Novel catalyst systems based on Ni(II), Ti(IV), and Cr(III) complexes for oligo-and polymerization of ethylene

The complex of Brookhart Ni(α-diimine)Cl2 (1) (α-diimine = 1,4-bis(2,6- diisopropylphenyl)-acenaphthenediimine) has been characterized after impregnation on silica (S1) and MAO-modified silicas (4.0, 8.0 and 23.0 wts.% Al/SiO2 called S2, S3 and S4, respectively). The treatment of these heterogeneous systems with MAO produces some active catalysts for the polymerization of the ethylene. A high catalytic activity has been gotten while using the system supported 1/S3 (196 kg of PE/mol[Ni].h.atm; toluene, Al/Ni = 1000, 30ºC, 60 min and atmospheric pressure of ethylene). The effects of polymerization conditions have been tested with the catalyst supported in S2 and the best catalytic activity has been gotten with solvent hexane, MAO as cocatalyst, molar ratio Al/Ni of 1000 and to the temperature of 30°C (285 kg of PE/mol[Ni].h.atm). When the reaction has been driven according to the in situ methodology, the activity practically doubled and polymers showed some similar properties. Polymers products by the supported catalysts showed the absence of melting fusion, results similar to those gotten with the homogeneous systems by DSC analysis. But then, polymers gotten with the transplanted system present according to the GPC’s curves the polydispersity (MwD) varies between 1.7 and 7.0. A polyethylene blend (BPE/LPE) was prepared using the complex Ni(α-diimine)Cl2 (1) (α-diimine = 1,4-bis(2,6-diisopropylphenyl)-acenaphthenediimine) and {TpMs*}TiCl3 (2) (TpMs* = hydridobis(3-mesitylpyrazol-1-yl)(5-mesitylpyrazol-1-yl)) supported in situ on MAO-modified silica (4.0 wts. -% Al/SiO2, S2). Reactions of polymerization of ethylene have been executed in the toluene in two different temperatures (0 and 30°C), varying the molars fraction of nickel (xNi), and using MAO as external cocatalyst. To all temperatures, the activities show a linear variation tendency with xNi and indicate the absence of the effect synergic between the species of nickel and the titanium. The maximum of activity have been found at 0°C. The melting temperature for the blends of polyethylene produced at 0 °C decrease whereas xNi increases indicating a good compatibility between phases of the polyethylene gotten with the two catalysts. The melting temperature for the blends of polyethylene showed be depend on the order according to which catalysts have been supported on the MAO-modified silica. The initial immobilization of 1 on the support (2/1/S2) product of polymers with a melting temperature (Tm) lower to the one of the polymer gotten when the titanium has been supported inicially (1/2/S2). The observation of polyethylenes gotten with the two systems (2/1/S2 and 1/2/S2) by scanning electron microscopy (SEM) showed the spherical polymer formation showing that the spherical morphology of the support to been reproduced. Are described the synthesis, the characterization and the catalytic properties for the oligomerization of the ethylene of four organometallics compounds of CrIII with ligands ([bis[2-(3,5-dimethyl-1-pyrazolyl)ethyl]amine] chromium (III) chloride (3a), [bis[2-(3,5- dimethyl-l-pyrazolyl)ethyl]benzylamine] chromium (III) chloride (3b), [bis[2-(3,5-dimethyl-lpyrazolyl) ethyl]ether] chromiun(III)chloride (3c), [bis[2-(3-phenyl-lpyrazolyl) ethyl]ether]chromiun(III)chloride (3d)). In relation of the oligomerization, at exception made of the compounds 3a, all complex of the chromium showed be active after activation with MAO and the TOF gotten have one effect differentiated to those formed with CrCl3(thf)3. The coordination of a tridentate ligand on the metallic center doesn't provoke any considerable changes on the formation of the C4 and C6, but the amount of C8 are decrease and the C10 and C12+ have increased. The Polymers produced by the catalyst 3a to 3 and 20 bar of ethylene have, according to analyses by DSC, the temperatures of fusion of 133,8 and 136ºC respectively. It indicates that in the two cases the production of high density polyethylene. The molar mass, gotten by GPC, is 46647 g/mols with MwD = 2,4 (3 bar). The system 3c/MAO showed values of TOF, activity and selectivity to different α-olefins according to the pressure of ethylene uses. Himself that shown a big sensibility to the concentration of ethylene solubilized.

An Oligosilsesquioxane Cage Functionalized with Molybdenum(II) Organometallic Fragments

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Fatores que influenciam na atividade de titanocenos em catálise homogênea de polimerização de estireno

É apresentada uma revisão bibliográfica com 42 referências abordando aspectos históricos dos compostos organometálicos de titânio, sua aplicação em sistemas catalíticos utilizando metalocenos de titânio e os fatores que influenciam a catálise de alfa-olefinas com as conseqüentes repercussões nas estruturas dos polímeros.

Mechanistic insights into the reaction between VO2+ and propene based on a DFT study

Calculations based on density functional theory have been carried out to investigate the free energy profiles at singlet and triplet electronic states associated with the gas-phase ion/molecule reactions of VO2++ ((1)A(1)/(3)A) with propene. The complex potential energy Surfaces, including Six reaction pathways (three dehydrogenation and three oxygen transfer processes), have been explored and analyzed. Along dehydrogenation reactive channels, three final products can be obtained: V(OH)(2)(+) ((1)Sigma(+)/(3)Sigma(-)) and allene (path Dehl), being the most kinetically and thermodynamically favorable reaction pathway, V(OH)(2)(+) ((1)Sigma(+)/(3)Sigma(-)) and propyne (path Deh2),and VO2+ ((1)A(1)/(3)A) and H-2 plus allene (path Deh3). The oxyoenation processes can yield its final products Vo(+) ((1)Delta/(3)Sigma) and acetone (path Ox1), VO+ ((1)Delta/(3)Sigma 2) and propanaldehyde (path Ox2), and VO+ ((1)Delta/(3)Sigma) and H-2 and propenaldehyde (path Ox3). Both paths Deh1 and Deh2 are associated with two consecutive hydrogen transfer processes from carbon atoms of the propene fragment to vanadyl oxygen atoms, while in path Deh3 the second hydrogen migration takes place to the vanadiurn atorn followed by the formation ola hydrogen molecule. Both paths Ox1 and Ox2 comprise an intramolecular hydrogen transfer between the ethylenic moiety of the propene fragment, while two consecutive hydrogen transfer processes take place from the propene fragment to oxygen and vanadium atoms of the vanadyl moiety along path Ox3. Three crossing points between both electronic states take place along path Deh1 (CP-Deh1) and path Deh2 (CP-Deh2) and in the entrance channel of oxidation processes (CP-Ox). A comparison with previous works on related reactions VO2+ + C2H4, VO2 + C2H6, and VO2+ + C3H8 allows us to rationalize the different reactivity patterns.

Highly selective nickel ethylene oligomerization catalysts based on sterically hindered tris(pyrazolyl)borate ligands

The reaction of TlTp' (Tp' = HB(3-mesitylpyrazolyl)(3)(-) (Tp(Ms)), HB(3-mesitylpyrazolyl)(2)(5-mesitylpyrazolyl)(-) (Tp(Ms)*)) with NiCl(2).6H(2)O affords Tp(Ms)NiCl (1) and Tp(Ms)*NiCl (2) in good yield. The compound 2 undergoes an isomerization process to form [{Tp(Ms)**}NiCl](2) (3) (Tp(Ms)** = HB(5-mesitylpyrazolyl)(2)(3-mesitylpyrazolyl)(-)) in 68% yield. Treatment of the tris(pyrazolyl)-borate nickel compounds 1 and 2 with alkylaluminum cocatalysts such as methylalumoxane (MAO) and trimethylaluminum (TMA) in toluene generates active catalysts for ethylene oligomerization. The compound 1 shows turnover frequencies in the range of (2.2-43.1) x 10(3) h(-1). Oligomerization reaction conditions can be adjusted that lead to selectivities as high as 81% for butene-1.

DFT study of the reaction between VO2+ and C2H6

The molecular mechanisms of the reaction VO2+ ((1)A(1)/(3)A'') + C2H6 ((1)A(g)) to yield V(OH)(2)(+) ((1)Sigma(+)/(3)Sigma(-)) + C2H4 ((1)A(g)) and/or VO+ ((1)Delta/(3)Sigma) + H2O ((1)A(1)) + C2H4 (Ag-1) have been investigated with density functional theory (DFT) at the B3LYP/6-311G(2d,p) level. Calculations including geometry optimization, vibrational analysis, and Gibbs free energy for the stationary points on the reactive potential energy surfaces at both the singlet (s) and first excited triplet (t) electronic states have been carried out. The most thermodynamically and kinetically favorable pathway is the formation of t-V(OH)(2)(+) + C2H4 along a four-step molecular mechanism (insertion, two consecutive hydrogen transfers, and elimination). A crossing point between s and t electronic states has been characterized. A comparison with previous works on VO2+ + C2H4 (Gracia et al. J. Phys. Chem. A 2003, 107, 3107-3120) and VO2+ + C3H8 (Engeser et al. Organometallics 2003, 22, 3933-3943) reactions allows us a rationalization of the different reactivity patterns. The catalytic role of water molecules in the tautomerization process between hydrated oxide cation, VO(H2O)(+,) and dihydroxide cation, V(OH)(2)(+), is achieved by a water-assisted mechanism.

Synthesis, characterization and thermal behaviour of solid-state compounds of 4-methoxybenzoate with some bivalent transition metal ions

Solid-state M-4-MeO-Bz compounds, where M stands for bivalent Mn, Co, Ni, Cu and Zn and 4-MeO-Bz is 4-methoxybenzoate, have been synthesized. Simultaneous thermogravimetry-differential thermal analysis (TG-DTA), differential scanning calorimetry (DSC), X-ray powder diffractometry, infrared spectroscopy, elemental analysis and complexometry were used to characterize and to study the thermal behaviour of these compounds. The results led to have information about the composition, dehydration, thermal stability and thermal decomposition of the isolated compounds. © 2005 Akadémiai Kiadó, Budapest.

Thermal studies on solid 2-chlorobenzylidenepyruvate of lighter trivalent lanthanides

Solid compounds of general formula LnL3 for La and Ce and LnL3·nH2O for Pr, Nd and Sm where Ln stands for trivalent lanthanides, L is 2-chlorobenzylidenepyruvate and n=2, 3 and 2 respectively, have been synthesized. On heating these compounds decompose in two or five steps. They lose the hydration water in the first step and the thermal decomposition of the anhydrous compounds occurs with the formation of the respective oxide, CeO2, Pr6O11 and Ln 2O3 (Ln=La, Nd, Sm) as final residue. The dehydration enthalpies found for these compounds (Pr, Nd and Sm) were: 140.1, 148.2 and 221.3 kJ mol-1, respectively. © 2005 Akadémiai Kiadó, Budapest.

Thermal study of nickel(II) pyrazolyl complexes

The thermal behavior of the pyrazolyl complexes [NiCl2(HPz) 4] (1), [Ni(NCS)2(HPz)4] (2), [NiCl 2(HdmPz)4]·2H2O (3) and [Ni(NCS) 2(HdmPz)4]·2H2O (4) (HPz=pyrazole, HdmPz=3,5-dimethylpyrazole) has been studied by thermogravimetry (TG) and differential thermal analysis (DTA). The TG data indicated that the thermal stability of [NiX2(HL)4] (X=Cl, NCS) compounds varies depending on the pyrazolyl ligand in the following order HL=HPz>HdmPz. From the thermal decomposition of 3 and 4 it was possible to isolate the intermediate compounds [Ni(μ-Cl)2(HdmPz)2] (3a) and [Ni(μ-1,3-NCS) 2(HdmPz)2] (4a), respectively. The final products of the thermal decompositions of 1-4 were identified as NiO by X-ray powder diffraction. © 2005 Akadémiai Kiadó, Budapest.

Thermal decomposition of palladium(ii) pyrazolyl complexes: Part II

Thermal behavior of pyrazolyl complexes [PdCl2(HPz)2] (1), [PdCl2(HdmPz)2] (2), [Pd(SCN)2(HPz) 2] (3), [Pd(SCN)2(HdmPz)2] (4), [Pd(N 3)2(HdmPz)2] (5), [Pd(PzNHCO)2] (6) and [Pd(dmPzNHCO)2] (7) (HPz=pyrazole, HdmPz=3,5-dimethylpyrazole) has been studied by TG and DTA. In general, the thermal stability of [PdX 2(HL)2] (HL=HPz, HdmPz) compounds varies in the following order: HdmPz>HPz as well, according to the trends X=Cl ->SOT->NNN-. Except for 5, the [PdX 2(HL)2] complexes showed higher thermal stability than the 6 and 7 chelates. No stable intermediates were isolated during the thermal decompositions because of the overlapping degradation processes. The final products of the thermal decompositions were identified as metallic palladium by X-ray powder diffraction. © 2005 Akadémiai Kiadó, Budapest.

Adsorption of heavy metal ions and epoxidation catalysis using a new polyhedral oligomeric silsesquioxane

The objective of this research was the preparation of a silsesquioxane functionalized with eight chloropropyl chains (T8-PrCl) and of a new derivative functionalized with a pendant linear chain (2-amino-1,3,4-thiadiazole - ATD; T8-Pr-ATD). The two nanostructured materials were characterized by 13C and 29Si NMR, FTIR and elemental analysis. The new nanostructured material, octakis[3-(2-amino-1,3,4-thiadiazole)propyl] octasilsesquioxane (T8-Pr-ATD), was tested as a ligand for transition-metal ions with a special attention to adsorption isotherms. The adsorption was performed using a batchwise process and the organofunctionalized surface showed the ability to adsorb the metal ions Cu (II), Co (II), and Ni (II) from water and ethanol. The adsorption isotherms were fitted by Langmuir, Freundlich, Temkin and Dubinin-Radushkevich (D-R) model. The kinetics of adsorption of metals were performed using three models such as pseudo-first order, pseudo-second order and Elovich. The Langmuir and Elovich models were the most appropriate to describe the adsorption and kinetic data, respectively. Furthermore, the T8-Pr-ATD was successfully applied to the analysis of environmental samples (river and sea water). Subsequently, a new nanomaterial was prepared by functionalization of the T8-Pr-ATD with a Mo (II) organometallic complex (T8-Pr-ATD-Mo). Only a few works in the literature have reported this type of substitution, and none dealt with ATD and Mo (II) complexes. The new Mo-silsesquioxane organometallic nanomaterial was tested as precursor in the epoxidation of cyclooctene and styrene. © 2012 Elsevier B.V.

Evaluation of the chemical interaction between carbon nanotubes functionalized with TGDDM tetrafunctional resin and hardener DDS

In this work, the chemical interaction between carbon nanotubes (MWCNT) functionalized with acyl chloride (SOCl2) and polymer chain tetrafuncional N,N,N′,N′-tetraglycidyl-4,4′- diaminodiphenylmethane (TGDDM) and hardener 4,4′diaminodiphenyl sulfone (DDS) has been monitored by Fourier transform infrared spectroscopy (FTIR) with a attenuated total reflectance (ATR) coupled. MWCNT were obtained from the pyrolysis of a mixture of camphor and ferrocene into a oven. The functionalization process was done by oxidative treatment in order to incorporate carboxylic group over the walls of MWCNT, before to be used SOCl2. The functionalized carbon nanotubes were evaluated by X-ray photoelectron spectroscopy (XPS), Raman and transmission electron microscopy (TEM). Nanostructured composites were processed by using epoxy resin with MWCNT in varying percentages. In this work it was observed that different percentages of functionalized nanotubes modify the interaction between the composite matrix and curing agent, where can be observed that in specimens with content less than 1 wt% MWCNT the chemical bond occurs preferentially from the opening of the SO double bond of the hardener and when is used MWCNT content higher than 1 wt% there is little chemical interaction with the SO bond of the hardener and most MWCNT binds to amine. © 2013 Elsevier Ltd.

Metallic chalcogenolates mediated modular Michael-aldol cascade reaction: an easy route to multi-functionalized chalcogenides and Morita-Baylis-Hillman adducts

Chalcogenolate mediated Michael-aldol cascade reactions consists of a very efficient route to multi-functionalized gamma-hydroxichalcogenides. Although, when selenolates are employed, these gamma-hydroxichalcogenides can be readily converted into the corresponding Morita-Baylis-Hillman adducts by oxidative elimination of the selenium moiety. In this context, herein we present a complete study on the scope and limitations of this reaction. (C) 2012 Elsevier Ltd. All rights reserved.

Tellurium in organic synthesis: a general approach to buteno- and butanolides

The naturally occurring butanolides (-)-blastmycinolactol, (+)-blastmycinone, (-)-NFX-2, (+)-anti-mycinone as well as the four stereoisomers of the butenolide Acaterin were prepared in high enantiomeric purity using hydroxy-vinyl tellurides as starting materials. (C) 2012 Elsevier Ltd. All rights reserved.

Regioregular improvement on the oxidative polymerization of poly-3-octylthiophenes by slow addition of oxidant at low temperature

Many pathways can be used to synthesize polythiophenes derivatives. The polycondensation reactions performed with organometallics are preferred since they lead to regioregular polymers (with high content of heat-to-tail coupling) which have enhanced conductivity and luminescence. However, these pathways have several steps; the reactants are highly moisture sensitive and expensive. On the other hand, the oxidative polymerization using FeCl3 is a one-pot reaction that requires less moisture sensitive reactants with lower cost, although the most common reaction conditions lead to polymers with low regioregularity. Here, we report that by changing the reaction conditions, such as FeCl3 addition rate and reaction temperature, poly-3-octylthiophenes with different the regioregularities can be obtained, reaching about 80% of heat-to-tail coupling. Different molar mass distributions and polydispersivities were obtained. The preliminary results suggest that the oxidative polymerization process could be improved to yield polythiophenes with higher regioregularity degree and narrower molar mass distributions by just setting some reaction conditions. We also verified that it is possible to solvent extract part of the lower regioregular fraction of the polymer further improving the regioregularity degree. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012