A series of α,α′-bis(arylimino)-2,3:5,6-bis(pentamethylene)pyridylcobalt chlorides was synthesized by the one-pot template reaction of α,α′-dioxo-2,3:5,6-bis(pentamethylene)pyridine, anilines, and cobalt chloride in refluxing acetic acid. The molecular structure of complex Co1 was determined by single-crystal X-ray crystallography, which revealed a distorted square-pyramidal geometry around the cobalt center. On activation with methylaluminoxane or modified methylaluminoxane, all of the complexes exhibited high activity toward ethylene polymerization with activities in the range of 10⁶ g of polyethylene (PE) per mole of Co per hour and produced highly linear PEs with low molecular weights and narrow polydispersity. The unimodal nature of the PEs indicated single-site active species of these cobalt catalyst systems. The influences of cobalt complexes and polymerization parameters on the catalytic behavior and the properties of the PEs were investigated in detail.

Isoprene polymerization was conducted in the cis-1,4-selective manner by combining neodymium chloride with 8-hydroxyquinoline derivatives and activating the system with triisobutylaluminium. The neodymium-based complex pre-catalysts with 8-hydroxyquinoline derivatives were synthesized and characterized as well as the molecular structure of a representative complex using single-crystal X-ray diffraction. All complexes exhibited high activity and stereospecificity (up to 97.3%) towards isoprene polymers with high molecular weight (10⁵ g mol⁻¹). The Al/Nd and isoprene/Nd molar ratios, reaction temperature and influence of 8-hydroxyquinoline substituents were investigated for correlations with catalytic activities and molecular weights of the polyisoprenes obtained. © 2015 Society of Chemical Industry

A series of 1-(2,6-dibenzhydryl-4-fluorophenylimino)- 2-aryliminoacenaphthylene derivatives (L1–L5) and their halonickel complexes LNiX₂ (X = Br, Ni1–Ni5; X = Cl, Ni6–Ni10) are synthesized and well characterized. The molecular structures of representative complexes Ni2 and Ni4 are confirmed as the distorted tetrahedron geometry around nickel atom by the single crystal X-ray diffraction. Upon activation with methylaluminoxane, all nickel complexes show high activities up to 1.49 × 10⁷ g of PE (mol of Ni)⁻¹ h⁻¹ toward ethylene polymerization, producing polyethylenes with high branches and molecular weights up to 1.62 × 10⁶ g mol⁻¹ as well as narrow polydispersity. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 1369–1378

2-[1-(2,6-Diisopropylphenylimino)ethyl]-6-[1-(pyren-1-ylimino)ethyl]pyridine (L1) and 2,6-bis[1-(pyren-1-ylimino)ethyl]pyridine (L2) were synthesized and used to prepare the corresponding Fe complexes Fe1 and Fe2 from FeCl₂. All new compounds were characterized, and single-crystal XRD analysis of Fe1 was performed. The π-conjugated pyrenyl substituent enhanced the catalytic activity of the Fe complexes, which display high activity in ethylene polymerization up to 10⁷ g_PE mol_Fe⁻¹ h⁻¹ (PE=polyethylene). These Fe complexes were easily immobilized on multiwalled carbon nanotubes (MWCNTs) through noncovalent π–π interactions. The supported precatalysts showed better ethylene polymerization activity than their homogeneous counterparts to produce well-dispersed MWCNT/PE composite materials.

Polyisoprene (PI) with a high content of cis-1,4 (up to 95%) or cis-1,4/3,4 binary structures was synthesized using a cobalt system in toluene. The cobalt system, which exhibited high activities (up to 3.50 × 10⁶ g PI (mol Co)⁻¹ h⁻¹), contained a series of 2-(benzimidazolyl)-6-(1-(arylimino)ethyl)pyridine cobalt(II) dichlorides activated with ethylaluminium sesquichloride. The nature of the ligands and the reaction conditions significantly affected both the catalytic performance of the cobalt complexes as well as the structures of the resultant PI. The stereospecific polymerization of isoprene could be tuned via changing either the co-catalyst or solvent: for example, increased content of 3,4 PI (up to 36.6%) was achievable in heptane in the presence of diethylaluminium chloride. Sequence distribution analysis by ¹³C NMR spectroscopy indicated that most 3,4 units occurred randomly in the PI chains. © 2013 Society of Chemical Industry

The reactions of MCl₅ or MOCl₃ with imidazole-based pro-ligand L¹H, 3,5-tBu₂-2-OH-C₆H₂-(4,5-Ph₂-1H-)imidazole, or oxazole-based ligand L²H, 3,5-tBu₂-2-OH-C₆H₂(1H-phenanthro[9,10-d])oxazole, following work-up, afforded octahedral complexes [MX(L^1, 2)], where MX=NbCl₄ (L¹, 1 a; L², 2 a), [NbOCl₂(NCMe)] (L¹, 1 b; L², 2 b), TaCl₄ (L¹, 1 c; L², 2 c), or [TaOCl₂(NCMe)] (L¹, 1 d). The treatment of α-diimine ligand L³, (2,6-iPr₂C₆H₃NCH)₂, with [MCl₄(thf)₂] (M=Nb, Ta) afforded [MCl₄(L³)] (M=Nb, 3 a; Ta, 3 b). The reaction of [MCl₃(dme)] (dme=1,2-dimethoxyethane; M=Nb, Ta) with bis(imino)pyridine ligand L⁴, 2,6-[2,6-iPr₂C₆H₃N(Me)C]₂C₅H₃N, afforded known complexes of the type [MCl₃(L⁴)] (M=Nb, 4 a; Ta, 4 b), whereas the reaction of 2-acetyl-6-iminopyridine ligand L⁵, 2-[2,6-iPr₂C₆H₃N(Me)C]-6-Ac-C₅H₃N, with the niobium precursor afforded the coupled product [({2-Ac-6-(2,6-iPr₂C₆H₃N(Me)C)C₅H₃N}NbOCl₂)₂] (5). The reaction of MCl₅ with Schiff-base pro-ligands L⁶H–L¹⁰H, 3,5-(R¹)₂-2-OH-C₆H₂CHN(2-OR²-C₆H₄), (L⁶H: R¹=tBu, R²=Ph; L⁷H: R¹=tBu, R²=Me; L⁸H: R¹=Cl, R²=Ph; L⁹H: R¹=Cl, R²=Me; L¹⁰H: R¹=Cl, R²=CF₃) afforded [MCl₄(L^6–10)] complexes (M=Nb, 6 a–10 a; M=Ta, 6 b–9 b). In the case of compound 8 b, the corresponding zwitterion was also synthesised, namely [Ta⁻Cl₅(L⁸H)⁺]⋅MeCN (8 c). Unexpectedly, the reaction of L⁷H with TaCl₅ at reflux in toluene led to the removal of the methyl group and the formation of trichloride 7 c [TaCl₃(L^7-Me)]; conducting the reaction at room temperature led to the formation of the expected methoxy compound (7 b). Upon activation with methylaluminoxane (MAO), these complexes displayed poor activities for the homogeneous polymerisation of ethylene. However, the use of chloroalkylaluminium reagents, such as dimethylaluminium chloride (DMAC) and methylaluminium dichloride (MADC), as co-catalysts in the presence of the reactivator ethyl trichloroacetate (ETA) generated thermally stable catalysts with, in the case of niobium, catalytic activities that were two orders of magnitude higher than those previously observed. The effects of steric hindrance and electronic configuration on the polymerisation activity of these tantalum and niobium pre-catalysts were investigated. Spectroscopic studies (¹H NMR, ¹³C NMR and ¹H¹H and ¹H¹³C correlations) on the reactions of compounds 4 a/4 b with either MAO(50) or AlMe₃/[CPh₃]⁺[B(C₆F₅)₄]⁻ were consistent with the formation of a diamagnetic cation of the form [L⁴AlMe₂]⁺ (MAO(50) is the product of the vacuum distillation of commercial MAO at +50 °C and contains only 1 mol % of Al in the form of free AlMe₃). In the presence of MAO, this cationic aluminium complex was not capable of initiating the ROMP (ring opening metathesis polymerisation) of norbornene, whereas the 4 a/4 b systems with MAO(50) were active. A parallel pressure reactor (PPR)-based homogeneous polymerisation screening by using pre-catalysts 1 b, 1 c, 2 a, 3 a and 6 a, in combination with MAO, revealed only moderate-to-good activities for the homo-polymerisation of ethylene and the co-polymerisation of ethylene/1-hexene. The molecular structures are reported for complexes 1 a–1 c, 2 b, 5, 6 a, 6 b, 7 a, 8 a and 8 c.

A series of 2-(1-{2,6-bis[bis(4-fluorophenyl)methyl]-4-methylphenylimino}ethyl)-6- [1-(arylimino)ethyl]pyridine ligands is synthesized and fully characterized. The corresponding iron complexes are prepared and characterized by single-crystal X-ray diffraction for representative iron complexes, among other methods, revealing a pseudo square-pyramidal geometry at the iron center. Upon activation with MMAO, all iron precatalysts exhibit high activity in ethylene polymerization, producing linear polyethylene. The observed activity is the highest reported for iron-based precatalysts of this type. The polymerization parameters are shown to strongly affect the catalytic behavior, and both the activity and the polymer properties (i.e. or /) can be controlled.

A series of trichlorotitanium complexes containing 2-(1-(arylimino)propyl)quinolin-8-olates was synthesized by stoichiometric reaction of titanium tetrachloride with the corresponding potassium 2-(1-(arylimino)propyl)quinolin-8-olates and was fully characterized by elemental analysis, nuclear magnetic resonance spectroscopy, and by single-crystal X-ray diffraction study of representative complexes. All titanium complexes, when activated with methylaluminoxane, exhibited high catalytic activity toward ethylene polymerization [up to 1.15 × 10⁶ g mol⁻¹(Ti) h⁻¹] and ethylene/α-olefin copolymerization [up to 1.54 × 10⁶ g mol⁻¹ (Ti) h⁻¹]. The incorporation of comonomer was confirmed to amount up to 2.82 mol % of 1-hexene or 1.94 mol % of 1-octene, respectively. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

A series of iron(II) dichloride complexes (Fe1–Fe7) ligated by 2-(2-benzoxazolyl)-6-[1-(arylimino)ethyl]pyridines was synthesized and characterized [aryl = 2,6-R¹₂C₆H₃; R¹ = Me (1), Et (2), iPr (3), Cl (4), Br (5); 2,6-Me₂C₆H₂-4-R², R² = Me (6), Br (7)]. The molecular structures of Fe1, Fe3, and Fe5 were determined by the single-crystal X-ray diffraction. Complexes Fe1 and Fe3 both display distorted trigonal-bipyramidal geometries, whereas complex Fe5 is a distorted square pyramid. Upon activation with modified methylaluminoxane, all iron complexes showed moderate to good activities [up to ca. 10⁶ g(product) × (mol Fe)^–1 h^–1 bar^–1] for the oligomerization and polymerization of ethylene, with high selectivity for vinyl-terminated oligomers or polyethylene waxes.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

The metal salts, FeCl^·₂4H₂O, FeCl₃, NiCl₂, CoCl₂, CuBr and some iron complexes were found to be efficient catalysts for hydrodebromination of bromoarenes under mild reaction conditions with two equivalents of Grignard reagents. Among them, the iron systems showed the best behavior regarding economic and environmental considerations. All the alkyl Grignard reagents (except CH₃MgCl) and p-tolylMgBr were promising reductive reagents with the formation of their homo-coupling products. Copyright © 2008 John Wiley & Sons, Ltd.

A series of N-(2-benzimidazolyquinolin-8-yl)benzamidate half-titanocene chlorides, Cp′TiLCl (C1–C8: Cp′ = C₅H₅, MeC₅H₄, or C₅Me₅; L = N-(benzimidazolyquinolin-8-yl)benzamides)), was synthesized by the KCl elimination reaction of half-titanocene trichlorides with the correspondent potassium N-(2-benzimidazolyquinolin-8-yl)benzamide. These half-titanocene complexes were fully characterized by elemental and NMR analyses, and the molecular structures of complexes C2 and C8 were determined by the single-crystal X-ray diffraction. The high stability of the pentamethylcyclopentadienyl complex (C8) was evident by no decomposing nature of its solution in air for one week. The oxo-bridged dimeric complex (C9) was isolated from the solution of the corresponding cyclopentadienyl complex (C3) solution in air. Complexes C1–C8 exhibited good to high catalytic activities toward ethylene polymerization and ethylene/α-olefin copolymerization in the presence of methylaluminoxane (MAO) cocatalyst. In the typical catalytic system of C1/MAO, the polymerization productivities were enhanced with either elevating reaction temperature or increasing the ratio of MAO to titanium precursor. In general, it was observed that higher the catalytic activity of the catalytic system lower the molecular weight of polyethylene. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3154–3169, 2009

A series of imino-indolate half-titanocene chlorides, Cp′Ti(L)Cl₂ (C1–C7: Cp′ = C₅H₅, MeC₅H₄, C₅Me₅, L = imino-indolate ligand), were synthesized by the reaction of Cp′TiCl₃ with sodium imino-indolates. All complexes were characterized by elemental analysis, ¹H and ¹³C NMR spectroscopy. Moreover, the molecular structures of two representative complexes C4 and C6 were confirmed by single crystal X-ray diffraction analysis. On activation with methylaluminoxane (MAO), these complexes showed good catalytic activities for ethylene polymerization (up to 7.68 × 10⁶ g/mol(Ti)·h) and ethylene/1-hexene copolymerization (up to 8.32 × 10⁶ g/mol(Ti)·h), producing polyolefins with high molecular weights (for polyethylene up to 1808 kg/mol, and for poly(ethylen-co-1-hexene) up to 3290 kg/mol). Half-titanocenes containing ligands with alkyl substituents showed higher catalytic activities, whereas the half-titanocenes bearing methyl substituents on the cyclopentadienyl groups showed lower productivities, but produced polymers with higher molecular weights. Moreover, the copolymerization of ethylene and methyl 10-undecenoate was demonstrated using the C1/MAO catalytic system. The functionalized polyolefins obtained contained about 1 mol % of methyl 10-undecenoate units and were fully characterized by several techniques such as FT-IR, ¹H NMR, ¹³C NMR, DSC, TGA and GPC analyses. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 357–372, 2009

{2-[1-(2,6-Diisopropylphenylimino)ethyl]pyridyl}palladiumdibromide (1) was synthesized and crystallized as red crystals from chloroform in the monoclinic space group P2₁/c or as yellow crystals from methanol in the triclinic space group P. Other solvents, such as THF and acetonitrile, gave mixtures of red and yellow crystals. With very little conformational differences between the molecules in the dimorphs of 1 the crystal packing is a herringbone array in 1-red and a parallel array in 1-yellow, with the supramolecular interactions differing in the Br···π and C–H···Br contacts. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

6-Benzimidazolylpyridyl-2-carboximidic half-titanocene complexes, Cp′TiLCl (Cp′ = C₅H₅, MeC₅H₄, C₅Me₅, L = 6-benzimidazolylpyridine-2-carboxylimidic, C1–C13), were synthesized and characterized along with single-crystal X-ray diffraction. The half-titanocene chlorides containing substituted cyclopentadienyl groups, especially pentamethylcyclopentadienyl groups were more stable, while those without substituents on the cyclopentadienyl groups were easily transformed into their dimeric oxo-bridged complexes, (CpTiL)₂O (C14 and C15). In the presence of excessive amounts of methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), all half-titanocene complexes showed high catalytic activities for ethylene polymerization. The substituents on the Cp groups affected the catalytic behaviors of the complexes significantly, with less substituents favoring increased activities and higher molecular weights of the resultant polyethylenes. Effects of reaction conditions on catalytic behaviors were systematically investigated with catalytic systems of mononuclear C1 and dimeric C14. With C1/MAO, large MAO amount significantly increases the catalytic activity, while the temperature only has a slight effect on the productivity. In the case of C14/MAO catalytic system, temperature above 60 °C and Al/Ti value higher than 5000 were necessary to observe good catalytic activities. In both systems, higher reaction temperature and low cocatalyst amount gave the polyethylenes with higher molecular weights. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3396–3410, 2008

A series of 6-(benzimidazol-2-yl)-N-organylpyridine-2-carboxamide were synthesized and transformed into 6-benzimidazolylpyridine-2-carboxylimidate as dianionic tridentate ligands. Bis(2-(6-methylpyridin-2-yl)-benzimidazolyl)titanium dichloride (C1) and titanium bis(6-benzimidazolylpyridine-2-carboxylimidate) (C2–C8) were synthesized in acceptable yields. These complexes were systematically characterized by elemental and NMR analyses. Crystallographic analysis revealed the distorted octahedral geometry around titanium in both complexes C1 and C4. Using MAO as cocatalyst, all complexes exhibited from good to high catalytic activities for ethylene polymerization. The neutral bis(6-benzimidazolylpyridine-2-carboxylimidate)titanium (C2–C8) showed high catalytic activities and good stability for prolonged reaction time and elevated reaction temperature; however, C1 showed a short lifetime in catalysis as being observed at very low activity after 5 min. The elevated reaction temperature enhanced the productivity of polyethylenes with low molecular weights, whereas the reaction with higher ethylene pressure resulted in better catalytic activity and resultant polyethylenes with higher molecular weights. At higher ratio of MAO to titanium precursor, the catalytic system generated better activity with producing polyethylenes with lower molecular weights. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3411–3423, 2008