Precatalysts For Polymerization Research Articles

Catalytic Polymerization in Dense CO2to Controlled Microstructure Polyethylenes

A series of partially novel, (κ2-N,O) Ni(II) methyl complexes coordinated by pyridine or N,N,N′,N′-tetramethylethylenediamine (tmeda), based on different κ2-N,O-chelating salicylaldimines, 2,6-diisopropylanilinotropone, and a ketoenamine, were studied as precatalysts for olefin polymerization in dense carbon dioxide. Bis(trifluoromethyl)phenyl substituents promote solubility in the CO2 reaction medium, as quantified by solubility studies of the free N,OH ligands over a range of CO2 densities (ρ = 0.2−0.9 g mL−1) at 25 and 50 °C and thus enhance catalyst activities. By appropriate choice of the catalyst precursor and polymerization reaction conditions (CO2 density, ethylene concentration, and temperature), strictly linear polyethylene with high molecular weight is obtained (<1 branch/1000 carbon atoms, Mw =106 g mol−1; Mw/Mn = 2) which displays typical thermal characteristics and density of ultrahigh molecular weight polyethylene. Copolymerization with 1-hexene, and particularly with norbornene, allows for...

Group 4 bis(chelate) metal complexes of monoanionic bidentate [E,O−] ligands (E = O, S): synthesis and application as α-olefin polymerization catalysts

Monoanionic bidentate phenoxy-ether [O(-),O] and phenoxy-thioether [O(-),S] ligands were synthesized and used to prepare octahedral group 4 metal complexes with general formula [O(-),E](2)ML(2) (complex 1: E = S, M = Hf, L = Bn; complex 2: E = O, M = Ti, L = NMe(2); complex 3: E = S, M = Ti, L = NMe(2); complex 4: E = S, M = Ti, L = Cl). Variable-temperature 1H NMR studies were performed on all the complexes 1-4 in the range of +20 to -70 degrees C. For the hafnium complex 1 a dynamic interchange of the Delta and Lambda enantiomers for a C2-symmetric isomer was revealed. Eyring analysis indicated that rearrangement of the ligands occurs via a non-dissociative mechanism. In the range of the explored temperatures, a broadening of the signals was observed for complexes 2-3. Finally, a reversible fluxional process between several isomers was revealed for complex 4. Complexes 1-4 were tested as pre-catalysts for ethylene and propene polymerization in combination with different activators and under variable conditions. Complex 1 was found to be inactive whereas complexes 2-4 showed moderate activities in the polymerization of ethylene and propene. A mixture of polymers with different microstructure was obtained in all cases, coherently with the fluxional behaviour of the pre-catalysts observed in solution.

Comparing families of olefin polymerization precatalysts using the percentage of buried volume

We report a systematic comparison of the steric properties of different stereoselective olefin polymerization catalysts using the percentage of buried volume, %V(Bur), as a molecular descriptor. For the first time, isoselective and syndioselective group 4 metallocenes are compared with group 4 isoselective phenoxy-amine and group 4 syndioselective phenoxy-imine catalysts using the same molecular descriptor. The results indicate that the basic bis-Cp skeleton of metallocenes is more hindered than the unsusbtituted skeleton of phenoxy-amine and phenoxy-imine based catalysts. The different effect of the same alkyl substituents on the different catalysts skeleton is also examined. A reasonable correlation is found between the experimental stereoselectivity and the %V(Bur).

Group 4 metal complexes bearing new tridentate (NNO) ligands: Benzyl migration and formation of unusual C–C coupled products

Abstract Group 4 metal complexes bearing new phenoxy(benzimidazolyl)-imine, -amine and -amide ligands have been synthesized. A series of metal chloride derivatives has been prepared via treatment of MCl4(THF)2 (M = Ti, Zr, Hf) with the in situ generated sodium salt of the (benzimidazolyl)imine phenol 1. Reaction of the pro-ligand 2 with TiCl4(THF)2 afforded the corresponding complex 8 in which the amine proton remains bound to the nitrogen donor. Benzyl complexes of zirconium and hafnium were synthesized via treatment of pro-ligands 1 and 2 with M(CH2Ph)4 precursors. The complexes [NNO]M(CH2Ph)3 (6 M = Zr, 7 M = Hf) were found to undergo benzyl migration from the metal centre to the imine carbon of the ligand backbone giving complexes 11 and 12; the migration follows first order kinetics. The reaction of 1 with Ti(NMe2)4 led to the formation of an unusual C–C coupled product in which a new piperazine ring has formed. Complexes 11 and 12 undergo related transformations, leading to analogous C–C coupled products which were characterized by X-ray crystallography. Deuterium labelling experiments were carried out to determine the mechanistic pathway of the reactions. Chloride and benzyl complexes 3–12 were screened as pre-catalysts for olefin polymerization.

Catalyst Site Epimerization during the Kinetic Resolution of Chiral α-Olefins by Polymerization

A new enantiopure C1-symmetric olefin polymerization precatalyst, (1,2-SiMe_2)_2{η^5-C_5H_2-4-((S)-CHEtCMe_3)}{η^5-C_5H-3,5-(CHMe_2)_2}ZrCl_2, (S)-2, was synthesized, and its use for the kinetic resolution of 3-methyl-substituted racemic α-olefins was investigated. Upon activation with methyl aluminoxane (MAO), selectivity factors for most olefins were greater when (S)-2 was used as the catalyst as compared to its previously reported methylneopentyl analogue, (1,2-SiMe_2)_2{η^5-C_5H_2-4-((S)-CHMeCCMe_3)}{η^5-C_5H-3,5-(CHMe_2)_2}ZrCl_2, (S)-1. Pentad analysis of polypropylene produced by the two catalysts at various propylene concentrations indicates that (S)-2 undergoes more efficient site epimerization (polymeryl chain swinging prior to subsequent monomer enchainment) at intermediate propylene concentrations compared to (S)-1. At high and low propylene concentrations, however, the two catalysts behave similarly. On the other hand, polymerization of 3,5,5-trimethyl-1-hexene at different olefin concentrations and temperatures illustrated that selectivity differences between the two catalysts are likely not a consequence of inefficient site epimerization for (S)-1.

Ethylene polymerization by (α‐diimine)nickel(II) complexes bearing different substituents on para‐position of imines activated with MMAO

AbstractA series of (α‐diimine)nickel(II) complexes [ArN = C(Nap)C = NAr]NiBr2 (Nap = 1,8‐naphthdiyl, Ar = 2,6‐Me2C6H3, 3a; Ar = 2,4,6‐Me3C6H23b; Ar = 2,6‐Me2‐4‐tBuC6H2, 3c; Ar = 2,6‐Me2‐4‐BrC6H2, 3d; Ar = 2,6‐Me2‐4‐ClC6H2, 3e; Ar = 2,6‐iPr2C6H3, 3f; Ar = 2,4,6‐iPr3C6H2, 3g; Ar = 2,6‐iPr‐4‐BrC6H2, 3h) have been synthesized, characterized, and investigated as precatalysts for ethylene polymerization in the presence of modified methylaluminoxane (MMAO). The substituents of α‐diimine ligands and their positions located significantly influence catalyst activity and polymer property. It is found that the catalytic activities of the nickel complex/MMAO systems and the microstructure of the polymer obtained are dominated by not only hindering effect of ortho‐position substituents but also electronical effect of para‐position substituents. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Polymerization of ethylene to branched polyethylene with silica and Merrifield resin supported nickel(II) catalysts with α-diimine ligands

Silica and Merrifield resin were used as carriers for the support of α-diimine nickel(II) precatalysts for ethylene polymerization. The α-diimine ligands containing allyl were modified by introducing the reactive Si–Cl end-group, allowing their immobilization via a direct reaction of the Si–Cl groups with the silanols on silica surface or the hydroxyls on the ethanolamine-modified Merrifield resin. The resulting supported α-diimine ligands were characterized by analytical and spectroscopic techniques (NMR and FT-IR). The complexation reactions of the supported ligands with NiBr 2(dimethylether) (DME) gave rise to supported α-diimine nickel(II) precatalysts. These heterogeneous precatalysts exhibited high activity for ethylene polymerization in the presence of modified methylaluminoxane (MMAO) as a cocatalyst. The molecular weights of the polyethylenes obtained with the supported precatalysts were much higher than those produced with the corresponding homogeneous precatalysts.

Ethylene polymerizations, and the copolymerizations of ethylene with hexene or norbornene with highly active mono(β‐enaminoketonato) vanadium(III) catalysts

AbstractFive novel vanadium(III) complexes [PhN = C(R2)CHC(R1)O]VCl2(THF)2 (4a: R1 = Ph, R2 = CF3; 4b: R1 = t‐Bu, R2 = CF3; 4c: R1 = CF3, R2 = CH3; 4d: R1 = Ph, R2 = CH3; 4e: R1 = Ph, R2 = H) have been synthesized and characterized. On activation with Et2AlCl, all the complexes, in the presence of ethyl trichloroacetate (ETA) as a promoter, are highly active precatalysts for ethylene polymerization, and produce high molecular weight and linear polymers. Catalyst activities more than 16.8 kg PE/mmolV h bar and weight‐average molecular weights higher than 173 kg/mol were observed under mild conditions. The copolymerizations of ethylene and norbornene or 1‐hexene with the precatalysts were also explored, which leads to high molecular weight copolymers with high comonomer incorporation. Catalyst activity, comonomer incorporation, and polymer molecular weight as well as polydispersity index can be controlled over a wide range by the variation of precatalyst structure and the reaction parameters such as Al/V molar ratio, comonomer feed concentration, and polymerization temperature. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2038–2048, 2008

Synthesis and characterization of a series of 2‐aminopyridine nickel(II) complexes and their catalytic properties toward ethylene polymerization

AbstractA series of 2‐aminopyridine Ni(II) complexes bearing different substituent groups {(2‐PyCH2NAr)NiBr, Ar = 2,4,6‐trimethylphenyl (3a), 2,6‐dichlorophenyl (3b), 2,6‐dimethylphenyl (3c), 2,6‐diisopropylphenyl (3d), 2,6‐difluorophenyl (3e); (2‐PyCH2NHAr)2NiBr2, Ar = 2,6‐diisopropylphenyl (4a)} have been synthesized and investigated as precatalysts for ethylene polymerization in the presence of methylaluminoxane (MAO). High molecular weight branched polymers as well as short‐chain oligomers were simultaneously produced with these complexes. Enhancing the steric bulk of the ortho‐aryl‐substituents of the catalyst resulted in higher ratio of solid polymer to oligomer and higher molecular weight of the polymer. With ortho‐haloid‐substitution, the catalysts afforded a product with low polymer/oligomer ratio (3b) and even only oligomers (3e) in which C14H28 had the maximum content. Compared with complex 3d containing ionic ligand, complex 4a containing neutral ligand exhibited obviously low catalytic activity for ethylene polymerization. The molecular weight, molecular weight distribution, and microstructure of the resulted polymer were characterized by gel permeation chromatography and 13C NMR spectrogram. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1618–1628, 2008

Synthesis of a new olefin polymerization catalyst supported by an sp3-C donor via insertion of a ligand-appended alkene into the Hf–C bond of a neutral pyridylamidohafnium trimethyl complex

A new living and isoselective propylene polymerization precatalyst was generated via the intramolecular insertion of a ligand-appended vinyl group into the Hf-C bond of a neutral pyridylamidohafnium trimethyl complex.

Transition-metal complexes of phenoxy-imine ligands modified with pendant imidazolium salts: Synthesis, characterisation and testing as ethylene polymerisation catalysts

Reaction between 3-((1 R,2 R)-2-{[1-(3,5-di- tert-butyl-2-hydroxy-phenyl)-meth-( E)-ylidene]-amino}-cyclohexyl)-1-isopropyl-4-phenyl-3 H-imidazol-1-ium bromide ( 1a) or the derivative 3-((1 R,2 R)-2-{[1-(2-hydroxy-5-nitro-phenyl)-meth-( E)-ylidene]-amino}-cyclohexyl)-1-isopropyl-4-phenyl-3 H-imidazol-1-ium bromide ( 1b) and metal halides MCl x .yTHF (M = Zr, x = 4, y = 2; M = V, x = y = 3; M = Cr, x = y = 3), in THF, at −78 °C gives the metal complexes of general formula [MCl x (κ 2- N, O-OC 6H 2R 1R 2C(H) N–C 6H 10–Im) 2][Br] 2 (where M = Zr, x = 2, R 1 = R 2 = t Bu, 2; M = Zr, x = 2, R 1 = H, R 2 = NO 2, 3; M = V, x = 1, R 1 = R 2 = t Bu, 4; M = Cr, x = 1, R 1 = R 2 = t Bu, 5; M = Fe, x = 0, R 1 = R 2 = t Bu, 6; Im = 1-isopropyl-4-phenyl- 3H-imidazol-1-ium-3-yl). 1H and 13C NMR spectroscopy of 2 and 3 indicate κ 2- N, O-ligand coordination via the phenoxy-imine moiety with pendant imidazolium salt that is corroborated by a single crystal structure of 6. Compounds 2, 3, 4 and 5 were tested as precatalysts for ethylene polymerisation in the presence of methylaluminoxane (MAO) cocatalyst, showing low activity. Selected polymer samples were characterised by GPC showing multimodal molecular weight distributions.

Polymer Microstructure Control in Catalytic Polymerization Exclusively by Electronic Effects of Remote Substituents

AbstractA series of (κ2‐N,O)salicylaldiminato nickel methyl pyridine complexes 8a–h‐pyr bearing 2,6‐di‐(4‐R′‐phenyl)phenyl groups on the imine nitrogen and varying in the remote substituents [R′=C8F17 (a), CF3 (b), F (7c), H (d), Me (e), tert.‐butyl (f), OMe (g), and NMe2 (h)] were studied as precatalysts for ethylene polymerization. Complexes 8a–h‐pyr catalyze the polymerization of ethylene to low molecular weight polyethylene. Decreasing molecular weight and increasing degrees of branching are observed in the order R′=C8F17≈CF3&gt;F&gt;H&gt;Me&gt;MeO&gt;tert‐butyl&gt;NMe2. X‐Ray diffraction analysis of complex 8c‐pyr and polymerization results obtained with complexes 8‐pyr indicate that it is not the sterics but the electronics of the R′ group that control the polymer microstructure. This is a rare example of a polymerization catalyst in which substituents effects can clearly be traced to electronics exclusively.

SYNDIOSPECIFIC POLYMERIZATION OF STYRENE WITH MULTI-NUCLEAR TITANIUM COMPLEXES

Two multi-nuclear titanium complexes [Ti(η5–Cp*)Cl(μ–O)]3(1) and [(η5–Cp*TiCl)(μ–O)2(η5–Cp*Ti)2(μ–O)(μ–O)2]2Ti (Cp* = C5Me5)(2) have been investigated as the precatalysts for syndiospecific polymerization of styrene. In the presence of modified methylaluminoxane (MMAO) as a cocatalyst, complexes 1 and 2 display much higher catalytic activities towards styrene polymerization, and produce the higher molecular weight polystyrenes with higher syndiotacticities and melting temperatures (Tm) than the mother complex Cp*TiCl3 does when the polymerization temperature is above 70°C and the Al/Ti molar ratio is in the low range especially.

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 1HCl 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 degrees 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 degrees C) and maintained very high activity for 60 min at 75 degrees 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.

Polymerization of ethylene and propene promoted by binaphthyl-bridged Schiff base complexes of titanium

Three new binaphthyl-bridged Schiff base complexes featuring different phenolate substituents ( meta-Me, ortho, para-di-Cl, ortho, para-di-Br) were synthesized. 1H and 13C NMR analyses indicated that the cis-β isomers are preferentially formed in any case. These complexes were tested as precatalysts for ethylene and propene polymerization comparing their behaviour to that of related titanium and zirconium complexes previously reported. The beneficial effect on polymerization activity of halogen atoms in the ortho, para positions of the phenolate rings was also demonstrated.

Novel highly active binuclear neutral nickel and palladium complexes as precatalysts for norbornene polymerization

A series of binuclear neutral nickel and palladium complexes [(XC 6H 2CH NC 6H 3- iPr 2)MRL] 2 4b– f (X = NO 2, M = Ni, R = Ph, L = PPh 3, 4b; X = H, M = Pd, R = Me, L = PPh 3, 4c; X = H, M = Pd, R = Me, L = Py, 4d; X = NO 2, M = Pd, R = Me, L = PPh 3, 4e; X = NO 2, M = Pd, R = Me, L = Py, 4f) and [(C 10H 7CH NC 6H 3- iPr 2)MRL] 2 8a– c (M = Ni, R = Ph, L = PPh 3, 8a; M = Pd, R = Me, L = PPh 3, 8b; M = Pd, R = Me, L = Py, 8c) have been synthesized and characterized. The structures of complexes 4e and 8b have also been confirmed by X-ray crystallographic analysis. With modified methylaluminoxane (MMAO) as cocatalysts, these complexes and complex [(C 6H 3CH NC 6H 3- iPr 2)NiPh(PPh 3)] 2 4a are capable of catalyzing the addition polymerization of norbornene (NBE) with the high activity up to 2.3 × 10 8 g PNBE/(mol M h). The structure of complexes affects considerably catalytic activity towards norbornene polymerization. The polymers obtained with nickel complexes are soluble, while those obtained with palladium complexes are insoluble. Palladium complexes 4c, 4e and 8b bearing PPh 3 ligands exhibit much higher activities than the corresponding complexes 4d, 4f and 8c bearing pyridine ligands under the same conditions.

Preparation of linear α‐olefins to high‐molecular weight polyethylenes using cationic α‐diimine nickel(II) complexes containing chloro‐substituted ligands

AbstractA series of α‐diimine nickel(II) complexes containing chloro‐substituted ligands, [(Ar)NC(C10H6)CN(Ar)]NiBr2 (4a, Ar = 2,3‐C6H3Cl2; 4b, Ar = 2,4‐C6H3Cl2; 4c, Ar = 2,5‐C6H3Cl2; 4d, Ar = 2,6‐C6H3Cl2; 4e, Ar = 2,4,6‐C6H2Cl3) and [(Ar)NC(C10H6)CN(Ar)]2NiBr2 (5a, Ar = 2,3‐C6H3Cl2; 5b, Ar = 2,4‐C6H3Cl2; 5c, Ar = 2,5‐C6H3Cl2), have been synthesized and investigated as precatalysts for ethylene polymerization. In the presence of modified methylaluminoxane (MMAO) as a cocatalyst, these complexes are highly effective catalysts for the oligomerization or polymerization of ethylene under mild conditions. The catalyst activity and the properties of the products were strongly affected by the aryl‐substituents of the ligands used. Depending on the catalyst structure, it is possible to obtain the products ranging from linear α‐olefins to high‐molecular weight polyethylenes. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1964–1974, 2006

Preparation of spherical MgCl 2 supported bis(imino)pyridyl iron(II) precatalyst for ethylene polymerization

The immobilization of the soluble precatalysts [(ArN C(Me)) 2C 5H 3N]FeCl 2, where Ar = 2,4,6-trimethylphenyl (A) or 2,6-diisopropylphenyl (B), on supports derived from a spherical MgCl 2–alcohol adduct yields active supported systems for ethylene polymerization. The activity of the supported catalysts and the resultant polymer properties are strongly dependent on the method of preparation. The highest activities are obtained using supports obtained by pretreatment of the MgCl 2–alcohol adduct with triethylaluminium (TEA). In addition, it was found that precatalyst A, having less steric bulk at the ortho-aryl position of the ligand, gave higher activity than precatalyst B, in line with the different behaviours of these precatalysts in homogeneous polymerization, while precatalyst B gave polyethylene with lower polydispersity.

C2- and Cs-symmetric diamidodichlorotitanium complexes: Syntheses, structures and 1-hexene polymerization catalysis

The complexes l-[CMe 2{CHMeN(2-Pr i -C 6H 4)} 2TiCl 2] ( 2) and u - [ CMe 2 { CHMeN ( 2 , 6 - Pr 2 i C 6 H 3 ) } 2 TiCl 2 ] ( 3), C 2- and C s -symmetric analogues, respectively, of McConville’s C 2 v hexene polymerization precatalyst [ ( CH 2 ) 3 { N ( 2 , 6 - Pr 2 i – C 6 H 3 ) } 2 TiCl 2 ] ( 1), were prepared by high-dilution salt-elimination from the lithium amides and characterized spectroscopically and crystallographically. Complex 2, though less active than 1, was a highly active catalyst of polymerization of 1-hexene when activated by MAO. Complex 3 was inactive under similar conditions. NMR analysis confirmed that there were more mmmm pentads in polymer produced by 2 than in the statistically atactic material produced by 1, though the isotacticity index was not high. The results are interpreted in terms of an isotactic/atactic block structure, caused by syn/ anti fluxion of the two 2-isopropylphenyl rings in 2. Kinetic profiles and polydispersities were consistent with a slow initiation step involving monomer, followed by rapid propagation, with some chain transfer to aluminium and only a small extent of β-hydride elimination. The rubber-like polymers were indistinguishable by thermal analysis from those prepared by Ziegler–Natta catalyst systems.

A Remarkably Facile Zirconium(IV) → Aluminum(III) β-Diketiminate Transmetalation That Also Results in a More Active Olefin Polymerization Catalyst upon Activation

(R-IAN)2ZrX2 complexes, where X = NMe2, Cl, have recently emerged as effective olefin polymerization precatalysts bearing chiral ligands formally of the β-diketimine class. An attempt to exchange dimethylamido ligands for alkyl (methyl) using the Jordan protocol resulted in a surprisingly facile transmetalation of the bidentate Me-IAN ligands from zirconium(IV) to aluminum(III). An initial study of the process and the finding that the (R-IAN)AlMe2 complexes that result are more potent precatalysts themselves provide a case study within the rapidly growing area of catalysis based on β-diketiminate metal complexes.