Search results for "Metallocene"
showing 10 items of 109 documents
Electrochemical study of dinuclear ruthenium(II)—arene compounds: Electrogeneration of Ru(II)—Ru(I) species
1987
Abstract The preparation and characterization of Ru(II)—arene compounds [{RuCl2(p-cym)}2(μ-L-L)] where p-cym = p-MeC6H4CHMe2; and L-L = diphenylphosphinomethane (I), 1,1′-bisdiphenylphosphinoferrocene (II), pyrazine (III) and 4,4′-bipyridine (IV), are described. Electrochemical data for these compounds obtained by cyclic voltammetry and coulometry are reported. The electrochemical reduction of compounds I or II yields ruthenium(O) species. However, compounds III or IV containing ligands with delocalized Π orbitals undergo one-electron reduction. The ESR signal detected during the electrolysis of compounds III or IV is consistent with one delocalized electron through the whole dinuclear unit.
Zum Ligandenaustausch des Ferrocens mit Methyl- und Ethyl-substituierten Naphthalinen
1988
Abstract The replacement of a Cp ligand of ferrocene by each of ten unsymmetrically substituted naphthalenes yields pairs of complex ions [arene-FeCp] + , which have been identified from their 1 H NMR spectra. The influence of the substituent on the ratio of the two isomers, and its temperature dependence implies a complex reaction mechanism involving an η 2 -bound intermediate of the associated naphthalene. The proton resonances of the alkyl groups of the naphthalenes are shifted to lowfield by complexation; this effect decreases with increasing distance from the iron. The resonance shift of the arene protons has a different sign for the complexed (highfield) and the uncomplexed part (lowf…
Rare earth metal complexes that contain linked amido-cyclopentadienyl ligands: ansa-metallocene mimics and “constrained geometry” catalysts
2003
A survey of group 3 metal complexes that contain a linked amido-cyclopentadienyl ligand is given. Originally designed as ansa-metallocene analogues for the development of single-component olefin polymerization catalysts, variations in the metals and ligand substituents have allowed the synthetic access to new rare earth metal complexes including olefin polymerization initiators, divalent complexes and heterobimetallic metallocenes. The linked amido-cyclopentadienyl ligands have made half-sandwich complexes of group 3 metals accessible in a more systematic manner and provided a better understanding of the electronic and steric constraints of chelating ligands for the larger rare earth metal …
Metallocene sulfide chemistry of niobium and tantalum: new insights into the formation of niobium-polysulfido complexes and synthesis, structure, and…
1992
The previously described reaction of Cp'2NbH3 (Cp' = t-BuC5H4) with S8 was investigated with regard to the kinetic stabilization of as yet elusive intermediates during the formation of the polysulfide complex Cp'4Nb2S9 (1). Therefore, the permethylated complex Cp*2NbS3H (2; Cp* = C5Me5) and the Ta complex Cp'2TaS2H (3) were synthesized in a related reaction and structurally investigated. Despite the problematic localization of the hydride atom during X-ray crystallographic studies, the molecules can be described in a proper manner: Characteristic of 2 and 3 are M(eta(2)-S2) cores to which either an SH (2) or a H (3) ligand is attached. Complex 3 is the first known tantalocene sulfide. It re…
Determination of zirconium traces in polymers by ICP-IDMS - a powerful and fast method for routine testing of zirconium residues in polyolefins
1999
Zirconium trace analyses play an important role for polyolefins produced by modern catalytic processes with zirconium metallocenes. A reliable and fast routine testing method by inductively coupled plasma isotope dilution mass spectrometry (ICP-IDMS) was therefore developed, which allows the determination of zirconium in polymers down to the low ng/g level. With respect to its precision, accuracy, and time-consumption this method is suitable for routine testing of production processes. A spike solution, enriched in the stable isotope 91Zr, was prepared and used for the isotope dilution procedure, which has the advantage of being an internal “one point” calibration method. The polyolefin sam…
Formation of arynezirconocenes from substituted diaryl bis (t-butylcyclopentadienyl) zirconium: application to the synthesis of new functionalizedort…
1991
The para-substituted diphenylzirconocenes [(t-BuCp)2Zr(p-C6H4R)2; R = Br, NMe2] (A) were easily obtained from the reaction of the appropriate organolithium reagent with bis(t-butylcyclopentadienyl)zirconium dichloride. Elimination of bromobenzene or N,N-dimethylaminobenzene from A by slight heating led to arynezirconocenes into which were inserted two equivalents of elementary chalcogens. As a result dichalcogenated zirconacycles [(t-BuCp)2ZrY2C6H3R; Y = S, Se] (B) were obtained. Complexes B constitute useful potential synthons in organic synthesis and a large family of new functionalized dichalcogenated benzenic compounds was prepared by reacting electrophiles. The structure of complexes B…
Synthesis and activity of zirconocene catalysts supported on silica-type sol-gel carrier for ethylene polymerization
2001
Synthesis and activity of bis(cyclopentadienyl)zirconium dichloride catalyst supported on unconventional silica-type material obtained in sol-gel process and activated by organoaluminium co-catalyst were studied. The effect of support modification conditions (thermal dehydration and/or modification by organoaluminium compound) and a type of co-catalyst on an activity of the catalytic system in ethylene polymerization and properties of resulting polymers were investigated and compared with results obtained earlier for vanadium catalysts supported on mentioned sol-gel carrier. The most appropriate method of the sol-gel silica-type support preparation is thermal pre-treating (200°C) followed b…
Improvement of biphasic polymerization by application of binary ionic liquid mixture
2013
Abstract The mixture of two ionic liquids, 1- n -butyl-3-methylimidazolium and 1-(2-phenylethyl)-3-methylimidazolium chloroaluminates, [C 4 -mim][AlCl 4 ] and [PhC 2 -mim][AlCl 4 ], were applied as a medium to immobilize the Cp 2 TiCl 2 titanocene catalyst for biphasic ionic liquid/hexane ethylene polymerization. The system makes possible to perform the reaction at lower temperatures, below the melting temperature of the aralkyl ionic liquid. A better separation of the ionic liquid phase was observed and an easier mass transfer of the polymer product from the ionic liquid to the hexane phase was obtained. The polyethylene reveals bimodal distribution of molecular weight. It is characterized…
(Co)polymerization behavior of supported metallocene catalysts. I. Ligand and substituent effect
2005
Ethylene polymerization and its copolymerization with 1-hexene with a set of supported metallocene catalysts were studied. As a carrier, the complex of mag- nesium chloride with tetrahydrofuran, which was previously pretreated with a triiso- butylaluminium (TIBA), was used. The investigated metallocene compound differs in the metal type (Zr or Ti), the nature of the alkyl substituent in the cyclopentadienyl ring, and the type of ligand (Cp or Ind). The effect of catalyst composition on the anchored metal content, catalyst activity, comonomer reactivity, and polymer proper- ties was investigated. The results obtained with supported catalysts were compared with those obtained with their homog…
(Co)polymerisation Behaviour of Supported Metallocene Catalysts: Carrier Effect
2006
The polymerisation and copolymerisation of ethylene with 1-hexene over metallocene catalysts L 2 ZrCl 2 / MAO (L = Cp, n-BuCp, t-BuCp, i-PrCp, Me 5 Cp) supported on different types of carriers (MgCl 2 (MeOH) 6 or silica with CH 3 surface groups obtained in the sol-gel process) were studied. It was demonstrated that both the metallocene structure and the type of inorganic support affected catalyst activity and polymer properties such as melting point, molecular weight and molecular weight distribution. The metallocene structure also determined comonomer incorporation, both for homogeneous and supported catalytic systems. When a catalyst is anchored on a support, it becomes less effective at …