Vanadium Modification Effects on the (SiO2/MgO/MgCl2)•TiClx Ziegler–Natta Polyethylene Catalyst

A novel vanadium‐modified (SiO₂/MgO/MgCl₂)·TiCl_x Ziegler–Natta ethylene polymerization catalyst with much better catalytic performance is successfully developed. The catalyst is prepared by co‐impregnation of aqueous solution of water‐soluble magnesium and vanadium compounds on SiO₂, and a supported thin layer of magnesium and vanadium oxides is formed over the surface of SiO₂ after high temperature calcination in dry air, followed by further reaction with titanium tetrachloride to synthesize the magnesium dichloride carrier in situ and to support the titanium species simultaneously. By characterization of the catalysts and the polymers and investigation of the polymerization behaviors, it is found that compared with the original (SiO₂/MgO/MgCl₂)·TiCl_x ZN catalyst, the introduction of vanadium species induce improved catalytic performance with 27% higher activity, 48% higher hydrogen response, and 60% higher 1‐hexene incorporation ability with better short chain branch distribution.

     

Organometallic vanadium-based heterogeneous catalysts for ethylene polymerization. Study of the deactivation process

Slurry polymerizations of ethylene over vanadium catalysts (based on VCl₄ and VOCl₃) and their MgCl₂(THF)₂-supported equivalents were studied. Unsupported vanadium catalysts were found to be unstable while the vanadium active sites deposited on the MgCl₂(THF)₂ complex are stable. A sharply outlined correlation was found between the concentration of vanadium(III) and catalyst productivity. The high activity and stability of the vanadium catalyst when supported on the magnesium complex is attributed to the increase of resistance to reduction of active vanadium(III) to inactive vanadium(II) by an organoaluminium co-catalyst.     

Ethylene polymerization with a supported vanadium catalyst obtained by the molecular deposition method

An active-phase monolayer has been deposited on SiO₂ using replacement of the surface OH groups by VOCl₃ vapour. The amount of vanadium fixed on the SiO₂ surface depends on the initial concentration of the silanol groups and ranges from 3.36 to 1.43%. In combination with diethyl aluminium chloride, the products are active catalysts for ethylene polymerization. The effects of the reaction conditions (the time of catalyst-complex formation, the catalyst life time and the temperature of polymerization) as well as the effect of the vanadium content, the A1:V ratio and the presence of diphenyl magnesium on the activity of the catalyst system have been investigated. The catalyst activity was found to depend strongly on the amount of vanadium fixed on the support surface. The maximum productivity obtained is about 22,000 gPE/g vanadium. Some basic characteristics of the synthesized polymer such as tensile strength, elongation at break, density and crystallization degree are given.     

Untersuchungen an katalytisch aktiven Oberflächenverbindungen. XI. Einfluß der Topologie der Silanolgruppen auf die Bildung von Vanadiumoxidclustern auf SiO2-Oberflächen

Studies on Catalytically Active Surface Compounds. XI. Influence of the Topology of Silanol Groups on the Formation of Vanadium Oxide Clusters on SiO₂ Surfaces Interaction of VOCl₃ dissolved in CCl₄ with silanol groups of Aerosil gives rise to reaction products, the Cl/V-ratio of which depends on thermal pretreatment of Aerosil and the amount of the vanadium fixed on the surface. Geometrically different arrangements of the silanol groups (centers) show kinetically differing behaviour, thus giving the possibility to establish a mathematic model for the interpretation of experimental data. Quantitative estimation of the population with silanol groups depending on the annealing temperature is achieved and correlated with the existence of two vanadium oxide surface species which differ with respect to their catalytic activity.     

Synthese,Kristallstruktur, Elektronenstruktur,spektroskopische und magnetische Eigenschaften von [VOCl2{P(SiMe3)3}2]: Ein Phosphankomplex mit fehlgeordneter VOCl2-Einheit

Synthesis, Crystal Structure, Electronic Structure, Spectroscopic and Magnetic Properties of [VOCl₂{P(SiMe₃)₃}₂]: A Phosphane Complex with a Disordered VOCl₂ Group VOCl₃ reacts with P(SiMe₃)₃ to form blue green crystals of [VOCl₂{P(SiMe₃)₃}₂] ( 1 ). The X-ray crystal structure analysis of 1 (cubic space group P2₁3: a = 1541.4(1) pm, Z = 4) reveals a slightly distorded trigonal bipyramidal coordination environment for the disordered vanadium(IV) center. Density functional calculations on the compound [VOCl₂{P(SiH₃)₃}₂] ( 2 ) are in accord with this observation. 1 has been characterized by ESR, vibrational (IR and Raman) and electronic absorption spectroscopy and magnetic measurements. The ESR spectra of 1 in a toluene solution (293 K and frozen solution at 6 K) exhibit hyperfine interactions of the unpaired electron with the ⁵¹V center (I = 7/2) and the ³¹P centers (I = 1/2) of the two equivalent phosphane ligands. The ligand-field transitions of the VOCl₂{P}₂ chromophore observed in the electronic absorption spectrum have been assigned on the basis of density functional calculations on 2 .     

Modification of the (SiO<Subscript>2</Subscript>/MgO/MgCl<Subscript>2</Subscript>)·TiCl<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Ziegler-Natta polyethylene catalysts using the third metal elements

Various (SiO₂/MgO/MgCl₂)·TiCl _x Ziegler-Natta catalysts modified by the third metal elements were synthesized by the co-impregnation of water-soluble magnesium and the third metal salts. Several key factors including the electronegativity of the third metal elements, catalyst performances in ethylene homo-polymerization, ethylene/1-hexene copolymerization and hydrogen response were systematically investigated. Both the catalyst performance and the polymer properties are influenced by the introduction of the third metal elements. Compared with the unmodified (SiO₂/MgO/MgCl₂)·TiCl _x Ziegler-Natta catalyst, activity and 1-hexene incorporation are enhanced by the introduction of zirconium, vanadium, aluminum and chromium, while deteriorated by the addition of ferrum, nickel, molybdenum and tungsten. Correlations of the catalyst activities and 1-hexene incorporation ability with the electronegativity of the third metal elements are discovered. It is found that the lower electronegativity of the third metal elements leads to the catalyst with higher activity and higher α-olefin co-polymerization ability. The polyethylene produced by a nickel modified catalyst showed broad molecular weight distribution (MWD) and the lowest average molecular weight (MW), while by using a ferrum modified catalyst, the resulting polyethylene had the highest MW, reaching the ultra-high MW area. Vanadium and chromium modified catalysts demonstrated the best hydrogen response.     

Tetrahedral Coordination in the First Structurally Characterized Dichlorooxovanadium(V) Alkoxide

Reaction of VOCl₃ with 2‐phenoxyethanol in n‐hexane in a 1:1 fashion gives dichlorooxo(2‐phenoxyethanolato)vanadium(V). HCl elimination yields the orange vanadium(V) complex, which is the first structurally characterized dichlorooxovanadium(V) alkoxide. The structure analysis reveals an unexpected tetrahedral coordination around the vanadium atom in the monomeric compound. Alcoholysis and hydrolysis reactions of [VOCl₂(OCH₂CH₂OPh)] are monitored by ⁵¹V NMR spectroscopy. Activated with Me₃SiCH₂MgCl or ⁿBu₂Mg the complex catalyses the polymerisation of styrene.     

Vanadium-based Ziegler-Natta catalyst supported on MgCl2(THF)2 for ethylene polymerization

A supported magnesium-vanadium-aluminium catalyst was prepared by depositing –with the use of a milling technique–VOCl₃ on the MgCl₂(THF)₂ support and subsequent activation with diethylaluminium chloride. Catalytic activity of the obtained system for ethylene polymerization was evaluated as a function of Mg/V and Al/V ratios as well as catalyst ageing time and polymerization temperature. High concentrations of THF in the catalytic system and considerable excess of an organoaluminium co-catalyst were found to have no deactivating action on vanadium active sites. The catalyst obtained is stable and its activity for ethylene polymerization is high. It yields polyethylene with higher molecular weight and higher melting point than offered by the materials produced with the use of a corresponding unsupported vanadium catalyst or a titanium-based system on the same magnesium support. Kinetic investigations confirmed stability of this catalyst irrespective of its concentration in the polymerization medium or of monomer concentration. Moreover, analysis of the kinetic findings revealed that over 80% of vanadium employed forms active polymerization sites.     

Effects of MgCl2 Crystallographic Structure on Active Centre Formation in Immobilized Single‐Centre and Ziegler–Natta Catalysts for Ethylene Polymerization

The ability of a MgCl₂ support to activate a transition metal catalyst has been found to depend both on the crystallographic structure of the support and on the nature of the catalyst. A high degree of crystallographic disorder can be very effective for the immobilization and activation of titanium and vanadium complexes, but is not necessarily effective for zirconocene activation. A highly disordered support prepared by the reaction of MgBu₂ with HCl gave high activity with TiCl₄ but low activity with (n‐PrCp)₂ZrCl₂. High polymerization activities with the zirconocene were only obtained with supports of type MgCl₂/AlR_n(OEt)_3−n prepared from the reaction of AlR₃ with MgCl₂ · 1.1EtOH. These supports are characterized by additional peaks in the X‐ray diffraction pattern, indicating the presence of a crystalline structure which is absent in the other supports and contains highly Lewis acidic sites able to generate the active metallocenium species.

     

Reactions of TiX4 and VOCl3 with P=S ligands

Summary The reactions of TiX₄ (X=Cl or Br) with the bidentate ligands, L, (Figure 1), yield hexacoordinate complexes TiX₄·L, whereas similar reactions with VOCl₃ lead to reduction of vanadium and give rise to vanadium(IV) pentacoordinate complexes, VOCl₂·L. All the compounds have been characterized by elemental analyses, i.r., visible and e.p.r. spectra. The occupation of the sixth coordination position in pentacoordinate complexes, VOCl₄·L, by different donor solvents, has been studied by means of visible and e.p.r. spectra.     

Nickel(II) and zinc(II) complexes with N-(5,6-dihydro-4H-1,3-thiazin-2-yl)-2-aminobenzimidazole (BzTz): Synthesis,spectral and structural characterization

The reaction of nickel and zinc chlorides and nitrates with the ligand N-(5,6-dihydro-4H-1,3-thiazin-2-yl)-2-aminobenzimidazole (BzTz) leads to the formation of the new complexes: [NiCl₂(BzTz)₂] (1), [Ni(NO₃)(BzTz)₂(H₂O)₃](NO₃) (2), [ZnCl₂(BzTz)₂] (3) and [Zn(NO₃)₂(BzTz)₂] (4). They have been characterized by spectroscopic methods (electronic, infrared and NMR) and magnetic susceptibility measurements. Additionally, the crystal structures of the complexes 1 and 3 have been determined by X-ray single-crystal diffraction. The ligand exhibits the N-benzimidazole coordination mode on interacting with the metal centers. The X-ray structure of the complexes 1 and 3 reveals a distorted tetrahedral coordination geometry around the metal center, with the metallic atoms coordinated to two chlorine atoms and two benzimidazole nitrogen atoms. These two complexes are isostructural, crystallizing in the monoclinic system and Cc space group. In complex 2 the geometry around the nickel atom could be described as a distorted octahedron whereas in case of complex 4 the zinc atom is in a distorted tetrahedral environment.     

Crystallographic report: Bis(3‐methyl‐2‐cyclopenten‐1‐one)dichloro‐oxovanadium(IV)

The crystal structure of the oxovanadium(IV) complex (CH₃C₅H₅O)₂VOCl₂ was determined. The molecule has trigonal bipyramidal geometry, with oxygen atoms of cyclopentenones in axial positions and oxygen and two chlorine atoms in equatorial positions. Copyright © 2005 John Wiley & Sons, Ltd.     

Ramanspektroskopische Untersuchungen an festem Vanadiumoxidtrichlorid VOCl3

A high resolution Raman spectrum of polycrystalline VOCl₃ at –196 °C has been recorded. Besides the chlorine isotope splitting a further splitting of 3 of the 6 fundamentals has been observed. The number of the Raman lines in the ₄ and ₆ region and the intensity ratios in the ₂ region will be explained by a factor group splitting of 2 VOCl₃ molecules in the unit cell.     

Magnesium chloride supported high mileage catalysts for olefin polymerization. XXI. Isospecific and regiospecific vanadium catalyst for propylene polymerization

Several CW–V catalysts were prepared by supporting VCl₄ on Mg Cl₂ with ethyl benzoate and CH–V catalysts prepared by reacting MgCl₂.ROH, phthalic anhydride, and VCl₄. These vanadium catalysts, activated with TEA (triethyl aluminum)/MPT (methyl-p-toluate) produce mainly (88–96%) refluxing n-heptane insoluble isotactic PP. The active site has $ k_{p,i} = 1580 \left( M {\rm s} \right)^{ - 1}, k_{tr,i}^{\rm A} = 2 \times 10^{ - 3} {\rm s}^{ - 1} , k_{tr}^{\rm H} = 3.8 \times 10^{ - 2} \left( {\rm torr} \right)^{ - {1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} {\rm s}^{ - 1}$ for the isospecific ones and $ k_{p,a} = 58 \left( M {\rm s} \right)^{ - 1} ,k_{tr,a}^{\rm A} = 3 \times 10^{ - 3} {\rm s}^{ -1}$ for the nonspecific sites. Catalyst of VCl₃ supported on MgCl₂ has comparable productivity as the VCl₄/MgCl₂ catalyst but catalyst of VCl₂ supported on MgCl₂ exhibit only one-ninth of the productivity. Extensive comparison has been made between the CW–V and the CW–Ti systems which revealed striking similarities between their polymerization behaviors. MgCl₂ exerts profound influence on the stereochemical control of the vanadium ion on its activity for monomer coordination and insertion.     

Ramanspektroskopische Untersuchungen an festem Vanadiumoxidtrichlorid VOCl3

A high resolution Raman spectrum of polycrystalline VOCl₃ at –196 °C has been recorded. Besides the chlorine isotope splitting a further splitting of 3 of the 6 fundamentals has been observed. The number of the Raman lines in the ₄ and ₆ region and the intensity ratios in the ₂ region will be explained by a factor group splitting of 2 VOCl₃ molecules in the unit cell.

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Nachweis und thermochemische Charakterisierung des Gasphasenmoleküls VOCl2

Proof of Existence and Thermochemical Characterization of the Gaseous Molecule VOCl₂ By use of the Knudsen-cell mass spectrometry the existence of VOCl₂(g). is proven. Lines of fragmentation are set up for VOCl₃(g). The vapor above V₂O₃(s) with Cl₂(g) is examined. The sublimation of VOCl₂ is measured at a temperature of 550–620 K. By 2nd law calculations the heat of sublimation is defined. The calculation for the gaseous VOCl₂ leads to Δ_BH°(VCl₂(g), 298 K) = ?(130,4 ± 1,5) kcal · mol^?1. The influence of VOCl₂(g) for chemical vapor transport reactions of vanadium oxides with Cl₂ is discussed by equilibrium calculations.     

Coordination behaviour of Schiff base 2-acetyl-2-thiazoline hydrazone (ATH) towards cobalt(II), nickel(II) and copper(II)

The synthesis and characterization of Co(II), Ni(II) and Cu(II) complexes of 2-acetyl-2-thiazoline hydrazone (ATH) are reported. Elemental analysis, IR spectroscopy, UV–Vis–NIR diffuse reflectance and magnetic susceptibility measurement, as well as, in the case of copper complex EPR spectroscopy, have been used to characterize the complexes. In addition, the structure of [NiCl₂(ATH)₂] (2) and [{CuCl(ATH)}₂(μ-Cl)₂] (3) have been determined by single crystal X-ray diffraction. In all complexes, the ligand ATH bonds to the metal ion through the imine and thiazoline nitrogen atoms. X-ray data indicates that the environment around the nickel atom in 2 may be described as a distorted octahedral geometry with the metallic atom coordinated to two chlorine atoms, two thiazoline nitrogen atoms and two imino nitrogen atoms. With regard to 3, it can be said that its structure consists of dimeric molecules in which copper ions are bridge by two chlorine ligands. The geometry about each copper ion approximates to a distorted square pyramid with each copper atom coordinated to one thiazoline nitrogen atom, one imine nitrogen atom, one terminal chlorine ligand and two bridge chlorine ligands. In compound 3, magnetic susceptibility measurements in the temperature range 2–300 K show an intradimer antiferromagnetic interaction (J = −7.5 cm⁻¹).     

Synthesis, properties, and crystal structure of the tin(IV) complex with N-(2-hydroxyethyl)ethylenediaminetriacetic acid [Sn(μ-Hedtra)(μ-OH)SnCl3(H2O)] · 3H2O

The binuclear tin(IV) complex with N-(2-hydroxyethyl)ethylenediamine-N,N′,N′-triacetic acid (H₄Hedtra) is synthesized. The compound is characterized by elemental analysis, thermogravimetry, and IR spectroscopy. An X-ray diffraction analysis of complex Sn(μ-Hedtra)(μ-OH)SnCl₃(H₂O)] · 3H₂O (I) is carried out. Structure I is formed by the binuclear complexes and molecules of water of crystallization. One of the tin atoms coordinates six “active” sites Hedtra^4? (the alcohol branch is deprotonated and forms a bridge between two tin atoms) and the bridging hydroxo group. The polyhedron is a pentagonal bipyramid. The octahedral environment of the second tin atom is formed by two bridging oxygen atoms, three chlorine atoms (fac isomer), and a coordination water molecule.     

Tetraphenylphosphonium-tetradecachlorotetraarsenat(III), (PPh4)2As4Cl14

Tetraphenylphosphonium Tetradecachlorotetraarsenate(III), (PPh₄)₂As₄Cl₁₄ The title compound was obtained by reaction of As₄S₄, PPh₄Cl and chlorine in dichloromethane. According to its X-ray crystal structure analysis, the As₄Cl ion can be described as an association product of two AsCl₄^? units and two AsCl₃ molecules. The As atoms and ten Cl atoms are approximately in a plane, the remaining four Cl atoms alternately take positions above and below this plane. The As atoms have distorted ψ octahedral coordination.     

Quantum-chemical study of the geometric and electronic structure of the chromate anion CrO 4 2− and a chromate group on the surface of finely divided silica by the CNDO/2 method

A comparative study of the geometric and electronic structure of the chromate anion CrO ₄ ^2– and a chromate group on the surface of finely divided silica (Si-O)₂-CrO₂, which was simulated by a CrO₉Si₆H₁₂ cluster, has been carried out by the SCF-MO-LCAO method in the all-valence-electron CNDO/2 approximation. The data obtained on the equilibrium geometry of the chromate group attest to the formation of a double bond between the Cr atom and each O atom (which is not bonded to Si). It has been shown that the support has a significant stabilizing influence on the energy of the MO's of the chromate group. The chromate group on an SiO₂ surface is characterized by partial delocalization of the frontier MO's among the skeletal bonds; however, the dominant contribution to the HOMO is made by the 2p AO of the oxygen atoms in the coordination shell of the Cr atom (70%), and the dominant contribution to the LUMO is made by the 3d AO of the chromium atom (50%). The positions and composition of the lowest unoccupied molecular orbitals point out the possibility of the display of electron-acceptor properties by a chromate group on an SiO₂ surface.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 5, pp. 602–606, September–October, 1988.