1,720,966 research outputs found
Structure-activity relationships in ethene and propene polymerizations mediated by bis(phenoxyamine)Zr-based catalysts
No full textPolymerization of ethene and propene at bis(phenoxyamine)Zr-based catalysts: so similar, so different!
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Improving the Behavior of Bis(phenoxyamine) Group 4 Metal Catalysts for Controlled Alkene Polymerization
No full textA study was conducted to improve the behavior of bis(phenoxyamine) group 4 metal catalysts for controlled alkene polymerization. The performance of bis(phenoxyamine)Hf homologues was investigated, assuming that a higher chain propagation to transfer ratio was associated with a longer duration of the controlled regime. The bis(phenoxyamine)Hf-dibenzyl complexes Hf-1 and Hf-2 were prepared similarly to the Zr-1 and Zr-2 Hf homologues. The complexes were activated with methylalumoxane (MAO) in combination with 2,6-di-tert-bytylphenol (TBP) to scavenge free trimethylaluminum and inhibit chain transfer through trans-alkylation. The complexes were also tested comparatively with Zr-1 and Zr-2 in ethene and propene polymerization at 25 °C in toluene solution
Activation of a bis(phenoxy-amine) precatalyst for olefin polymerisation: First evidence for an outer sphere ion pair with the methylborate counterion
No full textA bis(phenoxy-amine)ZrMe2 complex (1) was synthesized and activated with B(C6F5)3 obtaining an ion pair (2) having the MeB(C6F5)3- counterion in the second coordination sphere as deduced by NMR studies. Both DFT calculations and NMR investigations suggest that the activation is coupled with a change of the binding modality of the tetradentate ligand from cis(N,N)-trans(O,O) in the octahedral dimethyl precursor 1 to cis(N, N)-cis(O,O) in the ion pair 2. © 2009 The Royal Society of Chemistry
BIS-CHELATING LIGANDS BASED ON BIPYRIDINE OR BIS-ISOQUINOLINE MOIETIES WITH CONTROLLED ROTATION AROUND THE C-C BOND
No full textTwo unprecedented types of ligands, with comparable essential coordination features, are proposed as supports for metal centres in bimetallic promotion of organic syntheses, including asymmetric catalytic processes. Synthesis and characterization of the bis-chelating bipyridine ligands A with C2 symmetry and X-ray analysis of one bipyridine diimine palladium binuclear complex are described. Synthesis and X-ray analysis of the bis-phenylimino derivative of a dibenzodioxepine dialdehyde are also reported. This dialdehyde is a key intermediate in the attainment of bis-isoquinoline ligands B with the same symmetry as A
Bis-chelating ligands based on bipyridine moieties with controlled rotation around the C-C bond
No full textActivation of bis(phenoxy-amine) precatalysts for olefin polymerization: Relationships between the structure of ion pairs and their activity in catalysis.
No full textBinuclear complexes of bis-chelating ligands based on [1,4]dioxocino[6,5-b:7,8-b']dipyridine moieties
No full textLigands based on a [1,4]dioxocino[6,5-b:7,8-b0]dipyridine (doxpy) core were prepared and characterized. They all present two equal chelating moieties each one including one N, O, or S donor in addition to a pyridinic nitrogen. These ligands displayed high selectivity for the formation of binuclear complexes. At least one d8 ion (PdII or PtII) complex was prepared for each type of ligand. The stereochemical behavior of the ligands is discussed on the basis of NMR spectra.
Stable atropoisomers were obtained in the case of N-oxides or in case chiral centers were introduced in the ethereal bridge. As for the complexes, stable enantiomers appear to be in principle attainable for all the new compounds. A test on the cooperative ability of two PdII centers has been grounded on the microstructure of the styrene/CO copolymer catalytically produced by a binuclear pyridine-imino complex. In fact, comparison with the microstructure of the copolymers produced by related single-site mono- and (open-chain) binuclear catalysts reveals significant difference, thus giving indication of possible synergic metal activity
Coordination modes of 1,2,3,4-tetrahydro-1,4-diphenyl-1,4-benzodiphosphinine (bedip) to Pt and Pd metal ions: Synthesis and structural characterization of mono- and bi-nuclear complexes.
No full textWithin this study, coordination properties of the cyclic diphosphine 1,2,3,4-tetrahydro-1,4-diphenyl-1,4-benzodiphosphinine (bedip) are investigated, through the preparation of neutral and cationic Pt(II), Pt(IV) and Pd(II) complexes. The diphosphine acts as bridging ligand in the neutral Pt(II) and Pd(II) complexes, affording [MX(CH3)(μ-bedip)]2 (X = Cl, Br, I, CH3) species. Chelation is observed in all the remaining complexes. The molecular structures of [PtX(CH3)(μ-bedip)]2 (X = Br, I) and [PtI(CH3)3(bedip)] are also determined
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