Highly active/selective and adjustable zirconium polymerization catalysts stabilized by aminopyridinato ligands

This paper describes a substantial enhancement of the aminopyridinato ligand stabilized early transition metal chemistry by introducing the sterically very demanding 2,6-dialkylphenyl substituted aminopyridinato ligands derived from (2,6-diisopropylphenyl)-[6-(2,6-dimethylphenyl)-pyridin-2-yl]-amine (1a-H, ApH) and (2,6-diisopropylphenyl)-[6-(2,4,6-triisopropylphenyl)-pyridin-2-yl]- amine (1b-H, Ap^∗H). The corresponding bis aminopyridinato zirconium dichloro complexes, [Ap₂ZrCl₂] (3a) and [Ap₂^∗ZrCl₂] (3b) and the dimethyl analogues, [Ap₂ZrMe₂] (4a) and [Ap₂^∗ZrMe₂] (4b) (Me = methyl) were synthesized, using standard salt metathesis routes. Single-crystal X-ray diffraction was carried out for the dichloro derivatives. Both zirconium metal centers have a distorted octahedral environment with a cis-orientation of the chloride ligands in 3a and a closer to trans-arrangement in 3b. The dimethyl derivatives are proven to be highly active ethylene polymerization catalysts after activation with [R₂N(Me)H][B(C₆F₅)₄] (R = C₁₆H₃₃-C₁₈H₃₇). During attempted co-polymerizations of α-olefins (propylene) and ethylene high activity and selectivity for ethylene and nearly no co-monomer incorporation was observed. Increasing the steric bulk of the ligand going from (2,6-dimethylphenyl) to (2,4,6-triisopropylphenyl) substituted pyridines, switches the catalyst system from producing long chain α-olefins to polymerization of ethylene in a living fashion. In contrast to the dimethyl complexes only [Ap₂^∗ZrCl₂] in the presence of MAO at elevated temperature gave decent polymerization activity. NMR investigations of the reaction of dichloro complexes with 25 equiv. of MAO or AlMe₃ at room temperature revealed, that [Ap₂ZrCl₂] decomposes under ligand transfer to aluminum and formation of [ApAlMe₂], while [Ap₂^∗ZrCl₂] remains almost unreacted under the same conditions. The aminopyridinato dimethyl aluminum complexes, [ApAlMe₂] (5a) and [Ap^∗AlMe₂] (5b) were synthesized independently and structurally characterized. The aluminum complexes 5a and b show no catalytic activity towards ethylene, when “activated” with[R₂N(Me)H][B(C₆F₅)₄].     

Synthesis of novel zirconium complexes bearing mono‐Cp and tridentate Schiff base [ONO] ligands and their catalytic activities for olefin polymerization

A series of novel zirconium complexes {R²Cp[2‐R¹‐6‐(2‐CH₃OC₆H₄N?CH)C₆H₃O]ZrCl₂ ( 1 , R¹ = H, R² = H, 2 : R¹ = CH₃, R² = H; 3 , R¹ = ^tBu, R² = H; 4 , R¹ = H, R² = CH₃; 5 , R¹ = H, R² = n‐Bu)} bearing mono‐Cp and tridentate Schiff base [ONO] ligands are prepared by the reaction of corresponding lithium salt of Schiff base ligands with R²CpZrCl₃·DME. All complexes were well characterized by ¹H NMR, MS, IR and elemental analysis. The molecular structure of complex 1 was further confirmed by X‐ray diffraction study, where the bond angle of Cl? Zr? Cl is extremely wide [151.71(3)°]. A nine‐membered zirconoxacycle complex Cp(O? 2? C₆H₄N?CHC₆H₄‐2? O)ZrCl₂ ( 6 ) can be obtained by an intramolecular elimination of CH₃Cl from complex 1 or by the reaction of CpZrCl₃·DME with dilithium salt of ligand. When activated by excess methylaluminoxane (MAO), complexes 1–6 exhibit high catalytic activities for ethylene polymerization. The influence of polymerization temperature on the activities of ethylene polymerization is investigated, and these complexes show high thermal stability. Complex 6 is also active for the copolymerization of ethylene and 1‐hexene with low 1‐hexene incorporation ability (1.10%). Copyright © 2006 John Wiley & Sons, Ltd.     

Copolymerization of ethylene with cycloolefins by titanium complexes containing tridentate [o−NSR] ligands

A family of titanium complexes of the general formula [N‐(3,5‐di‐tert‐butylsalicylidene)‐2‐alkylsulfanylanilinato]Ti(IV)Cl₃ 5a – f was prepared from the reaction of TiCl₄ with the potassium salts of the corresponding ligands. These complexes were fully characterized by various spectroscopic techniques and elemental analyses. The molecular structures of 5b and 5e were further confirmed by single‐crystal X‐ray analyses. Complexes 5a – f (except for 5c ) exhibited good to high catalytic activities in ethylene copolymerization with cycloolefins such as norbornene, cyclopentene, dicyclopentadiene in the presence of modified methylaluminoxane. The reaction conditions and the steric hindrance of the alkyl substituents on sulfur atom in the precatalysts influenced strongly the copolymerization behaviors and the structures of the resultant copolymers. Complex 5c with bulky tert‐butylthio sidearm showed both low catalytic activity and comonomer incorporation ratio. The n‐alkylthio complexes 5a , 5d – f all exhibited good ethylene copolymerization capabilities with cycloolefins, which is superior to the corresponding phenylthio complex 5g . © 2008 Wiley Periodicals, Inc. JPolym Sci Part A: Polym Chem 46: 2807–2819, 2008     

Highly active titanium-based olefin polymerization catalysts bearing bulky aminopyridinato ligands

A series of titanium complexes have been prepared using either salt metathesis or amine elimination reactions. Reacting the potassium salt of Ap*H {Ap*H = N-(2,6-diisopropylphenyl)-[6-(2,4,6-triisopropylphenyl)pyridin-2-yl]amine} (1) with [TiCl(4)(THF)(2)] results in the formation of a nucleophilic ring-opening product of the coordinated tetrahydrofuran (THF) ligand [Ap*TiCl(2)(OC(4)H(8)Cl)] (7). Alkylation with benzylmagnesium chloride gave rise to the corresponding benzyl complex [Ap*TiBn(2)(OC(4)H(8)Cl)] (8). However, THF ring opening was overcome by adopting an amine elimination route instead of salt metathesis. Mono(aminopyridinato)titanium trichloro complexes were prepared in high yields using [(CH(3))(2)NTiCl(3)], together with the corresponding sterically demanding aminopyridine as the starting material. The synthesized complexes could then be alkylated selectively. These complexes were characterized by spectroscopic methods, and their behavior in olefin polymerization and copolymerization of ethene and propene was explored. These mono(aminopyridinato)titanium trichloro complexes are less active if activated with methylaluminoxane (MAO). However, the activity increases strongly if MAO is replaced by d-MAO ("dry methylaluminoxane"). The catalysts show moderate activity toward propene polymerization, while ethylene-propylene copolymers in high-productivity with separated propene units were observed. The catalysts are also highly active in the co- and terpolymerization of 2-ethylidenenorbornene (ENB) with ethylene or ethylene-propylene, together with a very good incorporation of ENB. In all cases, the activity increases with an increase in the steric bulk of the protecting ligand.     

Ethylene polymerization and ethylene/1-hexene copolymerization using homogeneous and heterogeneous unbridged bisindenyl zirconocene catalysts

Unbridged bis-substituted-indenyl zirconocene complexes, [(2,4-Me₂Ind)₂ZrCl₂, Met-1; (2,4,6-Me₃Ind)₂ZrCl₂, Met-2], were supported on silica and montmorillonite carriers (resulting in silica-supported catalysts MS-1 and MS-2, and montmorillonite-supported catalyst MT-1). Ethylene polymerization by homogeneous and heterogeneous catalysts showed high activity, affording polyethylenes with high molecular weight. The catalytic activity and the molecular weight of the polymer were improved using the heterogeneous systems. The activities for the ethylene/1-hexene copolymerization by heterogeneous systems were lower than those using homogeneous systems, however, the comonomer was incorporated efficiently into polymer in both the homo- and the heterogeneous systems, and moreover, the microstructure of the copolymer derived from the heterogeneous catalysts showed different characteristics from those resulting from the homogeneous systems. The r_Er_H values of the heterogeneous catalysts (1.82 for MS-1 and 0.70 for MS-2), are quite different from those of their homogeneous analogues (1.25 for Met-1 and 1.26 for Met-2).     

Highly active titanium-based olefin polymerization catalysts supported by bidentate phenoxyamide ligands

Phenoxyamide complexes of Ti-containing 2,6-X2C6H3 (X = Cl, Br) substituents, when activated by methyl aluminoxane, afford catalysts with very high activities for the polymerization of ethylene and with good incorporation of 1-hexene.     

Syntheses, reactions, and ethylene polymerization of titanium complexes with [N,N,S] ligands

Tridentate dianionic arylsulfide free ligands [ArNHCH(2)C(6)H(4)NHC(6)H(4)-2-SPh] (Ar = Ph (3a); Ar = 2,4,6-trimethylphenyl (3b); Ar = 2,6-diisopropylphenyl (3c)) have been prepared by reduction of the corresponding imine compounds [ArN[double bond, length as m-dash]CHC(6)H(4)NHC(6)H(4)-2-SPh] (Ar = Ph (2a); Ar = 2,4,6-trimethylphenyl (2b); Ar = 2,6-diisopropylphenyl (2c)) with LiAlH(4) in high yields. Reactions of TiCl(4) with the tridentate dianionic arylsulfide free ligands (3a-3c) afford five-coordinate and four-coordinate titanium complexes [κS, κ(2)N-(ArNHCH(2)C(6)H(4)NHC(6)H(4)-2-SPh)TiCl(2)] (Ar = Ph (4a); Ar = 2,4,6-trimethylphenyl (4b)] and [κ(2)N-(ArNHCH(2)C(6)H(4)NHC(6)H(4)-2-SPh)TiCl(2)] (Ar = 2,6-diisopropylphenyl (4c)], respectively. The molecular structures of compounds 2b, 2c, 3b and 3c·HCl have been characterized by single crystal X-ray diffraction analyses. Complexes 2a-4c are characterized by IR,(1)H-NMR spectra, and elemental analysis. EXAFS spectroscopy performed on complexes 4b and 4c reveals the expected different coordination geometry due to steric hindrance effect. When activated by excess methylaluminoxane (MAO), 4a-4c can be used as catalysts for ethylene polymerization and exhibit moderate to good activities.     

Living polymerization of propylene and 1-hexene using bis-Cp type metallocene catalysts

To check the possibility of living polymerization with a biscyclopentadienyl metallocene, propylene polymerization was conducted by Cp₂ZrMe₂ at –78°C or Cp₂HfMe₂ at –50°C using B(C₆F₅)₃ and AlOct₃ as a cocatalyst. The polymer yield increased linearly with polymerization time. The polypropylene obtained showed narrow molecular weight distribution (M_w/M_n 1.04–1.15). In addition, the number-average molecular weight increased in proportion to the polymerization time. It was, thus, found that living polymerization of propylene proceeds with the catalyst systems at a very low temperature. Isospecific living polymerization of 1-hexene also proceeded with the rac-(et)Ind₂ZrMe₂ catalyst at –78°C.     

Syntheses, characterization and ethylene polymerization of half-sandwich group IV metal complexes with tridentate [O,N,S] ligands

A series of half-sandwich group IV metal complexes with tridentate monoanionic phenoxy-imine arylsulfide [O NS] ligand [2-Bu t 4-Me-6-((2-(SC 6 H 5)C 6 H 4 N = CHC 6 H 2 O)](La) and dianionic phenoxy-amine arylsulfide [O N S] ligand [2-Bu t 4-Me-6-((2-(SC 6 H 5)C 6 H 4 N-CH 2 C 6 H 2 O)] 2(Lb) have been synthesized and characterized.Lb was obtained easily in high yield by reduction of ligand La with excess LiAlH 4 in cool diethyl ether.Half-sandwich Group IV metal complexes CpTi[O NS]Cl 2(1a),CpZr[O NS]Cl 2(1b),CpTi[O N S]Cl(2a),CpZr[O N S]Cl(2b) and Cp * Zr[O N S]Cl(2c) were synthesized by the reactions of La and Lb with CpTiCl 3,CpZrCl 3 and Cp * ZrCl 3,and characterized by IR,1 H-NMR,13 C-NMR and elemental analysis.In addition,an X-ray structure analysis was performed on ligand Lb.The title Group IV half-sandwich bearing tridentate [O,N,S] ligands show good catalytic activities for ethylene polymerization in the presence of methylaluminoxane(MAO) as co-catalyst up to 1.58 × 10 7 g-PE.mol-Zr 1.h 1.The good catalytic activities can be maintained even at high temperatures such as 100 ℃ exhibiting the excellent thermal stability for these half-sandwich metal pre-catalysts.     

Synthesis, ethylene polymerization and dynamic features of titanium and zirconium complexes bearing chelating malonate-based enaminoketonato ligands

Synthesis of new titanium and zirconium dichloro complexes bearing malonate-based enaminoketonato (N,O) ligand is described. NMR studies of the catalyst precursors reveal that synthesized complexes have different configurational isomers in solution state and that they undergo structural change within NMR timescale. After MAO activation complexes exhibited low to moderate activities in ethylene polymerization producing bi- or multimodal polyethylenes.     

Highly selective chromium-based ethylene trimerisation catalysts with bulky diphosphinoamine ligands

In situ prepared chromium catalysts containing bulky diphosphinoamine (PNP) ligands, upon activation with MAO, are extremely efficient catalysts for the trimerisation of ethylene to 1-hexene.     

Tetraalkyl titanium and zirconium metal chloride catalyst systems for ethylene polymerization

Coordination polymerization of olefins has become an industrially important, yet still poorly understood enterprise. The ethylene polymerization activity of (neophyl)_nZrCl_4-n shows a twentyfold increase from n = 4 to n = 3 and a further tenfold increase to n = 2. The heterogeneous MR₄/TiCl₄ catalysts (M = Ti, R = benzyl; M = Zr, R = benzyl, neophyl) have been developed. To explore the breadth of extendability, other metal chlorides (main group and transition metal) were substituted for TiCl₄. Indeed, excess AlCl₃ or MgCl₂ and the MR₄ compounds also produced ethylene polymerization catalysts. The inactivity of corresponding (neophyl)₄Ti systems is attributed to sterics. The abovementioned catalysts highlight the necessity of alkyl and chloride ligands at the transition metal catalyst centers.     

Our variations on iron and cobalt catalysts toward ethylene oligomerization and polymerization

Iron and cobalt complexes are a new family of catalysts for ethylene oligomerization and polymerization. The extensive researches on bis(imino)pyridyl metal complexes have been carried out with the aim of synthesizing their derivatives and finding suitable reaction parameters for the optimum activity. Beyond the modification works of bis(imino)pyridyl metal complexes, several alternative models with similar coordination sphere have been developed in our group. This review article describes our experiences in innovating new models of iron and cobalt complexes as catalysts for ethylene oligomerization and polymerization.     

Alkyl-substituted cyclopentadienyl- and phospholyl-zirconium/MAO catalysts for propene and 1-hexene oligomerization

The directed oligomerization of propene and 1-hexene was carried out with a series of Cp′(C₅H₅)ZrCl₂ and Cp₂′ZrCl₂ pre-catalysts (Cp′=C₅HMe₄, C₄Me₄P, C₅Me₅, C₅H₄^tBu, C₅H₃-1,3-^tBu₂, C₅H₂-1,2,4-^tBu₃) together with (C₅H₅)₂ZrCl₂. Oligomers in the molar mass range 300–1500 g/mol for propene and 200–3000 g/mol for 1-hexene were synthesized at 50 °C. The majority of oligomer molecules contain a double-bond end group. Oligomer characterization was carried out by gel permeation chromatography (GPC), ¹H and ¹³C NMR. Vinylidene double bonds (from β-hydrogen elimination) are solely found for the tert-butyl-substituted zirconocenes and for most of the unsymmetrical methyl-substituted Cp′(C₅H₅)ZrCl₂ systems (except Cp′=phospholyl). With (C₄Me₄P)(C₅H₅)ZrCl₂ and with the symmetrical methyl-containing Cp₂′ZrCl₂ pre-catalysts, also vinyl end groups (from β-methyl elimination) are observed in the case of oligopropenes. The vinylidene/vinyl ratio depends on the ligand and the vinyl content increases from C₅HMe₄ (65/35) over C₄Me₄P (61/39) to C₅Me₅ (9/91). The phospholyl zirconocenes and (C₅HMe₄)₂ZrCl₂ also exhibit chain-transfer to aluminum thereby giving saturated oligomers.     

Synthesis, structure and ethylene polymerization behavior of zirconium complexes with chelating ketoiminate ligands

Mixed ketoiminate/ketoimine/pentamethylcyclopentadienyl (Cp*) complex of zirconium, [(η⁵-Cp*){CH₃C(O)CHC(NHR)CH₃}{CH₃C(O)CHC(NR)CH₃}ZrCl₂] (R=4-CF₃Ph) (3) has been prepared in high yield by the reaction of one equivalent of 4-CF₃-phenyl-β-ketoimine (1a) and one equivalent of lithium 4-CF₃-phenyl-β-ketoiminate (2a) with one equivalent of Cp*ZrCl₃ in Et₂O. Bis(ketoiminate)zirconium dichloride complexes, 4 and 6, have been also prepared in high yield by the reaction of amine elimination of ketoimine ligands, respectively 1a and 1b, with Zr(NMe₂)₄ and followed by chlorination reaction with TMSCl. The X-ray crystallography reveals that the compound 3 is based on distorted octahedral geometry containing a ketoimine and a ketoiminate. The ketoiminate ligand coordinates to the zirconium as a bidentate ligand, leaving the metal center coordinatively unsaturated and thus leading to an additional binding of a ketoimine ligand to the metal to stabilize the complex 3. The zirconium complexes 3, 4 and 6 provide the moderate activity for the polymerization of ethylene in the presence of MMAO cocatalyst. Low molecular weight and high density polyethylene was obtained.     

Highly active ethylene polymerization and copolymerization with norbornene using bis(imino‐indolide) titanium dichloride–MAO system

A catalytic system of new titanium complexes with methylaluminoxane (MAO) was found to effectively polymerize ethylene for high molecular weight polyethylene as well as highly active copolymerization of ethylene and norbornene. The bis (imino‐indolide)titanium dichlorides (L₂TiCl₂, 1 – 5 ), were prepared by the reaction of N‐((3‐chloro‐1H‐indol‐2‐yl)methylene)benzenamines with TiCl₄, and characterized by elemental analysis, ¹H and ¹³C NMR spectroscopy. The solid‐state structures of 1 and 4 were determined by X‐ray diffraction analysis to reveal the six‐coordinated distorted octahedral geometry around the titanium atom with a pair of chlorides and ligands in cis‐forms. Upon activation by MAO, the complexes showed high activity for homopolymerization of ethylene and copolymerization of ethylene and norbornene. A positive “comonomer effect” was observed for copolymerization of ethylene and norbornene. Both experimental observations and paired interaction orbital (PIO) calculations indicated that the titanium complexes with electron‐withdrawing groups in ligands performed higher catalytic activities than those possessing electron‐donating groups. Relying on different complexes and reaction conditions, the resultant polyethylenes had the molecular weights M_w in the range of 200–2800 kg/mol. The influences on both catalytic activity and polyethylene molecular weights have been carefully checked with the nature of complexes and reaction conditions. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3415–3430, 2007     

Tuning of nickel 2-phosphinophenolates - catalysts for oligomerization and polymerization of ethylene

This short personal account summarizes recent work concerning the syntheses and structural aspects of neutral and cationic (organo)nickel and (organo)palladium 2-phosphinophenol(ate) complexes and catalysts for the oligo- or polymerization of ethylene.     

Ethylene polymerization and ethylene/hexene copolymerizaion with vandium catalysts bearing thiophenolphosphine ligands

Vanadium(Ⅲ) complexes bearing thiophenol-phosphine ligands (2a-2b) (2-R-6-PPh2-C6H2S) VCl2(THF)2 (2a: R=H; 2b: R=Me3Si) were prepared from VCl3(THF)3 by treating with 1.0 equiv of the ligand in tetrahydrofuran in the presence of excess triethylamine. The two complexes were characterized by FTIR and mass spectra as well as elemental analyses. On activation with Et2AlCl, these complexes exhibited high catalytic activities (up to 22.1 kg PE/(mmolV·h·bar)) even at high temperature (70℃), and produced high molecular weight polymers with unimodal molecular weight distributions, indicating the polymerization took place in a single-site nature. This result may be attributed to benefits of introduction of second-row donor atoms for adjusting charge density of the vanadium centers. In addition, these complexes also exhibited high catalytic activities for ethylene/1-hexene copolymerization. Catalytic activity, comonomer incorporation and polymer molecular weight can be controlled in a wide range by the variation of catalyst structure and the reaction parameters such as Al/V molar ratio, comonomer feed concentration and polymerization reaction temperature.     

Ethylene polymerization and ethylene-1-hexene copolymerization over immobilized metallocene catalysts

Ethylene polymerization and ethylene-1-hexene copolymerization in the presence of metallocene catalysts based on Cp₂ZrCl₂, rac-Et(Ind)₂ZrCl₂, rac-Me₂Si(2-Me-4-Ph-Ind)₂ZrCl₂, and rac-Me₂Si(2-Me-4-Ph-Ind)₂HfCl₂ been investigated. The catalysts have been immobilized on montmorillonite (MMT) containing methylaluminoxanes (MMT-H₂O)/AlMe₃ or isobutylaluminoxanes (MMT-H₂O)/ Ali-Bu₃ synthesized directly on the support surface. The immobilized catalysts, with the general formula (MMT-H₂O)/AlR₃/Zr(Hf)-cene, show a high activity comparable with the activity of the respective homogeneous systems, which depends on the nature of the metal and on the metallocene composition and structure. The catalytic properties of the metallocene systems depend strongly on the nature of the activator as a component of the catalytic complex. (MMT-H₂O)/Ali-Bu₃ is a more effective activator of the hafnocene precatalyst in the polymerization processes than oligomeric methylaluminoxane or methylaluminoxane synthesized on the support. The immobilization of the metallocenes on (MMT-H₂O)/AlR₃ leads to an increase in the molar mass of polyethylene and ethylene-1-hexene copolymers relative to the molar mass of the polymers synthesized using the respective homogeneous systems. The immobilized metallocene catalysts display high selectivity toward the insertion of a higher α-olefin (1-hexene) into the polymer chain, retaining this important property of their homogeneous counterparts.