Search results for "Ionic polymerization"
showing 10 items of 481 documents
Group 3 and 4 metal alkyl and hydrido complexes containing a linked amido-cyclopentadienyl ligand: “constrained geometry” polymerization catalysts fo…
2002
Abstract In order to understand the nature of the putative cationic 12-electron species [M(η 5 :η 1 -C 5 R 4 SiMe 2 NR′)R″] + of titanium catalysts supported by a linked amido-cyclopentadienyl ligand, several derivatives with different cyclopentadienyl C 5 R 4 and amido substituents R′ were studied systematically. The use of tridentate variants (C 5 R 4 SiMe 2 NCH 2 CH 2 X) 2− (C 5 R 4 =C 5 Me 4 , C 5 H 4 , C 5 H 3 t Bu ; X=OMe, SMe, NMe 2 ) allowed the NMR spectroscopic observation of the titanium benzyl cations [Ti(η 5 :η 1 -C 5 Me 4 SiMe 2 NCH 2 CH 2 X)(CH 2 Ph)] + . Isoelectronic neutral rare earth metal complexes [Ln(η 5 :η 1 -C 5 R 4 SiMe 2 NR′)R″] can be expected to be active for pol…
Neutral and cationic trimethylsilylmethyl complexes of the rare earth metals supported by a crown ether: synthesis and structural characterization
2003
The synthesis of a series of thermally robust, isolable trimethylsilylmethyl complexes of the rare earth metals stabilized by 12-crown-4 [Ln(CH2SiMe3)3(12-crown-4)] (Ln = Sc, Y, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) is reported. The crystallographically characterized yttrium and lutetium complexes [Ln(CH2SiMe3)3(12-crown-4)] exhibit facial coordination of the crown ether at the neutral lanthanide trialkyl unit. The coordination geometry can be derived from a capped octahedron. VT NMR spectroscopic studies revealed a labile coordination of the crown ether in thf solution. Reaction of the diamagnetic derivatives with triethylammonium tetraphenylborate in thf results in the clean formation of th…
CO Oxidation on Cationic Gold Clusters: A Theoretical Study
2008
Aiming at understanding the elementary steps governing the oxidation of CO catalyzed by dispersed or supported gold nanoclusters, the reactivity of molecular species, such as O2 and CO, on neutral and positively charged Au13 clusters have been studied using a DFT approach. Two CO oxidation mechanisms have been simulated, involving respectively the adsorption of CO and O2 on adjacent catalytic sites (two-sites mechanism) and the competitive interaction of the reactants on the same site (single-site mechanism). It is demonstrated that in the former scheme a definite interaction of CO and O2 with both the charged and neutral cluster is effective, but that a chemical reaction between the adsorb…
Anionic Cyclometalated Iridium(III) Complexes with a Bis-Tetrazolate Ancillary Ligand for Light-Emitting Electrochemical Cells
2017
none 10 si A series of monoanionic Ir(III) complexes (2-4) of general formula [Ir(C^N)2(b-trz)](TBA) are presented, where C^N indicates three different cyclometallating ligands (Hppy = 2-phenylpyridine; Hdfppy = 2-(2,4-difluoro-phenyl)pyridine; Hpqu = 2-methyl-3-phenylquinoxaline), b-trz is a bis-tetrazolate anionic N^N chelator (H2b-trz = di(1H-tetrazol-5-yl)methane), and TBA = tetrabutylammonium. 2-4 are prepared in good yields by means of the reaction of the suitable b-trz bidentate ligand with the desired iridium(III) precursor. The chelating nature of the ancillary ligand, thanks to an optimized structure and geometry, improves the stability of the complexes, which have been fully char…
Synthesis and characterization of new aromatic tweezers and complex formation with tropylium ion in 1,2-dichloroethane
2001
A series of benzene and pyridine tweezers bearing phenyl, naphthyl and anthryl receptor units was prepared and characterized. The x-ray crystal structure of the 1,3-bis(9-methanolanthracene)methylbenzene ligand (5) is reported. UV–visible and NMR spectroscopy were used to investigate the host–guest chemistry of the new ligands in complexation with tropylium tetrafluoroborate as a model aromatic cationic guest in 1,2-dichloroethane. The appearance of coloured charge-transfer absorption bands demonstrates the complex formation with a tropylium ion. The enlargement of aryl receptor size from phenyl and naphthyl to anthryl increases the stability of complexes. Electron donor–acceptor interactio…
A Singular Noninterpenetrating Coordination Polymer with the Pt3O4 Structure Containing Naked [Na+]4 Units
2006
The homoleptic low-spin complex [Fe(L)3]2+ where L is the bisbidentate ligand 1,10-phenanthroline-5,6-dione, coordinates Na+ ions via exo-oriented dione groups defining a three-dimensional cationic network {[Fe(L)3]4Na3}11+}n with Pt3O4 topology. The large volume generated by the network is filled with 11 perchlorate ions, 7 "NaClO4" ionic pairs, and 9 H2O molecules. Singular [Na+]4 units, in which the Na+ ions are practically uncoordinated, are formed.
Selective palladium-catalysed dimerisation of methyl acrylate in ionic liquids: towards a continuous processThis work was presented at the Green Solv…
2003
The activity and stability of cationic palladium complexes [Pd(PBu3)2S2]2+ used for the selective tail-to-tail dimerisation of methyl acrylate are significantly improved with the utilisation of ionic liquids like [BMIM][BF4] or the protonated N-butyl-imidazole, [HBIM][BF4]. Problems related to product inhibition and catalyst recycling are overcome by running the reaction in a two-phase mode, toluene being used as extractant. Catalyst stabilisation is further improved by trapping the ancillary ligand into the ionic liquid with an ionic tail: with the use of 1-dibutylphosphino-2-dimethylaminoethane, the catalyst is stable for more than 100 h, therefore demonstrating the feasibility of a conti…
The Kinetic Stability of Cationic Benzyl Titanium Complexes that Contain a Linked Amido-Cyclopentadienyl Ligand: The Influence of the Amido-Substitue…
2002
Cationic benzyl titanium complexes [Ti(η 5 : η 1 -C 5 Me 4 SiMe 2 NR')-(CH 2 Ph)] + were cleanly formed by the reaction of the dibenzyl titanium complexes [Ti(η 5 : η 1 -C 5 Me 4 SiMe 2 NR')(CH 2 Ph) 2 with B(C 6 F 5 ) 3 and [Ph 3 C][B(C 6 F 5 ) 4 ] in bromobenzene. NMR spectroscopic studies suggest that the benzyl titanium cations contain a fluxional η 2 -coordinated benzyl ligand. Kinetic analysis showed that the benzyl titanium cations decompose according to first-order kinetics and that the amido substituents R' (R' = Me, i Pr, t Bu) in the linked amido-cyclopentadienyl ligand influence the lability of these benzyl titanium cations. The order of the kinetic stability of the benzyl titan…
Cationic Cyclopentadienyl Phenylenediamido Titanium Species Generated by Reaction of TiCpR[1,2-C6H4(NCH2t-Bu)2]R (CpR = η5-C5H5, η5-C5Me5; R = CH3, C…
2006
The reaction of TiCpR[1,2-C6H4(NNp)2]R with the Lewis acid B(C6F5)3 in noncoordinating solvent affords the new zwitterionic species TiCpR[1,2-C6H4(NNp)2)][μ-RB(C6F5)3]. When the reaction is performed in dichloromethane, the [μ-RB(C6F5)3]- anion is displaced by solvent molecules, giving ionic products in which the anion is not coordinated. The cyclopentadienyl zwitterionic complexes TiCp[1,2-C6H4(NNp)2)[μ-RB(C6F5)3] decompose via ligand scrambling between boron and titanium to give the neutral titanium complex TiCp[1,2-C6H4(NNp)2](C6F5) along with the byproduct RB(C6F5)2. In contrast, the pentamethylcyclopentadienyl analogues TiCp*[1,2-C6H4(NNp)2][μ-RB(C6F5)3] evolve through C−H activation t…
Cationic Proteins Inhibit l-Arginine Uptake in Rat Alveolar Macrophages and Tracheal Epithelial Cells
1999
Eosinophil-derived cationic proteins play an essential role in the pathogenesis of bronchial asthma. We tested whether cationic proteins interfere with the cationic amino-acid transport in alveolar macrophages (AMPhi) and tracheal epithelial cells, and whether L-arginine-dependent pathways were affected. The effect of cationic polypeptides on cellular uptake of [(3)H]-L-arginine, nitrite accumulation, and the turnover of [(3)H]-L-arginine by nitric oxide (NO) synthase and arginase (formation of [(3)H]-L-citrulline and [(3)H]-L-ornithine, respectively) were studied. Poly-L-arginine reduced [(3)H]-L-arginine uptake in rat AMPhi and tracheal epithelial cells in a concentration-dependent manner…