Showing papers by "Wen-Hua Sun published in 2010"

Synthesis and characterisation of alkylaluminium benzimidazolates and their use in the ring-opening polymerisation of ε-caprolactone

Abstract: The stoichiometric reactions of 2-(benzimidazol-2-yl)-6-methylpyridine (L1) or 8-(benzimidazol-2-yl)quinaldine (L2) with trialkylaluminium reagents R3Al (R = Me, Et and iBu) afforded the corresponding dialkylaluminium benzimidazolate complexes R2AlL (L1, R = Me (1), Et (2), iBu (3); L2 R = Me (4), Et (5), iBu (6)). Treatment of L1 with one or two equivalents of Et2AlCl led to the adducts EtAl(L1)2·AlEtCl2 (7) or Et2AlL1·AlEtCl2 (8), respectively. Complex 7 was also available via treatment of 8 with one equivalent of L1. Reaction of L1 with two equivalents of AlR3 (R = Me or Et) afforded R2AlL1·AlR3 (R = Me, 9; R = Et, 10), which were also formed when 1 or 2 were reacted with AlR3. Reaction of L2 with two equivalents of AlR3 (R = Me or Et) gave the complexes R2AlL2·AlR3 (R = Me, 11; R = Et, 12), which were also formed in the stoichiometric reaction of 4 or 5 with AlR3 (R = Me or Et). Screening of these complexes in the presence of BnOH, for the ring-open polymerisation of e-caprolactone, revealed appreciable activities. Only the aluminium compounds ligated by 2-(benzimidazol-2-yl)-6-methylpyridine maintained high activity in the absence of BnOH. In all cases, polymers with bi- or multi-modal characteristics were produced.

Prospects and crucial problems in oligomerization and polymerization with iron and cobalt complex catalysts

Abstract: The discovery of highly active 2,6-bis(imino)pyridyl iron and cobalt complexes provided a milestone of late-transition metal catalysts for ethylene oligomerization and polymerization with being currently investigated for the scale-up process. The crucial problems are remaining in the catalytic systems: the catalytic systems targeting ethylene polymerization produce more oligomers at elevated reaction temperatures, however, there is a recognizable amount of high-molecular-weight polyethylene remained in the modified catalytic system for the oligomerization process. Beyond the modification of bis(imino)pyridyl metal complexes, several alternative procatalysts’ models have been developed in our group. This review highlighted the achievements in exploring new iron and cobalt complexes with tridentate NNN ligands as procatalysts for ethylene oligomerization and polymerization.

2-Ethyl-ketimino-1,10-phenanthroline iron(II) complexes as highly active catalysts for ethylene oligomerization

Abstract: A series of 2-(1-aryliminopropyl)-1,10-phenanthrolines (L1–L7) and their corresponding iron(II) chlorides (Fe1–Fe7) are synthesized and characterized by elemental and spectroscopic analyses. The molecular structures of 2-[1-(2,6-diisopropy1phenylimino)propyl]-1,10-phenanthroline (L3) and {2-[1-(2,6-diethylphenylimino)propyl]-1,10-phenanthroline}·FeCl2 (Fe2) are determined by the single crystal X-ray diffraction. All iron complexes, activated with methylaluminoxane (MAO), exhibit high activities in ethylene oligomerization with high selectivity for α-olefins produced. Compared with other 2-imino-phenanthrolines, the title complexes show better thermal stability, and their oligomerization products are potentially more useful due to lower contents of butenes and waxes observed.

2-(1H-2-Benzimidazolyl)-6-(1-(arylimino)ethyl)pyridylnickel Complexes: Synthesis, Characterization, and Ethylene Oligomerization

Abstract: A series of tridentate N,N,N-nickel complexes bearing 2-(1H-2-benzimidazolyl)-6-(1-(arylimino)ethyl)pyridines was synthesized and characterized by elemental and IR spectroscopic analysis. The molecular structures of representative complexes were determined by single-crystal diffraction, and these were found to have a six-coordinate distorted octahedral geometry around the Ni centre. On treatment with Et2AlCl, all nickel complexes exhibited good catalytic activities up to 106 g mol–1(Ni) h–1 for ethylene oligomerization with major dimerization. The steric and electronic effects on catalytic activities of metal complexes as well as the influence of various reaction parameters were carefully investigated.

Synthesis and ethylene polymerization by β-diketiminato zirconium chlorides

Abstract: Unsymmetrical β-diketiminato zirconium chlorides were prepared by an elimination reaction of ZrCl4 with the corresponding β-diketiminato lithium atoms [Li{N(Dipp)C(R)CHC( t Bu)NH}]2 (Dipp=2,6- i Pr2C6H3; R=Ph or Me). Two zirconium complexes were fully characterized by elemental, 1H, and 13C NMR analyses, and confirmed by single-crystal X-ray diffraction. These complexes, activated with methylaluminoxane (MAO) showed good activity towards ethylene polymerization, and produced high molecular weight polyethylene.

Synthesis and Characterization of 2,6‐Bis(imino)phenoxy Cobalt Complexes

Abstract: A series of cobalt complexes bearing 2,6-bis (imino) phenoxy ligands, LCoCl2 [L = 2,6-(ArNCH)(2)CH3C6H2OH] was synthesized by the reaction of the ligand 2,6-bis(imino) phenol with the equivalent mole of cobalt dichloride, and these complexes were characterized by elemental analyses, H-1 NMR, MS and ER spectra. The structure of one complex was determined by single crystal X-ray diffraction analysis.

Synthesis and characterization of tris(η5-cyclopentadienyl-μ-carbonyliron)-μ3-nitrosyl cluster: X-ray structure of [(η5-C5H5)(μ-CO)Fe]3(μ3-NO)·C4H8O

Abstract: Tris)(η5-cyclopentadienyl-μ-carbonyl-iron)-μ3-nitrosyl cluster was obtained from the reaction of cyclopentadienyl dicarbonyliron dimer with nitrogen monoxide in xylane. The cluster was characterised by elemental analyses, IR, MS and 1H NMR. The crystal structure of [(η5-C5H5)(μ-CO)Fe]3(μ3-NO)·C4H8O was determined by X-ray diffraction analysis. It crystallises in the orthorhombic space group Pnma, a=9.063(2), b=10.546(2), c=22.525(4) A, V=2150.3(7) A3, Z=4, Dc=1.68 g·cm−3; structure solution and refinement based on 1141 reflections with I ≥ 3.0σ (I) (MoKα, λ=0.71073 A) converged at R=0.0540. The infrared absorption band at 1325 cm−1 of the μ3-NO in the cluster, which is red shifted, shows that μ3-NO is activated.

Nitrosyl Complexes. 6. Reactions of Na[Fe(CO)3NO] with Cp*M(CO)3Cl (Cp*=η5−CH3C5H4, M = Mo or W): Crystal structures of Cp*M(CO)2NO and Cp*M(μ3‐NH)(μ2‐NO)(μ2‐CO)Fe2(CO)6

Abstract: Sodium nitrosylcarbonyliron reacts with methylcyclopentadienylcarbonylmetal (Mo or W) chloride in CH3OH/THF at room temperature to give Cp*Mo(CO)2NO(la) (Cp* = η5−CH3C5H4) or Cp*W(CO)2NO (1b), [Cp*Mo(CO)3]2 (2a) or [Cp*W(CO)3]2 (2b), and Cp*Mo(μ3-NH)(μ2-NO)-(μ2-CO)Fe2(CO)6 (3a) or Cp*W(μ3-NH)(μ2-NO)(μ2-CO)Fe2(CO)6 (3b), respectively. Complexes 1a, 1b, 3a and 3b were analyzed by IB, NMR, MS and elemental analyses, and the crystal structures of 1b, 3a and 3b were determined by X-ray diffraction method. The new clusters 3a and 3b have μ3-NH ligands which were formed by reduction of NO in the synthetic reactions.

General Regioselective Synthesis and Crystal Structure of Racemic 5‐Substituted 2,2‐Dimethyl‐3‐hydroxyimidazolidin‐4‐ones.

Abstract: Cyclic hydroxamic acids (III) are regioselectively obtained in a self-catalytic cyclocondensation reactions of racemic valine, leucine, and β-phenylalanine hydroxamic acids with acetone under mild reaction conditions.