Synthesis and Catalytic Evaluation in Olefin Metathesis of a Second-Generation Homobimetallic Ruthenium-Arene Complex Bearing a Vinylidene Ligand

in Organometallics (2011), 30(10), 2730-2738

The new homobimetallic ruthenium–vinylidene complex [(p-cymene)Ru(μ-Cl)3RuCl(═C═CHPh)(IMes)] (6) was isolated in high yield upon treatment of [(p-cymene)Ru(μ-Cl)3RuCl(η2-C2H4)(IMes)] (5) with a slight ... [more ▼]

The new homobimetallic ruthenium–vinylidene complex [(p-cymene)Ru(μ-Cl)3RuCl(═C═CHPh)(IMes)] (6) was isolated in high yield upon treatment of [(p-cymene)Ru(μ-Cl)3RuCl(η2-C2H4)(IMes)] (5) with a slight excess of phenylacetylene at −50 °C. Although it was very stable under normal atmosphere in the solid state, this product underwent an oxidative cleavage into the corresponding carbonyl compound [(p-cymene)Ru(μ-Cl)3RuCl(CO)(IMes)] (7) when dissolved in oxygen-containing solvents. Second-generation complexes 6 and 7 were characterized by IR and NMR spectroscopies, and their molecular structures were determined by X-ray diffraction analysis. The catalytic activity of complex 6 was probed in various types of olefin metathesis reactions. Compared to its first-generation analogue [(p-cymene)Ru(μ-Cl)3RuCl(═C═CHPh)(PCy3)], the new ruthenium initiator displayed an enhanced activity. It was also much more selective than ruthenium–ethylene complex 5. Aluminum chloride was a valuable cocatalyst for the ROMP of cyclooctene, whereas phenylacetylene was better suited to achieve the fast and quantitative RCM of α,ω-dienes into the corresponding di- or trisubstituted cycloolefins. The role of the terminal alkyne was rationalized by assuming that it would allow an enyne metathesis to take place, thereby transforming saturated vinylidene precursor 6 into a highly active mono- or bimetallic ruthenium–alkylidene species. [less ▲]

Synthesis and Catalytic Evaluation of Ruthenium-Arene Complexes Generated Using Imidazol(in)ium-2-carboxylates and Dithiocarboxylates

in Organometallics (2009), 28

The ability of five imidazol(in)ium-2-carboxylates and dithiocarboxylates bearing cyclohexyl, mesityl, or 2,6-diisopropylphenyl substituents on their nitrogen atoms to act as NHC precursors for in situ ... [more ▼]

The ability of five imidazol(in)ium-2-carboxylates and dithiocarboxylates bearing cyclohexyl, mesityl, or 2,6-diisopropylphenyl substituents on their nitrogen atoms to act as NHC precursors for in situ catalytic applications was probed in ruthenium-promoted ring-opening metathesis and atom transfer radical polymerizations. Results obtained with 1:2 mixtures of [RuCl2(p-cymene)]2 and NHC•CO2 adducts were in line with those reported previously starting from preformed [RuCl2(p-cymene)(NHC)] complexes, whereas the NHC•CS2 zwitterions were almost completely inactive. To account for this dichotomy, the preparation of preformed ruthenium‚àíarene complexes from [RuCl2(p-cymene)]2 and NHC•CX2 inner salts was thoroughly investigated. As expected, imidazolium-2-carboxylates lost their CO2 moiety and afforded [RuCl2(p-cymene)(NHC)] complexes in high yields, whereas the NHC•CS2 betaines retained their zwitterionic nature and led to cationic complexes of the [RuCl(p-cymene)(NHC•CS2)]PF6 type. These stable, 18-electron species are the first examples of well-defined transition-metal complexes bearing chelating NHC•CS2 ligands. They were characterized by various analytical techniques, and the molecular structure of [RuCl(p-cymene)(IMes•CS2)]PF6 was determined by X-ray diffraction analysis. [less ▲]

Synthesis and characterization of aromatic self-assembled monolayers containing methylene and ethyleneglycol entities by means of sum-frequency generation spectroscopy

in Thin Solid Films (2006), 500

We use infrared-visible sum-frequency generation (SFG) spectroscopy in order to investigate the adsorption properties on Pt(111) of molecules having CH3–C6H4–(O–CH2–CH2)n –O–(CH2)m –SH as general chemical ... [more ▼]

We use infrared-visible sum-frequency generation (SFG) spectroscopy in order to investigate the adsorption properties on Pt(111) of molecules having CH3–C6H4–(O–CH2–CH2)n –O–(CH2)m –SH as general chemical formula. We synthesized three molecules defined by the values m=5 n =4, m =11 n =4, m=11 n =8 and characterized them by Nuclear Magnetic Resonance spectroscopy. Thanks to spectroscopic measurements, we show that these molecules build self-assembled monolayers on Pt(111). First, the weak SFG signals arising from the ad-layer indicate low order and surface coverage of the substrate by these molecules. Next, the vibrational fingerprints of the aforementioned molecules are determined between 2825 and 3125 cm 1 and the observed SFG spectral features are ascribed on the basis of the analysis of shorter and simpler molecules (1- dodecanethiol, 4-methylbenzenethiol and CH3–C6H4–O–(CH2)11–SH) also adsorbed on Pt(111). The occurrence of methylene vibration modes indicates a significant amount of chain defects whatever the n and m numbers are. Finally, the identification of a particular vibration mode, characteristic of the aromatic ring, enables us to qualitatively discuss the effect of the number of methylene and ethylene glycol entities on its orientation. More precisely, higher these numbers, more tilted (with respect to the substrate normal) the aromatic ring plane is. [less ▲]

Synthesis and characterization of biodegradable homopolymers and block copolymers based on adipic anhydride

in Journal of Polymer Science. Part A, Polymer Chemistry (1997), 35(1), 183-192

Homopolymers of adipic anhydride (AA) and block copolymers of -caprolactone (-CL) and AA have been synthesized with aluminum triisopropoxide as an initiator. Homopolymerization was studied at 20°C in ... [more ▼]

Homopolymers of adipic anhydride (AA) and block copolymers of -caprolactone (-CL) and AA have been synthesized with aluminum triisopropoxide as an initiator. Homopolymerization was studied at 20°C in toluene and methylene chloride (CH2Cl2). The end-group analysis agrees with a coordination insertion mechanism based on the acyl-oxygen cleavage of the AA ring. Living poly(-caprolactone) (PCL) chains are very efficient macro-initiators for the polymerization of AA, with formation of diblock copolymers of a narrow molecular weight distribution. At our best knowledge, low molecular weight -aluminum alkoxide PCL macroinitiators (M¯n < 1000) allow the first valuable synthesis of PAA with a molecular weight as high as 58,000 and a quite narrow polydispersity (M¯w/M¯n = 1.2). Size-exclusion chromatography (SEC) and 13C NMR confirm the blocky structure of the copolymers, in agreement with DSC that shows two melting endotherms and two glass transitions characteristic of the crystalline and amorphous phases of PCL and PAA, respectively. Block copolymers of c-CL and AA are also sensitive to hydrolysis, which makes them possible candidates for biomedical applications. Initiation of the AA polymerization in bulk with aluminum triisopropoxide in the presence of various ligands is also discussed. [less ▲]

Synthesis and characterization of electrically conducting polyester/MWNTs nanocomposite foams

Poster (2005, June 01)

Synthesis and characterization of highly loaded Pt/carbon xerogel catalysts prepared by Strong Electrostatic Adsorption method

in Studies in Surface Science and Catalysis (2010), 175

Synthesis and characterization of inorganic, lamellar nanofillers with high aspect ratio

in Journal of the European Ceramic Society (2007), 27(2-3), 1023-1027

Mesostructured silica phases with lamellar structure were prepared by the liquid crystal templating (LCT) technique, from double chain alkylammonium surfactant and sodium silicate or ... [more ▼]

Mesostructured silica phases with lamellar structure were prepared by the liquid crystal templating (LCT) technique, from double chain alkylammonium surfactant and sodium silicate or tetraethylorthosilicate (TEOS) silica precursors. The structural characterization of these phases is presented and compared. Surface modification of the silica layers, together with elimination of the organic template, is considered. Finally, a representative model of the microstructural organization is proposed. (c) 2006 Elsevier Ltd. All rights reserved. [less ▲]

Synthesis and characterization of nanostructured mesoporous zirconia catalyst supports using non-ionic surfactants as templating agents

in Studies in Surface Science and Catalysis (2002), 143

The formation of nanostructured porous zirconia catalyst supports using non-ionic surfactants as templating agents has been studied in order to optimize the synthesis conditions without addition of ... [more ▼]

The formation of nanostructured porous zirconia catalyst supports using non-ionic surfactants as templating agents has been studied in order to optimize the synthesis conditions without addition of structure stabilizing agents such as sulfate or phosphate anions. The effect of the quantity of added zirconium source with respect to the surfactant concentration in solution has been studied. We also examined the role played by the surfactant during the synthesis. Further investigations have shown that the pore diameters could be increased towards the mesoporous domain if heating time and temperature are raised. The present work reveals that the control of the balance between the precipitation rate of zirconia and the interaction of zirconium source will be fatal in the formation of nanostructured porous zirconia. [less ▲]

Synthesis and characterization of non-covalent liquid crystalline diblock copolymers

in Macromolecular Chemistry and Physics (2000), 201(1), 31-41

Poly(dimethylaminoethylmethacrylate)-b-poly(sodium methacrylate) diblocks, (polyDMAEMA-b-polyMA), were synthesized as precursors of liquid crystalline (LC) copolymers. These LC copolymers were prepared by ... [more ▼]

Poly(dimethylaminoethylmethacrylate)-b-poly(sodium methacrylate) diblocks, (polyDMAEMA-b-polyMA), were synthesized as precursors of liquid crystalline (LC) copolymers. These LC copolymers were prepared by pro-ton-transfer between a carboxylic acid-containing meso-gen (A) and the dimethylamino substituent of the poly-DMAEMA block and by electrostatic interactions between the polyMA subunits and an ammonium-contain-ing mesogen (B). When mesogen A is complexed with DMAEMA units, a dramatic enhancement of the meso-phase stability is noted. The mesogenic properties of these LC copolymers were compared to those ones of the parent LC homopolymers, in relation to the copolymer composi-tion. The supramolecular organization of the LC diblock copolymers was studied by small-angle X-ray scattering (SAXS), and smectic mesophases were observed in some LC (co)polymers. For samples containing a major LC block, a smectic mesophase coexists with microphases formed by the second amorphous block. Different organizations, including a body-centered lattice of spheres and a hexagonal array of cylinders, were observed, depending on the investigated copolymers and their composition. When the LC block is the minor component, it forms microdomains too small for a liquid crystalline order to emerge. Moreover, no supramolecular organization of these dispersed microdomains was detected by SAXS. A homogeneous smectic mesophase was observed when the two blocks are bearing liquid crystalline moieties. [less ▲]

Synthesis and characterization of poly(methyl methacrylate)-block-poly(n-butyl acrylate)-block-poly(methyl methacrylate) copolymers by two-step controlled radical polymerization (ATRP) catalyzed by NiBr2(PPh3)2, 1+

in Macromolecules (1999), 32(25), 8277-8282

Poly(methyl methacrylate)-block-poly(n-butyl acrylate)-block-poly(methyl methacrylate) triblock copolymers (MnBM) have been synthesized by the sequential controlled radical polymerization (atom transfer ... [more ▼]

Poly(methyl methacrylate)-block-poly(n-butyl acrylate)-block-poly(methyl methacrylate) triblock copolymers (MnBM) have been synthesized by the sequential controlled radical polymerization (atom transfer radical polymerization, ATRP) of n-butyl acrylate (n-BuA) followed by methyl methacrylate (MMA). The polymerization of n-BuA has been first initiated by the difunctional (diethyl meso-2,5-dibromoadipate) initiator in the presence of the NiBr2(PPh3)2 catalyst. After isolation, the α,ω-dibromo poly(n-butyl acrylate) chains have been used as macroinitiators for the polymerization of either n-BuA or MMA leading to chain extension or to the desired triblock copolymers, respectively. The kinetic study of the two-step process has shown that the initiation of the MMA polymerization by the poly(n-BuA) macroinitiator is slow and leads to PMMA outer blocks of broad polydispersity. Differential scanning calorimetry (DSC) and dynamical mechanical analysis (DMA) have confirmed the two-phase morphology of the triblocks. Finally, DMA and tensile testing of these copolymers have emphasized poor mechanical properties in possible relation to the broad polydispersity of the PMMA outer blocks. [less ▲]