Shaofeng Liu

Chinese Academy of Sciences, Peping, Beijing, China

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Publications (13)50.89 Total impact

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    ABSTRACT: Stoichiometric reactions of YCl3(THF)3 with potassium 2-((arylimino)methyl)quinolin-8-olates or 2-(1-(arylimino)ethyl)quinolin-8-olates in THF solution gave the mononuclear LYCl2(DMSO)2 complexes 1–5 in the presence of DMSO and a representative dinuclear complex 6 in the absence of DMSO. All yttrium complexes were fully characterized by NMR measurements and elemental analysis, and the crystal structures of complexes 1 and 4–6 were determined by single-crystal X-ray diffraction. The structures indicate coordination number seven around the yttrium center and pentagonal bipyramidal geometries. The complexes all feature diapical YCl2 moieties and one tridentate organic ligand in the equatorial plane. Upon reaction of the yttrium precatalysts 1–6 with LiCH2Si(CH3)3 alone or with LiCH2Si(CH3)3 together with BnOH, the ring-opening polymerization (ROP) of ε-caprolactone (ε-CL) occurred with high efficiency. Depending on conditions, the ROP of ε-CL produced polycaprolactone with narrow molecular distribution and in a living manner. Theoretical studies of the chlorine/CH2SiMe3 and Me3SiCH2/BnO ligand exchange reactions suggest that the replacement of the apical ligands can proceed without significantly affecting the equatorial ligands. These results suggest that one of the apical Y–CH2SiMe3 bonds within the LY(CH2SiMe3)2 intermediate catalyzes the polymerization in the BnOH-free process. Most polymers generated by BnOH-assisted catalysis possess Mn values that are similar to Mn,cal values based on Y–OBn, suggesting that one apical Y–OBn bond of the diapical LY(OBn)(CH2SiMe3) intermediate catalyzes most or all of the ring polymerization of ε-CL.
    Organometallics 11/2012; 31(23):8178–8188. DOI:10.1021/om300778g · 4.25 Impact Factor
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    ABSTRACT: A series of trimetallic yttrium complexes, L7Y3Cl2 [L = N-(2-methylquinolin-8-yl)-p-R-benzamides, 1: R = H; 2: R = OMe; 3: R = Me; 4: R = Cl], has been synthesized by the stoichiometric reaction of YCl3(THF)2 with the corresponding potassium amidates. All complexes have been characterized by elemental analysis and NMR spectroscopy. The molecular structure of complex 1 bearing seven amidate ligands was confirmed by single-crystal X-ray diffraction. Screening of these complexes, in the presence of BnOH, for ring-opening polymerization of caprolactone (ε-CL) revealed effective activities.
    New Journal of Chemistry 10/2012; 36(11):2392-2396. DOI:10.1039/C2NJ40711F · 3.16 Impact Factor
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    ABSTRACT: To gain a deeper knowledge of the nature of the species formed in situ by reaction of a catalyst precursor complex and typical cocatalysts used for ethylene oligomerization or polymerization, the Cr(III) complex fac-[Cr(NPN)Cl3] (1; NPN = bis(2-picolyl)phenylphosphine) was reacted with MAO and partial methylation to give the mononuclear complex fac-[Cr(NPN)Cl2.23Me0.77] (2) was observed, whereas reaction with AlMe3 in toluene led to partial halide abstraction and produced the dinuclear, chloride-bridged dicationic complex [{fac-Cr(NPN)Me(μ-Cl)}2][AlMexCl4–x]2 (3·[AlMexCl4–x]2), in which the metal centers are bridged by two chloride ligands. The complex fac-[Cr(NPN)Cl2Et] (4) was isolated in high yield from the reaction of 1 with AlEt3 and contains a rare example of CrIII–Et function. Upon treatment of 1 with EtAlCl2, the dinuclear Cr(III) complex [{fac-Cr(NPN)}2(μ-Cl)3][AlCl4]3 (5·[AlCl4]3) was obtained, which contains three bridging chlorides. Thus, under the conditions investigated, MAO and AlEt3 behaved as alkylation agents, whereas AlMe3 and EtAlCl2 reacted as cationization agents. On activation with MAO and under comparable conditions, 1–5 exhibited similar catalytic properties, with activities between 2700 and 2800 g of C2H4/((g of Cr) h), but the major oligomer produced using the 4/MAO system was 1-decene. The neutral alkyl complexes 2 and 4 and the cationic complexes 3 and 5 did not exhibit catalytic activity for ethylene oligomerization in the absence of MAO. The structures of the complexes 2, 3·[AlMexCl4–x]2, 4, and 5·[AlCl4]3 have been determined by single-crystal X-ray diffraction.
    Organometallics 06/2011; 30(13):3549–3558. DOI:10.1021/om200243a · 4.25 Impact Factor
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    ABSTRACT: A series of chromium(III) complexes, LCrCl3 (C1–C6: L = 2-(1H-benzo[d]imidazol-2-yl)-N-(2,6-R1-4-R2-phenyl)quinoline-8-carboxamide; C1: R1 = iPr, R2 = H; C2: R1 = Et, R2 = H; C3: R1 = Me, R2 = H; C4: R1 = Me, R2 = Me; C5: R1 = H, R2 = H; C6: R1 = F, R2 = H), was synthesized and characterized by IR spectroscopy, elemental analysis, mass spectra, and magnetic moments. The X-ray crystallographic analysis of complexes C2 and C3 reveals distorted octahedral geometries around the chromium atoms. Upon activation with MAO, these complexes exhibit high activities for ethylene oligomerization (up to 1.28 × 107 g·mol–1(Cr)·h–1) and ethylene polymerization (up to 6.30 × 106 g·mol–1(Cr)·h–1). The oligomers were produced with high selectivity for α-olefins (>99%), and the distribution closely resembled the Schultz–Flory rule. Various reaction parameters were investigated in detail, and the results revealed that both the steric and electronic effects of the ligands effect the catalytic activities of these chromium complexes as well as the distribution of the products formed.
    Organometallics 05/2011; 30(11):3001–3009. DOI:10.1021/om2001124 · 4.25 Impact Factor
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    ABSTRACT: 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
    Journal of Polymer Science Part A Polymer Chemistry 04/2011; 49(8). DOI:10.1002/pola.24617 · 3.54 Impact Factor
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    ABSTRACT: The stoichiometric reactions of 2-(2,6-R-phenylimino)quinolin-8-ol (L1-L5, L1: R = Me, L2: R = Et, L3: R = (i)Pr, L4: R = Cl, L5: R = F) with Me(3)Al afforded the dimeric aluminium complexes [Me(2)AlL](2) (1-5) in good yields. By contrast, stoichiometric reactions of 2-(1-(2,6-R-phenylimino)propyl) quinolin-8-ol (L6-L10, L6: R = Me, L7: R = Et, L8: R = (i)Pr, L9: R = Cl, L10: R = F)) with Me(3)Al gave the mononuclear aluminium complexes Me(2)AlL (6-10) accompanied with by-products of the form Me(2)AlL·Me(3)Al (11-15). All methylaluminium complexes were characterized by NMR spectroscopy, elemental analysis, and the molecular structures of complexes 3, 6 and 8 were determined by single-crystal X-ray diffraction. Aluminium compounds 1-5 possessed negligible activity towards the ring-opening polymerization of ε-caprolactone either in the presence or absence of BnOH. In contrast, in the presence of BnOH, the mononuclear aluminium compounds 6-10 could efficiently initiate the ring-opening polymerization of ε-caprolactone; the polymerization proceeded in a living manner.
    Dalton Transactions 02/2011; 40(11):2645-53. DOI:10.1039/c0dt01207f · 4.10 Impact Factor
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    ABSTRACT: Reaction of TlPF(6) with the Cr(III) complex fac-[CrCl(3)(NPN)] (NPN = bis(2-picolyl)phenyl phosphine) did not lead to precipitation of TlCl but rather to addition of the Tl(+) cation to the CrCl(3) moiety, which resulted in a pseudo-dimeric adduct which has an unusual tetranuclear centrosymmetric structure in the solid state.
    Dalton Transactions 09/2010; 39(34):7881-3. DOI:10.1039/c0dt00810a · 4.10 Impact Factor
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    ABSTRACT: A series of amidate half-titanocene dichlorides, Cp′TiLCl2 [Cp′ = Cp (as η5-C5H5) or Cp* (as η5-C5Me5), L = N-(2-methylquinolin-8-yl)-p-R-benzamides; C1: Cp′ = Cp, R = OMe; C2: Cp′ = Cp, R = Me; C3: Cp′ = Cp, R = H; C4: Cp′ = Cp, R = F; C5: Cp′ = Cp, R = Cl; C6: Cp′ = Cp*, R = OMe; C7: Cp′ = Cp*, R = Me], have been synthesized by the stoichiometric reaction of Cp′TiCl3 with the corresponding potassium amidates. All complexes are fully characterized by elemental and NMR analyses. The molecular structures of complexes C2 and C4 are confirmed by single-crystal X-ray diffraction, and the amidate moieties coordinate the titanium center by imino and alkoxide groups. The systems C1−C7/MAO show much higher activities toward ethylene polymerization than CpTiCl3/MAO or Cp*TiCl3/MAO systems. The procatalysts (C6 and C7) bearing a Cp* ligand exhibit higher activities than their analogues (C1−C5) containing a Cp ligand, while the amidate ligands containing electron-donating groups positively affect the catalytic behavior. Both increasing the ratio of MAO to titanium and reducing reaction temperature enhance the productivities; however, the molecular weights of the resultant polymers decrease with higher activities. Moreover, the C6/MAO system performs with high activity in the copolymerization of ethylene and 1-hexene or 1-octene.
    Organometallics 04/2010; 29(11). DOI:10.1021/om1000748 · 4.25 Impact Factor
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    ABSTRACT: A variety of Pd(II) complexes containing the neutral N,P,N-ligand bis(2-picolyl)phenylphosphine (N(py)PN(py)) have been synthesised and characterized by IR and NMR spectroscopy and X-ray diffraction. The neutral complex [PdCl(2)(N(py)PN(py)-N,P)] (1) has been selectively obtained in high yield by reaction of [PdCl(2)(NCPh)(2)] with the ligand in dichloromethane. The cationic complexes [PdCl(N(py)PN(py)-N,P,N)]PF(6) (2) and [Pd(N(py)PN(py)-N,P,N)(NCMe)](PF(6))(2) (5) have been prepared from the same reagents by addition to the reaction mixture of one or two equivalents of TlPF(6), respectively. It was found that dynamic exchange of the pyridine rings of 1 occurs on the NMR time-scale and possible mechanisms are discussed. As a by-product of the synthesis of 2, the unexpected dinuclear complex [Pd(2)Cl(2)(mu-N(py)PN(py))(2)](PF(6))(2) (3) has been isolated in 10% yield. Its molecular structure in the solid state reveals the presence of two N(py)PN(py) chelating/bridging ligands. The cationic complex [Pd(2)Cl(2)(mu-N(py)PN(py))(2)](2+) was then selectively obtained by reaction of cis-[Pd(N(py)PN(py)-N,P)(2)](BF(4))(2) (4) with [PdCl(2)(cod)]. (1)H- and (31)P{(1)H} NMR studies have demonstrated that 3 converts slowly into 2 in DMSO solution. The Ir(I) complexes [IrCl(cod)(N(py)PN(py))] (6) and [Ir(cod)(N(py)PN(py)-N,P,N)]BAr(F) (7) have also been prepared, the latter exhibits a trigonal bipyramidal structure with the ligand displaying a facial coordination mode. Compound 7 represents a rare example of an Ir(I) complex bearing a N,P,N-chelating ligand.
    Dalton Transactions 03/2010; 39(10):2563-72. DOI:10.1039/b919679j · 4.10 Impact Factor
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    ABSTRACT: A series of 2-benzimidazolyl-N-phenylquinoline-8-carboxamide half-titanocene chlorides, CpTiLCl (C1−C6: Cp = η5-C5H5; L = 2-(1H-benzo[d]imidazol-2-yl)-N-(2,6-R1-4-R2-phenyl)quinoline-8-carboxamide derivatives; C1: R1 = i-Pr, R2 = H; C2: R1 = Et, R2 = H; C3: R1 = Me, R2 = H; C4: R1 = Me, R2 = Me; C5: R1 = H, R2 = H; C6: R1 = F, R2 = H), have been synthesized by the stoichiometric reaction of half-titanocene trichlorides with the corresponding potassium 2-benzimidazolyl-N-phenylquinoline-8-carboxamide. All complexes are fully characterized by elemental and NMR analyses, as well as single-crystal X-ray diffraction for complexes C1, C2, and C6. In addition, the oxo-bridged dinuclear complex C7 was separated from the solution of C6 in air. These complexes, C1−C6, activated with methylaluminoxane (MAO), exhibit high catalytic activities toward both ethylene polymerization and copolymerization of ethylene with α-olefins. According to the catalytic system of C1/MAO, both elevating the reaction temperature and increasing the ratio of MAO to titanium precursor enhance the productivities; however, the molecular weights of the resultant polymers obtained decrease against their higher activities. Moreover, copolymerizations of ethylene with either 1-hexene or 1-octene effectively produce copolymers with incorporated comonomers of 2.0−5.0% mol.
    Organometallics 01/2010; 29(4). DOI:10.1021/om9010033 · 4.25 Impact Factor
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    ABSTRACT: 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
    Journal of Polymer Science Part A Polymer Chemistry 06/2009; 47(12):3154 - 3169. DOI:10.1002/pola.23413 · 3.54 Impact Factor
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    ABSTRACT: 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
    Journal of Polymer Science Part A Polymer Chemistry 05/2008; 46(10):3396 - 3410. DOI:10.1002/pola.22693 · 3.54 Impact Factor
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    ABSTRACT: 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
    Journal of Polymer Science Part A Polymer Chemistry 05/2008; 46(10):3411 - 3423. DOI:10.1002/pola.22694 · 3.54 Impact Factor

Publication Stats

160 Citations
50.89 Total Impact Points

Institutions

  • 2008–2012
    • Chinese Academy of Sciences
      • • Institute of Chemistry
      • • Key Laboratory of Engineering Plastics
      Peping, Beijing, China
  • 2011
    • Inner Mongolia University
      Suiyüan, Inner Mongolia, China
  • 2010–2011
    • University of Strasbourg
      • Laboratoire de Chimie de Coordination
      Strasburg, Alsace, France