Nickel Diimine Complexes Research Articles

Preparation of silyl-terminated branched polyethylenes catalyzed by Brookhart's nickel diimine complex activated with hydrosilane/B(C6F5)3.

Brookhart's nickel α-diimine complex [(κ2-N,N-BIAN)NiCl2] (1) (where BIAN = {Ar-NAceN-Ar}, Ace = acenaphthen-1,2-diyl, and Ar = 2,6-(iPr)2-C6H3) activated with a hydrosilane/B(C6F5)3 (SiHB) adduct forms a highly active catalytic system for ethylene polymerization. Under optimal conditions, the activity of the system depends on the nature of hydrosilane and decreases in the order R3SiH > Ph2SiH2 > PhSiH3. The decrease in system activity within the hydrosilane series is correlated with increasing formation of Ni(I) species. In addition to their activation effect, hydrosilanes act as efficient chain termination/chain transfer agents, with the Si/Ni ratio controlling the molecular weight of the resulting polyethylene (PE). The use of Et3SiH generated elastomeric, highly branched polymers with a saturated chain-end, while systems using Ph2SiH2 and PhSiH3 led to branched end-functionalized PEs terminated with the hydrosilyl functionality (i.e. br-PE-SiPh2H or br-PE-SiPhH2).

Improvement of catalytic activity for α‐diimine nickel complex with active sites stabilized by bulky boron counterions at elevated temperature

Three α‐diimine Ni (II) catalysts (Cat.1, Cat.2 and Cat.3) were synthesized and investigated for ethylene polymerization using alkyl aluminum and organoboron compounds as binary cocatalyst. The effects of different alkyl aluminum and boron complexes on ethylene polymerization catalyzed by Cat.1, Cat.2, and Cat.3 were studied. The sodium tetrakis[3,5‐bis (trifluoromethyl)phenyl]borate (NaBArF) was found to have best promotion for the catalytic activity of Cat.1, compared to negative effect of dimethylanilinium tetrakis (pentafluorophenyl)borate (TTB) and trityl tetrakis (pentafluorophenyl)borate (AB). All the three catalysts showed higher catalytic activity when NaBArF was introduced into the catalytic system, especially for Cat.3 (increased by 41.3% at 70°C). There was still minor increase of the catalytic activity for Cat.2 which have much better thermostability than Cat.3. The charging sequence of NaBArF and the [B]/[Ni] ratio have significant effects on the catalytic activity. The better catalytic performance of Cat.1/AlEt2Cl/NaBArF could be explained by its ability to raise the number of active centers. Namely, the molar percentage of active centers of Cat.1/AlEt2Cl/NaBArF was still above 30%, which was 1.7 times that of Cat.1/AlEt2Cl even if polymerization ran up to 30 min based on 2‐thiophenecarbonyl chloride (TPCC) quench‐labeling method. Lower [Al]/[Ni] ratio but more active centers and longer active centers lifetime of this binary cocatalyst is promising for improving the activity of ethylene polymerization industrially at elevated temperature.

Activated carbon fibers as a support for nickel diimine complexes and their application in ethylene oligomerization

In this work, we demonstrate the synthesis and characterization of a new class of β-diimine ligand combined with the alkoxysilane group CPTMS ((3-chloropropyl)trimethoxysilane), covalently anchored to the surface of activated carbon fibers (ACF).

Bispentiptycenyl–Diimine–Nickel Complexes for Ethene Polymerization and Copolymerization with Polar Monomers

Ni2+ coordinated within a bowl-shaped diimine ligand with two pentiptycenyl-substituents [(diimine)NiBr2] displays excellent activity for the polymerization of ethene (7 atm) with activities of up to 34 × 103 kg(mol Ni)−1 h–1 following activation with Et2AlCl. The resulting polymer is characterized by high molecular weights (Mn = 150 × 103 g·mol–1), low branching (12/1000 C), and a high melting point (Tm = 133 °C). The polymerization of ethene with polar comonomers leads to the formation of the respective polar polymers with very efficient incorporation of comonomer. The activity of the catalyst critically depends on the molar ratio of Et2AlCl activator and the polar functional group.

Chain-Walking Polymerization of Linear Internal Octenes Catalyzed by α-Diimine Nickel Complexes

The chain-walking polymerization of linear internal alkenes (i.e., trans-2-, 3-, and 4-octenes) using α-diimine nickel catalysts activated with modified methylaluminoxane (MMAO) was studied in comparison with the corresponding terminal alkene polymerization. The rates of polymerization were found to decrease in the following order: 1-octene > 4-octene ≥ 2-octene ≫ 3-octene. The obtained branched poly(2-octene)s and poly(4-octene)s with high molecular weight and Mw/Mn less than 2 were amorphous polymers with low glass transition temperature (Tg) of approximately −66 °C. At 0 °C, 4-octene polymerized in a living/controlled manner. The NMR analyses of the polymers showed that the chain-walking polymerization of 4-octene gave periodically branched polymers with the constant branching density, while that of 2-octene gave the polymer possessing fewer branches than the expected value due to monomer-isomerization. The (n+2),(n+3)- and (n+3),(n+2)-insertions of the internal (n+2)-alkene [CH3(CH2)nCH═CH(CH2)mCH3] f...

ETHYLENE POLYMERIZATION WITH NICKEL DIIMINE COMPLEXES CONTAINING PSEUDOHALIDES

Nickel-diimine complexes DADNiX2 (DAD= 2,6-iPr2-C6H3-N=C(Me)-C(Me)=N-2,6-iPr2-C6H3) containing the non-chelating pseudo-halide ligands isothyocyanate and isoseleniumcyanate (X= NCS 1 and NCSe 2) were synthesized and used in ethylene polymerization activated by methyaluminoxane (MAO) at temperatures from 0 to 50°C. Polymerizations with these complexes were compared with the analogous Ni-diimines halide (X= Br 3) as non-chelating ligand. All systems were very active in this polymerization. The increase of reaction temperature favored the increase in catalytic activity. The catalyst system 1/MAO was more stable than the others, showing the best catalytic activity at the molar ratio Al/Ni between 200 and 300. System 2/MAO showed to be the less stable and less active, particularly at 50°C. Polyethylenes obtained with systems 1, 2 and 3 show high molecular weights, are branched polymers, and predominately amorphous, but the majority still present DSC endothermal events related to melting of small crystals. When halide (Br) are compared with these pseudo-halides, different activities, polymerization kinetics and characteristics of the final polymer indicated modification in the active species caused by the non-chelating ligand. Polymer molecular weight and branching content was not significantly influenced by the non-chelating ligand, being much more dependent on the MAO/Ni molar ratio and polymerization temperature.

Copolymerization of ethylene with polar monomer by α - diimine nickel complex

Copolymerization of ethylene and ethyl acrylate was carried out by α-diimine nickel catalyst [ArN=CH-CH=NAr]NiBr2 (Ar = 2,6-C6H3(CH3)2) in the presence of methylaluminoxane (MAO). The effects of experimental conditions in which mole ratio of Al/Ni, concentration of polar monomer, polymerization temperature, ethylene pressure and polymerization time varied on ethylene-ethyl acrylate copolymerization were investigated. The structures of the obtained copolymers were characterized by high-temperature NMR and FT-IR. It was found that Al/Ni mole ratio was 1000, the concentration of ethyl acrylate was 10 mmol/L, the polymerization temperature was 30 °C, the ethylene pressure was 10 atm, the polymerization time was 4 h, the molecular weight of the polymer and the incorporation of ethyl acrylate in the copolymer reached the good result.

New nickel(II) diimine complexes bearing phenyl and sec‐phenethyl groups: synthesis, characterization and ethylene polymerization behaviour

A series of nickel(II) catalysts containing phenyl and chiral sec‐phenethyl groups, {[(4‐R1‐2‐R2C6H2NC)2Nap]NiBr2} (Nap: 1,8‐naphthdiyl, R1 = Me, R2 = Ph (3a); R1 = Me, R2 = sec‐phenethyl (3b); R1 = Cl, R2 = sec‐phenethyl (3c); R1 = Me, R2 = Me (3d) were synthesized and characterized. All organic compounds were fully characterized by FT‐IR and NMR spectroscopy and elemental analysis. The single crystal for X‐ray crystallography was isolated from 3a in CH2Cl2/n‐hexane under air; the crystal structure showed a binuclear complex 3a′, in which each nickel atom was six‐coordinate. The two nickel atoms together with two bromine atoms form a planar four‐membered ring, with a bromine and H2O axial ligands. These complexes, activated by diethylaluminum chloride and chiral nickel pre‐catalysts rac‐3c, exhibited good activities (up to 2.85 × 106 g PE (mol Ni h bar)−1) for ethylene polymerization, and produced polyethylene products with a high degree of branching (up to 117 branched per 1000 carbons) at high temperature. The type and amount of branches of the polyethylenes obtained were determined by 1H and 13C NMR spectroscopy. Copyright © 2014 John Wiley & Sons, Ltd.

Copolymerization of Ethylene with Vinyl Monomers using Heterogeneous Catalysts Consisting of α‐Diimine Ni(II) Complexes Immobilized into a Fluorotetrasilicic Mica Interlayer in the Presence of an Alkylaluminum Compound

Abstractα‐Diimine nickel complexes immobilized into fluorotetrasilicic mica interlayers are prepared by the reaction of an α‐diimine ligand and nickel‐ion‐exchanged fluorotetrasilicic mica, and these are used for the copolymerization of ethylene with linear α‐olefins (1‐hexene, 1‐octene, and 1‐decene), cyclic olefins (norbornene and cyclopentene), or polar vinyl monomers (methyl acrylate and 5‐hexenenitrile). The copolymerization of ethylene with α‐olefins affords linear low‐density polyethylene including methyl and alkyl branches. The incorporation of cyclopentene into the main chain is proved by the 13C NMR spectrum of the ethylene/cyclopentene copolymer. No significant activity is observed during the copolymerization of ethylene with norbornene, methyl acrylate, or 5‐hexenenitrile. magnified image

Photodynamic activity of a nickel diimine complex and its interaction with DNA

Employing 1,3-diphenylisobenzofuran as a probe, the photodynamic activity of a nickel diimine complex, bis(o-diiminobenzosemiquinonato)nickel(II), in red light has been studied by fluorescence spectra. These results show that the nickel complex can generate singlet oxygen efficiently after irradiation in red light. The interaction of the metal complex with DNA has also been studied by electronic absorption spectra, fluorescence spectra and viscosity measurements. The electronic spectra of the metal complex exhibit dramatic hypochromism on interaction with DNA. Scatchard plot analyses indicate that the metal complex can competitively inhibit the binding between DNA and ethidium bromide. Viscosity experiments show that the binding of the metal complex increases the relative viscosity of DNA. These results suggest that the photoactive nickel diimine complex may interact with DNA by intercalation binding mode. Potential applications of the complex in photodynamic therapy are discussed.

Buffered Aluminum Chloride as a Highly Efficient Cocatalyst for Olefin Dimerization and Polymerization

AbstractA binary cocatalyst system based on simple aluminum chloride and weak Lewis bases such as triphenylbismuth or N‐methylpyrrole has been developed. A donor–acceptor interaction kept aluminum chloride dissolved in toluene or methylene chloride. The systems were investigated by use of 27Al NMR spectroscopy and were used as cocatalysts in nickel‐catalyzed dimerization and polymerization reactions of α‐olefins. Their Lewis acidities correlated to the line width of the 27Al NMR signals and were influenced by the solvent and the type and amount of buffer. For propene dimerization reactions, dimer selectivities of up to 95 % were achieved. Ethene was dimerized to give butenes (up to 92 %), of which 79 % were 1‐butene. With a Brookhart‐type nickel diimine complex, ethene was polymerized with a cocatalyst solely based on aluminum chloride. Up to 38 wt % of the reaction products were polyethylene with a typical molecular weight of 140 kg mol−1. The donor–acceptor interactions of triphenylbismuth and N‐methylpyrrole with aluminum chloride were successfully transferred to Lewis acidic chloroaluminate ionic liquids. Ethene was polymerized with a nickel diimine complex dissolved in buffered chloroaluminate ionic liquids in the absence of alkylaluminum groups.

Control of morphology in olefin polymerization catalyzed by nickel diimine complexes encapsulated into polybutadiene based support

A commercially available hydroxyl terminated low molecular cis-1,4-polybutadiene was modified by carboxylic functions and used as an effective support in single-site α-olefin polymerization. Dynamic light scattering analysis of support solution in heptane confirmed increased ability to self-assembly of modified polybutadienes in the presence of methylaluminoxane cocatalyst (MAO). α-Diimine nickel and bis(indenyl)zirconium dichloride catalysts activated by trimethylaluminium or MAO cocatalysts were encapsulated into polymer micellar aggregates and used for ethylene and octadec-1-ene polymerization. Furthermore, the effects of cocatalyst type and concentration on the micelle-formation process, activity and morphology of polyethylene (polyoctadec-1-ene) particles were investigated. In the presence of polybutadiene supports, formation of spherical micrometric PE beads was observed during MAO cocatalyzed ethylene polymerization, whereas the activity of polymerization was not decreased.

Living/controlled hex-1-ene polymerization initiated by nickel diimine complexes activated by non-MAO cocatalysts: Kinetic and UV–vis study

Living/controlled polymerization of hex-1-ene initiated by nickel diimine catalysts of general form [ArN=C(1,8-naphthalenediyl)C=NAr]NiBr2 activated by simple organoaluminium compounds was investigated. Polyhexenes with a very narrow molar mass distribution and molar mass controlled by the monomer/initiator ratio were prepared using diethylaluminiumchloride, ethylaluminiumdichloride and methylaluminiumdichloride as cocatalysts for nickel complexes 1 (Ar = 2,6-iPr2C6H3) and 2 (Ar = 2-tBuC6H4). Nickel complexes with smaller aryl substituents (3, Ar = 2,6-Me2C6H3; 4 Ar = 2,4,6-Me3C6H2; 5, Ar = 2,6-Et2C6H3) undergo transfer reactions significantly. For the most bulky complex 1 activated by ethylaluminiumdichloride living hex-1-ene polymerization was achieved, proved by the reinitiation of polymer growth upon the addition of fresh monomer. The effect of Al/Ni ratio on the activity of the catalytic systems was studied by dilatometry. The catalytic systems were investigated by UV–vis spectrometry and a new interpretation of their absorption spectra was suggested.

Preparation of Polyethylene/Montmorillonite Nanocomposites Through in situ Polymerization Using a Montmorillonite‐Supported Nickel Diimine Catalyst

AbstractPE/MMT nanocomposites were prepared through in situ polymerization using a nickel diimine catalyst supported on commercially available MMTs such as Cloisite Na+, Cloisite 30B, and Cloisite 93A. XRD patterns revealed that the layers of Cloisite 30B and Cloisite 93A were intercalated after treatment with TMA and the nickel diimine complex. The catalyst supported on Cloisite 30B showed high yields without additional activator and produced nanocomposites with high melting and decomposition temperatures. The thermal properties and crystallinity could be controlled by varying the clay content in the nanocomposite. The morphologies of the resulting particles and the dispersion of the MMT layers in the polymer matrix were characterized by SEM and TEM.magnified image

Ethylene slurry polymerization using nickel diimine catalysts covalently-attached onto MgCl2-based supports

MgCl 2 /alcohol adducts were recrystallized with alkyl aluminums and used as catalysts supports for nickel diimine complexes functionalized with amine groups. These supported catalysts were used to polymerize ethylene in a slurry reactor. The MgCl 2 -based supported nickel diimine catalysts had higher activities than the equivalent SiO 2 -supported nickel diimine catalysts, even without the use of activators. These catalysts made polyethylene with melting temperatures and molecular weights higher than those made with the equivalent homogeneous catalysts. Interestingly, the catalyst activity and polymer molecular weight could be controlled by changing the support composition. In addition, covalent chemical bonds between the functionalized nickel diimine complex and the MgCl 2 -based supports avoided catalyst leaching during polymerization, leading to the production of polymer particles with good morphology. The mechanical strength of the resulting polymer particles, however, was lower than those made with SiO 2 -supported nickel diimine catalysts.

Living/controlled olefin polymerization initiated by nickel diimine complexes: The effect of ligand ortho substituent bulkiness

Abstract Polymerization of hex-1-ene and propene initiated by several methylalumoxane-activated diimine complexes was critically investigated. Effect of bulkiness of ortho aryl diimine substituents on extent of transfer reactions was examined. All of the complexes allowed us to prepare poly(hex-1-ene) with a very narrow molar mass distribution, molar mass being controlled by stoichiometry in a broad range of reaction conditions. Poly(hex-1-ene)s with molar mass between 15 and 220 kg mol −1 and dispersity ( M w / M n ) between 1.01 and 1.20 were prepared by varying the catalyst, temperature and monomer concentration. Livingness of hex-1-ene polymerization was demonstrated for the first time for nickel complex bearing ethyl ortho aryl substituents by reinitiation of chain growth upon addition of a new portion of monomer. Complexes with ortho methyl substituents did not allow complete reinitiation of chain growth and despite its good control over molar mass cannot be classified as a living polymerization catalyst. Chain branching can effectively be controlled by the choice of the ligand structure due to the chain-walking mechanism. Transfer reactions were more pronounced in propene polymerization. Polypropylene with narrow molar mass distribution could not be prepared using complexes with methyl substituents.

Nickel(II) Complexes Bearing NH2CH2CH2CH2NH2 and o‐C6H4(NH2)2 Ligands: Synthesis, Structures and Their Ethylene Polymerization Behavior

AbstractTwo nickel complexes [Ni(NH2CH2CH2CH2NH2)3]Cl2 (1) and [Ni(C6H4N2H4)2Cl2] (2) have been obtained and characterized by IR and single crystal X‐ray diffraction analysis. In complex 1, the nickel atom was in a chiral pseudo‐octahedral [NiN6] geometry environment, which was coordinated by three 1,3‐propylenediamine to form three six‐membered rings. However in complex 2, besides connected with two o‐phenylenediamine through four Ni–N bonds to form two five‐membered rings, the nickel center was coordinated by two Cl to form trans‐Ni‐Cl2, which was different from general reported diimine nickel complexes. Activated with MAO, MMAO or Et2AlCl, these nickel complexes exhibited considerable good catalytic activity [up to 3.59×106 g·mol−1·h−1 for complex 2] for ethylene polymerization with main products as dimers or trimers of ethylene.

A new strategy to prepare branching polyethylene by using an α-diimine nickel (II) complex covalently supported on MgCl2/AlRn(OEt)3-n

A new strategy was developed to prepare MgCl2-supported nickel-diimine catalysts for ethylene polymerization, in which an amino-functionalized nickel-diimine complex, bis(4-(4-amine-3,5-diisopropylbenzyl)-2,6-diisopropylphenylimino)acenaphtheneNiBr2 (abbreviaed as NiLBr2), was covalently supported on MgCl2/AlRn(OEt)3-n. The most significant feature of the supported catalyst is that it polymerizes ethylene with high activities in the presence of inexpensive general alkylaluminum compounds. According to the results of high temperature GPC, the number-average molecular weights of the polymers ranged from 0.35 × 106 to 1.08 × 106 and the polydispersities ranged from two to three. By modulating the polymerization temperatures, the products of different morphologies were obtained. The resultant PE was confirmed by 13C NMR to contain significant amounts of not only methyl but also ethyl, propyl, butyl, amyl, and long branches (longer than six carbons).

Biphasic Ni-Catalyzed Ethylene Oligomerization in Ionic Liquids

Diimine nickel complexes activated with aluminoxane in chloroaluminate ionic liquids are highly active catalysts either for the biphasic ethylene oligomerization or for polymerization depending on the bulkiness of the diimine ligand. The activation of Ni(0) with a Bronsted acid in different non-chloroaluminate ionic liquids is also reported. The nature of the ionic liquid and the presence or not of a nitrogen ligand affect significantly the catalytic performances. The olefinic products are weakly soluble in ionic liquids and can be separated from the catalytic ionic phase by simple decantation. The nickel catalysts are immobilized and stabilized in the ionic liquids and can be recycled.

New Nickel(II) Diimine Complexes and the Control of Polyethylene Microstructure by Catalyst Design

Starting from differently substituted boronic acids as versatile building block, new "ortho-aryl" alpha-diimine ligands a-h were synthesized in an easy, high-yielding route. Reaction of the complex precursor diacetylacetonato-nickel(II) with a trityl salt, like [CPh3] [B(C6F5)4] or [CPh3] [SbCl6], in the presence of the diimine ligands afford the monocationic, square planar complexes 2a-g in almost quantitative yields. Suitable crystals (2d',e,f,g) were submitted for X-ray diffraction analysis. A geometry model was developed to describe the orientation of ligand fragments around the nickel(II) center that influence the polymer microstructure. At elevated reaction temperature and pressure, and in the presence of hydrogen, 2a-e catalyze the homopolymerization of ethylene to give branched PE products ranging from HD- to LLD-PE grades. The polymerization results indicate the possibility of precise microstructure control depending on the particular complex substitution. Preliminary investigations on material density and mechanical behavior by uniaxial stretching until failure point toward new material properties that can result from the simple ethylene monomer by catalyst design.