Search Results (5)

A series of para-trifluoromethoxy-substituted and fluorobenzhydryl-functionalized 1,2-bis(imine)acenaphthene ligands: 1-[2,6-{(4-F-C₆H₄)₂CH}₂-4-F₃COC₆H₂N]-2-(ArN)C₂C₁₀H₆ (Ar = 2,6-Me₂C₆H₃ L1, 2,6-Et₂C₆H₃ L2, 2,6-iPr₂C₆H₃ L3, 2,4,6-Me₃C₆H₂ L4, 2,6-Et₂-4-MeC₆H₂ L5), were synthesized and used to generate their corresponding nickel(II) bromide complexes (Ni1–Ni5). Elemental analysis, ¹⁹F NMR, and FT-IR spectroscopy were employed to characterize these five nickel complexes. Single-crystal X-ray diffraction of Ni2 and Ni4 confirmed distorted tetrahedral geometries. Upon activation with either EtAlCl₂ (ethylaluminum dichloride) or EASC (ethyl aluminum sesquichloride), these complexes showed exceptional high activities (up to 22.0 × 10⁶ g PE mol⁻¹ (Ni) h⁻¹) and remarkable thermal stability (4.82 × 10⁶ g PE mol⁻¹(Ni) h⁻¹ at 80 °C) towards ethylene polymerization. The resulting polyethylenes are highly branched, with the type and extent of branches tunable by temperature, solvent, and co-catalyst choice. Moreover, these polymers demonstrated excellent tensile strength (σ_b up to 20.7 MPa) and elastic recovery (up to 58%), characteristic of thermoplastic elastomers (TPEs). These results highlight the dual role of trifluoromethoxy and fluorobenzhydryl groups in enhancing catalytic performance and polymer properties. Full article

In this study, 2-t-butyl-4-arylimino-2,3-dihydroacridylnickel dibromides were synthesized by nickel-template one-pot condensation, and well characterized along with the single-crystal X-ray diffraction to one representative complex, revealing a distorted tetrahedral geometry around nickel. When activated with modified methylaluminoxane (MMAO), all nickel complexes exhibited high activities (up to 1.91 × 10⁶ g mol⁻¹ (Ni) h⁻¹) toward major trimerization of ethylene. When activated with ethylaluminum dichloride (EtAlCl₂), however, the title complexes performed good activities (up to 1.05 × 10⁶ g mol⁻¹ (Ni) h⁻¹) for selective dimerization of ethylene. In comparison to analogous nickel complexes, higher activities were achieved with the substituent of t-butyl group, especially in the rare case of nickel complexes performing trimerization of ethylene. Full article

There exist a number of classical methods for the synthesis of substituted pyrazines. Among this variety of reactions, the synthesis of substituted pyrazines from nitriles does not stand out in either the number of known examples or in product yield. However, the one-stage character of the transformation, together with the uncertainty of its mechanism, aroused our interest in this catalytic reaction. Here, we report the successful implementation of the Cp₂TiCl₂-catalyzed reaction of aliphatic nitriles with EtAlCl₂ and Mg, which led to the selective preparation of 2,3,5,6-tetraalkyl-substituted pyrazines, 2,4,5-trisubstituted-1H-imidazole or 2-aminocyclopent-1-ene-carbonitrile depending on reaction conditions and substituents. Full article

Four examples of para-nitro substituted 2-(arylimino)pyridine-nickel(II) bromide complexes of general formula, [2-{(2,6-R-4-NO₂C₆H₂)N=CMe}C₅H₄N]NiBr₂, but differentiable by the steric/electronic properties displayed by the ortho-groups [R = i-Pr (Ni1), Et (Ni2), CHPh₂ (Ni3), CH(4-FPh)₂ (Ni4)], have been prepared in good yield. For comparative purposes, the meta-nitro complex, [2-{(2,6-i-Pr₂-3-NO₂-4-(4-FPh)₂C₆H)N=CMe}C₅H₄N]NiBr₂ (Ni5), has also been synthesized. The molecular structures of mononuclear Ni3·xH₂O (x = 2, 3) and bromide-bridged dinuclear Ni4 and Ni5 are disclosed. Upon activation with either ethylaluminum dichloride (EtAlCl₂) or modified methylaluminoxane (MMAO), all precatalysts displayed good catalytic performance at operating temperatures between 30 °C and 60 °C with higher activities generally seen using EtAlCl₂ [up to 4.7 × 10⁶ g PE (mol of Ni)⁻¹ h⁻¹]: Ni2 ~ Ni5 > Ni1 ~ Ni4 > Ni3. In terms of the resultant polyethylene (PE), Ni4/EtAlCl₂ formed the highest molecular weight of the series (M_w up to 1.4 × 10⁵ g mol⁻¹) with dispersities (M_w/M_n) ranging from narrow to broad (M_w/M_n range: 2.2–24.4). Moreover, the melting temperatures (T_m) of the polymers generated via EtAlCl₂ activation fell in a narrow range, 117.8–126.0 °C, which resembles that seen for industrial-grade linear-low density polyethylene (LLDPE). Indeed, their ¹³C NMR spectra revealed significant amounts of uniformly distributed long-chain branches (LCBs), while internal vinylene groups constituted the major type of chain unsaturation [vinylene:vinyl = 5.3:1 (EtAlCl₂) and 9.9:1 (MMAO)]. Full article

The aim of the research is the development of a one-pot method for the synthesis of lignans, natural compounds that show a wide spectrum of biological activities. For this purpose, the ansa-zirconocenes of various structures were tested as catalysts of allylbenzene cyclometalation with ethylaluminum dichloride (EtAlCl₂) and Mg. The effects of the organophosphorus compounds, hexamethylphosphoramide (HMPA) and triphenylphosphine (PPh₃), on the chemo- and regioselectivity of the reaction were studied. The use of η⁵-indenyl or fluorenyl ansa-complexes with ethanediyl or dimethylsilylene bridges, as well as a biscyclopentadienyl complex with Si-bound ligands as catalysts in the presence of HMPA, yields the formation of cyclometalation products in a total yield of 70%. Cyclometalation product composition is represented by two regioisomers, 3,4-dibenzyl- and 2,4-dibenzyl-substituted alumolanes, with a ratio of (1-2):1, in which hydrolysis provides corresponding dibenzylbutane lignan and 9,8′-neo-lignan. Full article