Catalyst Precursors For Ethylene Polymerization Research Articles

Diamido Complexes of Titanium and Zirconium as Catalyst Precursors for Ethylene Polymerization

A series of 8 new complexes of titanium and zirconium with diamido ligands bearing an ethylene and propylene bridge between the two amido groups were synthesized and tested for ethylene polymerization. Titanium complexes bearing an ethylene bridge between the two amido groups showed higher activities than the derivatives with a propylene bridge. In the case of the zirconium complexes, the propylene bridged complexes were more active than the corresponding ethylene bridged. The introduction of bulky groups on the ligand structure resulted in an increase in the activity. DFT calculations were performed to determine the activation energy barriers for different reaction steps. The calculated activation energy for the insertion of ethylene into an M-CH3 bond is in the range of 12.2-16.8 kcal/mol and the activation energy for the chain termination via β-H transfer reaction is 12.5-14.4 kcal/mol.

2,2′-Bis(methylene)biphenylidene-bridged bis(3-indenyl) dichloride complexes of Ti, Zr and Hf as catalyst precursors for ethylene polymerization

ansa metallocene complexes of Ti, Zr and Hf were synthesized, characterized and tested as catalysts for homogeneous ethylene polymerization. The ligand system comprises two indenyl moieties tethered at the 1,1′-positions via a 2,2′-dimethyl biphenylene bridge. The ligand precursor was obtained by the reduction of diphenic acid using lithium aluminum hydride (LiAlH4), followed by the reaction with phosphorus tribromide, and, finally, the reaction with indenyllithium. The corresponding group (IV) metal complexes were synthesized by deprotonation of the ligand precursors using n-BuLi followed by reactions of the corresponding metal tetrachloride. After activation with methylaluminoxane (MAO), the zirconium and hafnium complexes proved as highly active catalysts for ethylene polymerization. The zirconium complex 6 showed the best performance with 12,460 kg PE/mol cat. h. The titanium complex 5 showed no catalytic activity obviously because of decomposition reactions.

Unbridged 1- and 2-substituted bis(silylindenyl) zirconium(IV) and hafnium(IV) dichloride complexes as catalyst precursors for ethylene polymerization

Twelve unbridged metallocene dichloride complexes of the types [1-(4-XC6H4SiMe2)-η5-Ind]2MCl2 and [2-(4-XC6H4SiMe2)-η5-Ind]2MCl2 (X=Me, MeO, F; M=Zr, Hf) with differently 1- and 2-substituted indenyl ligands have been synthesized, characterized and applied for catalytic ethylene polymerization. After activation with methylaluminoxane (MAO), all complexes are catalysts for ethylene polymerization. However, in nearly all cases, the species with the silyl substituent in the 1-position show much higher activities than those with the same substituent in 2-position of the indenyl moiety. For instance, the MAO activated complex bis(η5-1-(dimethyl-4-tolylsilyl)idenyl) zirconium(IV) dichloride (3), displayed an almost five times higher activity (3980kg PE/mol cat.h) than the isomeric bis(η5-2-(dimethyl-4-tolylsilyl)indenyl) zirconium(IV) dichloride (19)/MAO catalyst (870kg PE/mol cat.h). The same trend was observed for the para-fluorophenyl silyl indenyl complexes 23 and 17. This behavior may be explained in a way that the same silyl substituent in position 2 can exert more steric hindrance around the metal center compared to the 1-substituted analogues. The GPC characterization of the produced polyethylenes showed that some of the resins have a bimodal molecular weight distribution indicating at least two different active sites that are involved in the polymerization process.

Molecular weight control in organochromium olefin polymerization catalysis by hemilabile ligand-metal interactions.

A series of Cr(III) complexes based on quinoline-cyclopentadienyl ligands with additional hemilabile side arms were prepared and used as single-site catalyst precursors for ethylene polymerization. The additional donor functions interact with the metal centers only after activation with the co-catalyst. Evidence for this comes from DFT-calculations and from the differing behavior of the complexes in ethylene polymerization. All complexes investigated show very high catalytic activity and the additional side arm minimizes chain-transfer reactions, leading to increase of molecular weights of the resulting polymers.

Synthesis, structural characterization, and ethylene polymerization behavior of (arylimido)vanadium(V) complexes bearing tridentate Schiff base ligands

A series of novel (arylimido)vanadium(V) complexes bearing tridentate salicylaldiminato chelating ligands, V(N-2,6-Me2C6H3)Cl2[(O-2-tBu-4-R-C6H3)CHND] (R = H, D = 2-CH3OC6H4 (2a); 2-CH3SC6H4 (2b); 2-Ph2PC6H4 (2c); 8-C9H6N (quinoline) (2d); CH2C5H4N (2e); R = tBu, D = 2-Ph2PC6H4 (2f)), were prepared from V(NAr)Cl3 by reacting with 1.0 equiv of the ligands in the presence of triethylamine in tetrahydrofuran. These complexes were characterized by 1H, 13C, 31P, and 51V NMR spectra and elemental analysis. The structures of 2c and 2f were further confirmed by X-ray crystallographic analysis. These (arylimido)vanadium(V) complexes are effective catalyst precursors for ethylene polymerization in the presence of Et2AlCl as a cocatalyst and ethyl trichloroacetate as a reactivating agent. Complex 2c with a PPh2 group in the sidearm was found to exhibit an exceptional activity up to 133800 kg polyethylene/molV h for ethylene polymerization at 75 °C, which is one of the highest activities displayed by homogeneous vanadium(V) catalysts at high temperature. Moreover, high molecular weight polymers with unimodal molecular weight distribution can be obtained, indicating the single site behavior of these catalysts. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 2633-2642

Ethylene polymerization with long‐lifetime monopendant thienyl‐substituted group 4 metallocenes

A series of group 4 metallocenes (RCp)[Cp―(bridge)―(2‐C4H3S)]MCl2 [M = Ti (C1, C2, C3, C4); M = Zr (C5, C6, C7, C8)] bearing a pendant thiophene group on a cyclopentadienyl ring have been synthesized, characterized and tested as catalyst precursors for ethylene polymerization. The molecular structures of representative titanocenes C2 and C4 were confirmed by single‐crystal X‐ray diffraction and revealed that both complexes exist in an expected coordination environment for a monomeric bent metallocene. No intramolecular coordination between the thiophene group and the titanium center could be observed in the solid state. Upon activation by methylaluminoxane (MAO), titanocenes C1, C2, C3, C4 showed moderate catalytic activities and produced high‐ or ultra‐high‐molecular‐weight polyethylene (Mv 70.5–227.1 × 104 g mol−1). Titanocene C3 is more active and long‐lived, with a lifetime of nearly 9 h at 30 °C. At elevated temperatures of 80–110 °C, zirconocenes C5, C6, C7, C8 displayed high catalytic activities (up to 27.6 × 105 g PE (mol Zr)−1 h−1), giving high‐molecular‐weight polyethylene (Mv 11.2–53.7 × 104 g mol−1). Even at 80 °C, a long lifetime of at least 2 h was observed for the C8/MAO catalyst system. Copyright © 2014 John Wiley & Sons, Ltd.

Highly active half-sandwich chromium(iii) catalysts bearing bis(imino)pyrrole ligands for ethylene (co)polymerization

A series of novel half-sandwich chromium(iii) complexes bearing bis(imino)pyrrole complexes was synthesized, characterized, and investigated as catalyst precursors for ethylene polymerization and ethylene/norbornene copolymerization.

Zirconium complexes bearing bis(phenoxy‐imine) ligands with bulky o‐bis(aryl)methyl‐substituted aniline groups: synthesis, characterization and ethylene polymerization behavior

A series of bis(phenoxy‐imine) zirconium complexes bearing bulky o‐bis(aryl)methyl‐substituted aryl groups on the aniline moiety have been synthesized, characterized and tested as catalyst precursors for ethylene polymerization. 1H NMR spectroscopy suggests that these complexes exist as a single chiral C2‐symmetric isomer in the solution. X‐ray crystallographic analysis of the resulting biszwitterionic‐type adduct complex C1 · 2HCl reveals that the phenoxy‐imine groups function as a monodentate phenoxy ligand and the oxygen atoms are oriented trans to each other at the central metal atom. Using modified methylaluminoxane (MMAO) as co‐catalyst, C1 · 2HCl, C2–C6 exclusively produce linear aluminium‐terminated polyethylenes (Al‐PEs) with high activity (up to 16.89 × 106 g PE (mol Zr h)−1, suggesting that chain transfer to aluminum is the predominant termination mechanism. It is noteworthy that the introduction of an excessively bulky o‐bis(aryl)methyl substituent adjacent to the imine‐N produces low molecular‐weight Al‐PEs (Mv 1.6–10.1 × 103) due to the enhanced rate of chain transfer to alkylaluminium groups during polymerization. Copyright © 2013 John Wiley & Sons, Ltd.

Olefin Polymerization by Half-Titanocenes Containing η2-Pyrazolato Ligands−MAO Catalyst Systems

A series of half-titanocenes containing pyrazolato ligands, Cp′TiCl2(3,5-R2C3HN2) (1a−d, 2a−c, 3a−c) [Cp′ = Cp (1), Cp* (2), tert-BuC5H4 (tert-BuCp, 3); R = H (a), Me (b), iPr (c), Ph (d)], have been employed as the catalyst precursors for ethylene polymerization, syndiospecific styrene polymerization, and copolymerization of ethylene with 1-hexene, styrene, and norbornene (NBE) in the presence of MAO cocatalyst. The Cp* analogues, especially 2a,b, exhibited high catalytic activities for ethylene polymerization affording the polymer with unimodal molecular weight distributions, whereas the Cp analogue (especially 1b,c) and the tert-BuCp analogues (3a−c) exhibited high catalytic activities for syndiospecific styrene polymerization. The ethylene/styrene copolymerization using the tert-BuCp−diisopropyl analogue (3c) −MAO catalyst system proceeds in a living manner, irrespective of the styrene concentration employed (in toluene at 25 °C), and the same system exhibited relatively high catalytic activity for the ethylene/NBE copolymerization with highly efficient NBE incorporation.

フェノキシ配位子を有する新規ヒドロトリス(ビラゾイル)ボラン配位チタン錯体の合成・同定、およびエチレン重合における配位子効果

フェノキシ配位子を有する新規ヒドロトリス(ビラゾイル)ボラン配位チタン錯体の合成・同定、およびエチレン重合における配位子効果

Synthesis of (Arylimido)vanadium(V) Complexes Containing (2-Anilidomethyl)pyridine Ligands and Their Use as the Catalyst Precursors for Olefin Polymerization

A series of (arylimido)vanadium(V) dichloride complexes containing (2-anilidomethyl)pyridine ligands of the type V(NAr)Cl2[2-Ar′NCH2(C5H4N)] [Ar = 2,6-Me2C6H3; Ar′ = 2,6-Me2C6H3 (1a), 2,6-iPr2C6H3 (1b), 2,6-F2C6H3 (1c)] have been prepared from V(NAr)Cl3 by treating with Li[2-Ar′NCH2(C5H4N)], and the structures of 1b,c have been determined by X-ray crystallography. These complexes are effective catalyst precursors for ethylene polymerization in the presence of Al cocatalysts: 1b showed the highest catalytic activities in the presence of Et2AlCl (6000 kg PE/mol V·h), and the observed activities of 1a,b in the presence of Et2AlCl were much higher than those in the presence of MAO. V(NAr)(CH2SiMe3)2[2-Ar′NCH2(C5H4N)] (2a,b) have been prepared by treating 1a,b with 2.0 equiv of LiCH2SiMe3, and their structures have been determined by X-ray crystallography. The dialkyl complex 2b cleanly reacted with 2.0 equiv of (CF3)2CHOH in C6D6 at 25 °C to afford V(NAr)(CH2SiMe3)[OCH(CF3)2][2-Ar′NCH2(C5H4N)] (3), and the reaction with 3.0 equiv of (CF3)2CHOH eventually afforded V(NAr)[OCH(CF3)2]2[2-Ar′NCH2(C5H4N)] (4) from 3 after 3 days. The dialkyl complexes 2a,b showed catalytic activities for ring-opening metathesis polymerization (ROMP) of norbornene in benzene at 80 °C in the presence of PMe3. The ROMP did not occur in the absence of PMe3 under the same conditions, suggesting that an additional coordination of PMe3 may be required to induce the α-hydrogen elimination.

Thermostable α-Diimine Nickel(II) Catalyst for Ethylene Polymerization: Effects of the Substituted Backbone Structure on Catalytic Properties and Branching Structure of Polyethylene

On the basis of the strategy of promoting thermostability of α-diimine nickel catalyst by ligand backbone framework, a series of α-diimine nickel(II) complexes with bulky camphyl or diaryl-substituted backbones, [2,6-(R2)2C6H3−N═C(R1)−C(R1)═N−2,6-(R2)2C6H3]NiBr2 (1a, R1 = Ph, R2 = CH3; 2a, R1 = 4-methylphenyl, R2 = CH3; 3a, R1 = 4-fluorophenyl, R2 = CH3; 4a, R1 = camphyl, R2 = CH3; 4b, R1 = camphyl, R2 = i-Pr), were synthesized and used as catalyst precursors for ethylene polymerization. Crystallographic analysis revealed that the bulky camphyl backbone has a valid steric-effect on the nickel center by blocking the axial site for the metal center and suppressing the potential rotation of the CAr−N bond. Ethylene polymerizations catalyzed by these nickel α-diimine complexes activated by MAO were systematically investigated and the influences of the substituted backbones as well as reaction temperature on the catalytic activity, molecular weight and branching structure of the polymers were evaluated. It was...

Ethylene polymerization in supercritical carbon dioxide with binuclear nickel(ii) catalysts

A series of new, highly fluorinated neutral (kappa(2)-N,O) chelated Ni(II) binuclear complexes based on salicylaldimines bridged in p-position of the N-aryl group were prepared. The complexes are single-component catalyst precursors for ethylene polymerization in supercritical carbon dioxide and toluene. Solubility of the catalyst precursors in supercritical carbon dioxide is effected by a large number of up to 18 trifluoromethyl groups per molecule. Semicrystalline polyethylene with a low degree of branching is formed (ca. 10 branches/1000 carbon atoms). Polymer microstructures are independent of the nature of the bridging moiety, while stability of the catalysts appears to differ.

Synthesis of (1-Adamantylimido)vanadium(V) Complexes Containing Aryloxo, Ketimide Ligands: Effect of Ligand Substituents in Olefin Insertion/Metathesis Polymerization

A series of (1-adamantylimido)vanadium(V) complexes containing anionic donor ligands of the type, V(NAd)Cl2(L) [Ad = 1-adamantyl; L = O-2,6-Me2C6H3 (2), O-2,6-(i)Pr2C6H3 (3), NC(t)Bu2 (5), NC((t)Bu)CH2SiMe3 (6), NC((t)Bu)Ph (7), NCPh2 (8)], have been prepared from V(NAd)Cl 3, which was in turn prepared from VOCl3 by treatment with 1-adamantylisocyanate in octane, by treatment with the corresponding lithium salts (lithium phenoxides, lithium ketimides) in Et2O. These complexes (2, 3, 5-8) were identified by NMR spectroscopy and elemental analysis, and the structures for 2 and 5 were determined by X-ray crystallography. The reaction of V(NAd)Cl3 with 2,6-dimethylphenol in n-hexane afforded the tris(aryloxo) analogue V(NAd)(O-2,6-Me2C6H3)3 (4), the structure of which was determined by X-ray crystallography. 8 gradually decomposed in toluene to give a dimeric species, [N(Ad)H3](+)[V2(mu2-Cl)3Cl2(NAd)2(NCPh2)2](-) (10), but 8 was stabilized as a PMe 3 coordinated species, V(NAd)Cl2(NCPh2)(PMe3)2 (9): the structures for 9 and 10 were determined by X-ray crystallography. These complexes were evaluated as catalyst precursors for ethylene polymerization in the presence of MAO. The ketimide analogues, especially 5, exhibited moderate catalytic activity, and the activity with a series of V(NAd)Cl2(L)-MAO catalyst systems increased in the order: L = NC(t)Bu2 (5, 516 kg-PE/mol x V x h) > NC((t)Bu)Ph (7, 300) > NCPh2 (8, 105) > NC((t)Bu)CH2SiMe3 (6, 70.8). These complexes (2, 3, 5, 6) were found to be effective as catalyst precursors for the ring-opening metathesis polymerization (ROMP) of norbornene (NBE) in the presence of MeMgBr and PMe3.

Highly Active Binuclear Neutral Nickel(II) Catalysts Affording High Molecular Weight Polyethylene

A series of new binuclear neutral κ2-N,O-chelated Ni(II) complexes [(H2C)n{[(2,6-R2-4-yl-C6H2)-N═C(H)-(3,5-I2-2-O-C6H2)-κ2-N,O]Ni(CH3)(pyridine)}2] (R = iPr, 3,5-(CF3)2C6H3; n = 0, 1) are reported. The complexes are single-component catalyst precursors for ethylene polymerization. Catalyst activities exceed those of mononuclear analogues studied substantially. With 3.4 × 105 TO h−1, high molecular weight polymer is obtained (Mw 9.2 × 105 g mol−1; Mn 2.8 × 105 g mol−1). Semicrystalline polyethylene with a low degree of branching is formed (2 to 12 branches/1000 carbon atoms; prepared at 30 to 70 °C polymerization temperature), with Tm 112 to 136 °C. Polymerization in aqueous emulsion affords polyethylene dispersions.

2-AMINOMETHYLPYRIDINE NICKEL(II) COMPLEXES — SYNTHESIS, MOLECULAR STRUCTURE AND CATALYSIS OF ETHYLENE POLYMERIZATION

A series of new nickel(II) complexes with 2-aminomethylpyridine ligands, (2-PyCH2NHAr)2NiBr2 (Ar = 2,6-dimethylphenyl 2a; 2,6-diisopropylphenyl 2b, 2,6-difluorophenyl 2c), have been synthesized and used as catalyst precursors for ethylene polymerization in the presence of methylaluminoxane (MAO). The catalysts containing ortho-alkyl-substituents afford high molecular weight branched polyethylenes as well as a certain amount of oligomers. Enhancing the steric bulk of the alkyl substituent of the catalyst resulted in higher ratio of solid polymer to oligomer and higher molecular weight of the polymer. Catalyst 2c containing ortho-fluoro-substituents exhibited the highest catalytic activity, but only oligomers in which C12H24 had the maximum content were obtained by the catalyst. The molecular weight, molecular weight distribution, and microstructure of the resulted polymer were characterized by gel permeation chromatography and 13C-NMR spectrogram.

Nickel(II)−Methyl Complexes with Water-Soluble Ligands L [(salicylaldiminato-κ2N,O)NiMe(L)] and Their Catalytic Properties in Disperse Aqueous Systems

Neutral (salicylaldiminato)nickel(II) methyl complexes [{6-C(H)NAr-2,4-I2C6H2O-κ2N,O}NiMe(L)] (Ar = 2,6-{3,5-(F3C)2C6H3}2C6H3) with different water-soluble ligands L (2a, L = 1,3,5-triaza-7-phosphaadamantane; 2b, L = hexamethylenetetramine (urotropine); 2c, L = tetraethylammonium pyridine-3-sulfonate; 2d, L = amino-terminated poly(ethylene glycol) monomethoxy ether) were prepared. 2a−d are potentially water-soluble catalyst precursors for ethylene polymerization, which form a water-insoluble active site [{κ2-N,O}NiR(ethylene)] (R = growing chain). Only complex 2d was found to be water-soluble (>2 mmol L-1); 2c is soluble in water/2-propanol mixtures. In toluene as a reaction medium, only the relatively weakly coordinated tertiary amine complex 2b is polymerization active (1.7 × 104 TO). In aqueous systems 2c,d are also active due to compartmentalization of the active site in the polymer particles and of L in the aqueous phase. Polyethylene particle sizes vary from 18 nm (dispersions formed with 2d) to over 0.5 μm (2c) to suspensions (2b) depending on the initial state of the reaction mixture, correlated with catalyst solubility.

New o-methoxyphenylcyclopentadienylchromium (III) complexes: Synthesis, structures and catalytic properties for ethylene polymerization

Two new ligands 1-(2-methoxyphenyl)-3,4-diphenylcyclopentadiene ( 1) and 1-(2-methoxyphenyl)-2,3,4,5-tetramethylcyclopentadiene ( 2), as well as their corresponding cyclopentadienylchromium complexes η 5-1-(2-methoxyphenyl)-3,4-diphenylcyclopentadienyl chromium dichloride ( 3) and η 5-1-(2-methoxyphenyl)-2,3,4,5-tetramethylcyclopentadienyl chromium dichloride ( 4) were synthesized and characterized. Molecular structures of 3 and 4 were determined by single-crystal X-ray diffraction. Complexes 3 and 4 were tested as catalyst precursors for ethylene polymerization. When activated with Al( i Bu) 3 and Ph 3 C + B ( C 6 F 5 ) 4 - , complex 3 shows reasonable catalytic activity while 4 exhibits high catalytic activity for ethylene polymerization. The effects of temperature and Al/Cr ratio on the catalytic activity were studied. The molecular weight and melting temperature of the produced polyethylenes were determined.

Synthesis and characterization of phosphorous-bridged bisphenoxy titanium complexes and their application to ethylene polymerization

Phosphorous-bridged bisphenoxy titanium complexes were synthesized and their ethylene polymerization behavior was investigated. Bis[3- tert-butyl-5-methyl-2-phenoxy](phenyl)phosphine tetrahydrofuran titanium dichloride ( 4a) was obtained by treatment of 3 equiv of n-BuLi with bis[3- tert-butyl-2-hydroxy-5-methylphenyl](phenyl)phosphine hydrochloride salt ( 3a) followed by TiCl 4(THF) 2 in THF. THF-free complexes 5a– 5d were synthesized more conveniently by the direct reaction of MOM-protected ligands ( 2a– 2d) with TiCl 4 in toluene. X-ray analysis of 4a revealed that the ligand is bonded to the octahedral titanium (IV) center in a facial fashion and two chlorine atoms possess cis-geometry. Complexes 4a and 5a– 5d were utilized as catalyst precursors for ethylene polymerization. Complex 5c gave high molecular weight polyethylene ( M w = 1,170,000, M w/ M n = 2.0) upon activation with Al( i Bu) 3/[Ph 3C][B(C 6F 5) 4] (TB). Ethylene polymerization activity of 5d activated with Al( i Bu) 3/TB reached 49.0 × 10 6 g mol (cat) −1 h −1.

Ethylene polymerization and oligomerization catalyzed by bulky β-diketiminato Ni(II) and β-diimine Ni(II) complexes/methylaluminoxane systems

β-Diketiminato complexes Ni{(N(Ar)C(Me)) 2CH}Br ( 9), Ni{(N(Ar)C(Me)) 2CH} Pph 3Br ( 10) and β-diimine complexes Ni{(N(Ar)C(Me)) 2CH 2}Br 2 ( 5) (Ar = 2,6-iPr 2C 6H 3 ( a), 2,6-Me 2C 6H 3 ( b)) were used as catalyst precursors for ethylene polymerization in the presence of methylaluminoxane (MAO). High molecular weight ethylene polymers as well as short chain oligomers (C4–C8) were simultaneously produced from the catalysis reactions. Ethylene polymers obtained by using these β-N–N Ni(II)/MAO catalyst systems are mainly methyl branched. Small amounts of even number branches were also observed in the 13C NMR spectra of the obtained ethylene polymers, which are believed generating from the incorporation of simultaneously produced α-olefins. Except methyl branch and the branches derived from the incorporation of α-olefin oligomers, the formation of other branch types via the chain walking process is not favored in β-diketiminato Ni(II) systems.