Search results for "Isoprene"
showing 10 items of 47 documents
Dinuclear chloroneodymium quinolinylcarboxylates: The molecular structures affected by water and the catalytic behavior toward isoprene polymerization
2016
Abstract A series of dinuclear chloroneodymium quinolinylcarboxylate compounds was synthesized and characterized. The nature and importance of metal-organic aggregations have been considered as an important factor regarding the molecular structure and catalytic performance. The neodymium center in all the title compounds exhibits the coordination numbers of 8. Cage aggregation was observed in the solid state, and the cyclic arrangement was achieved when water molecules were incorporated into the structure. Upon the activation with Al(i-Bu)3, all the title neodymium compounds form the efficient catalysts for isoprene polymerization. The catalytic activities are not strongly affected by the m…
Molecular Characterization and Source Identification of Atmospheric Particulate Organosulfates Using Ultrahigh Resolution Mass Spectrometry.
2019
Organosulfates (OSs) have been observed as substantial constituents of atmospheric organic aerosol (OA) in a wide range of environments; however, the chemical composition, sources, and formation mechanism of OSs are still not well understood. In this study, we first created an "OS precursor map" based on the elemental composition of previous OS chamber experiments. Then, according to this "OS precursor map", we estimated the possible sources and molecular structures of OSs in atmospheric PM2.5 (particles with aerodynamic diameter ≤ 2.5 μm) samples, which were collected in urban areas of Beijing (China) and Mainz (Germany) and analyzed by ultrahigh-performance liquid chromatography (UHPLC) c…
Radical Formation by Fine Particulate Matter Associated with Highly Oxygenated Molecules
2019
Highly oxygenated molecules (HOMs) play an important role in the formation and evolution of secondary organic aerosols (SOA). However, the abundance of HOMs in different environments and their relation to the oxidative potential of fine particulate matter (PM) are largely unknown. Here, we investigated the relative HOM abundance and radical yield of laboratory-generated SOA and fine PM in ambient air ranging from remote forest areas to highly polluted megacities. By electron paramagnetic resonance and mass spectrometric investigations, we found that the relative abundance of HOMs, especially the dimeric and low-volatility types, in ambient fine PM was positively correlated with the formatio…
Understanding the participation of 3-nitropyridine in polar Diels–Alder reactions. A DFT study
2015
The reactivity of 3-nitropyridine acting as an electrophilic dienophile in polar Diels-Alder (P-DA) reactions toward three different dienes of increased nucleophilicity has been theoretically studied using DFT methods at the MPWB1K/6-31G(d) level. It has been observed that this aromatic heterocyclic system suffers cycloaddition reactions yielding isoquinoline derivatives. The present DFT study establishes that while the P-DA reactions with isoprene and 1-methoxy-1,3-butadiene take place through a two-stage one-step mechanism, the use of the strong nucleophilic Danishefsky's diene changes the mechanism to a two-step one with formation of a zwitterionic intermediate. These P-DA reactions are …
Polar Diels–Alder reactions using electrophilic nitrobenzothiophenes. A combined experimental and DFT study
2015
Abstract The reactions between 2- and 3-nitrobenzothiophenes with three dienes of different nucleophilicity, 1-methoxy-3-trimethylsilyloxy-1,3-butadiene, 1-trimethylsilyloxy-1,3-butadiene and isoprene developed in anhydrous benzene and alternative under microwave irradiation with molecular solvents or in free solvent conditions, respectively, for produce dibenzothiophenes permit to conclude that both nitroheterocycles act as electrophile with the cited dienes. In the cases of the dienes 1-methoxy-3-trimethylsilyloxy-1,3-butadiene and 1-trimethylsilyloxy-1,3-butadiene which posses major nucleophilicity the observed product is the normal cycloaddition one. However when the diene is isoprene t…
Dialkyl(butadiene)cyclopentadienylmolybdenum(III) Complexes. Synthesis, Characterization, and Reactivity
2000
International audience; Treatment of CpMo(η4-diene)Cl2 (diene = 1,3-butadiene, C4H6, 1‘; isoprene, C5H8, 1‘ ‘; 2,3-dimethyl-1,3-butadiene, C6H10, 1‘ ‘) in diethyl ether at low temperature with 2 equiv of alkylmagnesium RMgX reagents affords the corresponding dialkyl complexes CpMo(η4-1,3-diene)R2 (2, 2‘, 2‘ ‘, R = CH3, a; CH2Ph, b; CH2SiMe3, c). These species are isolable in moderate yields and have been fully characterized by EPR, elemental analyses, and cyclic voltammetry. They all show a reversible reduction process at relatively low potentials and an irreversible oxidation. The structure of 2‘ ‘a was confirmed by single-crystal X-ray diffraction. The mixed complex CpMo(η4-C4H6)Cl(CH3), …
Kinetics of Anionic Living Copolymerization of Isoprene and Styrene Using in Situ NIR Spectroscopy: Temperature Effects on Monomer Sequence and Morph…
2019
The living anionic copolymerization of isoprene (I) and styrene (S) can afford a variety of different polymer microstructures that strongly depend on experimental parameters such as solvent, counte...
Ionic liquids and microwave irradiation as synergistic combination for polar Diels–Alder reactions using properly substituted heterocycles as dienoph…
2012
For the DA reactions between nitropyrrole derivatives and isoprene, the combination of microwave irradiation and protic ionic liquid, has a notable synergistic effect. DFT calculations suggest that a supplementary energy ranking in the IR region of 1700-1400 cm-1 can favour the structural changes in the reactants to reach the TS. Fil: Mancini, Pedro Maximo Emilio. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Departamento de Química; Argentina Fil: Ormachea, Carla. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Departamento de Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa F…
Synthesis and X-ray Crystal Structures of (C5HiPr4)Ln(BH4)2(THF)(Ln = Nd and Sm), Versatile Precursors for Polymerization Catalysts
2000
The new half metallocenes [(C5HiPr4)Ln(BH4)2(THF)] [Ln = Sm (1) and Nd (2)], and [(C5HiPr4)U(BH4)3] (3) have been synthesized. The crystal structures of 1 and 2 and of the metallocenes [(C5HiPr4)2Ln(BH4)] [Ln = Sm (4) and Nd (5)] have been determined. The substitution of the BH4 groups of 1 and 2 by a nitrogen-based ligand is possible. In the presence of butyllithium, these complexes show an activity in isoprene and styrene polymerization.
Stereospecific Polymerization of Isoprene with Nd(BH4)3(THF)3/MgBu2 as Catalyst
2004
The neodymium trisborohydride Nd(BH 4 ) 3 - (THF) 3 (THF = tetrahydrofuran) has been used as a catalyst precursor for isoprene polymerization for the first time. Associated to an excess of Al(Et) 3 , the resulting catalyst is moderately active, giving a mixture of cis- and trans- polymer. Addition of a stoichiometric amount of MgBu 2 to Nd(BH 4 ) 3 (THF) 3 affords a stereospecific catalyst providing trans-1,4-polyisoprene, more than 96% regular. That dual component Nd/Mg system also shows a better efficiency and good control of the molecular weights. A molecular structure is tentatively attributed to a bimetallic active species, based on 1 H NMR experiments.