Highly Active Neutral Nickel(II) Catalysts for Ethylene Polymerization Bearing Modified,beta-Ketoiminato Ligands

A series of novel neutral nickel complexes 4a-e bearing modified beta-ketoiminato ligands [(2,6-(Pr2C6H3)-Pr-i)N=C(R-1)CHC(2 '-R2C6H4)O]Ni(Ph)(PPh3) (4a, R-1 R-2 = H; 4b, R-1 = H, R-2 = Ph; 4c, R-1 = H, R-2 = Naphth; 4d, R-1 = CH3, R-2 = Ph; 4e, R-1 = CF3, R-2 Ph) have been synthesized and characterized. Molecular structures of 4b and 4e were further confirmed by X-ray crystallographic analysis. Activated with B(C6F5)(3), all the complexes are active for the polymerization of ethylene to branched polyethylenes. Ligand structure, i.e., substituents R-1 and R-2, greatly influences not only catalytic activity but also the molecular weight and branch content of the polyethylene produced. The phenyl-substituted complex 4b exhibits the highest activity of lip to 145 kg PE/mol(Ni)center dot h center dot atm under optimized conditions, which is about 10 times more than unsubstituted complex 4a (14.0 kg PE/mol(Ni center dot)h center dot atm). Highly branched polyethylene with 103 branches per 1000 carbon atoms has been prepared using catalyst 4e.

Synthesis, molecular structures, and norbornene addition polymerization activity of the neutral nickel catalysts supported by beta-diketiminato [N, N], ketiminato [N, O], and Schiff-Base [N, O] ligands

A series of neutral nickel complexes [Ni(Ph)(PPh3)(N, O)] with Schiff-base ligands (N, O) [N, O = 5-Me-3-tert-Bu-(Ar-N=CH)C6H2O (1, Ar = 2,6-Me2C6H3; 2, Ar = 2,6-i-Pr2C6H3)], [Ni(Ph)(PPh3)(N,O)1, with beta-ketiminato ligands (N, O) [N, O = CH3COCHC=(CH3)N-Ar (3, Ar = 2,6-Me2C6H3; 4, Ar = 2,6-i-Pr2C6H3)] and [Ni(N, N)(PPh3)], and with beta-diketiminato ligands (N, N) [5, N, N = [2,6-i-Pr-2(C6H3)N=C(CH3)](2)CH] have been synthesized and characterized. The molecular structures of complexes 1, 4, and 5 have been confirmed by X-ray single-crystal analyses. Although their ligands have similar structures, complex 4 possesses a structure similar to that of four-coordination nickel with complex 1, while complex 5 reveals a rare three-coordination nickel geometry. These compounds show high catalytic activities of up to 3.16 x 10(7) g PNB mol(-1) Ni h(-1) for the addition polymerization of norbornene in the presence of modified methylaluminoxane (MMAO) as cocatalyst. Catalytic activities, polymer yield, molecular weights, and molecular weight distributions of polyborbornene have been investigated under various reaction conditions.

Ethylene polymerization by self-immobilized neutral nickel catalysts bearing allyl groups

[Ni(Ph)(PPh3)(N,O)] complexes containing phenyliminophenolato ligands (N,O) (1: N,O = A; 2: N,O = B; 3: N,O = Q 4: N,O = D; 5: N,O = E) have been synthesized and characterized. The molecular structure of 4 was determined by single-crystal X-ray analysis. Complexes 2-5 bearing allyl groups have been investigated as self-immobilized catalysts for ethylene polymerization without the use of co-catalysts. The high ethylene polymerization activities of ca. 10(5) g.PE mol(-1) Ni.h(-1) and high molecular weight (M-w approximate to 10(5)) of polyethylene could be accomplished by changing the ligand structures and reaction conditions. The self-immobilization of catalysts brings about a dramatic increase in the catalytic activities of ethylene polymerization.

Synthesis of 2-benzylthio-5-phenyl-3,4-disubstituted thiophenes by intramolecular condensation of alpha-oxo ketene dibenzylthioacetals

A facile route to 2-benzylthio-5-phenyl-3,4-disubstituted thiophenes was described. Catalyzed by sodium hydroxide, the title compounds were synthesized in moderate to good yields simply from the intramolecular aldol type condensation of alpha-oxo ketene dibenzylthioacetals. The chemical selectivity for this annulation reaction was studied and discussed.

Self-immobilized catalysts for ethylene polymerization: neutral, single-component salicylaldiminato phenyl nickel(II) complexes bearing allyl substituents

A new family of self-immobilized ethylene polymerization catalysts, derived from neutral, single-component salicylaldiminato phenyl nickel complexes, is described.

A nickel molybdenum phosphate with tunnel: Hydrothermal synthesis and structure of (NH3CH2CH2NH3)(4)center dot(NH3CH2CH2NH2)center dot Na center dot[Ni2Mo12O30(PO4)(HPO4)(4)(H2PO4)(3)]center dot 6H(2)O

A nickel molybdenum phosphate, (NH3CH2CH2NH3)(4).(NH3CH2CH2NH2). Na .[Ni2Mo12O30(PO4)(HPO4)(4)(H2PO4)(3)]. 6H(2)O, invoicing molybdenum present in V oxidation, has been hydrothermally synthesized and structurally characterized by single crystal X-ray diffraction. Deep brown-red crystals are formed in the triclinic system, space group P (1) over bar, a = 12,011(2), b = 14,612(3), c = 21.252(4) Angstrom, alpha = 80.54(2)degrees, beta = 83.10(2)degrees, gamma = 76.29(2)degrees, V = 3561.4(12) Angstrom(3), Z = 2, lambda(MoK alpha) = 0.71073 Angstrom (R(F) = 0.0529 for 9880 reflections), Data mere collected on a Siemens P4 diffractometer at 20 degrees C in the range of 1.75 degrees < theta < 23.02 degrees using the omega-scan technique. The structure was solved by direct methods using the program SHELXTL-93 and refined with the method of fun-matrix least-squares on F-2. The structure of the title compound may be considered to be two [Mo6O15(HPO4)(H2PO4)(3)](5-) units bonded together with a nickel atom, although several P-O groups are not protonated on account of coordination with a Na+ cation, The one-dimensional tunnels were formed in the solid of the title compound. A probe reaction of the oxidation of acetaldehyde with H2O2 using the title compound as catalyst was carried out in a liquid- solid system, showing that the title compound had high catalytic activity in the reaction, (C) 1999 Academic Press.

Complete hydrodechlorination of chlorobenzene and its derivatives over supported nickel catalysts under liquid phase conditions

Liquid phase hydrodechlorination of chlorobenzene was studied over Ni/active carbon (Ni/AC), Ni/gamma-Al2O3, Ni/SiO2 and Raney Ni. The complete hydrodechlorination of chlorobenzene was realized at 333-343 K on Ni/AC under hydrogen atmosphere of 1.0 MPa in the presence of alkaline hydroxide. Aryl halides, three chlorotoluenes (o-, m- and p-), three chloroanilines, three chlorobenzotrifluorides, three dichlorobenzenes and two trichlorobenzenes (1,2,3- and 1,2,4-) were also completely hydrodechlorinated under the similar conditions. Chlorobenzene derivatives having either an electron-donating group or an electron-withdrawing group decreased their reactivities with respect to the unsubstituted chlorobenzene.

Adsorption of metal cations by hydrous aluminium(III) or iron(III) hydroxide precipitates: enhancement by EDTA and related chelate molecules

Stoichiometrically equivalent concentrations of ethylenediaminetetraacetate, EDTA, and of related chelating anions increase the adsorption of ca. millimolar concentrations heavy metal aqua-ions on amorphous precipitates of aluminium(III) or iron(III) hydroxide and, although higher concentrations decrease the adsorption, poly-EDTA, a polyelectrolyte containing EDTA functional groups, shows no such decrease.

Monohalogénocyclopropanations stéréosélectives à l'aide de carbénoïdes de zinc, couplages croisés de cyclopropylsilanols, cyclisations d'iodures d'alkyle catalysées par le nickel

Les cyclopropanes sont des unités qui sont très importantes en raison de leur présence dans de nombreux produits naturels, dans certaines molécules synthétiques ayant une activité biologique, ainsi que dans plusieurs intermédiaires synthétiques. Les travaux décrits dans cet ouvrage portent sur l’halogénocyclopropanation stéréosélective d’alcools allyliques en présence d’un ligand chiral stœchiométrique de type dioxaborolane et de carbénoïdes de zinc substitués dérivés de composés organozinciques et d’haloformes. Nous avons ainsi développé des conditions pour l’iodo-, la chloro- et la fluorocyclopropanation stéréosélective. Une étude mécanistique portant sur la nature des carbénoïdes alpha-chlorés et alpha-bromés a révélé qu’il y a un échange des halogènes portés par ces carbénoïdes. Lors de la chlorocyclopropanation, le carbénoïde le plus réactif (alpha-chloré) réagit de façon prédominante en vertu du principe de Curtin-Hammet. Les iodocyclopropanes énantioenrichis ont pu être fonctionnalisés via une réaction d’échange lithium-iode suivie du traitement avec des électrophiles, ou via une réaction de transmétallation au zinc suivie d’un couplage de Negishi. Ainsi, toute une gamme de cyclopropanes 1,2,3-substitués énantioenrichis a pu être synthétisée. Dans l’optique de développer de nouvelles méthodologies de fonctionnalisation des cyclopropanes, nous nous sommes par la suite tournés vers le couplage croisé de type Hiyama-Denmark des cyclopropylsilanols. Dans cette voie synthétique, le groupement silanol a deux fonctions : il sert de groupement proximal basique lors de la cyclopropanation de Simmons-Smith et il subit la transmétallation au cours du couplage croisé. Dans l’étape du couplage croisé, la nature des ligands liés à l’atome de silicium s’est avérée cruciale au bon déroulement de la réaction. Ainsi, l’échange de ligands avec le diéthyl éthérate de trifluoroborane générant le cyclopropyltrifluorosilane in situ est requis pour obtenir de bons rendements. Le dernier volet de cet ouvrage porte sur la cyclisation d’iodures d’alkyle par substitution aromatique par voie homolytique catalysée par le nickel. Une série de composés de type tétrahydronaphtalène et thiochromane ont été préparés selon cette méthode. Une étude mécanistique a confirmé la nature radicalaire de cette réaction et suggère fortement l’action catalytique du nickel. De plus, des études de spectrométrie RMN DOSY ont montré une association entre le complexe de nickel et le substrat ainsi que la base employés dans cette réaction.

Effect of a calcium hydroxide-based paste associated to chlorhexidine on RAW 264.7 macrophage cell line culture

Objective. The objective of this study was to evaluate the effect of a calcium hydroxide Ca(OH)(2)-based paste (Calen) associated or not to 0.4% chlorhexidine digluconate (CHX) on RAW 264.7 macrophage cell line culture. Study design. The cell viability (MTT assay), immunostimulating properties (NO dosage), and anti-inflammatory properties (NO, TNF-alpha, and IL-1 alpha dosage) were evaluated after cell exposure to the materials. Data were analyzed statistically by Kruskal-Wallis test at 5% significance level. Results. There was low immunostimulating activity of the Calen paste associated or not to 0.4% CHX in the different materials` concentrations evaluated (P > .05). Anti-inflammatory activity with inhibition of NO and cytokine (TNF-alpha and IL1-alpha) release was observed only with Ca(OH)(2) + CHX at the highest concentration (25 mu g/mL). Conclusion. As the Calen paste associated to 0.4% CHX did not alter cell viability or the immunostimulating and anti-inflammatory properties, the addition of CHX brought no benefits to the Ca(OH)(2)-based paste with regard to the tested parameters. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2008;106:e44-e51)

Synthesis, characterization and evaluation of antileishmanial activity of copper(II) with fluorinated alpha-hydroxycarboxylate ligands

In this study, Cu(II) complexes with fluorinated ligands were produced aiming at the development of new, less toxic antileishmanial metallodrugs. Complexes of the general formula CuL(2) (L = lactate, trifluorolactate, 2-hydroxyisobutyrate, trifluoro-2-hydroxyisobutyrate) were synthesized in methanolic medium, purified by crystallization and characterized by elemental analysis and electronic and infrared spectroscopies. In vitro experiments with Leishmania amazonensis promastigotes showed that the trifluorolactate derivative more active than its non-fluorinated counterpart. Our results indicate that fluorinated chelators may be interesting to increase metal toxicity and/or open new paths for metallodrug chemotherapy against leishmaniasis.

Identification of species formed after pyridine adsorption on iron, cobalt, nickel and silver electrodes by SERS and theoretical calculations

The adsorption of pyridine (py) on Fe, Co, Ni and Ag electrodes was studied using surface-enhanced Raman scattering (SERS) to gain insight into the nature of the adsorbed species. The wavenumber values and relative intensities of the SERS bands were compared to the normal Raman spectrum of the chemically prepared transition metal complexes. Raman spectra of model clusters M(4)(py) (four metal atoms bonded to one py moiety) and M(4)(alpha-pyridil) where M = Ag, Fe, Co or Ni were calculated by density functional theory (DFT) and used to interpret the experimental SERS results. The similarity of the calculated M(4)(py) spectra with the experimental SERS spectra confirm the molecular adsorption of py on the surface of the metallic electrodes. All these results exclude the formation of adsorbed alpha-pyridil species, as suggested previously. Copyright (C) 2009 John Wiley & Sons, Ltd.

Catalytic Enantioselective alpha-Arylation of Carbonyl Compounds

Enantioselective creation of benzylic quaternary centers still is a continuous challenge to many synthetic organic chemists. Among the existing methods for installation of this type of center, the direct asymmetric alpha-arylation of carbonyl compounds is very attractive due to the ready availability of the coupling substrates. Herein, we present some new tools to the catalytic asymmetric alpha-arylation of carbonyl compounds that overcame many of the drawbacks posted in previous methods for this type of reaction.

Mechanism of calcium hydroxide-induced neutrophil migration into air-pouch cavity

The aim of this study was to investigate cellular migration induced by calcium hydroxide to air-pouch cavities in mice. The migration was more specific to neutrophil and was dose and time dependent (peaking 96 h after stimulation). This migration was inhibited by pretreatment with thalidomide, indomethacin, MK886, meloxicam, dexamethasone, MK886 associated with indomethacin, and MK886 associated with indomethacin and dexamethasone. The air-pouch exudate from animals stimulated with calcium hydroxide showed an increase of leukotriene-B4 (LTB4), interleukin-1 beta, tumor necrosis factor alpha (TNF-alpha), cytokine-induced neutrophil chemoattractant (KC), and macrophage inflammatory protein 2 (MIP-2) release. Pretreatment with 3% thioglycollate increased the macrophage population in the air pouch but did not change neutrophil migration. Depleting the resident mast cells through chronic pretreatment with compound 48/80 did not alter neutrophil migration in response to calcium hydroxide. It was possible to conclude that calcium hydroxide-induced neutrophil migration to the air-pouch cavity in mice is mediated by LTB4, TNF-alpha, KC, MIP-2, and prostaglandins, but it was not dependent on macrophages or mast cells.

Evaluation of mineral trioxide aggregate and calcium hydroxide cement as pulp-capping agents in human teeth

This study evaluated the histomorphologic response of human dental pulps capped with mineral trioxide aggregate (MTA) and Ca(OH)(2) cement (CH). Pulp exposures were performed on the occlusal floor of 40 human permanent premolars. After that, the pulp was capped either with CH or MTA and restored with composite resin. After 30 and 60 days, teeth were extracted and processed for histologic exam and categorized in a histologic score system. The data were subjected to Kruskal-Wallis and Conover tests (alpha = .05). All groups performed well in terms of hard tissue bridge formation, inflammatory response, and other pulpal findings. However, a lower response of CH30 was observed for the dentin bridge formation, when compared with MTA30 and MTA60 groups. Although the pulp healing with calcium hydroxide was slower than that of MTA, both materials were successful for pulp capping in human teeth.