Tentative Identification of the Reactive Species in the Reaction of Cp2 TiCl2 with Salts of Diacids

The tentative identification of the reactive species in the condensation of Cp₂ TiCl₂ with salts of diacids to form titanium polysters is made. The reactive species are believed to be the same for both aqueous solution and interfacial systems, i.e., R -CO₂ ^? and Cp₂ Ti²⁺ with reaction occurring in the aqueous phase. The condensation of Cp₂ TiCl₂ with disodium terephthalate in interfacial systems occurs via a pseudo-first-order reaction:

Rate = K[Cp₂ TiCl₂] The rate-determining step (s) is believed to be diffusion of CP₂ TiCl₂ into the aqueous layer and/or hydrolysis of Cp₂ TiCl₂     

Preparation of functionalized montmorillonites and their application in supported zirconocene catalysts for ethylene polymerization

Ethylene polymerization was carried out with zirconocene catalysts supported on montmorillonite (or functionalized montmorillonite). The functionalized montmorillonite was from simple ion exchange of [CH₃O₂CCH₂NH₃]⁺ (MeGlyH⁺) ions with interlamellar cations of layered montmorillonites. The functionalized montmorillonites [high‐purity montmorillonite (MMT)‐MeGlyH⁺] had larger interlayer spacing (12.69 Å) than montmorillonites without treatment (9.65 Å). The zirconocene catalyst system [Cp₂ZrCl₂/methylaluminoxane (MAO)/MMT‐MeGlyH⁺] had much higher Zr loading and higher activities than those of other zirconocene catalyst systems (Cp₂ZrCl₂/MMT, Cp₂ZrCl₂/MMT‐MeGlyH⁺, Cp₂ZrCl₂/MAO/MMT, [Cp₂ZrCl]⁺[BF₄]/MMT, [Cp₂ZrCl]⁺[BF₄]^?/MMT‐MeGlyH⁺, [Cp₂ZrCl]⁺[BF₄]^?/MAO/MMT‐MeGlyH⁺, and [Cp₂ZrCl]⁺[BF₄]^?/MAO/MMT). The polyethylenes with good bulk density were obtained from the catalyst systems, particularly (Cp₂ZrCl₂/MAO/MMT‐MeGlyH⁺). MeGlyH⁺ and MAO seemed to play important roles for preparation of the supported zirconocenes and polymerization of ethylene. The difference in Zr loading and catalytic activity among the supported zirconocene catalysts is discussed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1892–1898, 2002     

A metallocene catalyst system for olefin polymerization using a heteropolyacid as the counter-anion

Polymerization of ethylene and propene were conducted with bis(cyclopentadienylzirconium dichloride) (Cp₂ZrCl₂) and ethylenebis(1-indenyl)zirconium dichloride (Et(Ind)₂ZrCl₂) combined with trialkylaluminium compounds using heteropolyacids as the counter-anions, giving linear polyethylene and isotactic polypropene, respectively. No polymer was obtained when using Cp₂Zr(CH₃)₂ instead of Cp₂ZrCl₂. The mechanism of the formation of active species is briefly discussed on the basis of these results.     

Generation of active site confined inside supercage of NaY zeolite on a nano-scale and its ethylene polymerization

To generate an active site that consisted of one Cp₂ZrCl₂ molecule and 1-2 MAO molecules inside supercage of NaY zeolite, two preparation ways for supported catalyst were estimated. First, higher concentration of MAO and Cp₂ZrCl₂, and long reaction time were introduced during the preparation of supported catalyst. It showed activity in ethylene polymerization without any additional MAO. It indicates that Cp₂ZrCl₂ coordinated with only 1-2 MAO molecules could be an active site due to the fact that supercage has nano-scaled diameter of supercage, 1.2 nm, and it could contain only 1-2 MAO molecules inside it theoretically. In situ generation of active site between NaY/MAO and homogeneous Cp₂ZrCl₂ also showed experimental evidence that an active site was generated inside the supercage of NaY zeolite. It showed low activity with long activation time, suggesting the presence of a diffusion effect of Cp₂ZrCl₂ in the pore of NaY. However, NaY/Cp₂ZrCl₂ and homogeneous MAO system showed the characteristic PE polymerization with homogeneous catalyst, indicating that active site was not generated inside the supercage of NaY.     

Active center determination of ethylene polymerisation catalysts using a quenching method with tritiated methanol

The subject of this work is ethylene polymerisation using Kaminsky type catalysts: Cp₂MR₂=methylaluminoxane [M=Zr, W, Nb; R=Cl, CH₃]. Active center determination and kinetic studies of the (Cp₂WCl₂+methylaluminoxane) and Cp₂ZrCl₂+methylaluminoxane) systems are described, using a quenching method with tritiated methanol. The activity of the polymer was determined by liquid scintillation counting. We have found 0.5% and 87% of active centers, respectively for W and Zr system. The catalytic activity of complexes Cp₂WCl₂ and Cp₂NbCl₂ was compared with that of Cp₂ZrCl₂. The W and Nb complexes are found to be less active than the Zr complex.     

Surface chemistry of selected supported metallocene catalysts studied by DR‐FTIR,CPMAS NMR,and XPS techniques

Two supported metallocene catalysts (CS 1: PQ 3030/MAO/Cp₂ZrCl₂ and CS 2: PQ 3030‐BuGeCl₃/MAO/Cp₂ ZrCl₂) were prepared by sequentially loading MAO and Cp₂ZrCl₂ on partially dehydroxylated silica PQ 3030. In catalyst CS 2, ⁿBuGeCl₃ was used to functionalize the silica. These catalysts were characterized by DR‐FTIR spectroscopy, CPMAS NMR spectroscopy, and XPS. Their catalytic performance was evaluated by polymerizing ethylene using the MAO cocatalyst and characterizing the resulting polymers by GPC. Both catalysts produced two metallocenium cations (Cation 1: [Cp₂ZrCl]⁺ and Cation 2: [Cp₂ZrMe]⁺) with comparable equilibrium concentrations and showed varying solid‐state electronic environments. The modified supports (PQ 3030/MAO and PQ 3030‐BuGeCl₃/MAO) acted as weakly coordinating polyanions and stabilized the above cations. BuGeCl₃ did not affect the solid‐state electronic environment. However, it increased the surface cocatalyst to catalyst molar ratio (Al:Zr), acted as a spacer, increased catalyst activity, and enhanced chain‐transfer reactions. The separately fed MAO cocatalyst shifted the equilibrium between Cation 1 and Cation 2 toward the right. Consequently, more Cation 2 was generated, which acted as the effective and active single‐site catalytic species producing monomodal PDI. Copyright © 2006 John Wiley & Sons, Ltd.     

Effect of substituents on the catalytic properties of bis(cyclopentadienyl) zirconocene dichlorides in polymerization of ethene

Comparative analysis of catalytic activity of substituted bis(cyclopentadienyl)zirconium dichlorides with the general formula (R _n Cp)₂ZrCl₂ (Cp₂ZrCl₂, (MeCp)₂ZrCl₂, (PrⁱCp)₂ZrCl₂, (Prⁱ ₂Cp)₂ZrCl₂, (BuⁿCp)₂ZrCl₂, (BuⁱCp)₂ZrCl₂, (Bu^tCp)₂ZrCl₂, Cp^* ₂ZrCl₂ (Cp^*=Me₅C₅), (Me₃SiCp)₂ZrCl₂, (cyclo-C₆H₁₁Cp)₂ZrCl₂, and [(cyclo-C₆H₁₁)₂Cp]₂ZrCl₂) in ethene polymerization using polymethylalumoxane as the cocatalyst was performed. The molecular mass characteristics of the polyethylene samples obtained were determined. A linear correlation of the specific activity of the catalysts and the turnover number with the electronic and steric characteristics of substituents at the Cp ring of the complexes was established for the first time. Analysis of the polymerization kinetics and the obtained correlation between the specific activity of the complexes and molecular mass characteristics of the polyethylene samples suggest that alkyl substituents participate in reactions responsible for the restriction of the polymer chain growth and regeneration of the active center. These interactions most likely involve associates of AlMe₃ with polymethylalumoxane molecules.     

Triboluminescence of zirconium η<Superscript>5</Superscript>-complexes

This work describes a comparative study of tribo- and photoluminescence of metallocenes (Cp₂HfCl₂, Cp₂TiCl₂, Cp₂ZrCl₂, (CpMe)₂ZrCl₂, rac-Me₂C(3-Bu^t-Cp)₂ZrCl₂, Ind*₂ZrCl₂). Occurring under mechanodestruction of polycrystals, triboluminescence of zirconium bis-cyclopentadienyl complexes, Cp₂ZrCl₂, (CpMe)₂ZrCl₂, and rac-Me₂C(3-Bu^t-Cp)₂ZrCl₂ has been revealed for the first time. The triboluminescence spectrum in air is similar to the photoluminescence spectrum of zirconocene polycrystals. The triboluminescence spectrum does not show *N₂ luminescence. Ne and Ar lines are observed in the triboluminescence spectrum in the atmosphere of these gases. An increase in the number of substituents in zirconocene ligands leads to a bathochromic shift of the emission band maximum in triboluminescence spectra of the complexes. Possible mechanisms of zirconocene triboluminescence excitation are discussed.     

Unusual features of ethylene copolymerization reactions with binary metallocene catalysts

Ethylene/1-hexene copolymers produced with MAO-activated binary metallocene catalysts, such as combinations Cp₂ZrCl₂ + (Me₅Cp)₂ZrCl₂, (Ind-H₄)₂ZrCl₂ + (Me₅Cp)₂ZrCl₂, Cp₂ZrCl₂ + Cp₂TiCl₂, etc., contain three types of components. Two of the components can be attributed to active centers derived from each individual metallocene complex, and one or two materials are produced with different types of active center. Some of the binary catalysts generate the three components in comparable proportions, whereas other catalysts produce copolymers with one dominant component, which does not resemble the copolymers produced with the individual complexes. A mechanism is proposed for the formation of the “new” copolymer materials.     

Synthesis of zirconium poly-O-amidoximes

Synthesis of zirconium poly-O-amidoximes was affected by using both interfacial and aqueous solution techniques. Reaction is rapid. The yield for the synthesis of analogous titanium product is Cp₂ZrCl₂ > Cp₂TiCl₂ which is consistent with that predicted by the hard-soft acid–base theory.     

Copolymerization of poly(propylene) macromonomer and ethylene with metallocene catalysts

Copolymerization of ethylene and poly(propylene) macromonomer(PPM) with Mn⇋710 was conducted with the (t-butylamido)dimethyl(tetramethyl-η⁵-cyclopentadienyl)silanetitanium dichloride(CGC-Ti), ethylenebis(tetrahydroindenyl)zirconium dichloride(Et[IndH₄]₂ZrCl₂), bis(cyclopentadienyl)zirconium dichloride(Cp₂ZrCl₂) and bis(cyclopentadienyl)titanium dichloride(Cp₂TiCl₂) catalysts using methylaluminoxane as cocatalyst. From the detail analysis of resulting copolymers by DSC, IR and ¹³C NMR, it was proved that PPM is copolymerized with ethylene to give poly(ethylene-co-PPM). The ability of incorporating PPM in the copolymer was found to increase in the following order: Cp₂ZrCl₂ «Cp₂TiCl₂ < Et[IndH₄]₂ZrCl₂ «CGC-Ti.     

Comparison of the catalytic activity of Ziegler-type catalysts based on Cp2ZrCl2 and (Cp2ZrCl)2O

The rates of ethylene polymerization catalyzed by Cp₂ZrCl₂-polymethylalumoxane and (Cp₂ZrCl)₂O-polymethylalumoxane are equal. According to NMR and ESR spectral data, the same precatalyst, presumably Cp₂ZrMe₂, is formed in both systems by the action of AlMe₃. This accounts for the equal catalytic activity of the systems based on Cp₂ZrCl₂ and (Cp₂ZrCl)₂O. A scheme of reactions resulting in cleavage of the Zr-O-Zr bridge is proposed and confirmed by spectroscopic data.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2104–2107, December, 1993.     

Metallocene ion pairs: A direct insight into the reaction equilibria and polymerization by 13C NMR spectroscopy

The reaction equilibria of Cp₂Ti¹³CH₃Cl and Cp₂Ti(CH₃)₂ with AlMe₃ (TMA) and/or methylaluminoxane (MAO) have been investigated by ¹³C NMR. Several adducts have been identified. A study of the ¹³C 90% enriched ethylene polymerization in an NMR tube in the presence of the above catalytic systems, in the most experimentally significant conditions, and a comparison of the NMR data with the catalytic activity have been made as well. It has been shown that: i) some species are side products, inactive for addition ethylene polymerization; ii) active cation-like species such as Cp₂TiMe⁺Cl·[AlMeO]_n- and Cp₂TiMe⁺Me·[AlMeO]_n- are formed in titanocene-MAO systems. Concerning the role of AlMe₃, contained in MAO solutions, it has been shown that: a) AlMe₃ is mainly bound to MAO; b) if some “free” AlMe₃ exists in solution it is not the actual cocatalyst in the metallocene-MAO based catalytic systems; c) the amount of AlMe₃ influences either active or inactive species.     

Metallocene/mao polymerization catalysts supported on cyclodextrin

By treating cyclodextrin(CD) with methylaluminoxane (MAO such as PMAO or MMAO) or trimethylaluminium (TMA) followed by Cp₂ZrCl₂, CD/PMAO/Cp₂ZrCl₂, CD/MMAO/Cp₂ZrCl₂ and CD/TMA/Cp₂ZrCl₂ catalysts were prepared. The catalysts were analyzed by ¹³C-CP/MAS NMR spectrometer and ICP to examine the structure of catalyst and content of Zr and Al. Ethylene polymerization was conducted with MAO or TMA as cocatalyst. Styrene polymerization was also carried out with α-CD/MMAO/Cp*TiCl₃ and α-CD/TMA/Cp*TiCl₃ catalysts. While the ordinary trialkylaluminium such as TMA as well as MAO can be used as cocatalyst for ethylene polymerization, only MAO could initiate the styrene polymerization with α-CD supported catalysts.     

Combined polymerization catalysis of nickel complex and zirconocene for branched polyethylene

The polymerization behavior of 2-(2′-pyridyl) quinoxaline nickel dibromide/Cp₂ZrCl₂/MAO system was investigated in three ways: the Ni catalyst was added first, followed by addition of Zr catalyst (method I); the Ni and Zr catalysts were added simultaneously (method II); and the Zr catalyst was added first, followed by addition of Ni catalyst (method III). Results of GC-MS, GPC,¹³C NMR and DSC investigations indicated that the properties of resulting polyethylene were greatly varied by changing feeding orders of the two catalysts. Decreasing Ni/Zr molar ratio or increasing polymerization temperature gave corresponding polyethylenes with less branches and higher melting point. Compared to the procedure using Cp₂ZrCl₂ catalyst only, the activity of Zr catalyst in those combined system decreased because of the competition of ethylene between the [Ni−C] and [Zr−C] active centers. In addition, other zirconocenes were also employed as copolymerization catalysts in the combined system with nickel complex. compared to Cp₂ZrCl₂ case, the ethyl-bridged Zr catalyst performed better for polymerization of ethylene while the Si-bridged Zr catalyst showed better copolymerization ability.     

Triazamethylenemethane complexes of zirconium and tantalum

Addition of [Li₂(THF)₄][C(NPh)₃] (2) to a THF solution of Cp^*ZrCl₃ (Cp^*=C₅Me₅) yields, after recrystallization in Et₂O, the zwitterionic species Cp^*[C(NPh)₃]ZrCl₂Li(Et₂O)(THF) (3). Treating 3 with excess methylaluminoxane (MAO) affords a homogeneous Ziegler–Natta catalyst for ethylene polymerization. Addition of LiNPh₂ to 3 allows for Cl substitution to give the new product Cp^*[C(NPh)₃]Zr(NPh₂)ClLi(THF)₂ (4). A single crystal diffraction study of 4 reveals that the [C(NPh)₃] ligand is η²-bound. The group 5 complex Cp^*[C(NPh)₃]TaMe₂ (5) was prepared by addition of 2 to Cp^*TaMe₂Cl(OSO₃CF₃). The X-ray diffraction structure of 5 shows that the [C(NPh)₃] ligand is η²-bound to tantalum and that, when compared to 4, there is less electron delocalization across the inner core of [C(NPh)₃].     

Mechanism of Cp<Subscript>2</Subscript>ZrCl<Subscript>2</Subscript>-catalyzed olefin hydroalumination by alkylalanes

The composition of intermediates of the Cp₂ZrCl₂-catalyzed hydroalumination of α-olefins by isobutylalanes (HAlBuⁱ ₂, AlBuⁱ ₃, ClAlBuⁱ ₂) was studied by dynamic ¹H and ¹³C NMR pectroscopy. The reaction of Cp₂ZrCl₂ with isobutylalanes affords the complex (Cp₂ZrHCl·HAlBuⁱ ₂)₂ responsible for α-olefin hydroalumination.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 311–322, February, 2005.     

Metallocene-methylaluminoxane catalysts for olefin polymerization. V. Comparison of Cp2ZrCl2 and CpZrCl3

The ethylene polymerization by Cp₂ZrCl₂/MAO (Cp = η⁵: cyclopentadienyl; MAO = methyl aluminoxane) and CpZrCl₃/MAO have been studied. The MW and PD (= M _w/M _w) of polymers obtained after 2.5-60 min are the same, which indicate short chain lifetime. The values of rate constants for Cp₂ZrCl₂ at 70°C are: k_p = 168?1670 (M s)^?1 and k_tr^A1 = 0.012-0.81 s^?1 depending upon [Zr] and [MAO,] k_tr^β = 0.28 s^?1, and k_tr^H = 0.2 M^?1 torr^?1/2 s^?1. These chain transfer rate constant values are two to three orders of magnitude greater than the corresponding values found for MgCl₂ supported titanium catalysts. One significant difference between the heterogeneous and homogeneous catalysts is that the former decays according to an apparent second order kinetics, whereas the latter decay is simple first order at 0°C and biphasic first order at higher temperatures. The productivity of the catalysts depends weekly on temperature while the MW decreases strongly with increase of temperature above 30°C. All the active species were formed upon mixing Cp₂ZrCl₂ with MAO while it took up to 20 min for the CpZnCl₃/MAO system. The productivity of the former increase more strongly with the decrease of [Zr] than the latter. Otherwise, the two catalyst systems have all their kinetic parameters differing less than a factor of two.     

Shape and diffusion of the monomer‐controlled copolymerization of ethylene and α‐olefins over Cp2ZrCl2 confined in the nanospace of the supercage of NaY

Cp₂ZrCl₂ confined inside the supercage of NaY zeolites [NaY/methylaluminoxane (MAO)/Cp₂ZrCl₂] exhibited the shape and diffusion of a monomer‐controlled copolymerization mechanism that strongly depended on the molecular structure of the monomer and its size. For the ethylene–propylene copolymerization, NaY/MAO/Cp₂ZrCl₂ showed the effect of the comonomer on the increase in the polymerization rate in the presence of propylene, whereas the ethylene/1‐hexene copolymerization showed little comonomer effect, and the ethylene/1‐octene copolymerization instead showed a comonomer depression effect on the polymerization rate. Isobutylene, having a larger kinetic diameter, had little influence on the copolymerization behaviors with NaY/MAO/Cp₂ZrCl₂ for the ethylene–isobutylene copolymerization, which showed evidence of the shape and diffusion of a monomer‐controlled mechanism. The content of the comonomer in the copolymer chain prepared with NaY/MAO/Cp₂ZrCl₂ decreased by about one‐half in comparison with that of Cp₂ZrCl₂. A differential scanning calorimetry study on the melting endotherms after the successive annealing of the copolymers showed that the copolymers of NaY/MAO/Cp₂ZrCl₂ had narrow comonomer distributions, whereas those of homogeneous Cp₂ZrCl₂ were broad. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2171–2179, 2003     

Synthesis and properties of poly‐1‐olefins

The oligomerization and polymerization of 1‐pentene using Cp₂ZrCl₂, Cp₂HfCl₂, [(CH₃)₅C₅]₂ZrCl₂, rac‐[C₂H₄(Ind)₂]ZrCl₂, [(CH₃)₂Si(Ind)₂]ZrCl₂, (CH₃)₂Si(2‐methylbenz[e]indenyl)₂ZrCl₂, Cp₂ZrCl{O(Me)CW(CO)₅}, Cp₂ZrCl(OMe) and methylaluminoxane (MAO) has been studied. The degree of polymerization was highly dependent on the metallocene catalyst. Oligomers ranging from the dimer of 1‐pentene to polymers of poly‐1‐pentene with a molar mass M_w = 149000 g/mol were formed. Cp₂ZrCl{O(Me)CW(CO)₅} is a new highly active catalyst for the oligomerization of 1‐pentene to low molecular weight products. The activity decreases in the order Cp₂ZrCl{O(Me)CW(CO)₅} > Cp₂ZrCl₂ > Cp₂ZrCl(OMe). Furthermore, poly‐1‐olefins ranging from poly‐1‐pentene to poly‐1‐octadecene were synthesized with (CH₃)₂Si(2‐methyl‐benz[e]indenyl)₂ZrCl₂ and methylaluminoxane (MAO) at different temperatures. The temperature dependence of the molar mass can be described by a common exponential decay function irrespective of the investigated monomer.