Umsetzungen von ω-alkenylsubstituierten Zirconocendichloridkomplexen mit n-Alkyllithiumverbindungen in Gegenwart von Alkenen bzw. Alkinen

The reaction of ω-alkenyl substituted zirconocene dichloride complexes with two equivalents of n-butyllithium is strongly influenced in the presence of alkenes and alkynes. Metallacyclic zirconocene complexes of novel structures are obtained. The additives alkenes and alkynes compete with the ω-alkenyl substituents and the intermediate 1-butene for the formation of a metallacyclic structure. The reaction of ω-alkenyl substituted zirconocene dichloride complexes with two equivalents of ethyllithium and n-hexyllithium gives analogous reactions and metallacycles as with n-butyllithium.     

Synthesis, structure, and ethene polymerisation catalysis of 1- or 2-silyl substituted bis[indenyl]zirconium(IV) dichlorides

The systematic syntheses of 1- and 2-substituted silylindenes, with a wide variety of substitution patterns on the silyl moiety, and their corresponding zirconocene dichlorides are presented. The rac- and meso-diastereomers of the 1-substituted zirconocene dichlorides can in most cases be separated. Instable zirconocenes were observed for certain substitution patterns. Two of the obtained zirconocene dichlorides, bis[2-(dimethylsilyl)indenyl]zirconium dichloride (4a) and bis[2-(trimethylsilyl)indenyl]zirconium dichloride (4b), were characterised by single crystal X-ray diffraction. On the basis of DFT results, the two compounds are geometrically similar, i.e. the additional methyl group on the silyl moiety only affects the conformational energy profile. Differences in their catalyst performance in the homopolymerisation studies with ethane are thus attributed to conformational control. For the remaining complexes, sterically less demanding silyl groups seem to be favoured with respect to the catalyst performance. All the 2-isomers have lower polymerisation activities than the unsubstituted bis[indenyl]zirconium dichloride/MAO system. Curiously, the rac-bis[1-(dimethylphenylsilyl)indenyl]zirconium dichloride/MAO system is found to be the most active catalyst in ethene homopolymerisations.     

Photolytic cyclopentadienyl ligand exchange between dicyclopentadienylzirconium dichloride and related systems.

Irradition of benzene solutions of zirconocene dichloride and zirconocene- d₁₀ dichloride with 313 nm light leads to the formation of zirconocene-d₅ dichloride with a quantum yield of 0.021 mol/Ei. The equilibrium constant is 2.8 Zirconocene dichloride exchanges a cyclopentadienyl ligand photolytically with bis(methylcyclopentadienyl)zirconium dichloride with the constant equal to 2.3.     

Kinetics of the complex-radical polymerization of methyl methacrylate in the presence of initiating metallocene systems

The kinetics of methyl methacrylate polymerization in the presence of benzoyl peroxide + metallocene (ferrocene, titanocene dichloride, and zirconocene dichloride) initiating systems is considered, and the effects of the nature and amount of metallocene in the system are reported. The polymerization is assumed to be a complex-radical process. The structure of the complex-radical sites of chain propagation and a scheme of their formation are deduced from quantum-chemical calculations.     

Ethylene polymerization using crosslinked polystyrene as support for zirconocene dichloride/methylaluminoxane

In this paper we report on a zirconocene dichloride/methylaluminoxane catalyst system supported on a crosslinked polystyrene in order to provide ethylene polymerization catalysts for gas phase or slurry processes. Our novel approach uses the Diels‐Alder reaction of cyclopentadiene functions as the final, cross‐linking synthetic step. This provides polymer supported zirconocene catalysts with a homogeneous distribution of active sites. The catalysts were shown to be highly active and to form spherical beads as proven by scanning electron microscopy.     

Zirconocene Dichloride–Catalyzed Pinacol Coupling of Aromatic Aldehydes and Ketones

The reductive coupling of aromatic aldehydes and ketones has been achieved using a catalytic amount of zirconocene dichloride in the presence of magnesium metal and chlorotrimethylsilane in THF at room temperature to afford the corresponding 1,2‐diols in good yields and diastereoselectivity.     

Zirconocene-catalyzed alkylative dimerization of 2-methylene-1,3-dithiane via a single electron transfer process to provide symmetrical vic-bis(dithiane)s

A mixture of tertiary alkyl halide and 2-methylene-1,3-dithiane was treated with butylmagnesium bromide in the presence of a catalytic amount of zirconocene dichloride. The reaction resulted in alkylative dimerization to yield the corresponding vic-bis(dithiane). The reaction would proceed as follows. A single electron transfer from low-valent zirconocene to alkyl halide would generate the corresponding alkyl radical. The radical adds to 2-methylene-1,3-dithiane to afford the corresponding radical stabilized by the two sulfur atoms. A couple of the stable radicals finally undergo dimerization.     

Zirconocene-promoted synthesis of substituted tetrahydropyrans

Zirconocene reagents derived from zirconocene dichloride and two equivalents of butyllithium react with allylic, homoallylic diene ethers. Hydrolysis of the reaction products yields substituted tetrahydropyrans. The reaction is postulated to occur via cyclization of the diene to form a zirconacyclopentane. This cyclization occurs without allylic rearrangement.     

Complex-radical polymerization of methyl methacrylate in the presence of metallocenes

The effects of the nature of metallocene (ferrocene, titanocene dichloride, and zirconocene dichloride) and its content in benzoyl peroxide-metallocene initiating systems on the kinetics of polymerization of methyl methacrylate have been studied. The kinetic features of polymerization and changes in the molecular characteristics of poly(methyl methacrylate) indicate that the process occurs via the complex-radical mechanism. On the basis of quantum-chemical calculations, a scheme describing the formation of complex-radical centers of chain propagation for the benzoyl peroxide-ferrocene system is proposed.     

Polymerization and copolymerization of ethene initiated with disiloxane-bridged biscyclopentadienylzirconium complexes and methylaluminoxane

The disiloxane-bridged zirconocene complexes, tetramethyldisiloxanediylbis (cyclopentadienyl)zirconium dichloride and tetramethyldisiloxanediylbis(cyclopentadienyl) dimethylzirconium initiate the homopolymerization of ethene as well as the copolymerization of ethene and α-olefin with a modified methylaluminoxane as cocatalyst. The catalyst systems give resonable activity but the molecular weight of polyethene decreases drastically with increasing polymerization temperature.     

二氯二茂锆取代芳肟的合成与结构

二氯二茂锆与等当量的各种芳肟的钠盐在二氯甲烷中反应，得到１０种二氯二茂锆取代衍生物，均为新化合物。这些化合物对水、空气和光敏感，稳定性差。对它们的合成及ＩＲ，＾１ＨＮＭＲ进行了初步讨论。     

Cp2TiCl2及Cp2ZrCl2存在下炔烃还原偶联反应的区域选择性

经五元钛、锆杂环,由非对称炔烃,区域选择性地合成了一系列立体专一的(Z,Z)-四芳基-1,3-丁二烯,并通过物理、化学方法证明了产物结构.     

A Sterically Hindered Zirconocene Complex (1,2-Ph2C5H3)2ZrCl2:Synthesis, Structure and Properties as Olefin Polymerization Catalyst

SinceKaminskyeIal.discoveredthehighlyactivezirconocenedich1oride/methyl-aluminoxane(MAO)catalyticsystemforolefinpolymerization',intensiveresearchworkhasbeenfocusedondevelopingnewgroup4metal1ocenecatalystsforimprovingcatalystactivitiesandpolymerproperties"'.Inthedevelopmentofnewmetallocenecatalystsystems,liganddesignandmodificationhaveplayedanimportantrole.lthasbeenknownthatevenminormodificationofagivenligandframeworkcouldresultinsignificantchangesincatalystactivitiesandpolymerproperties'.Int…     

Sterically demanding bis(2-silylindenyl)zirconium(IV) dichlorides as polymerisation catalyst precursors

A set of different 1- and 2-silyl-substituted zirconocene dichloride/MAO catalyst systems was investigated with respect to their performance in ethene/1-hexene copolymerisations. In-depth studies of bis(2-dimethylsilylindenyl) zirconium(IV) dichloride ( 1 ) revealed a multi-site behaviour, illustrating sensitivity to the reaction temperature and the comonomer mole fraction. Surprisingly, an upper limit is observed for the latter, leading to complete catalyst inhibition. Analysis of the chain termination processes implies the possibility of a predominant, although in general less favourable, β-hydride elimination route under certain polymerisation conditions.     

A one-step synthesis of bis(h5-cyclopentadienyl)zirconacyclopentadiene compounds

Bis(h⁵-cyclopentadienyl)zirconacyclopentadiene complexes were prepared by reduction of zirconocene dichloride in THF with magnesium in the presence of various alkynes. Hydrolysis leads to the corresponding (E,E)-butadiene derivatives.     

A facile synthesis of 2-oxo-cyclopentenylphosphonates by carbonylation of zirconacyclopentenylphosphonate with oxalyl chloride

Addition of oxalyl chloride to zirconacycles prepared from 1-alkynylphosphonates 1 zirconocene dichloride, and two equivalents of EtMgBr smoothly produced novel 2-oxo-cyclopentenylphosphonates 6 in 58–81% isolated yields in the presence of a copper catalyst.     

Palladium-catalyzed arylation of cyclopentadienes

Cyclopentadiene and metallocenes, typically zirconocene dichloride, are suitable substrates for multiple arylations with aryl bromides in palladium-catalyzed reactions. Thus, various aryl bromides bearing either an electron-donating or an electron-withdrawing substituent can react with these substrates to afford the corresponding 1,2,3,4,5-pentaaryl-1,3-cyclopentadienes in a single preparative step. Derivatives of cyclopentadiene, including di- and trisubstituted cyclopentadienes, and indene are arylated in a similar fashion.     

Donor- and acceptor-modified metallocene-based homogeneous Ziegler-Natta catalysts

The polymerization kinetics of propene polymerization using metallocene/methylaluminoxane (MAO) homogeneous catalysts have been investigated to explore the role of donor/acceptor interactions and to enhance the catalyst productivities. In the case of the non-stereospecific Cp₂ZrCl₂/MAO model system it has been demonstrated that, in addition to the well known irreversible deactivation, reversible deactivations, which are second order relative to the zirconium active site concentration, account for the decay of the polymerization rate. While MAO injection during polymerization enhances the polymerization rate, zirconocene addition deactivates the catalyst which can be reactivated by injecting additional MAO. A sequence of dynamic equilibria involving the formation of active cationic metallocene intermediates as well as inactive zirconocene species, e.g., zirconocene dimers, is proposed. Lewis base and Lewis acid additives have been added as probes to examine the role of such equilibria in the case of metallocene-based catalyst systems such as MAO-activated Cp₂ZrCl₂, racemic ethylenebisindenyl zirconium dichloride (EBIZrCl₂), and racemic ethylenebis (4,5,6,7-tetrahydroindenyl) zirconium dichloride (EBTHIZrCl₂). While the conventional donors such as 2,6-ditert.butyl-4-methylphenol (BHT) and 2,2,6,6-tetramethylpiperidine (TMP) reduce catalyst productivities, even at very low donor/Al molar ratios, increasing propene concentration and addition of trimethylboroxine (TMB) substantially enhance catalyst productivities and affect molecular weights of the polypropylene produced with metallocene/MAO catalysts.     

Composition distribution of ethylene or propylene–norbornene copolymers obtained with zirconocene catalysts

Copolymerization of ethylene or propylene and norbornene (NB) was carried out with stereospecific zirconocene catalysts rac‐ethylenebis(indenyl)zirconium dichloride, rac‐dimethylsilylenebis(indenyl)zirconium dichloride ( 2 ), rac‐dimethylsilylenebis(2‐methylindenyl)zirconium dichloride, and diphenylmethylene(cyclopentadienyl)(9‐fluorenyl)zirconium dichloride combined with cocatalysts at 40 °C. Temperature‐rising elution fractionation of the copolymers was carried out with cross‐fractionation chromatography with o‐dichlorobenzene as a solvent, and a broad distribution of the copolymer composition was detected. The fraction eluted at lower temperature contained higher NB. The effect of the polymerization time was examined in the ethylene–NB copolymerization with catalyst 2 , and the higher‐temperature elution fraction increased with increasing polymerization time. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 441–448, 2003     

Radical Copolymerization of Methyl Methacrylate and Styrene in the Presence of Metallocenes

The effect of ferrocene and zirconocene dichloride on the rate and constants of copolymerization of methyl methacrylate with styrene was studied. The results obtained suggest that the metallocenes in the elementary steps of the reaction.__________Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 2, 2005, pp. 297–300.Original Russian Text Copyright © 2005 by Yumagulova, Kolesov, Monakov.