A series of ethylene-bridged C₁-symmetric ansa-(3-R-indenyl)(fluorenyl) zirconocene complexes (1, 2, 3, 4, 5, 6, 7, 8, 9) incorporating a pendant arene substituent on the 3-position of indenyl ring have been synthesized. The structure of complex 4 was further confirmed by X-ray diffraction analysis. When activated with methylaluminoxane, four sterically less encumbered complexes 1, 2, 4 and 5 could catalyze the dimerization of propylene in toluene at 100°C to afford 2-methyl-1-pentene with high selectivities up to 95.7–98.4% and moderate activities of 2.00 × 10⁴ to 7.89 × 10⁴ g (mol-Zr⋅h)⁻¹. Copyright © 2014 John Wiley & Sons, Ltd.

A series of group 4 metallocenes (RCp)[Cp―(bridge)―(2-C₄H₃S)]MCl₂ [M = Ti (C1, C2, C3, C4); M = Zr (C5, C6, C7, C8)] bearing a pendant thiophene group on a cyclopentadienyl ring have been synthesized, characterized and tested as catalyst precursors for ethylene polymerization. The molecular structures of representative titanocenes C2 and C4 were confirmed by single-crystal X-ray diffraction and revealed that both complexes exist in an expected coordination environment for a monomeric bent metallocene. No intramolecular coordination between the thiophene group and the titanium center could be observed in the solid state. Upon activation by methylaluminoxane (MAO), titanocenes C1, C2, C3, C4 showed moderate catalytic activities and produced high- or ultra-high-molecular-weight polyethylene (M_v 70.5–227.1 × 10⁴ g mol⁻¹). Titanocene C3 is more active and long-lived, with a lifetime of nearly 9 h at 30 °C. At elevated temperatures of 80–110 °C, zirconocenes C5, C6, C7, C8 displayed high catalytic activities (up to 27.6 × 10⁵ g PE (mol Zr)⁻¹ h⁻¹), giving high-molecular-weight polyethylene (M_v 11.2–53.7 × 10⁴ g mol⁻¹). Even at 80 °C, a long lifetime of at least 2 h was observed for the C8/MAO catalyst system. Copyright © 2014 John Wiley & Sons, Ltd.

A series of bis(phenoxy-imine) zirconium complexes bearing bulky o-bis(aryl)methyl-substituted aryl groups on the aniline moiety have been synthesized, characterized and tested as catalyst precursors for ethylene polymerization. ¹H NMR spectroscopy suggests that these complexes exist as a single chiral C₂-symmetric isomer in the solution. X-ray crystallographic analysis of the resulting biszwitterionic-type adduct complex C1 · 2HCl reveals that the phenoxy-imine groups function as a monodentate phenoxy ligand and the oxygen atoms are oriented trans to each other at the central metal atom. Using modified methylaluminoxane (MMAO) as co-catalyst, C1 · 2HCl, C2–C6 exclusively produce linear aluminium-terminated polyethylenes (Al-PEs) with high activity (up to 16.89 × 10⁶ g PE (mol Zr h)⁻¹, suggesting that chain transfer to aluminum is the predominant termination mechanism. It is noteworthy that the introduction of an excessively bulky o-bis(aryl)methyl substituent adjacent to the imine-N produces low molecular-weight Al-PEs (M_v 1.6–10.1 × 10³) due to the enhanced rate of chain transfer to alkylaluminium groups during polymerization. Copyright © 2013 John Wiley & Sons, Ltd.

Asymmetric double silylene-bridged binuclear complexes [(η⁵-RC₅H₄)MCl₂]₂[μ, μ-(SiMe₂)₂(η⁵-t-BuC₅H₂)(η⁵-C₅H₃)][R = H, M = Ti (1); R = Me, M = Ti (2); R = allyl, M = Ti(3); R = H, M = Zr (4); R = allyl, M= Zr (6)]; and [(η⁵-C₅H₅)TiCl₂]₂[μ, μ-(SiMe₂)₂(η⁵-Me₃SiC₅H₂)(η⁵-C₅H₃)] (5) were synthesized by the reaction of (η⁵-RC₅H₄) TiCl₃ or (η⁵-RC₅H₄)ZrCl₃·DME (R = H, allyl) with [μ, μ- (SiMe₂)₂(η⁵-t-BuC₅H₂)(η⁵-C₅H₃)] Li₂ or [μ, μ-(SiMe₂)₂(η⁵-Me₃Si C₅H₂)(η⁵-C₅H₃)]Li₂ in THF, and they were all well characterized by ¹H NMR, MS, IR, and EA. When activated with methylaluminoxane (MAO), they are efficient catalysts for the polymerization of ethylene (Complex 4, 5.99 × 10⁵ g-PE/mol·Zr·h) and the polymer with multipeak broaden molecular weight distribution (PD = Mw/Mn) was obtained (polymer sample gained by complex 3, PD = 25.03). The copolymerization results indicate that 1-hexene could incorporate into the growing PE chain with these complexes in the presence of MAO (Complex 4, 1.07 × 10⁶ g-PE/mol·Zr·h; 1-hexene content, 1.57% mol). © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2891–2900, 2013

A series of neutral nickel complexes featuring N-fluorinated phenyl salicylaldiminato chelate ligands was synthesized, and the novel molecular structure of complex C14 was further confirmed by X-ray crystallographic analysis. The neutral nickel complexes showed high activity up to 9.96×10⁵ g oligomers/(mol Ni·h) and high selectivity of C₆ in catalyzing ethylene oligomerization using methylaluminoxane (MAO) as cocatalyst. It was observed that the strong electron-withdrawing effect of the fluorinated salicylaldiminato ligand was able to significantly increase the catalytic activity for oligomerization of ethylene. In addition, the influence of reaction parameters such as Al/Ni molar ratio, reaction temperature, a variety of cocatalyst and ethylene pressure on catalytic activity was investigated.

The synthesis of long-chain branched polyethylene includes the generation of vinyl-terminated polyethylene macromonomers and the copolymerization of these macromonomers with ethylene. Four new bridged cyclopentadienyl indenyl (fluorenyl) zirconocene complexes 1a–b, 2a–b were prepared and showed high activities for ethylene homopolymerization upon the activation of methylaluminoxane. The steric bulk of bridged substituent has a profound effect on the catalytic activity as well as on the molecular weight of resulting polyethylene. Complex 1b showed the highest activity of up to 5.32 × 10⁶ g PE/(mol Zr h) for ethylene homopolymerization at 70 °C, which was higher than that of Cp₂ZrCl₂. The polyethylenes produced with complexes 1a–d/MAO are mostly vinyl-terminated, possess low molecular weight and fit as macromonomers. The (p-MePh)₂C-bridged cyclopentadienyl indenyl zirconocene complex 1a could produce polyethylene macromonomer with selectivity for the vinyl-terminal as high as 94.9%. Copyright © 2010 John Wiley & Sons, Ltd.