Preparation of a Porous polymer by a catalyst‐free diels‐alder reaction and its structural modification by post‐reaction

A microporous polymer is prepared by a catalyst‐free Diels–Alder reaction. A cyclopentadiene with both a diene and a dienophile functionality and a dienophilic maleimide are used for the Diels–Alder reaction. 1,3,5‐Tris(bromomethyl)‐2,4,6‐trimethylbenzene is reacted with sodium cyclopentadienide to produce the multicyclopentadiene‐functionalized monomer. A crosslinked polymer ( CDAP ) is obtained by the reaction of the cyclopentadiene monomer with N,N′‐1,4‐phenylenedimaleimide. The thermal dissociation of the cyclopentadiene dimeric unit and the subsequent Diels–Alder reaction with the maleimide group are investigated by the model reaction. We are able to restructure the crosslinked polymer network by taking advantage of the thermal reversibility of the Diels–Alder linkage. After the post thermal treatment, the BET surface area of the polymer ( CDAP‐T ) is greatly increased from 317 to 1038 m² g^?1. CDAP‐T is functionalized with pyrene by bromination with N‐bromosuccinimide and the subsequent substitution reaction with aminopyrene. The adsorption property of the pyrene‐functionalized polymer for an aromatic dye is investigated using malachite green. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3646–3653     

Polymerization of cyclopentadiene initiated by methylaluminoxane

The polymerization of cyclopentadiene (CPD) was effectively initiated by methylaluminoxane (MAO) to generate poly(cyclopentadiene) (polyCPD). The effects on the polymerization of some reaction parameters such as the monomer concentration, the initiator concentration, and solvents were investigated. The conversion of CPD was monitored with gas chromatography to investigate the reaction kinetics. The polymerization rate was proportional to the concentrations of MAO in the first order and of the CPD monomer in the second order, and a reasonable cationic polymerization mechanism was suggested on the basis of the kinetic study. PolyCPD obtained at a low temperature could be dissolved in toluene or chloroform, and this indicated lower cross‐coupling during the polymerization reaction. ¹H NMR and IR analysis of the polymer indicated that there were almost equal amounts of 1,2‐enchainment and 1,4‐enchainment in the polymer chain. The measurement of polyCPD showed its unique properties as a potential candidate for stable wrappings or electronic packaging materials. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 264–272, 2006     

Ethene and ethyne molecules interacting with Cu+ sites in zeolites—Quantitative infrared spectroscopic studies

Infrared spectroscopic studies have been carried out to address the question of the Cu⁺ cation migration from hexagonal prisms (S_I) and cubooctahedra (S_I′) to supercages upon adsorption of ethene and ethyne in CuNaY and CuNaX zeolites. The quantitative assessment of Cu⁺ content in supercages before ethene and ethyne adsorption was evaluated on the basis of carbon monoxide adsorption experiments and molar absorptivities of Cu⁺(CO) bands. The same procedure was adapted to estimate the concentration of Cu⁺ inside supercages in the presence of ethene and ethyne, where the appropriate molar absorptivities of CC and CC bands was applied. This method seems to be complementary to XRD studies. Since it is insufficient to know the distribution of the cations between S_n positions, the actual number of the cationic sites engaged into the interaction with the reagents under the working conditions of the material was found with the use of IR spectroscopy.     

Detailed combustion kinetics of cyclopentadiene studied in a shock‐tube

Mixtures of cyclopentadiene and oxygen diluted in argon were used to obtain ignition delay data in a single pulse shock‐tube. The temperatures ranged from 1278–2110 K and the experimental pressures were between 2.43 and 12.45 atm. The fuel concentrations ranged from 0.5 to 2.5% and the oxygen concentrations were between 3.3 and 16.6%. A Semenov ignition delay expression was determined: τ = 10^?12.5 exp(+34500/RT) [C₅H₆]^0.06 [O₂]^?0.95 [Ar]^0.29 sec The concentrations are in mol/cc and the activation energy is in cal/mol. Gas‐chromatographic analyses were run on samples quenched before the ignition. The kinetics of combustion of cyclopentadiene was modeled with a full scheme containing 439 elementary reactions and a reduced scheme containing 125 reactions. Both ignition delay times and product distribution served as modeling targets. The mechanism of combustion of cyclopentadiene is discussed in connection to the combustion of aromatic fuels. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 491–508, 2001     

Preparation of (1R,4S)-4-hydroxycyclopent-2-en-1-yl acetate via Novozym-435® catalyzed desymmetrization of cis-3,5-Diacetoxy-1-cyclopentene

Photooxidation of cyclopentadiene has been carried out in methanol using white light of LED lamp, rose bengal as photo initiator, and compressed air at 0?°C. Under conditions of [thiourea] ? [cyclopentadiene], the consumption of thiourea follows a pseudo-first-order reaction kinetics with half life of 75?±?10?min; corr. coeff. r?=?0.989. Slow addition of the monomer and maintaining excess thiourea concentration in reaction mass improves the yield. cis-3,5-Dihydroxy-1-cyclopentene is acetylated without isolation to obtain cis-3,5-Diacetoxy-1-cyclopentene of high purity (>99%) with overall isolated yield of 30%. Desymmetrization of the diacetate to (1R,4S)-4-hydroxycyclopent-2-en-1-yl acetate has been carried out via enzymatic transesterification with methanol in methyl tert-butyl ether (MTBE) at 5?°C using Novozym-435^®. The enantiomerically pure monoacetate (e.e. >99%) was obtained in 95% isolated yield. The recovered enzyme was reused for more than 10 times without loss in yield and selectivity. The entire protocol does not require purification of final product by chromatography.     

Distribution of Europium Ions in Ion-Exchanged NaX and NaY Zeolites

The chemical environments of europium-exchanged NaX (Si/Al =1.16) and NaY (Si/Al = 2.29) zeolites have been investigated by means of ¹²⁹Xe NMR and isotherm measurements of adsorbed xenon. EuNaX and EuNaY samples with varied concentrations of Eu cations were subjected to diverse chemical and thermal treatments, namely dehydration, reduction, oxidation, and re-reduction. Thermal analyses of hydrated EuNaX and EuNaY samples indicate that both the structural stability and the saturation concentration of water increase with increasing Eu content. For dehydrated EuNaY zeolites, the Eu³⁺ cations tend to replace Na⁺ ions at S2 sites and tend to be located in framework supercages; similar behavior is found for Eu²⁺ ions after reduction. After subsequent oxidation, Eu³⁺ ions migrate from supercages into small sodalite and/or D6R cages; similar results were deduced for samples after re-reduction. In contrast to the behavior observed in EuNaY, Eu³⁺ ions tend to exchange for Na⁺ ions in the sodalite and/or D6R cages in dehydrated EuNaX zeolites, regardless of the thermal treatment; this behavior is ascribed to the existence of unlocalized S3 Na⁺ in EuNaX samples.     

Rates of Proton Abstraction from Conjugated Dienes in the Gas Phase

The rates of proton transfer from 2, 4-hexadiene, 1, 3-cycloheptadiene, cyclopentadiene and acetone to t-butoxide have been measured in the gas phase using pulsed-ion-cyclotron-resonance spectroscopy. The rate constants are (units of 10^?10 cm³ molecule^?1 s^?1): 2.7 ± 0.4, 3.8 ± 0.4, 6.1 ± 0.7 and 10.8 ± 1.5, respectively. These results are analyzed in terms of the properties of the encounter complex and reaction transition states. The reaction profile for t-butoxide + cyclopentadiene is modeled using RRKM theory and an estimate for the central barrier height is obtained.     

Spectroscopic study of 2,3-Bis(p-methoxybenzoyl)cyclopentadiene as potential iron(III)-chelating agent

2,3-Bis(p-methoxybenzoyl)cyclopentadiene was studied as iron(III)-chelating agent. Its pK _a value was determined by spectrophotometry (pK _a = 8.27 ± 0.02 at 25 ± 0.1°C; λ = 421 nm). 2,3-Bis(p-methoxybenzoyl)cyclopentadiene reacts with Fe³⁺ ions in aqueous ethanol (1:1, by volume) to give a 2:1 ligandmetal complex. The effects of different factors on the complex formation were studied. The reaction of 2,3-bis(p-methoxybenzoyl)cyclopentadiene with Fe³⁺ ions can be used as an alternative method for spectrophotometric determination of iron(III) in a range of concentrations from 0.1 to 1 μg cm⁻³, where the Beer law is fulfilled with a correlation coefficient of 0.9992. The results of spectrophotometric determination of iron(III) in geological materials (iron rock) showed very good agreement with those obtained by the atomic absorption measurements. Published in Russian in Zhurnal Obshchei Khimii, 2006, Vol. 76, No. 5, pp. 790–793. The text was submitted by the authors in English.     

Polarity of Molecules: A New Approach for Freshman Chemistry

The study of charged aromatic species greatly enhances discussions of the theory of aromaticity. The conveniently low acidity of cyclopentadiene (pK_a = 15) affords the opportunity to generate the aromatic cyclopentadienyl anion in an organic laboratory class. This experiment describes the preparation of a solution of deuterated dimethylsulfinyl anion in an NMR tube, followed by the addition of freshly prepared cyclopentadiene. The ¹H NMR spectrum of the resulting aromatic anion is compared with that of the isoelectronic (but uncharged) benzene, and contrasted with the spectra of several nonaromatic and antiaromatic compounds. Treatment of the anion with an equivalent of trifluoroacetic acid quantitatively affords cyclopentadiene.     

Nature and centers of localization of extraframework particles in Y zeolite dealuminated by silicon tetrachloride

X-ray diffraction, XPS, and NMR have been used to investigate the nature and centers of localization of nonframework particles in Y zeolite dealuminated by silicon tetrachloride. It has been established that the reaction products formed upon dealumination consist mainly of aluminum compounds that migrate from the volume of the zeolite to the surface and are also partially localized in internal supercages and small cages (sodalite cells). Water washing removes the particles localized in the supercages but does not affect the particles localized in sodalite cells. It has been shown that, by plotting maps of electron density on the basis of x-ray powder diffraction patterns, the sites of localization of extraframework particles can be determined. The results are consistent with those obtained by other methods, and the maps of electron density give a graphic picture of changes in internal structure of the Y zeolite.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1729–1734, August, 1989.The authors wish to express their appreciation to V. M. Mastikhin for assistance in taking the²⁷Al and²⁹Si NMR spectra.     

FT-IR study of the interaction of oxygen,argon, helium,nitrogen and xenon with hydroxyl groups in H-Y zeolite at low temperatures

Adsorptions of O₂, Ar, He, N₂ and Xe on H-Y zeolite at low temperatures were studied by transmission Fouriertransform infrared spectroscopy. For the O₂ adsorption, a weak v(OO) band was observed at 1550 cm⁻¹. The formation of a weak hydrogen-bonding of O₂ and Ar with the bridging OH-groups in the supercage was observed, while these molecules did not interact chemically nor physically with the bridging OH-groups in the small cavities. These results indicate that O₂ and Ar can approach the acid sites in the supercages, but cannot approach those in the small cavities. However, a slight physical interaction (not the H-bonding) of He with the OH groups in the small cavities was observed, suggesting that He would be able to approach near the sites. N₂ adsorption gave two v(NN) bands at 2353 and 2338 cm⁻¹, which have been attributed to the N2 species adsorbed on Lewis acid sites and on Br0nsted acid sites, respectively. It was observed that N₂ and Xe interact strongly with the bridging OH-groups in the supercages as well as weakly with the silanol groups. On the basis of the IR-spectroscopic data on the strength of the interaction with the small and nonpolar gases, the acidic properties of H-Y was compared with those of H-MOR and H-ZSM-5.     

Di-cyclopentadienyl- und di-indenyl-calcium-komplexe mit ammoniak und tetrahydrofuran

Dicyclopentadienyl- and diindenyl-calcium and their complexes with twofold coordinated ammonia and tetrahydrofuran are obtained by metalation of cyclopentadiene or indene with calcium or calcium amide in liquid ammonia and subsequent treatment with tetrahydrofuran and heat. IR and ¹H NMR spectroscopy are used for structure elucidation. The reactivity of the complexes both in alkylation and in interaction with carbonyl compounds is studied. In this manner alkyl, hydroxyalkyl and alkylidene derivatives of cyclopentadiene and indene axe obtained.     

Silicon-29 NMR Study of Alkali-Exchanged NaY Zeolites

High-resolution solid-state ²⁹Si NMR has been applied to the study of partially exchanged Li, K, and Cs NaY zeolites. The order of the ²⁹Si chemical shifts of dehydrated samples is Li, Na-Y < Na-Y < K, Na-Y. The correlation between the ²⁹Si chemical shift and the Li or K loading on Li, Na-Y or K, Na-Y was rationalized in terms of the interaction between the framework and the cations inside the small cages. Because of the restrictive migration of large Cs⁺ ions from the supercages to the small cages, the ²⁹Si chemical shift of Cs, Na-Y was found to be similar to that of Na-Y.     

1,2,3,4‐Tetrasubstituted Cyclopentadienes and Their Applications for Metallocenes: Efficient Synthesis through Zirconocene‐ and CuCl‐Mediated Intermolecular Coupling of Two Alkynes and One Diiodomethane

1,2,3,4‐Tetrasubstituted cyclopentadienes and indene derivatives with identical or different substituents were obtained in good to excellent isolated yields through a zirconocene‐ and CuCl‐mediated intermolecular coupling process. This synthetic procedure involved three organic partners, including one CH₂I₂, and two different or identical alkynes. Two alkynes or one diyne undergo Cp₂Zr^II‐mediated (Cp=η⁵‐C₅H₅) pair‐selective reductive coupling to afford the corresponding zirconacyclopentadiene derivatives, which react, in the presence of CuCl and 1,3‐dimethyl‐3,4,5,6‐tetrahydro‐2(1 H)‐pyrimidinone (DMPU), with CH₂I₂ through intermolecular followed by intramolecular coupling to afford the cyclopentadiene derivatives. An application of the prepared tetrasubstituted cyclopentadiene derivatives was demonstrated by the facile synthesis of the corresponding zirconocene complexes [(^4RCp)₂ZrCl₂] and [(^4RCp)₂ZrR′₂] (R′=Me, Et, or nBu). The unique 1,2,3,4‐tetrasubstituted cyclopentadiene ligands and the corresponding metallocenes are expected to have further applications in organometallic chemistry and organic synthesis.     

The Influence of the Synthesis Temperature on Cobalt Phthalocyanine Encapsulation in Zeolite Y

Several characterization techniques were applied to study the effect of the synthesis temperature on the physicochemical properties of cobalt phthalocyanine incoporated into zeolite Y. The cobalt phthalocyanine was synthesized in the supercages of zeolite Y by the template synthesis method at two different temperatures of 200 and300 °C and characterized by diffuse reflectance spectroscopy, Fourier transform infraredspectroscopy, pore volume analysis, unit cell dimension calculation, UV-vis spectroscopy,thermogravimetric analysis and X-ray diffraction. The results show that the catalyst synthesizedat 200 °C contains 11 wt.% cobalt phthalocyanine and almost all of thiscomplex is encapsulated in the supercages as monomeric species. At higher temperature aconsiderable amount of the cobalt phthalocyanine is hosted in the mesopores and/or on theexternal surface of the zeolite as aggregates. The migration of one part of the cobalt cationsfrom the supercages to the small cages at 300 °C decreases the formation of thenon-aggregated encapsulated phthalocyanine molecules in the zeolite supercages. Theaggregated cobalt phthalocyanine formed at the surface corresponds to the -polymorph stateof the phthalocyanine.     

Adsorption de CO2 par des zeolithes X echangees par des cations bivalents

Adsorption of carbon dioxide by X zeolites exchanged with bivalent cations. The adsorption of carbon dioxide by X zeolites exchanged by Mg²⁺, Sr²⁺, Zn²⁺ and Cu²⁺ cations was studied by thermogravimetry. The corresponding isosteric heats of adsorption decrease with the filling of pore volume, except for Cu(63)X. This evolution of the heat indicates a specific interaction between cations present within supercages and CO₂ molecules. Several models have been used in order to describe the experimental isotherms. The best fit of sorption isotherm data was obtained with the Sips model.     

Effect of the solvent on the radius of exchange interactions of d<Superscript>0</Superscript>-metal complexes with cyclopentadiene

The effect of solvent on the efficiency of exchange-resonant energy transfer from d⁰-organometallic π-complexes to nonphosphorescent cyclopentadiene in glassy organic solvents at 77 K was studied. The radius of nonradiative energy transfer depends on the solvation of metal complexes of this series.     

Diels-Alder reaction of methyl coumalate with 1,3-dienes

Reaction of methyl coumalate (1b) with 1,3-butadienes at 100° afforded the tetrahydrocoumarins (6) and the 4-methoxycarbonyltricyclo[3.2.1.0^2,7]octenes (7). The similar reaction of 1b with cyclohexadiene gave exclusively tetrahydronaphthalene-2-carboxylate. With cyclopentadiene, 1b afforded a product (10) resulting from the addition reaction in which cyclopentadiene acted as a dienophile. The reaction giving 6 is the first example of the reaction of a 2-pyrone as a dienophile.     

The configuration and conformation of the tricyclo[4.4.1.12,5]dodecan-11-ols determined by 1H NMR spectroscopy using the shift reagent Eu(fod)3

The isomeric tricyclo[4.4.1.1^2,5]dodecan-11-ols have been synthesized from the (6+4) cycloaddition product of tropone with cyclopentadiene. The configuration and conformation of each isomer was determined from the proton shift gradients induced in the olefinic proton signals in the ¹H NMR spectra of intermediate compounds by Eu(fod)₃.     

Pd(II)‐catalyzed polymerization of optically active norbornene carboxylic acid esters

(?)‐(1S,2R)‐Norbornene‐2‐carboxylic acid alkyl esters (alkyl = Me, Bz, L ‐menthyl, or D ‐menthyl) were successfully prepared by the Diels–Alder reaction of cyclopentadiene with (R)‐(?)‐pantolactone‐O‐yl acrylate followed by epimerization and column chromatography. The enantiomeric excess was 99.9%. These monomers were polymerized by Pd(II)‐based catalysts, and high yields of the polymers were obtained. The methyl ester gave an optically active polymer of high optical rotation (monomer [α]_D = ?24.7, polymer [α]_D = ?98.5). This high rotation value of the polymer was attributed to the isotactic chain regulation of the polymer. This high rotation was not observed with methyl esters prepared by the transesterification of menthyl esters. The stereoregular polymer exhibited notable resonance peaks at 39 ppm in ¹³C NMR spectra. No crystallinity was observed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1263–1270, 2006