Titanium and zirconium complexes with aminoiminophosphorane ligands

A series of titanium and zirconium complexes based on aminoiminophosphorane ligands [Ph₂P(Nt‐Bu)(NR)]₂MCl₂ ( 4 , M = Ti, R = Ph; 5 , M = Zr, R = Ph; 6 , M = Ti, R = SiMe₃; 7 , M = Zr, R = SiMe₃) have been synthesized by the reaction of the ligands with TiCl₄ and ZrCl₄. The structure of complex 4 has been determined by X‐ray crystallography. The observed very weak interaction between Ti and P suggests partial π‐electron delocalization through both Ti and P. The complexes 4–7 are inactive for ethylene polymerization in the presence of modified methylaluminoxane (MMAO) or i‐Bu₃Al–Ph₃CB(C₆F₅)₄ under atmospheric pressure, and is probably the result of low monomer ethylene concentration and steric congestion around the central metal. Copyright © 2005 John Wiley & Sons, Ltd.     

Homoleptic alkenyls of the early transition metals and related compounds

The first stable homoleptic alkenyls of the early transition metals, MR_n, (R = C(Ph)=CMe₂; M = Ti, Zr, Hf, n = 4; and M = Cr, n = 3) and the related species (C₅H₅)₂MR₂ (M = Ti, Zr) and (C₅H₅)₂Zr(Cl)R have been prepared using appropriate organolithium reagents. Cleavage and insertion reactions are reported for the new compounds.     

The Influence of the growing polymer chain on the catalytic complex in homogeneous ziegler-natta polymerization: Density functional calculations on model systems TiCI2R+ and ZrCl2R+

The influence of the growing chain on the electronic structure of soluble Ziegler-Natta catalysts was investigated through quantum-mechanical calculations for model systems MCI₂R⁺ with M = Ti, Zr and R = C_nH_2n+1 where n = 1–7. The theoretical results show an increase in the energy of the Lowest Unoccupied Molecular Orbital (LUMO) of the cation and a decrease of the transition metal charge in the early stages of polymerization. This behaviour could explain the experimentally observed initial acceleration of the monomer insertion rate as reported in literature for ethylene polymerization with TiCp₂CH₃Cl·AlCl₂CH₃ system.     

Polymer-supported Ziegler–Natta catalysts. I. A preliminary study of catalyst synthesis

Polymer-supported Ziegler–Natta catalysts based on various polymer carriers were synthesized by different methods, including (1) loading TiCl₄ directly onto the polymer supports; (2) loading TiCl₄ onto the polymer supports modified by magnesium chloride (MgCl₂); (3) loading TiCl₄ onto the polymer supports modified by Grignard reagent (RMgCl); and (4) loading TiCl₄ onto the polymer supports modified by magnesium alkyls (MgR₂). The activity and kinetic features of the catalysts for ethylene polymerization were examined. Among the combinations tested, the best was found to be TiCl₄/n-Bu₂Mg.Et₃Al/poly(ethylene-co-acrylic acid) (92:8), which produced a catalyst of very high activity for ethylene polymerization. © 1994 John Wiley & Sons, Inc.     

Monomer-Isomerization polymerization. XXVIII. Catalytic activity of transition metals and alkylaluminums in monomer-isomerization polymerization of 2-butene

Monomer-isomerization polymerization of cis-2-butene (c2B) with Ziegler–Natta catalysts was studied to find a highly active catalyst. Among the transition metals [TiCl₃, TiCl₄, VCl₃, VOCl₃, and V (acac)₃] and alkylauminums used, TiCl₃? R₃Al (R = C₂H₅ and i-C₄H₉) was found to show a high-activity for monomer-isomerization polymerization of c2B. The polymer yield was low with TiCl₄? (C₂H₅)₃Al catalyst. However, when NiCl₂ was added to this catalyst, the polymer yield increased. With TiCl₃? (C₂H₅)₃Al catalyst, the effect of the Al/Ti molar ratio was observed and a maximum for the polymer yields was obtained at molar ratios of 2.0–3.0, but the isomerization increased as a function of Al/Ti molar ratio. The valence state of titanium on active sites for isomerization and polymerization is discussed.     

A kind of novel nonmetallocene catalysts for ethylene polymerization

A kind of novel bridged nonmetallocene catalysts was synthesized by the treatment of N,N‐imidazole and N,N‐phenylimidazole with n‐BuLi, and MCl₄ (M = Ti, Zr) in THF. Those catalysts were performed for ethylene polymerization after activated by methylaluminoxane (MAO). The effects of polymerization temperature, Al/M ratio, pressure of monomer, and concentration of catalysts on ethylene polymerization behaviors were investigated in detail. Those results revealed that the catalyst system was favorable for ethylene polymerization with high catalytic activity. The polymer was characterized by ¹³C NMR, WAXD, GPC, and DSC. The result confirmed that the obtained polyethylene featured broad molecular weight distribution around 20, linear structure, and relative low melting temperature. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 33–37, 2008     

Ethylene polymerization using novel titanium catalytic precursors bearing N,N‐dialkylcarbamato ligands

Polymerization catalysts based on N,N‐dialkylcarbamato complexes of titanium(IV) appear particularly interesting, because these novel catalytic precursors are rather cheap and easy to synthesize and handle. This contribution reports ethylene polymerization behavior of titanium(IV) complexes of general formula Ti(O₂CNR₂)₄ R = Me ( I ) and Et ( II ) and TiCl₂(O₂CNMe₂)₂ ( III ). These precursors in conjunction with methylaluminoxane resulted active catalysts for the polymerization of ethylene, affording high‐density polyethylene with limited branch content. The influence of the polymerization parameters was studied with particular reference to the type of catalyst components, solvent, temperature, monomer concentration, and Al/Ti ratio. The nature of the solvent appears crucial for catalytic performances: when toluene was replaced by chlorobenzene, a significant increase of the productivity was ascertained. The obtained polymers were characterized by DSC, size exclusion chromatography, FTIR, and NMR techniques. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Ti complex catalysts including thiobisphenoxy group as a ligand for olefin polymerization

Titanium complexes were prepared by the reaction of 2,2′-thiobis(6-tert-butyl-4-methylphenol) (TBP) with TiCl₄ or Ti(OPrⁱ)₄. These complexes in combination with methyalumoxane as cocatalyst are highly active towards ethylene and propene, giving polymers having high molecular weights. The polymerization activities for ethylene and propene are comparable to those of Cp₂ZrCl₂-MAO catalyst. Polypropylene obtained had extremely high molecular weight (Mw>6 million) and low regioregularity (30% of head-to-head and tail-to-tail linkages). Highly syndiotactic polystyrene was obtained with these catalysts with activity up to 27 kg polymer per g Ti and hour. Copolymerization of styrene with ethylene gave highly alternating copolymer with isotactic styrene units. These catalysts are also active toward both conjugated and nonconjugated dienes such as butadiene and 1,5-hexadiene. Polybutadiene had mainly cis-1,4-structure (98%). The structure of poly(1,5-hexadiene) is rather complicated, which is quite different from that prepared with heterogeneous TiCl₃ catalysts.     

Titanium and Zirconium Complexes with Non‐Salicylaldimine‐Type Imine–Phenoxy Chelate Ligands: Syntheses,Structures, and Ethylene‐Polymerization Behavior

New Ti and Zr complexes that bear imine–phenoxy chelate ligands, [{2,4‐di‐tBu‐6‐(RCH=N)‐C₆H₄O}₂MCl₂] ( 1 : M=Ti, R=Ph; 2 : M=Ti, R=C₆F₅; 3 : M=Zr, R=Ph; 4 : M=Zr, R=C₆F₅), were synthesized and investigated as precatalysts for ethylene polymerization. ¹H NMR spectroscopy suggests that these complexes exist as mixtures of structural isomers. X‐ray crystallographic analysis of the adduct 1 ?HCl reveals that it exists as a zwitterionic complex in which H and Cl are situated in close proximity to one of the imine nitrogen atoms and the central metal, respectively. The X‐ray molecular structure also indicates that one imine phenoxy group with the syn C?N configuration functions as a bidentate ligand, whereas the other, of the anti C?N form, acts as a monodentate phenoxy ligand. Although Zr complexes 3 and 4 with methylaluminoxane (MAO) or [Ph₃C]⁺[B(C₆F₅)₄]^?/AliBu₃ displayed moderate activity, the Ti congeners 1 and 2 , in association with an appropriate activator, catalyzed ethylene polymerization with high efficiency. Upon activation with MAO at 25 °C, 2 displayed a very high activity of 19900 (kg PE) (mol Ti)^?1 h^?1, which is comparable to that for [Cp₂TiCl₂] and [Cp₂ZrCl₂], although increasing the polymerization temperature did result in a marked decrease in activity. Complex 2 contains a C₆F₅ group on the imine nitrogen atom and mediated nonliving‐type polymerization, unlike the corresponding salicylaldimine‐type complex. Conversely, with [Ph₃C]⁺[B(C₆F₅)₄]^?/AliBu₃ activation, 1 exhibited enhanced activity as the temperature was increased (25–75 °C) and maintained very high activity for 60 min at 75 °C (18740 (kg PE) (mol Ti)^?1 h^?1). ¹H NMR spectroscopic studies of the reaction suggest that this thermally robust catalyst system generates an amine–phenoxy complex as the catalytically active species. The combinations 1 /[Ph₃C]⁺[B(C₆F₅)₄]^?/AliBu₃ and 2 /MAO also worked as high‐activity catalysts for the copolymerization of ethylene and propylene.     

Olefin polymerization and copolymerization by complexes bearing [ONNO]‐Type salan ligands: Effect of ligand structure and metal type (titanium,zirconium, and vanadium)

A series of novel titanium(IV) complexes bearing tetradentate [ONNO] salan type ligands: [Ti{2,2′‐(OC₆H₃‐5‐t‐Bu)₂‐NHRNH}Cl₂] (Lig¹TiCl₂: R = C₂H₄; Lig²TiCl₂: R = C₄H₈; Lig³TiCl₂: R = C₆H₁₂) and [Ti{2,2′‐(OC₆H₂‐3,5‐di‐t‐Bu)₂‐NHC₆H₁₂NH}Cl₂] (Lig⁴TiCl₂) were synthesized and used in the (co)polymerization of olefins. Vanadium and zirconium complexes: [ M{2,2′‐(OC₆H₃‐3,5‐di‐t‐Bu)₂‐NHC₆H₁₂NH}Cl₂] (Lig⁴VCl₂: M = V; Lig⁴ZrCl₂: M = Zr) were also synthesized for comparative investigations. All the complexes turned out active in 1‐octene polymerization after activation by MAO and/or Al(i‐Bu)₃/[Ph₃C][B(C₆F₅)₄]. The catalytic performance of titanium complexes was strictly dependent on their structures and it improves for the increasing length of the aliphatic linkage between nitrogen atoms (Lig¹TiCl₂ << Lig²TiCl₂ < Lig³TiCl₂) and declines after adding additional tert‐Bu group on the aromatic rings (Lig³TiCl₂ < Lig⁴TiCl₂). The activity of all titanium complexes in ethylene polymerization was moderate and the properties of polyethylene was dependent on the ligand structure, cocatalyst type, and reaction conditions. The Et₂AlCl‐activated complexes gave polymers with lover molecular weights and bimodal distribution, whereas ultra‐high molecular weight PE (up to 3588 kg mol^?1) and narrow MWD was formed for MAO as a cocatalyst. Vanadium complex yielded PE with the highest productivity (1925.3 kg mol_v^?1), with high molecular weight (1986 kg mol^?1) and with very narrow molecular weight distribution (1.5). Copolymerization tests showed that titanium complexes yielded ethylene/1‐octene copolymers, whereas vanadium catalysts produced product mixtures. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2111–2123     

Monomer-isomerization polymerization. XXVI. Formation of polyallylcyclohexane from propenylcyclohexane through monomer-isomerization polymerization with Ziegler–Natta catalysts

Monomer-isomerization polymerization of propenycyclohexane (PCH) with TiCl₃ and R_3-xAICI_x (R = C₂H₅ or i-C₄H₉, x = 1–3) catalysts was studied. It was found that PCH underwent monomer-isomerization polymerization to give a high molecular weight polymer consisting of an allylcyclohexane (ACH) repeat unit. Among the alkyaluminum cocatalysts examined, (C₂H₅)₃Al was the most effective cocatalyst for the monomer-isomerization polymerization of PCH, and a maximum for the polymerization was observed at a molar ratio of Al/Ti of about 2.0. The addition of isomerization catalysts such as nickel acetylacetonate [Ni(acac)₂] to the TiCl₃–(C₂H₅)₃Al catalyst accelerated the monomer-isomerization polymerization of PCH and gave a maximum for the polymerization at a Ni/Ti molar ratio of 0.5. PCH also undergoes monomer-isomerization copolymerization with 2-butene (2B).     

Quantitative evaluation of catalytic effect of metal chlorides on the decomposition reaction of NaAlH4

The hydrogen desorption (or decomposition) reaction of NaAlH₄ is expressed as , and its desorption rate is accelerated by mixing metal chloride catalysts (e.g., TiCl₃). This catalytic effect of metal chlorides, MCl_n, is theoretically estimated in a quantitative way using atomization energy concept. The atomization energies, ΔE_M for metal ion and ΔE_Cl for chloride ion in various metal chlorides are evaluated using the energy density analysis of the total energy. It is shown that the hydrogen desorption reaction rate increases with increasing n × ΔE_M values of metal chlorides. This indicates that the metal ion in MCl_n interacts mainly with hydrogen or [AlH₄]^? complex anion in NaAlH₄. To confirm this calculated result, experiments are performed using NaAlH₄ mixed with Ti‐based catalysts. The hydrogen desorption rate is enhanced in the order, TiCl₃ > TiO₂ > Ti metal nanopowder, indicating that the Ti ions in TiCl₃ or TiO₂ work to promote the catalytic reaction more effectively than the neutral Ti atoms in Ti metal nanopowder. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Propylene polymerization with catalysts containing divalent titanium

The behavior in propylene polymerization of divalent titanium compounds of type [η⁶-areneTiAl₂Cl₈], both as such and supported on activated MgCl₂, has been studied and compared to that of the simple catalyst MgCl₂/TiCl₄. Triethylaluminium was used as cocatalyst. The Ti–arene complexes were active both in the presence and in the absence of hydrogen, in contrast to earlier reports that divalent titanium species are active for ethylene but not for propylene polymerization. ¹³C-NMR analysis of low molecular weight polymer fractions indicated that the hydrogen activation effect observed for the MgCl₂-supported catalysts should be ascribed to reactivation of 2,1-inserted (“dormant”) sites via chain transfer, rather than to (re)generation of active trivalent Ti via oxidative addition of hydrogen to divalent species. Decay in activity during polymerization was observed with both catalysts, indicating that for MgCl₂/TiCl₄ catalysts decay is not necessarily due to overreduction of Ti to the divalent state during polymerization. In ethylene polymerization both catalysts exhibited an acceleration rather than a decay profile. It is suggested that the observed decay in activity during propylene polymerization may be due to the formation of clustered species that are too hindered for propylene but that allow ethylene polymerization. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 2645–2652, 1997     

Study of (π-C5H5)2Ti(CH3)Cl and (π-C5H5)2Ti(C6H5)Cl in soluble Ziegler catalysts

Soluble ethylene polymerization catalysts derived from (π-C₅H₅)₂Ti(R)Cl and R ′AlCl₂, where R = methyl or phenyl and R ′ = methyl or ethyl, were studied both by polymerization kinetics at 0°C and by diagnostic experiments. It was found that the first insertion of ethylene into the Ti? R bond is difficult when R = methyl or phenyl, and for this reason these catalysts show a different overall behavior than when R = ethyl or higher alkyl.     

Monomer-isomerization polymerization. XXIII.. Monomer-isomerization polymerization of 5-phenyl-2-pentene with ziegler–natta catalysts

5-Phenyl-2-pentene (5Ph2P) was found to undergo monomer-isomerization polymerization with TiCl₃–R₃Al (R = C₂H₅ or i-C₄H₉, Al/Ti > 2) catalysts to give a polymer consisting of exclusively 5-phenyl-1-pentene (5Ph1P) unit. The geometric and positional isomerizations of 5Ph2P to its terminal and other internal isomers were observed to occur during polymerization. The catalyst activity of alkylaluminum examined to TiCl₃ was in the following order: (C₂H₅)₃Al > (i-C₄H₉)₃Al > (C₂H₅)₂AlCl. The rate of monomer-isomerization polymerization of 5Ph2P with TiCl₃–(C₂H₅)₃Al catalyst was influenced by both the Al/Ti molar ratio and the addition of nickel acetylacetonate [Ni(acac)₂], and the maximum rate was observed at Al/Ti = 2.0 and Ni/Ti = 0.4 in molar ratios.     

Copolymerization of 2‐butene and ethylene with catalysts based on titanium and zirconium complexes

The polymerization of 2‐butene and its copolymerization with ethylene have been investigated using four kinds of dichlorobis(β‐diketonato)titanium complexes, [ArN(CH₂)₃NAr]TiCl₂ (Ar = 2,6‐ⁱPr₂C₆H₃) and typical metallocene catalysts. The obtained copolymers display lower melting points than those produced of homopolyethylene under the same polymerization conditions. ¹³C NMR analysis indicates that 9.3 mol‐% of 2‐butene units were incorporated into the polymer chains with Ti(BFA)₂Cl₂‐MAO as the catalyst system. With the trans‐2‐butene a higher copolymerization rate was observed than with cis‐2‐butene. A highly regioselective catalyst system for propene polymerization, [ArN(CH₂)₃NAr]TiCl₂ complex using a mixture of triisobutylaluminium and Ph₃CB(C₆F₅)₄ as cocatalyst, was found to copolymerize a mixture of 1‐butene and trans‐2‐butene with ethylene up to 3.1 mol‐%. Monomer isomerization‐polymerization proceeds with typical metallocene catalysts to produce copolymers consisting of ethylene and 1‐butene.     

Olefin polymerization with titanium tetrachloride catalysts supported on surface-modified silica

After modification of silica with benzoyl chloride (BC) to obtain BC-modified SiO₂ (BC-SiO₂), BC-SiO₂/TiCl₄ and BC-SiO₂/BEM/TiCl₄ catalysts were prepared by treating the BC-SiO₂ with TiCl₄ directly or with butylethylmagnesium (BEM) followed by TiCl₄, respectively. During the modification, BC reacts with hydroxyl groups of silica. In this way the corresponding ester is anchored on the silica surface and the CO group is coordinated with Ti and/or Mg. In addition, BEM is converted to MgCl₂ in the reaction with TiCl₄. These catalysts have reasonable activities for ethylene or propene polymerization.     

Highly active MgCl2‐supported CpMCl3 (M = Ti,Zr) catalysts for ethylene polymerization

Monocyclopentadienyl compounds, CpMCl₃ (M = Ti, Zr) supported on activated MgCl₂ were used for the polymerizations of ethylene in the presence of methylaluminoxane (MAO) or a common alkylaluminium as a cocatalyst. By supporting CpMCl₃ on MgCl₂, the catalyst activity was increased drastically to show high activity similar to MgCl₂‐supported TiCl₄ catalysts. The activity of the CpZrCl₃ /MgCl₂ catalyst was higher than that of the CpTiCl₃/MgCl₂ one. Both catalysts gave polymers with high molecular weight (M_w) and broad molecular weight distribution (M_w/M_n) in comparison with the corresponding soluble half‐metallocene catalysts.     

Syntheses of Some New Group 4 non-Cp Complexes Bearing Schiff-base, Thiophene Diamide Ligands Respectively and Their Catalytic Activities for a-Olefin Polymerization

Totally sixteen new titanium and zirconium non-Cp complexes supported by Schiff-base, or thiophene diamide ligands have been synthesized. The complexes are obtained by the reaction of M(OPr-i)4(M=Ti,Zr) with the corresponding Schiff-base ligand in 1:1 molar ratio in good yield. The thiophene diamide titanium complex has been prepared from trimethylsilyl amine [N,S,N] ligand and TiCl4 in toluene at 120℃. All complexes are well charac-terized by ^1H NMR, IR, MS and elemental analysis. When activated by excess methylaluminoxane (MAO), complexes show moderate catalytic activity for ethylene polymerization, and complex If (R^1=CH3,R^2=Br) exhibits the highest activity for ethylene and styrene polymerization. When the complexes were preactivated by triethylaluminum (TEA), both polymerization activities and syndiotacticity of the polymers were greatly improved.     

Olefin polymerization with Me4Cp–Amido complexes with electron‐withdrawing groups

A series of Me₄Cp–amido complexes {[η⁵:η¹‐(Me₄C₅)SiMe₂NR]TiCl₂; R = t‐Bu, 1 ; C₆H₅, 2 ; C₆F₅, 3 ; SO₂Ph, 4 ; or SO₂Me, 5 } were prepared and investigated for olefin polymerization in the presence of methylaluminoxane (MAO). X‐ray crystallography of complexes 3 and 4 revealed very long Ti N bonds relative to the bonds of 1 . These complexes were employed for ethylene–styrene copolymerizations, styrene homopolymerizations, and propylene homopolymerizations in the presence of MAO. The productivities of the catalysts derived from 3 – 5 were much lower than the productivity of the catalyst derived from 1 for the propylene polymerizations and ethylene–styrene copolymerizations, whereas the styrene polymerization activities were much higher for the catalysts derived from 3 – 5 than for the catalyst derived from 1 . The polymerization behavior of the catalysts derived from the metallocenes 3 – 5 were more reminiscent of monocyclopentadienyl titanocene Cp′TiX₃/MAO catalysts than of CpATiX₂/MAO catalysts such as 1 containing alkylamido ligands. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4649–4660, 2000