Active Catalysts For Ethylene Oligomerization Research Articles

A comparison of the catalytic activities of oxovanadium(IV) and cobalt(II) complex compounds in the oligomerization of ethylene

The polymerization and oligomerization of olefins, especially ethylene, is a process of great industrial and scientific importance in polymer chemistry. Catalysts are an essential part of this reaction, and a new report of a catalyst improving this process is worthy of special attention. During this study, nine complex compounds based on oxovanadium(IV) and cobalt(II) ions in combination with organic ligands, e.g., dipicolinic acid, 2,2′-bipyridine, iminodiacetic acid, diglycolic acid, thiodiacetic acid, 1,10-phenanthroline were synthesized. The compound [VO(tda) · 0.5 H2O] is a new complex not previously reported in the literature, and its synthesis and structure are described in this article. The high catalytic activity values in other oligomerization processes in other olefins led us to use the synthesized compounds as precatalysts in the oligomerization reaction. Subsequently, their catalytic activity was also calculated in this process. The obtained oligomerization products were then analyzed by IR, MALDI-TOF-MS, TG, DSC, and SEM techniques to characterize the obtained products and verify the correctness of the oligomerization reaction. Based on the obtained data, the catalytic activity values were compared and the most active catalyst was selected. The best catalyst was a cobalt(II) compound containing an iminodiacetic acid anion and 2,2′-bipyridine in its structure. However, all complexes can be classified as highly active and active catalysts for ethylene oligomerization. The presented studies show novel catalysts that have in their structure other metal ions than those most commonly used in the literature so far. Additionally, coordination compounds of this type have not been previously used in ethylene oligomerization. Moreover, these studies are a source of knowledge on the correlation between catalyst structure and catalytic activity value, thanks to which they provide essential information necessary for the design of next-generation catalysts used for ethylene oligomerization and polymerization.

Ethylene oligomerization reactions catalyzed by recyclable Fe(II), Ni(II) and Co(II) complexes immobilized on Fe3O4 magnetic nanoparticles

• Fe 3 O 4 MNPs immobilized metal complexes synthesized and characterized • Activation with EtAlCl 2 afford active ethylene oligomerization catalysts • Butene and hexene oligomers major products in heptane • Immobilized complexes effectively recycled via magnetic separation • Recycled catalysts maintained both catalytic activity and selectivity. Reactions of Fe 3 O 4 magnetic nanoparticles supported ligands, phenol((triethoxysilyl)propylimino)ethyl ( L1@Fe 3 O 4 ) and phenol((triethoxysilyl)propylimino)methyl ( L2@Fe 3 O 4 ) with appropriate metal salts afforded the respective immobilized complexes Ni1@Fe 3 O 4 , Ni2@Fe 3 O 4 , Co1@Fe 3 O 4 , Co2@Fe 3 O 4 , Fe1@Fe 3 O 4 and Fe2@Fe 3 O 4 . The complexes were characterized using FT-IR spectroscopy, thermogravimetric analyses (TGA), transmission electron microscopy (TEM), scanning electron microscopy (SEM), powder X-ray diffraction (PXRD), energy dispersive X-ray (EDX), inductively coupled plasma optical emission spectroscopy (ICP-OES) and vibrational sample magnetometry (VSM). Activation of the complexes with EtAlCl 2 afforded active catalysts for ethylene oligomerization to a tune of 97 600 g mol −1 h −1 under optimized conditions. Both ethylene oligomers and alkylated products were obtained depending on the solvent medium. The identity of the ligand and metal atom influenced the catalytic performance of the complexes. The immobilized complexes were recycled via magnetic separation in five successive runs without significant loss of catalytic activity and selectivity.

New chromium(III)-based catalysts for ethylene oligomerization

The report focuses on the new precatalysts for ethylene oligomerization. The five chromium(III) complex compounds containing the following ligands: dipicolinate anion, oxalate anion, 5-aminopyridine-2-carboxylate anion, 2,2′-bipyridine and 4,4′-dimethoxy-2,2′-bipyridine have been examined towards catalytic activity for ethylene oligomerization. The chromium(III) complexes have been activated by modified methylaluminoxane. The obtained oligomers have been investigated by MALDI-TOF–MS, thermal analysis and infrared spectroscopy. The results revealed that the examined chromium(III) complexes are highly active catalysts for ethylene oligomerization. The values of catalytic activities of the examined complexes are in the range 1860 – 3798 g∙mmol-1∙h-1∙bar-1.

Synthesis and characterization of Ni(II) complexes bearing of 2‐(1H–benzimidazol‐2‐yl)‐phenol derivatives as highly active catalysts for ethylene oligomerization

Novel Ni(II) complexes of 2‐(1H–benzimidazol‐2‐yl)‐phenol derivatives (HLx: x = 1–5; C1–C5) have been synthesized and characterized. In the mononuclear complexes, the ligands were coordinated as bidentate, via one imine nitrogen and the phenolate oxygen atoms. The structures of the compounds were confirmed on the basis of FT‐IR, UV–Vis, 1H‐, 13C–NMR, inductively coupled plasma and elemental analyses (C, H and N). The purity of these compounds was ascertained by melting point (m.p.) and thin‐layer chromatography. The geometry optimization and vibrational frequency calculations of the compounds were performed using Gaussian 09 program with B3LYP/TZVP level of theory. All Ni(II) complexes were activated with diethylaluminum chloride (Et2AlCl), so that C2 showed the highest activity [6600 kg mol−1 (Ni) h−1], where the ligand contains a chlorine substituent. Oligomers obtained from the complexes consist mainly of dimer and trimer, and also exhibit high selectivity for linear 1‐butene and 1‐hexene. Both the steric and electronic effects of coordinative ligands affect the catalytic activity and the properties of the catalytic products.

Ethylene oligomerization studies by nickel(ii) complexes chelated by (amino)pyridine ligands: experimental and density functional theory studies

Reductions of imine compounds 2-methoxy-N-(1-(pyridin-2-yl)ethylidene)ethanamine (L1), 2-methoxy-N-((pyridin-2-yl)methylene)ethanamine (L2), N,N-diethyl-N-((pyridin-2-yl)methylene)ethane-1,2-diamine (L3) and 2-((pyridin-2-yl)methyleneamino)ethanol (L4) using NABH4 produced their corresponding amine analogues N-(2-methoxyethyl)-1-(pyridin-2-yl)ethanamine (L1a), 2-methoxy-N-((pyridin-2-yl)methyl)-ethanamine (L2a), N,N-diethyl-N-((pyridin-2-yl)methyl)ethane-1,2-diamine (L3a) and 2-((pyridin-2-yl)methylamino)ethanol (L4a) in good yields. Reactions of the (amino)pyridine ligands L1a–L4a with [NiBr2(DME)] afforded nickel(II) complexes, [NiBr2(L1a)2] (1), [NiBr2(L2a)2] (2), [NiBr2(L3a)2] (3) and [NiBr2(L4a)2] (4), respectively in quantitative yields. Molecular structures of complexes 2 and 4 confirmed the formation of the bis(chelated)nickel(II) complexes. Activation of complexes 1–4 with either EtAlCl2 or methylaluminoxane (MAO), produced active ethylene oligomerization catalysts to afford mostly ethylene dimers (C4), in addition to trimmers (C6) and tetramers (C8). Density functional theory studies provided valuable insight into the reactivity trends and influence of complex structure on the ethylene oligomerization reactions.

Trans‐1,2‐Diphenylethylene Linked Isoindoline–Salicylaldiminato Nickel(II) Halide Complexes: Synthesis, Structure, Dehydrogenation, and Catalytic Activity toward Olefin Homopolymerization

AbstractTridentate ligands 4‐R1‐6‐R2‐2‐{[trans‐2‐(isoindolin‐2‐yl)‐1,2‐diphenylethylimino]methyl}phenol [R1 = R2 = H, H(La); R1 = R2 = tert‐butyl, H(Lb); R1 = Ph, R2 = H, H(Lc)] in which a substituted salicylaldimine moiety and an isoindoline are linked by a trans‐1,2‐diphenylethylene moiety have been prepared. Deprotonation of these tridentate ligands H(La)–H(Lc) by NaH at room temperature in tetrahydrofuran (THF), followed by treatment with 1 equiv. of [(PPh3)2NiX2] (X = Cl, Br, I) at room temperature afforded the desired nickel complexes [(L)NiX] (X = Cl, L = La, 1; X = Cl, L = Lb, 2; X = Cl, L = Lc, 3; X = Br, L = Lb, 4; X = I, L = Lb, 5) in moderate yields. The structures of 2 and 4 were unequivocally confirmed by single‐crystal X‐ray diffraction in the solid state. The metal atom has a distorted square‐planar coordination geometry and is coordinated to the two nitrogen atoms and one oxygen atom from the tridentate ligand and one halide atom. Dehydrogenation of the chelate tridentate ligand (Lb) in the presence of oxygen afforded the corresponding nickel complexes [(Lb*)NiX] (X = Br, 6; X = I, 7). X‐ray analysis showed that in these complexes the two bridged benzylic carbon atoms of (Lb)– were oxidized and a cis‐stilbene moiety, which includes a C=C double bond (1.205–1.268 Å) was formed. These nickel complexes with such trans‐1,2‐diphenylethylene bridged tridentate ligands proved to be active catalysts for ethylene oligomerization in the presence of methylaluminoxane (MAO) and produced butene and hexene with catalytic activities of 0.49 × 105–3.25 × 105 g mol–1 Ni h–1 at 30 °C, under 20 bar of ethylene, and with an MAO/Ni ratio of 250. They were also active catalysts for the homopolymerization of norbornene and styrene and displayed activities of up to 1.89 × 105 and 7.36 × 105 g mol–1 Ni h–1, respectively.

Nickel and Palladium Complexes with New Phosphinito-Imine Ligands and Their Application as Ethylene Oligomerization Catalysts

Phosphinito-imines, a new class of P,N donors, are readily generated by reaction of bulky arylamide anions [R2CONAr]− (R2 = Me or t-Bu; Ar = 2,6-i-Pr2C6H4) with chlorophosphines ClP(R1)2. In solution, free phosphinito-imines exist in equilibrium with the corresponding amidophosphine tautomers, containing a nitrogen-bound P(R1)2 group. However, reacting the tautomer mixtures with metal precursor complexes, such as NiBr2(dme) or PdCl2(cod), selectively affords stable phosphinito-imine complexes MX2(P-N) (M = Ni, Pd) in excellent yields. These complexes are diamagnetic and exhibit square-planar structures in the solid state, but in solution, the Ni derivatives exchange with a small amount of the corresponding high-spin tetrahedral isomers. On treatment with MMAO or DEAC, NiX2(P-N) complexes become active ethylene oligomerization catalysts, affording mainly butenes along with smaller amounts of hexenes and octenes. The activity and the selectivity of these catalysts depend on the structure of the phosphinito-imine ligand and the cocatalyst used. When activated with DEAC, complexes containing the P(i-Pr)2 moiety are extremely active, achieving TOFs over 106 mol C2H4/mol Ni·h and high selectivity for butenes.

Highly Active Ethylene Oligomerization Catalysts

Reaction of RN(H)PBr(Ph)2N(H)R [R = t-Bu, i-Pr, Ph] with two equivalents of n-BuLi followed by reaction with CrCl2(THF)2 afforded the divalent chromium complexes [(t-Bu)NP(Ph)2N(t-Bu)]Cr(μ2-Cl)2Li(THF)2 (1), [(i-Pr)NP(Ph)2N(i-Pr)]Cr(μ2-Cl)2Li(THF)2 (2), and [{[(Ph)NP(Ph)2N(Ph)]Cr}2(μ2-Cl)3][Li(DME)3] (3). The trivalent analogue of 1, {[(t-Bu)NP(Ph)2N(t-Bu)]Cr(μ2-Cl)3(μ3-Cl)2}{Li (THF)2} (4), was obtained in a similar manner via treatment of the double deprotonated ligand with CrCl3(THF)3. Both reactions of the divalent1 or trivalent4 with AlMe3 yielded the trivalent and cationic complex {[(t-Bu)NP(Ph)2N(t-Bu)]2Cr}{(Me3Al)2Cl}·toluene (5). Upon activation with MAO, 1–3 produced unprecedented and potentially useful catalytic systems for nonselective ethylene oligomerization devoid of polymer. Divalent chromium is clearly the species responsible for the catalytic behavior, ruling out that nonselective oligomerization proceeds via a redox metallacycle mechanism. The absence of polymer in combination with the record activity makes 1 competitive with the best performing industrially used systems.

Pyrazolyl iron, cobalt, nickel, and palladium complexes: synthesis, molecular structures, and evaluation as ethylene oligomerization catalysts

Reactions of [2-(3,5-dimethyl-pyrazol-1-yl)-ethanol] ( L1) and [1-(2-chloro-ethyl)-3,5-dimethyl-1H-pyrazole] ( L2) with Fe(II), Co(II), Ni(II), and Pd(II) salts gave the complexes [( L1) 2FeCl 2] ( 1), [( L1) 2CoCl 2] ( 2), [( L1) 2NiBr 2] ( 3), [( L1) 2Pd(Me)Cl] ( 5), [( L2) 2CoCl 2] ( 6), and [( L2) 2NiBr 2] ( 7). Whereas L2 behaves as a monodentate ligand, L1 can behave as either a monodentate or bidentate ligand depending on the nature of the metal centre. For palladium, L1 is monodentate in the solid state structure of 5 but bidentate in the structure of 4, obtained during attempts to crystallize 3. While the activation of iron, cobalt and palladium complexes with EtAlCl 2 did not produce active ethylene oligomerization catalysts, the nickel complexes 3 and 7 produced active ethylene oligomerization catalysts. Activities as high as 4329 kg/mol Ni h were obtained. Catalyst 3 produced mainly butenes (57%) and hexenes (43%); of which a combined 20% were converted to Friedel-Crafts alkylated-toluene. Catalyst 7, on other hand, produced mainly butenes (90%) and small amounts of hexenes (10%) which were then completely converted to the corresponding Friedel-Crafts alkylated-toluene products. This difference in product distribution in catalysis performed by complexes 3 and 7 is indicative of the role of the OH functionality in L1 on the EtAlCl 2 co-catalysts.

Oligomerization of Ethylene Using New Tridentate Iron Catalysts Bearing α-Diimine Ligands with Pendant S and P Donors

Stoichiometric Schiff base condensations of sterically bulky primary amines with acenaphthenequinone yield isolable monoimines. In the presence of iron(II) chloride, the remaining ketone reacts with a second primary amine bearing a pendant donor atom to give asymmetric, tridentate, α-diimine complexes that possess remarkable structural variability. A series of NNP and NNS tridentate iron(II) complexes are prepared; these coordination compounds become active catalysts for ethylene oligomerization when activated with methylalumoxanes. X-ray crystallographic studies of the precatalyst complexes confirm that the ligand binds in a tridentate fashion. Correlations between the precatalyst solid-state structures and catalyst activity and α-olefin product distribution are explored.

2-Ethyl-ketimino-1,10-phenanthroline iron(II) complexes as highly active catalysts for ethylene oligomerization

A series of 2-(1-aryliminopropyl)-1,10-phenanthrolines ( L1– L7) and their corresponding iron(II) chlorides ( Fe1– Fe7) are synthesized and characterized by elemental and spectroscopic analyses. The molecular structures of 2-[1-(2,6-diisopropy1phenylimino)propyl]-1,10-phenanthroline ( L3) and {2-[1-(2,6-diethylphenylimino)propyl]-1,10-phenanthroline}·FeCl 2 ( Fe2) are determined by the single crystal X-ray diffraction. All iron complexes, activated with methylaluminoxane (MAO), exhibit high activities in ethylene oligomerization with high selectivity for α-olefins produced. Compared with other 2-imino-phenanthrolines, the title complexes show better thermal stability, and their oligomerization products are potentially more useful due to lower contents of butenes and waxes observed.

Ethylene oligomerization using nickel dithiolene complexes Ni(S2C2R2)2 (R = Ph, CF3) and the crystal structure of Ni[S2C2(CF3)2

Nickel bis(dithiolene) complexes have been known for over four decades, yet little is known regarding the chemistry of this important subclass of inorganic coordination complexes in olefin oligomerization or polymerization. We report here that Ni(S2C2R2)2 (R=Ph, CF3) are converted to active catalysts for ethylene oligomerization when activated with methylaluminoxane (MAO). The catalyst activity is comparable to some nickel coordination complexes with N-donor ligands under similar conditions. The products are mainly butenes and hexenes, with small amounts of higher oligomers. The product distribution pattern is consistent with a nickel hydride species being the active center, where fast β-hydride elimination limits the products to mostly butenes and hexenes. The exact nature of the active center and the reaction mechanism remain to be investigated. In addition, we determined the crystal structure for Ni[S2C2(CF3)2]2. The molecule crystallizes in the P21/n space group and adopts a planar geometry with expected bond lengths and angles. Comparing this structure with that for the donor–acceptor complex with perylene reveals elongation of both the Ni–S and the S–C bonds in the latter, suggesting reduction of Ni[S2C2(CF3)2]2 may have occurred in the latter.

Palladium complexes of multidentate pyrazolylmethyl pyridine ligands: Synthesis, structures and phenylacetylene polymerization

The compounds, 2,6-bis(3,5-dimethylpyrazol-1-ylmethyl)pyridine ( MeNˆNˆN) ( L1) and 2,6-bis(3,5-ditertbutylpyrazol-1-ylmethyl)pyridine ( tBu NˆNˆN) ( L2), react with either [Pd(NCMe) 2Cl 2] or [Pd(COD)ClMe] to form the mononuclear palladium complexes [Pd( MeNˆNˆN)Cl 2] ( 1), [Pd( MeNˆNˆN)ClMe] ( 2), [Pd( tBu NˆNˆN)Cl 2] ( 3) and [Pd( tBu NˆNˆN)ClMe] ( 4). Reactions of 1, 2 and 4 with the halide abstractor, NaBAr 4 (Ar = 3,5-(CF 3) 2C 6H 3), led to the formation of stable tridentate cationic species [Pd( MeNˆNˆN)Cl] +( 5), [Pd( MeNˆNˆN)Me] + ( 6) and [Pd( tBu NˆNˆN)Cl] + ( 7) respectively. The analogous carbonyl linker cationic species [Pd{(3,5-Me 2pz-CO) 2-py}Cl] + ( 9) and [Pd{(3,5- t Bu 2pz-CO) 2-py}Cl] + ( 10), prepared by halide abstraction of the neutral complexes [Pd{(3,5-Me 2pz-CO) 2-py}Cl 2] and [Pd{(3,5- t Bu 2pz-CO) 2-py}Cl 2] by NaBAr 4, were however less stable with t 1/2 of 14 and 2 days respectively. Attempts to crystallize 1 and 3 from the mother liquor resulted in the isolation of the salts [Pd( MeNˆNˆN)Cl] 2[Pd 2Cl 6] ( 11) and [Pd( tBu NˆNˆN)Cl] 2[Pd 2Cl 6] ( 12). Although when complexes 1– 4 were reacted with modified methylaluminoxane (MMAO) or NaBAr 4, no active catalysts for ethylene oligomerization or polymerization were formed, activation with silver triflate (AgOTf) produced active catalysts that oligomerized and polymerized phenylacetylene to a mixture of cis-transoidal and trans-cisoidal polyphenylacetylene.

Cobalt and Nickel Complexes Bearing 2,6‐Bis(imino)phenoxy Ligands:Synthesis and Ethylene Oligomerization Study

A series of new cobalt and nickel complexes MLX2 (M = Co or Ni, X = Cl) bearing 2,6‐bis(imino)phenoxy ligands have been synthesized. Treatment of the complexes with methylaluminoxane (MAO) leads to active catalysts for ethylene oligomerization. The oligomers are olefins from C4 to C6.

Iron Complexes Bearing 2-Imino-1,10-phenanthrolinyl Ligands as Highly Active Catalysts for Ethylene Oligomerization

A series of iron complexes ligated by 2-imino-1,10-phenanthrolinyl ligands, LFeCl2 (L = 2-(ArNCR)-1,10-phen), were synthesized and sufficiently characterized by elemental and spectroscopic analysis along with X-ray diffraction analysis. Activated with methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), these iron(II) complexes show high catalytic activities up to 8.95 × 107 g mol-1(Fe) h-1 for ethylene oligomerization. The distribution of oligomers produced follows Schluz−Flory rules with high selectivity for α-olefins. Both the steric and electronic effects of coordinative ligands affect the catalytic activity and the properties of the catalytic products. The parameters of the reaction conditions were also investigated to explore the catalytic potentials of these complexes.

Influence of alcohols on the formation of the nickel complexes active in ethene oligomerization in the catalytic system Ni(PPh 3) 4/BF 3·OEt 2

The influence of ethanol and selected other alcohols on the formation of active nickel complexes for ethylene oligomerization was studied for the Ni(PPh 3) 4/BF 3·OEt 2 system by EPR and 1H NMR spectroscopy. Both the presence of Ni(I) complexes and Ni(II) hydrides could be established. Coordinatively unsaturated Ni(I) complexes were shown to be the active catalysts for ethylene oligomerization, whereas the Ni(II) hydrides were shown to be inactive. The alcohol act as a promoter for the Ni(PPh 3) 4/BF 3·OEt 2 by facilitating the formation of the active Ni(I) complexes.

Ni(II) complexes bearing 2-aryliminobenzimidazole: synthesis, structure and ethylene oligomerization study

A series of nickel complexes bearing 2-aryliminobenzimidazole ligands were synthesized. Single-crystal X-ray analysis of complex 2 shows the nickel center adopts a distorted square-pyramidal geometry. Treatment of the complexes with methylaluminoxane (MAO) leads to active catalysts for ethylene oligomerization.

Cobalt and Nickel Complexes Bearing 2‐(2‐pyridyl)‐Benzimidazole: Synthesis and Ethylene Oligomerization

A series of cobalt and nickel complexes MLX2 (M=Co or Ni, X=Cl) bearing 2‐(2‐pyridyl)benzimidazole ligands were synthesized. Treatment of the complexes with methylaluminoxane (MAO) leads to active catalysts for ethylene oligomerization. The oligomers were olefins from C2 to C6.

Highly Selective Nickel Ethylene Oligomerization Catalysts Based on Sterically Hindered Tris(pyrazolyl)borate Ligands

The reaction of TlTp‘ (Tp‘ = HB(3-mesitylpyrazolyl)3- (TpMs), HB(3-mesitylpyrazolyl)2(5-mesitylpyrazolyl)- (TpMs*)) with NiCl2·6H2O affords TpMsNiCl (1) and TpMs*NiCl (2) in good yield. The compound 2 undergoes an isomerization process to form [{TpMs**}NiCl]2 (3) (TpMs**= HB(5-mesitylpyrazolyl)2(3-mesitylpyrazolyl)-) in 68% yield. Treatment of the tris(pyrazolyl)borate nickel compounds 1 and 2 with alkylaluminum cocatalysts such as methylalumoxane (MAO) and trimethylaluminum (TMA) in toluene generates active catalysts for ethylene oligomerization. The compound 1 shows turnover frequencies in the range of (2.2−43.1) × 103 h-1. Oligomerization reaction conditions can be adjusted that lead to selectivities as high as 81% for butene-1.

Dipyridylamine Ligands − Synthesis, Coordination Chemistry of the Group 10 Metals and Application of Nickel Complexes in Ethylene Oligomerization

A great variety of 2,2′-bipyridylamines can be synthesized starting from primary amines or 2-aminopyridines (for instance, symmetrically and unsymmetrically substituted as well as chiral ligands) by palladium-catalyzed aryl amination. The reaction of such ligands with [PdCl2(COD)] or [NiBr2(DME)] (COD = cycloocta-1,5-diene; DME = 1,2-dimethoxyethane) led to the corresponding dichloro or dibromo complexes. The results of X-ray crystal structure analyses of selected compounds show that the ligands coordinate through the two pyridine N-atoms. Their palladium complexes have a slightly distorted planar coordination (in the case of nickel a distorted tetrahedral coordination), with N−M−N angles of 96.0(2)° (M = Ni) and 85.7° (averaged, M = Pd). The nickel complexes are highly active ethylene oligomerization catalysts if activated with Et3Al2Cl3.