Zirconium‐chelate and mono‐η‐ cyclopentadienyl zirconium‐chelate/ methylalumoxane systems as soluble Ziegler–Natta olefin polymerization catalysts

Zirconium‐chelate and mono‐η‐cyclopentadienyl zirconium‐chelate complexes were tested as ethene and propene polymerization catalysts in combination with methylalumoxane (MAO) as a co‐catalyst: in particular (acac) _nZrCl_4−n (1a–c) (acac = acetylacetonato), (dbm) _nZrCl_4−n (2a–2c) (dbm = dibenzoylmethanato = 1,3‐diphenylpropanedionato) (n = 2–4) and (dbm)₂ZrCl₂(thf) (3) (thf = tetrahydrofuran), (η‐C₅H₅)[H₂B (C₃H₃N₂)₂]ZrCl₂ (4), (η‐C₅H₅)[HB (C₃H₃N₂)₃] ZrCl₂ (5) and (η‐C₅H₅)[(Me₃SiN)₂ CPh]ZrCl₂ (6). Polymerization productivities comparable with the (η‐C₅H₅)₂ZrCl₂ reference system were observed towards ethene for all of the above complexes. In addition, compound 6 showed some minor polymerization activity towards propene. Ethylalumoxane or isobutylalumoxane did not exhibit a co‐catalytic activity for these chelate complexes; in combination with MAO these higher alumoxanes were even found to be deactivating ⁹¹Zr NMR data are reported for 1b, 1c, 4 and 5. Copyright © 2000 John Wiley & Sons, Ltd.     

A Tunable Trifluoromethyliodonium Reagent

Four complexes of MCl₄ (M=Ti, Zr, Hf) with the hypervalent trifluoromethyl iodine reagent trifluoromethyl‐1,3‐dihydro‐3,3‐dimethyl‐1,2‐benziodoxole ( 1 ,=L) are described. With TiCl₄, an I?O bond cleavage occurs, leading to the formation of the trifluoromethyliodonium alcoholate complexes [Ti₂Cl₆(L)₄]Cl₂ ( 2 a ) and Ti₂Cl₈(L) ( 2 b ). Reactions with ZrCl₄ and HfCl₄ form the complexes ZrCl₄(L)₂ ( 3 ) and HfCl₄(L)₂ ( 4 ), respectively, wherein the original I?O bond is retained and elongated compared to that in free 1 . Therefore, the reactivity of 1 can be easily and practically fine‐tuned by addition of different metal chlorides, following the order ZrCl₄/HfCl₄<TiCl₄<2 TiCl₄. Complexes 2 a , 3 , and 4 are remarkably bench‐stable forms of activated reagent 1 , while 2 b is readily accessible in situ. 2 a and 2 b represent the first “real” trifluoromethyliodonium reagents derived from iodanes, that is, with the I?O bond being completely cleaved. The new complexes were shown to be useful for the trifluoromethylation of para‐toluenesulfonate under aprotic conditions.     

Tetradentate schiff base ligand/MCln initiating systems for the controlled cationic polymerization of isobutyl vinyl ether: Effects of the ligand framework

We investigated the cationic polymerization of vinyl ethers using metal complex catalysts with salen and salphen ligands. Metal complexes were generated in situ from the reaction of a ligand and a metal chloride. The choice of a ligand and a central metal was crucial for tuning the catalyst function such as catalytic activity and controllability of the polymerization. Among metal chlorides employed, ZrCl₄ was the most efficient for controlled polymerization. Cationic polymerization of isobutyl vinyl ether (IBVE) proceeded using the salen and salphen‐type ligand/ZrCl₄ initiating systems, yielding polymers with predetermined molecular weights and narrow molecular weight distributions. Importantly, the structural effects of the complex catalysts were responsible for the polymerization behavior. For example, the polymerization using the salen‐type ligand/ZrCl₄ system was much slower than that using the salphen‐type ligand/ZrCl₄ system. In addition, the polymerization of IBVE using the salen‐type ligand/FeCl₃ system proceeded in a controlled manner, which was in contrast to uncontrolled polymerization using the salphen‐type ligand/FeCl₃ system. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 989–996     

Ramanspektroskopische Untersuchungen an PCl5 II. Das System PCl5—ZrCl4

Raman spectra of some solid and molten PCl₅–ZrCl₄ mixtures have been recorded. ZrCl₆ ^2– complex ions accompanied by at least one more chlorozirconate species are present in the solid as well as in the melt. The newRaman frequencies are attributed to ZrCl₅ ^–, which fundamentals are given and assignment is proposed to be analogous to TiCl₅ ^–. The presence of ZrCl₆ ^2– and ZrCl₅ ^– can be explained by the equilibrium ZrCl₆ ^2–+PCl₄ ⁺ZrCl₅ ^–+PCl₅.

     

A Variable-Pressure 2D 1H-NMR Study of the Mechanism of Trimethyl Phosphate Intermolecular Exchange and cis/trains-Isomerisation of Tetrachlorobis(trimethyl phosphate)zirconium(IV)

In chloroform, [ZrCl₄·2(MeO)₃PO] exists in both cis- and trans-isomeric forms. Three reactions can be envisaged in the presence of excess (MeO)₃PO = L: (1) cis-[ZrCl₄·2L] + *L?cis-[ZrCl₄·L*L]+ L; (2) trans-[ZrCl₄·2L] + *L ? trans-[ZrCl₄·L*L] + L; (3) cis-[ZrCl₄·2L]? trans-[ZrCl₄·2L]. To distinguish between these possible reaction pathways, we have used 2D ₁H-NMR spectroscopy. For the first time, variable-pressure 2D exchange spectra were used for mechanistic assignments. cis/trans-Isomerisation was found to be the fastest reaction (in CHCl₃/CDCl₃), with a small acceleration at higher pressure: it is concluded to be an intramolecular process with a slightly contracted six-coordinate transition state. The intermolecular (MeO)₃PO exchange on the cis- and trans-isomer are second-order processes and are strongly accelerated by increased pressure: I_a mechanisms are suggested without ruling out limiting A mechanisms.     

Polymerization of 1-vinylcyclohexene in the presence of group 4 metallocenes – MAO catalysts

1-Vinylcyclohexene was polymerized in the presence of several homogeneous catalytic systems consisting of methylaluminoxane and group 4 metallocenes such as CpTiCl₃, [isopropyl(cyclopentadienyl)(1-fluorenyl)]ZrCl₂,rac-[ethylenebis(1-indenyl)] ZrCl₂, (CH₃)₂Si(Cp)₂ZrCl₂, CpZrCl₃. The structure of the polymers depends on the catalyst. In fact, with CpTiCl₃, [isopropyl(cyclopentadienyl)(1-fluorenyl)]ZrCl₂ and rac-[ethylenebis-(1-indenyl)]ZrCl₂ the polymers are chemo-, regio- and stereoregular with 1,4 cis, 1,4 trans and 1,2 isotactic structure, respectively.     

Synthesis and performance of ansa-metallocene catalysts with substituted heterocyclic and indenyl ligands

Synthesis of new ansa-metallocene catalysts incorporating branched alkyl groups alpha to the bridgehead carbon of indenyl and thiapentalenyl ligands is reported. Me₂Si(2-Me-4-Ph-Indenyl)₂ZrCl₂ and Me₂Si(2,5-Me₂-3-Ph-Thiapentalenyl)₂ZrCl₂ type metallocenes with one and two isopropyl groups substituted for 2-methyl substitutents were prepared and used as procatalysts in propylene polymerizations and E/P copolymerizations. The 2-isopropyl groups influenced catalyst activity, molecular weight, and the relative amounts of microstructure errors. In contrast to procatalysts with only 2-methyl groups, polymer molecular weights increased in E/P copolymerizations with 2-isopropyl substituted complexes. The text was submitted by the authors in English.     

Defined synthesis of copolymers using metallocene catalysis

The copolymerization of propene with small amounts of ethene, catalyzed by tetrahydroindenyl zirconocenes such as [En(H₄Ind)₂]ZrCl₂ or [Me₂Si(H₄Ind)₂]ZrCl₂ and MAO in liquid propene produces polymers with much higher activities and molecular weights than the homopolymerization of propene. The normal bisindenyl complexes doesn't present such differences. The investigation of the microstructure shows for the tetrahydroindenyl catalyst that after a 2,1-insertion of a propene unit the system is in a sleeping state and can be activated when an ethene unit is inserted. In this case these catalysts become faster than the ansa bis-indenyl catalysts. An active catalyst for the copolymerization of ethene and norbornene is the more temperature stable [Me₃PhPen(Flu)]ZrCl₂. This catalyst produces atactic copolymers with high molecular weights of over 900 000 g/mol at 30°C and 38 mol% of norbornene content.     

Symmetrical and lopsided zirconocene pro-catalysts

Me₂C[1-Cp-9-Flu]ZrCl₂ derivatives with H-, CH₃-and (CH₃)₃C- substituents β to the Cp bridgehead carbon atom as well as complexes having mono- or di-substituted fluorenyl ligands (R = CH₃-, (CH₃)₃C-, CH₃O-, CH₃OCH₂-, (CH₃)₃CC≡C-, (CH₃)₂N-, F-, and Cl-) have been investigated as propylene polymerization pro-catalysts. Steric effects from the β-Cp substituents determine the iso-, hemi-iso-, and syndio-specificities of the catalysts. The relative stereospecificities of Me₂Si[1-Cp-3t-Bu-9-Flu]ZrCl₂ and rac-Me₂Si[1-Ind-3-t-Bu]₂ZrCl₂ are in accord with molecular models. The more un-symmetrical the catalysts are the more m and mm stereosequences there are in s-PP. The m dyads also increase with the concentration of Me₂C[1-Cp-9-Flu-2-OMe]ZrCl₂.     

Azidokomplexe des Zirkoniums: ZrCl3N3, [ZrCl4N3]22⊝, [ZrCl4(N3)2]2⊝; die Kristallstruktur von (PPh4)2[ZrCl4N3]2

Azido Complexes of Zirconium: ZrCl₃N₃, [ZrCl₄N₃]₂^2?, [ZrCl₄(N₃)₂]^2?; Crystal Structure of (PPh₄)₂ [ZrCl₄N₃]₂ Highly explosive ZrCl₃N₃ is formed by the reaction of ZrCl₄ with iodine azide in dichloromethane suspension. According to the i.r. spectra, the compound is polymeric by azide and chlorine bridges. Zirconium tetrachloride reacts with one and two moles of tetraphenylphosphonium azide respectively, forming the thermally and mechanically stable complexes (PPh₄)₂[ZrCl₄N₃]₂ and (PPh₄)₂[ZrCl₄(N₃)₂]. The crystal structure of (PPh₄)₂[ZrCl₄N₃]₂ was determined by X-ray methods (1942 reflexions, R = 6.5%). The complex crystallizes in the monoclinic space group P2₁/n with two formula units per unit cell. The structure consists of tetraphenylphosphonium cations and dimeric anions [ZrCl₄N₃]₂^2?, in which the Zr atoms are linked by the α-N atoms of the azide groups, forming a centrosymmetric Zr₂N₂ ring with symmetry D_2h. According to the i.r. spectra, the azide groups in the complex (PPh₄)₂[ZrCl₄(N₃)₂] are covalently bonded at the Zr atom in trans positions.     

Synthesis of Mixed-ring Zirconocene Complexes Containing Alkenyl Group and Ethylene Polymerization Catalyzed with Them

Four new mixed‐ring zirconium completes, [CH₂ = CH(CH₂)_n ‐C₅H₄](RC₅H₄)ZrCl₂ [n = l, R = CH₃OCH₂CH₂(3); n = 2, R = CH₃OCH₂CH₂ (4); n = 2, R=Me₃Si (5); n = 2, R = allyl (6)], have been prepared by the reaction of CH₂ = CH(CH₂)_n C₅H₄ZrCl₃, DME[n = l (1); n = 2 (2)] with RC₅H₄Li. When activated with methylaluminoxane (MAO), the catalytic activities of the above complexes in ethylene polymerization were tested. Complexes 5 and 6 show high activities similar to Cp₂ZrCl₂. Introduction of methoxyethyl group into Cp‐ligand dramatically decreases the catalytic activities of complexes 3 and 4, which can be overcome by increasing the amount of MAO. For complex 5, the dependence of activity and molecular weight (Mη) on the Al/Zr ratio, the polymerization time (t_P), polymerization temperature (T_P) and the polymerization solvent volume (V) was investigated.     

The synthesis and polymerization behavior of bimetallic pyridine diamide complexes containing transition metal (Ti,Zr)

Titanium and zirconium complexes with a pyridine diamide ligand, [2,6-(RNCH₂)₂NC₅H₃]²⁻ (PDMP; R = 2,6-dimethylphenyl) have been synthesized and their catalytic behaviors investigated for ethylene polymerization. It was found that the zirconium complexes, [PDMP]ZrCl₂ (7) and [PDMP][ZrCl₃ × THF]₂ (8), gave higher activities than the titanium complexes, [PDMP]TiCl₂ (5) and [PDMP][TiCl₃]₂ (6). The bimetallic complexes (6, 8) gave higher activities than the corresponding monometallic complexes (5, 7). The titanium complexes gave polymers with higher molecular weight (M_w) than the zirconium complexes. The molecular weight distribution (M_w/M_n) of the polymers obtained from the pyridine diamide complexes were much broader than that of the normal metallocene catalysts. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3756–3762, 1999     

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,Structure and Raman Data of the New Binuclear Zirconium Complex [Ph4P]2[(ZrCl4Py)2O], with a Zr‐O‐Zr Bridge

The new Zirconium(IV) coordination compound [Ph₄P]₂[(ZrCl₄Py)₂O] (Ph = phenyl, Py = pyridine) was synthesized by dissolving ZrCl₄, [Ph₄P]Cl and a stoichiometric amount of NaOH/Na mixture in pyridine or pyridine/organic solvent mixtures. The title phase was obtained as colourless crystals. The crystal structure of [Ph₄P]₂[(ZrCl₄Py)₂O] was determined. It crystallizes monoclinic, P2₁/c, Z = 4, a = 13.412(2), b = 13.461(2), c = 16.442(3) Å, β = 102.72(1)°. The structure consists of isolated tetraphenylphosphonium cations and [(ZrCl₄Py)₂O]^2? complex anions. The centrosymmetric complex anion contains a linear Zr–O–Zr bridge. Each Zr atom is coordinated by one oxygen dianion, the N atom of one pyridine ring and four chloro ligands in a distorted octahedral geometry. The Raman spectrum of [Ph₄P]₂[(ZrCl₄Py)₂O] is also reported. Most of the observed frequencies can be assigned to vibrations of the tetraphenylphosphonium cations and the pyridine rings.     

New zirconocenes with 4,5,6,7-tetrahydroindene ligands. Synthesis and catalytic activity in the polymerization of ethylene and copolymerization of ethylene with hex-1-ene

A series of symmetric and nonsymmetric tetrahydroindenyl zirconium complexes was obtained by the reaction of ZrCl₄ or (CpTMS)ZrCl₃ with lithium salts of the corresponding tetrahydroindenes. Activated with methylalumoxane, these complexes exhibit high activity in polymerization of ethylene (up to 6.8?10⁶ g PE (mol Zr h)^–1), as well as in copolymerization of ethylene and hex-1-ene (up to 8.6?10⁶ g PE (mol Zr h)^–1).     

Sitting-atop complex formation of free base meso-tetraarylporphyrins with zirconium(IV) chloride

We have succeeded in the preparation and spectroscopic characterization of sitting-atop (SAT) complexes of meso-tetraarylporphyrins (H₂t(X)pp) with zirconium(IV) chloride under mild conditions and at room temperature, where two pyrrolenine nitrogens in the SAT complexes, [(H₂t(X)pp)ZrCl₄], coordinate to a zirconium atom and two protons still remain on the pyrrole nitrogens. UV–Vis and NMR (¹H and ¹³C) spectral data show that the porphyrin core of the SAT complexes is distorted and two pyrrolenine nitrogen atoms of the porphyrin act as electron donors to the zirconium atom of ZrCl₄.     

Syntheses and characterizations of trinuclear and dinuclear “half-sandwich” zirconocene phosphates and phosphonates

A series of six-coordinate “half-sandwich” zirconocene phosphates and phosphonates have been synthesized by the reaction of Cp₂ZrCl₂ with (diphenyl-, dibenzyl-)phosphate and methylphenylphosphinic acid under different conditions. All of the complexes were characterized by elemental analysis, FT-IR and NMR (¹H, ¹³C) spectroscopy. Except for complex 3, the structures of complexes 1, 2, 4, 5, and 6 were confirmed by X-ray crystallography. The structure analyses reveal that complexes 1, 2, and 3 are trinuclear complexes with fascinating μ₃-oxygen bridging ligands, central to a Zr–O backbone (Cp₂ZrCl₂:ligand is 1:1) while complexes 4, 5, and 6 are centrosymmetric dinuclear complexes built up about the trapezoidal Zr₂(μ₂-OH)₂ unit (Cp₂ZrCl₂:ligand is 1:2).     

Heterogeneous Ziegler‐Natta Catalyst Based on Neodymium for the Stereospecific Polymerization of Butadiene

The synthesis of a series of neodymium complexes supported on modified silica is reported. In an initial step the silanol groups were masked by a Lewis acid (BCl₃, AlCl₃, TiCl₄, ZrCl₄, SnCl₄, SbCl₅, HfCl₄), and then a soluble arene complex Nd(η⁶‐C₆H₅Me)(AlCl₄)₃ formed in situ was reacted with the modified silica. The supported complexes are active and highly stereospecific for butadiene polymerization; 1,4‐cis insertion is superior by 99%. The catalyst based on a treatment of silica with BCl₃ is the most efficient.     

Mass Spectrometric Characterization of Methylaluminoxane‐Activated Metallocene Complexes

Electrospray‐ionization mass spectrometric studies of poly(methylaluminoxane) (MAO) in the presence of [Cp₂ZrMe₂], [Cp₂ZrMe(Cl)], and [Cp₂ZrCl₂] in fluorobenzene (PhF) solution are reported. The results demonstrate that alkylation and ionization are separate events that occur at competitive rates in a polar solvent. Furthermore, there are significant differences in ion‐pair speciation that result from the use of metallocene dichloride complexes in comparison to alkylated precursors at otherwise identical Al/Zr ratios. Finally, the counter anions that form are dependent on the choice of precursor and Al/Zr ratio; halogenated aluminoxane anions [(MeAlO)_x(Me₃Al)_y?z(Me₂AlCl)_zMe]^? (z=1, 2, 3…?) are observed using metal chloride complexes and under some conditions may predominate over their non‐halogenated precursors [(MeAlO)_x(Me₃Al)_yMe]^?. Specifically, this halogenation process appears selective for the anions that form in comparison to the neutral components of MAO. Only at very high Al/Zr ratios is the same “native” anion distribution observed when using [Cp₂ZrCl₂] when compared with [Cp₂ZrMe₂]. Together, the results suggest that the need for a large excess of MAO when using metallocene dichloride complexes is a reflection of competitive alkylation vs. ionization, the persistence of unreactive, homodinuclear ion pairs in the case of [Cp₂ZrCl₂], as well as a change in ion pairing resulting from modification of the anions formed at lower Al/Zr ratios. Models for neutral precursors and anions are examined computationally.     

Crystal structure of ansa-Me2Si-(2Me-4-p-Tol-cyclopenta[b]indol-3-yl)2ZrCl2 and its catalytic properties in the polymerization of propylene

A new zirconocene ansa-Me₂Si-(2Me-4-p-Tol-cyclopenta[b]indol-3-yl)₂ZrCl₂ complex (I), in which the Cp ligand is fused with the indole ring, has been synthesized and studied by X-ray diffraction analysis. Light brown crystals are triclinic, space group P [`1]\bar 1; M = 734.92, a = 9.252(2) ?, b = 12.914(3) ?, c = 15.619(3) ?, α = 111.83(3)°, β = 81.03(3)°, γ = 117.77(3)°, V = 1569(3) ?³, Z = 2, ρ_calc = 1.525 g/cm³. The structural parameters of complex I are compared with the known bis-indenyl zirconium complexes: rac-Me₂Si(Ind)₂ZrCl₂ (II) and rac-Me₂Si(2Me-2Ph-1-Ind)₂ZrCl₂ (III) and analogous substituted rac-Me₂Si(2,5-Me₂-3Ph-6-Cp[b]Tp)₂ZrCl₂ (IV) and rac-Me₂Si(2,5-Me₂-1Ph-4-Cp[b]Py)₂ZrCl₂ (V). Complex I alkylated by the Grignard reagent (MgMe₂) in the presence of the Al-iso-Bu₃ cocatalyst is an efficient catalyst for the polymerization of propylene into isotactic polypropylene.