Search Results (3)

Several cobalt(II) complexes Co1–Co3 bearing pyridine–oxime ligands (L1 = pyridine-2-aldoxime for Co1; L2 = 6-methylpyridine-2-aldoxime for Co2; L3 = phenyl-2-pyridylketoxime for Co3) and picolinaldehyde O-methyl oxime (L4)-supported Co4 were synthesized and well characterized by FT-IR, mass spectrum and elemental analysis. The single-crystal X-ray diffraction of complex Co2 reveals that the cobalt center of CoCl₂ is coordinated with two 6-methylpyridine-2-aldoxime ligands binding with N_pyridine and N_oxime atoms, which feature a distorted octahedral structure. These Co complexes Co1–Co4 displayed extremely high activity toward isoprene polymerization upon activation with small amount of AlClEt₂ in toluene, giving polyisoprene with high activity up to 16.3 × 10⁵ (mol of Co)⁻¹(h)⁻¹. And, the generated polyisoprene displayed high molecular weights and narrow molecular distribution with a cis-1,4-enriched selectivity. The type of cobalt complexes, cocatalyst and reaction temperature all have effects on the polymerization activity but not on the microstructure of polymer. Full article

Iron complexes of the types [Fe(HL)₂Cl₂] (Fe1: HL¹ = pyridine-2-aldoxime; Fe2: HL² = 6-methylpyridine-2-aldoxime; Fe3: HL³ = phenyl-2-pyridylketoxime; Fe4: HL⁴ = picolinaldehyde O-methyl oxime) were prepared and characterized by elemental analysis and IR spectroscopy. The crystal structure of Fe2, determined by single-crystal X-ray diffraction, featured a distorted octahedral coordination of the iron center binding with two ligands of HL². The X-ray structure and infrared spectral data indicated that pyridine-oxime ligands act as unionized bidentate ligand by coordinating with N_pyridine and N_oxime. The catalytic performance for isoprene polymerization, catalyzed by these pyridine-oxime-ligated iron complexes, was examined. For a binary catalytic system combined with MAO, complexes Fe1, Fe3 and Fe4 were found to be highly active (up to 6.5 × 10⁶ g/mol·h) in cis-1,4-alt-3,4 enchained polymerization, with average molecular weights in the range of 60–653 kg/mol and narrow PDI values of 1.7–3.5, even with very low amounts of MAO (Al/Fe = 5). Upon activation with [Ph₃C][B(C₆F₅)₄]/AlR₃ for the ternary catalytic system, theses complexes showed extremely high activities, as well about 98% yield after 2 min, to afford cis-1,4-alt-3,4-polyisoprene with a molecular weight of 140–420 kg/mol. Full article

The present work describes the reactions of CdI₂ with 2-pyridyl aldoxime (2paoH), 3-pyridyl aldoxime (3paoH), 4-pyridyl aldoxime (4paoH), 2-6-diacetylpyridine dioxime (dapdoH₂) and 2,6-pyridyl diamidoxime (LH₄). The primary goal was to contribute to understanding the molecular basis of the very good liquid extraction ability of 2-pyridyl ketoximes with long aliphatic chains towards toxic Cd(II) and the inability of their 4-pyridyl isomers for this extraction. Our systematic investigation provided access to coordination complexes [CdI₂(2paoH)₂] (1), {[CdI₂(3paoH)₂]}_n (2), {[CdI₂(4paoH)₂]}_n (3) and [CdI₂(dapdoH₂)] (4). The reaction of CdI₂ and LH₄ in EtOH resulted in a Cd(II)-involving reaction of the bis(amidoxime) and isolation of [CdI₂(L’H₂)] (5), where L’H₂ is the new ligand 2,6-bis(ethoxy)pyridine diimine. A mechanism of this transformation has been proposed. The structures of 1, 2, 3, 4·2EtOH and 5 were determined by single-crystal X-ray crystallography. The complexes have been characterized by FT-IR and FT-Raman spectra in the solid state and the data are discussed in terms of structural features. The stability of the complexes in DMSO was investigated by ¹H NMR spectroscopy. Our studies confirm that the excellent extraction ability of 2-pyridyl ketoximes is due to the chelating nature of the extractants leading to thermodynamically stable Cd(II) complexes. The monodentate coordination of 4-pyridyl ketoximes (as confirmed in our model complexes with 4paoH and 3paoH) seems to be responsible for their poor performance as extractants. Full article