugated and non-conjugated dienes, and aromatic compounds. These include cyclopentene, 1,5-cyclooctadiene, norbornadiene, 2,3-dimethyl-1,3-butadiene, and benzene on the Si(001) surface, and for cyclopentene on the Ge(001) surface. Factors controlling the selectivity of various reaction pathways and the consequences for preparation of ordered organic overlayers are discussed.

Copolymerization of ethylene and non-conjugated dienes with Cp 2ZrCl 2/MAO catalyst system

Ethylene was copolymerized with linear, non-conjugated dienes by the metallocene catalyst system Cp 2ZrCl 2/MAO at 90°C. The dienes were 1,5-hexadiene (HD), 1,7-octadiene (OD) and 7-methyl-1,6-octadiene (MOD). Incorporation of the dienes was studied by 1H and 13C–NMR and FTIR. According to the results, HD formed only five-member rings to polyethylene, even though selectivity towards cyclization has been reported to decrease when HD concentration in the reactor increases over 50 mol%. OD and MOD were incorporated by 1,2-addition forming branches to the copolymer. The conversion of MOD remained under 4%, and was noticeably lower than that of HD and OD (25–40%). However, the effect of MOD on the physical properties of the copolymer was significant, whereas HD addition had almost no effect on the molar mass. The conversion of all dienes decreased when the diene concentration in the reactor was increased.

Copolymerization of Propene and Nonconjugated Diene Involving Intramolecular Cyclization with Metallocene/Methylaluminoxane

Copolymerizations of propene with 1,5-hexadiene and 1,7-octadiene were carried out with isospecific rac-dimethylsilylenebis(indenyl)zirconium dichloride (1) and syndiospecific diphenylmethylene(cyclopentadienyl)(9-fluorenyl)zirconium dichloride (2) combined with methylaluminoxane. Microstructures of the copolymers were determined by 1H NMR, 13C NMR, and DEPT (distortionless enhancement of polarization transfer) spectroscopies. Incorporation of nonconjugated dienes in the copolymer was higher with 2 than with 1. Intramolecular cycloaddition of the nonconjugated dienes proceeded regardless of the catalysts. Stereoselectivity in cycloaddition of 1,5-hexadiene was investigated based on the structures of isolated methylene-1,3-cyclopentane units. It was found that 1,5-hexadiene was inserted stereospecifically by enantiomorphic site control with both catalysts. The diastereoselectivity of the cyclization step of 1,2-inserted 1,5-hexadiene was, however, found to be independent of stereospecificity of the catalyst. The cyclization selectivity of 1,5-hexadiene copolymerization was higher than that of 1,7-octadiene copolymerization. 1 gave the copolymers with higher selective in cyclization than 2 in the propene/1,5-hexadiene copolymerization, while the opposite tendency was observed in the propene/1,7-octadiene copolymerization. Decrease of cyclization selectivity was observed with the increases of 1,5-hexadiene and 1,7-octadiene concentration in both copolymerizations. Propene insertion could disturb the cyclization of 1,2-inserted dienes, which declined the cyclization selectivity of the copolymers, except propene/1,5-hexadiene copolymerization with 2.

Enantio- and Diastereoselective Catalytic Carboalumination of 1-Alkenes and α,ω-Dienes with Cationic Zirconocenes: Scope and Mechanism

Bis(pentamethylcyclopentadienyl) dimethylzirconium (Cp*2ZrMe2) and bis(1-(−)-neomenthylindenyl) dimethylzirconium ((NMIn)2ZrMe2) upon activation by tris(pentafluorophenyl)borane are efficient catalysts for the carboalumination of a variety of 1-alkenes and nonconjugated dienes. The organoalane products can be oxidized to alcohol products, which are isolated in 50−90% yield. (NMIn)2ZrMe2 carboaluminates 1-alkenes and dienes with moderate (55−65%) enantioselectivities. In contrast, ethylenebis(tetrahydroindenyl) dimethylzirconium ((EBTHI)ZrMe2) and related zirconocenes give low activities and selectivities in the carboalumination reaction. Study of the interaction of zirconocene methyl cations with trimethylaluminum by 1H NMR shows that [(EBTHI)ZrMe][MeB(C6F5)3] forms a stable bis(μ-methyl) aluminum adduct. Zirconocene methyl cations derived from Cp*2ZrMe2 and (NMIn)2ZrMe2 react slowly with large excesses of trimethylaluminum to form weakly bound trimethylaluminum adducts. The difference in trimethylaluminu...

Study of Pd-elimination under carbonylation conditions: Regioselective formation of esters

The regioselective synthesis of methyl esters is achieved by carbonylation of two different types of organometallic derivatives resulting from insertion of non-conjugated dienes into a Pd-aryl bond. When the diene and the Pd-aryl synthon [PdPfBr(NCMe) 2] (Pf = C 6F 5) are mixed at low temperature, solutions of η 1-η 2-enylpalladium complexes can be isolated and converted into β-aryl methyl esters by reaction with CO in the presence of methanolic solutions of sodium methoxide. When the reactions are carried out at room temperature η 3-allylpalladium complexes are isolated, and their carbonylation gives β,γ-unsaturated esters.