2-(7-methyl-1H-benzoimidazol-2-yl)-6-(1-aryliminoethyl)pyridinylnickel complexes: Synthesis, characterization and their ethylene oligomerization

A series of 2-(methyl-substituted-1H-benzoimidazol-2-yl)-6-(1-aryliminoethyl)pyridines (L1–L6) were synthesized and used as N^N^N tridentate ligands for their nickel complexes (C1–C12). All ligands were fully characterized by elemental, NMR and IR spectroscopic analyses, while their nickel complexes were characterized by elemental and IR spectroscopic analyses. The single-crystal X-ray diffraction reveals that the complexes C1, C3 and C9 have distorted octahedral geometry around the Ni center. All nickel complexes, activated with Et₂AlCl, exhibit good catalytic activities toward ethylene oligomerization with major dimerization.     

Preparation,characterization, DFT calculations and ethylene oligomerization studies of iron(II) complexes bearing 2-(1H-benzimidazol-2-yl)-phenol derivatives

Five 2-(1H-benzimidazol-2-yl)-phenol derivatives including 1H (HL₁), 5-chloro-(HL₂), 5-methyl-(HL₃), 5,6-dichloro-(HL₄), and 5,6-dimethyl-(HL₅) were synthesized by the reaction of their corresponding benzene-1,2-diamine precursors and 2-hydroxybenzaldehyde which subsequently was employed in complexation with Fe(II) to prepare complexes C1–C5, respectively. Indeed, in all complexes, the ligands were coordinated as bidentate, via the C=N nitrogen and hydroxy oxygen atom of benzimidazole moiety and phenol ring, respectively. The compounds were characterized by FTIR, UV–vis, ¹H- and ¹³C-NMR spectropscopy, ICP, and elemental analysis (C, H, and N). The purity of these compounds was determined by melting point (m.p )and TLC. The synthesized ligands and complexes were geometrically optimized by Gaussian09 software at B3LYP/TZVP level of theory and satisfactory theoretical–experimental agreement was achieved for analysis of IR data of the compounds. Catalytic behavior of the iron(II) complexes was investigated for ethylene reactivity. On activation with diethylaluminum chloride (Et₂AlCl), iron(II) complex (C4) showed the highest activity (1686 kg oligomers.mol^?1(Fe).h^?1) for ethylene oligomerization when it contains chlorine substituents and exhibits good selectivity for linear 1-butene. The steric and electronic effects of ligands were investigated in detail on the influence of their catalytic activities.     

Chromium(III) complexes ligated by 2-(1-isopropyl-2-benzimidazolyl)-6-(1-(arylimino)ethyl)pyridines: Synthesis, characterization and their ethylene oligomerization and polymerization

A series of chromium(III) complexes bearing 2-(1-isopropyl-2-benzimidazolyl)-6-(1-(arylimino)ethyl)pyridines were synthesized and characterized by IR spectroscopic and elemental analysis. The X-ray crystallographic analysis revealed a distorted octahedral geometry of the chromium complexes. When activated by Et₂AlCl, MAO or MMAO, these chromium complexes exhibited catalytic activities for ethylene oligomerization and polymerization; while the good to high activities (up to 3.95 × 10⁶ g mol⁻¹ (Cr) h⁻¹) were observed in the catalytic systems with MMAO. Therefore, various reaction parameters of the catalytic system with MMAO were investigated in detail. The steric and electronic effects of ligands affected the catalytic activities and the distribution of the products predominantly. Interestingly, sometimes their distributions of oligomers did not resemble the rules of Schulz-Flory or Poisson due to the hexenes produced in low yield.     

Nickel complexes bearing 2-(1H-benzimidazol-2-yl)-phenoxy ligands: Synthesis, characterization and ethylene oligomerization

A series of 2-(1H-benzimidazol-2-yl)-phenols and their nickel complexes have been synthesized and characterized by elemental and spectroscopic analysis. The molecular structures of ligand L4 and complex C5 were confirmed by X-ray diffraction analysis. X-ray crystallographic analysis revealed that complex C5 has a six-coordinated distorted octahedral geometry. Upon activation with Et₂AlCl, these nickel(II) complexes showed good activity for ethylene oligomerization. When PPh₃ was added as an auxiliary ligand to the catalytic system, an increased activity as high as 1.60 × 10⁷ g mol⁻¹ (Ni) h⁻¹ was observed. The ligand environment and reaction conditions remarkably affected the catalytic behavior of these nickel complexes.     

Synthesis,characterization, and antibacterial activity of triorganotin(IV) complexes of 2-methylphenol

The triorganotin(IV) complex Ph₃Sn(OPhMe-2) (1) has been synthesized by the reaction of Ph₃SnCl with NaOPhMe-2, while complexes of composition n-Bu₃Sn(OPhMe-2) (2) and Me₃Sn(OPhMe-2) (3) (where ?OPhMe-2 = ?OC₆H₄CH₃-2) have been obtained from the reaction of n-Bu₃SnCl and Me₃SnCl with 2-methylphenol in the presence of triethylamine in carbon tetrachloride. The complexes have been characterized by elemental analyses, molar conductance measurements, molecular weight determination, and IR, ¹H NMR, ¹³C NMR, and mass spectral studies. Thermal behavior of the complexes has been studied by TG and DTA techniques. The organotin(IV) complexes have also been screened for antibacterial activity and exhibit appreciable activity. The reactions of the complexes with 3- and 4-cyanopyridines yielded 1 : 1 adducts authenticated by physicochemical and IR and ¹H NMR spectral data.     

Atmospheric reactivity of ethylene catalyzed by β‐diketiminato Ni(II)/methylaluminoxane system

Atmospheric ethylene reactions were studied with backbone fluorinated β‐diketiminato Ni(II) complexes CH{C(CF₃)NAr}₂NiBr (1, Ar = 2,6‐Me₂C₆H₃, and 2 2,6‐ⁱPr₂C₆H₃) activated by methylaluminoxane (MAO). The catalytic systems exhibit the characteristics of catalyzing simultaneously polymerization and oligomerization of ethylene, indicating different active species involved in the reaction system. In an effort to investigate the alkylation species involved in the β‐diketiminato nickel (II)/MAO system, the reaction of 1 with methylaluminoxane were studied. With ¹⁹F{¹H NMR} spectra, two sets of new signals different from 1 were presented. Two alkylation products were proposed precursors of active species for producing oligomer and polymer of ethylene in the β‐diketiminato Ni(II)/MAO system. Copyright © 2014 John Wiley & Sons, Ltd.     

2-Acetyloxymethyl-substituted 5,6,7-trihydroquinolinyl-8-ylideneamine-Ni(II) chlorides and their application in ethylene dimerization/trimerization

Six examples of 2-acetyloxymethyl-substituted 5,6,7-trihydroquinolinyl-8-ylideneamine-nickel(II) chlorides, [2-(CH₂OC(O)Me)-8-{N(Ar)}C₉H₈N]NiCl₂ (Ar = 2,6-Me₂C₆H₃ Ni1 , 2,6-Et₂C₆H₃ Ni2 , 2,6-i-Pr₂C₆H₃ Ni3 , 2,4,6-Me₃C₆H₂ Ni4 , 2,6-Et₂–4-MeC₆H₂ Ni5 , 2,4,6-t-Bu₃C₆H₂ Ni6 ), have been prepared by a one-pot template reaction of 2-(hydroxymethyl)-6,7-dihydroquinolin-8(5H)-one with nickel dichloride hexahydrate, the corresponding aniline and acetic acid. All complexes were characterized by elemental analysis and IR spectroscopy, while dinuclear Ni2 and mononuclear Ni3 ·OH₂ have additionally been the subject of single crystal X-ray diffraction studies; in both structures the acetyloxymethyl group remained uncoordinated. On activationof Ni1 – Ni6 with MMAO, hexenes (C6: ca. 48% 1-hexene) formed the major product of ethylene oligomerization along with minor quantities of butenes (C4); high overall activities of up to 1.33 × 10⁶ g·mol–1 (Ni)h–1 (for mesityl-containing Ni4 ) were achieved at 30 ^oCand 10 atm C₂H₄. By comparison with MAO as co-catalyst, Ni1 – Ni6 exhibited lower activities but displayed a specificity towards ethylene dimerization (C4: 64–99% 1-butene). Furthermore, sizable induction periods were a feature of the MAO runs with Ni1 /MAO reaching peak catalytic activity only after 45 mins.     

Novel nickel (II) complexes chelating β‐diketiminate ligands: synthesis and simultaneous polymerization and oligomerization of ethylene

Two novel nickel (II) complexes, CH{C(CF₃)NAr}₂NiBr ( 1 , Ar = 2,6‐ⁱPr₂C₆H₃ and 2 , 2,6‐Me₂C₆H₃), were synthesized by the reaction of the lithium salt of fluorinated β‐diketiminate backbone ligands with (1,2‐dimethoxyethane) nickel (II) bromide [(DME)NiBr₂]. The solid‐state structure of nickel (II) complex 2 as a dimer reveals four‐coordination and a tetrahedral geometry with bromide bridged by single crystal X‐ray measurement. Both complexes catalyze simultaneous polymerization and oligomerization of ethylene when activated by methylaluminoxane (MAO). It was found that the reaction temperature has a pronounced effect on the activity of ethylene polymerization and the molecular weight of obtained polyethylene. In addition, the nickel catalytic systems predominantly produce linear polyethylene with unsaturated end groups. Copyright © 2006 John Wiley & Sons, Ltd.     

2-(1-(Arylimino)propyl)quinolin-8-olate half-titanocene dichlorides: synthesis, characterization and ethylene (co-)polymerization behaviour

A series of 2-(1-(arylimino)propyl)quinolin-8-olate half-titanocene dichlorides, Cp'TiCl(2)L (Cp' = η(5)-C(5)H(5) or η(5)-C(5)Me(5), L = 2-(1-(2,6-R(1)-4-R(2)-phenylimino)propyl)quinolin-8-olate), was synthesized via the stoichiometric reaction of Cp'TiCl(3) with the corresponding potassium 2-(1-(2,6-R(1)-4-R(2)-phenylimino)propyl)quinolin-8-olate salt. All titanium compounds were characterized by elemental analysis, (1)H NMR and (13)C NMR spectroscopy; the molecular structures of two representative compounds were determined by single crystal X-ray diffraction. On activation with methylaluminoxane (MAO), all half-titanocene compounds showed high activity in ethylene polymerization, and furthermore, performed with good to high activities in the co-polymerization of ethylene with either 1-hexene or 1-octene affording polyethylenes with high co-monomer incorporation. Less bulky ortho-substituents (R(1)) on the phenylimino groups were found to enhance the catalytic activities of their titanium compounds. In general, the titanium pro-catalysts containing η(5)-C(5)Me(5) (C7-C12) exhibited higher activities than did their analogues bearing η(5)-C(5)H(5) (C1-C6). Some of the resultant polyolefins were ultrahigh molecular weight polyethylene.     

Synthesis,characterization and ethylene oligomerization and polymerization of 2-(1H-2-benzimidazolyl)-6-(1-(arylimino)ethyl)pyridylchromium chlorides

A series of N^N^N tridentate chromium complexes (C1–C6) bearing 2-(1H-2-benzimidazolyl)-6-(1-(arylimino)ethyl)pyridine derivatives was synthesized and characterized by elemental and spectroscopic analysis along with single-crystal X-ray crystallography. X-ray crystallographic analyses reveal chromium complex C1 as a distorted six-coordinated octahedral geometry. On treatment with modified methylaluminoxane (MMAO), the chromium complexes exhibited high activities for ethylene oligomerization (up to 1.50 × 10⁶ g mol⁻¹ (Cr) h⁻¹) and polymerization (up to 2.06 × 10⁶ g mol⁻¹ (Cr) h⁻¹) at 10 atm ethylene pressure. Various reaction parameters were investigated in detail, and less steric hindrance and electron-withdrawing substituents of ligands enhance the catalytic activities of their chromium complexes.     

Synthesis, characterization and catalytic behavior toward ethylene of cobalt(II) and iron(II) complexes bearing 2-(1-aryliminoethylidene)quinolines

A series of 2-(1-aryliminoethylidene)quinolines (L) were synthesized and used as bidentate N^N ligands in coordinating with metal (cobalt and iron) chlorides to form complexes of the type LMCl₂, cobalt(II) (Co1-Co5) and iron(II) (Fe1-Fe5). All organic compounds and metal complexes were fully characterized, and the molecular structures of the representative complexes Co3·DMF and Fe4·DMF were confirmed as distorted bipyramidal geometry at the metal by single-crystal X-ray diffraction. Upon activation with either methylaluminoxane (MAO) or modified methylaluminoxane (MMAO) under 10 atm ethylene, all complexes showed high activities in ethylene dimerization with activities of up to 1.82 × 10⁶ g mol⁻¹ (Co) h⁻¹ and 5.89 × 10⁵ g mol⁻¹ (Fe) h⁻¹, respectively.     

Bis(β‐enaminoketonato) vanadium (III or IV) complexes as catalysts for olefin polymerization

Bis(β‐enaminoketonato) vanadium(III) complexes ( 2a–c ) [O(R₁)C?C(H)_xC(R₂)?NC₆H₅]₂VCl(THF) and the corresponding vanadium(IV) complexes ( 3a–c ) [O(R₁)C?C(H)_xC(R₂)? NC₆H₅]₂VO (R₁ = ? (CH₂)₄? , R₂ = H, x = 0, a ; R₁ = ? C₆H₅, R₂ = H, x = 1, b ; R₁ = ? C₆H₅, R₂ = ? C₆H₅, x = 1, c ) have been synthesized from VCl₃(THF)₃ and VOCl₂(THF)₂, respectively, by treating with 2.0 equivalent β‐enaminoketonato ligands in tetrahydrofuran. Structures of 2b and 3a–c were further confirmed by X‐ray crystallographic analysis. The complexes were investigated as the catalysts for ethylene polymerization in the presence of Et₂AlCl. Complexes 2a–c and 3a–c exhibited high catalytic activities (up to 23.76 kg of PE/mmol_V h bar), and afforded polymers with unimodal molecular weight distributions at 70 °C indicating the good thermal stability. The catalytic behaviors were influenced not only by the oxidation state of the catalyst precursors but also by the ligand structures. Complexes 2a–c and 3a–c were also effective catalyst precursors for ethylene/1‐hexene copolymerization. The influence of polymerization parameters such as reaction temperature, Al/V molar ratio and hexene feed concentration on the ethylene/hexene copolymerization behaviors have bee also investigated in detail. In addition, the agents such as AlMe₃, AlⁱBu₃, MeMgBr, MgCl₂, and ZnEt₂ were applied to control the molecular weight and molecular weight distribution modal. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3062–3072, 2010     

Bis(diphenylphosphano)alkan- und 1-(Diphenylphosphano)-2-(2-pyridino)ethan-N-Arylsulfinylamin-Nickel(0)-Komplexe

Bis(diphenylphosphano)alkane- and 1-Diphenylphosphano-2-(2-pyridino)ethane-N-arylsulfinylamine Nickel(0) Complexes Synthesis and properties of the bis(diphenylphosphano)alkane-N-phenyl-sulfinylamine-nickel(0) complexes [Ni{Ph₂P(CH₂)_nPPh₂}(PhNSO)] (n = 2 dppe, n = 3 dppp, n = 4 dppb) as well as of the 1-(diphenylphosphano)-2-(2-pyridino)ethane nickel(0) complexes [Ni(dpppe)₂], [Ni(dpppe)(p-TolNSO)] and [Ni(dpppe)(PPh₃)₂] are described. These compounds have been characterized by i. r. and ³¹P n.m.r. spectroscopy. The N-arylsulfinylamine ligands are η²-(N, S)-side on coordinated.     

Syntheses and structures of iron carbonyl complexes derived from N-(5-methyl-2-thienylmethylidene)-2-thiolethylamine and N-(6-methyl-2-pyridylmethylidene)-2-thiolethylamine

The reaction of N-(5-methyl-2-thienylmethylidene)-2-thiolethylamine (1) with Fe₂(CO)₉ in refluxing acetonitrile yielded di-(μ₃-thia)nonacarbonyltriiron (2), μ-[N-(5-methyl-2-thienylmethyl)-η¹:η¹(N);η¹:η¹(S)-2-thiolatoethylamido]hexacarbonyldiiron (3), and N-(5-methyl-2-thienylmethylidene)amine (4). If the reaction was carried out at 45 °C, di-μ-[N-(5-methyl-2-thienylmethylidene)-η¹(N);η¹(S)-2-thiolethylamino]-μ-carbonyl-tetracarbonyldiiron (5) and trace amount of 4 were obtained. Stirring 5 in refluxing acetonitrile led to the thermal decomposition of 5, and ligand 1 was recovered quantitatively. However, in the presence of excess amount of Fe₂(CO)₉ in refluxing acetonitrile, complex 5 was converted into 2-4. On the other hand, the reaction of N-(6-methyl-2-pyridylmethylidene)-2-thiolethylamine (6) with Fe₂(CO)₉ in refluxing acetonitrile produced 2, μ-[N-(6-methyl-2-pyridylmethyl)-η¹ (N_py);η¹:η¹(N); η¹:η¹(S)-2-thiolatoethylamido]pentacarbonyldiiron (7), and μ-[N-(6-methyl-2-pyridylmethylidene)-η²(C,N);η¹:η¹(S)-2- thiolethylamino]hexacarbonyldiiron (8). Reactions of both complex 7 and 8 with NOBF₄ gave μ-[(6-methyl-2-pyridylmethyl)-η¹(N_py);η¹:η¹(N);η¹:η¹(S)-2-thiolatoethylamido](acetonitrile)tricarbonylnitrosyldiiron (9). These reaction products were well characterized spectrally. The molecular structures of complexes 3, 7-9 have been determined by means of X-ray diffraction. Intramolecular 1,5-hydrogen shift from the thiol to the methine carbon was observed in complexes 3, 7, and 9.     

Chromium(III) complexes bearing 2-benzoxazolyl-6-arylimino-pyridines: Synthesis and their ethylene reactivity

A series of chromium(III) complexes bearing 2-benzoxazolyl-6-aryliminopyridines was synthesized and characterized by IR spectroscopic and CHN analysis. The X-ray crystallographic analysis of complex Cr3 revealed a distorted octahedral geometry. When activated by Et₂AlCl, MAO or MMAO, these chromium complexes exhibited activities towards ethylene reactivity. High activities of ethylene oligomerization (up to 9.19 × 10⁶ g mol⁻¹ (Cr) h⁻¹) were observed in the catalytic system using MMAO as a cocatalyst, meanwhile good activities of ethylene polymerization were achieved (up to 5.20 × 10⁵ g mol⁻¹ (Cr) h⁻¹) by using MAO as a cocatalyst. Various reaction parameters were investigated in detail, and the steric and electronic effects of ligands were discussed.     

o-Trityl phenoxy-imino vanadium (III) complexes: synthesis,characterization, and catalysis on ethylene (co)polymerization

Several phenoxy-imine ligands bearing o-trityl group in phenoxy moiety RN=CHArOH (Ar = C₆H₂(CPh₃)^tBu, R = 2,6-Me₂C₆H₃ ( L ₁ H ); 2,6-ⁱPr₂C₆H₃ ( L ₂ H ); 3,5-(CF₃)₂C₆H₃ ( L ₃ H ); 3,5-(OMe)₂C₆H₃ ( L ₄ H ); CHPh₂ ( L ₅ H ); CPh₃ ( L ₆ H )) were synthesized and characterized by¹H NMR and ¹³C NMR spectroscopy. The vanadium complexes based on these ligands LVCl₂(THF)₂ ( 1–6 ) were synthesized via conventional transmetalation reaction in moderate to high yields. Complexes 1–6 were fully characterized by FT-IR, elemental analyses and the molecular structures of 1 , 2 ·H₂O, (2 ·H₂O ) ₂ (μ-Cl) ₂ , 4 , and 5 were confirmed by X-ray crystallographic analysis in which the six-coordinated vanadium centers are in a typical octahedral geometry. Upon activation with Et₂AlCl in toluene, complexes 1–6 showed high activities in ethylene polymerization affording polymers with moderate molecular weight (5.9–11.8 × 10⁴ Da). Moreover, in hexane or CH₂Cl₂, 1–6 /Et₂AlCl exhibited enhanced activities. When activated with MAO or MMAO in toluene, these complexes showed relatively low activities but afforded polymers with ultra-high molecular weight (up to 3.30 × 10⁶ Da). 1–6 /Et₂AlCl also showed high activities in ethylene/1-hexene copolymerization at room temperature giving moderate molecular-weight polymers (6.5–11.4 × 10⁴ Da) with co-monomer incorporation being of 6.0 ~ 7.8%.     

Syntheses,spectroscopic characterizations and crystal structures of diorganotin(IV)-oxo-carboxylates with 2-pyrazinecarboxylic acid or (2-pyrimidylthio)acetic acid

Eight diorganotin(IV)-oxo-carboxylates {[R₂Sn(O(O)CR′)]₂O}₂?·?Y (R′?=?C₄H₃N₂Y?= H₂OR?=?ⁿBu 1, Y?=?0 R?=?Me 2, Y?=?0 R?=?C₆H₅ 3, Y?=?0 R?=?C₆H₅CH₂ 4; R′?=?CH₂SC₄H₃N₂-2,6Y?=?0 R?=?ⁿBu 5, Y?=?CH₂Cl₂R?=?Me 6, Y?=?0 R?=?C₆H₅ 7, Y?=?0 R?= C₆H₅CH₂ 8) have been prepared in 1?:?1 molar ratios by reactions of diorganotin(IV) oxide with 2-pyrazinecarboxylic acid or (2-pyrimidylthio)acetic acid, respectively. All the complexes are characterized by elemental analysis, IR, ¹H NMR and ¹³C NMR spectra. Except for 2, 4 and 7, the complexes are also characterized by X-ray crystallography diffraction analyses, which reveal that the complexes adopt the familiar dicarboxylato tetraorganodistannoxane structural mode. Among them, the evident difference is that weak intramolecular interactions between Sn and N atoms are recognized in complexes 1 and 3. However, for complex 5 two different coordination modes are found in the same lattice.     

Synthesis and reactivity of new methylallylpalladium(II) complexes with bidentate 2-(methylthio-N-benzylidene)anilines

This work describes the synthesis, characterisation and reactivity of new methylallyl Pd(II) complexes that contain bidentate 2-(methylthio-N-benzylidene)anilines as ligands. The reaction of the binuclear complex [(η³-Me-allyl)Pd(μ-Cl)₂] with AgBF₄ causes the total abstraction of the chloride bridges, with the subsequent formation of an intermediary fragment of Pd(II). This fragment in turn reacts with neutral bidentate 2-(methylthio-N-benzylidene)anilines to give cationic complexes of Pd(II) of general formula [(η³-Me-allyl)Pd(η²-S,N-MeSC₆H₄NCHC₆H₄(X)Y)]BF₄ [X=H, Y=H (1); X=F, Y=H (2); X=Me, Y=H (3); X=H, Y=Cl (4); X=H, Y=Me₂N (5); X=H, Y=NO₂ (6)]. The new complexes were characterised by means of elemental analysis, IR, NMR [¹H, ¹⁹F{¹H}, ¹³C{¹H}, ³¹P{¹H}, Dept, ¹H-¹H-COSY, HSQC, HMBC] and mass spectroscopies. The reaction of the Pd(II) complexes with nucleophiles such as NaI, (EtO)₂PS₂K, KCN, KSCN or NaH lead to the deco-ordination of the bidentate ligands to give dimeric or polymeric complexes of Pd(II). The reactivity pattern observed is discussed by a theoretical analysis based on Fukui functions.     

Novel neutral arylnickel(II) phosphine catalysts containing 2-oxazolinylphenolato N-O chelate ligands for ethylene oligomerization and propylene dimerization

A series of new neutral arylnickel(II) phosphine complexes 1 bearing 2-oxazolinylphenolato ligands [2-(4-R¹-5-R²-C₃H₂NO)-C₆H₄O]Ni(2-R⁴-4-R³-C₆H₃)(PPh₃) were synthesized by reactions of sodium salts of 2-(4,5-dihydro-2-oxazolyl)phenol derivatives with trans-Ni(Ar)(Cl)(PPh₃)₂ or by direct reactions of the ligands with trans-Ni(Ar)(Cl)(PPh₃)₂ in the presence of NEt₃. These neutral Ni(II) complexes 1 exhibited high activities and selectivities in ethylene oligomerization and propylene dimerization. The catalytic activities and the product distributions were dependent on the selection of various organoaluminum cocatalysts and phosphine scavenger (Ni(COD)₂). The effects of various reaction conditions on ethylene oligomerization were also examined. The highest activity of 5.51 × 10⁵ g oligomers/(mol Ni · h) and 83% selectivity of C₆ internal olefins were obtained in 1a/MAO catalytic system in ethylene oligomerization. The oligomers consisted mainly of lower carbon olefins in the range of C₄-C₈. Complexes 1 showed the moderate tolerance of polar additives in ethylene oligomerization. The highest activity of 1a/MAO in propylene dimerization reached to 1.32 × 10⁵ g oligomers/(mol Ni · h).     

N-(Pyridin-2-yl)picolinamide tetranickel clusters: Synthesis,structure and ethylene oligomerization

A series of N-(pyridin-2-yl)picolinamide derivatives was synthesized and characterized. Tetranickel complexes were obtained by stoichiometric reaction of NiBr₂ and corresponding ligands, and characterized by elemental and spectroscopic analysis. Moreover, the coordination pattern of complex 3a was confirmed by single-crystal X-ray diffraction. In the structure, two ligands linked two nickel atoms to form a unit, and two units were bridged via μ₃-OMe and μ₂-Br to form a tetranickel cluster. These Ni(II) complexes were investigated in ethylene oligomerization and found to exhibit remarkable catalytic activities upon activation with MAO. Reaction conditions as well as ligand environment significantly affected the catalytic performance of the nickel complexes; the highest activity could be achieved to be 2.7 × 10⁶ g mol⁻¹ Ni h⁻¹.