Erlin Yue

8-(2-Cycloalkylphenylimino)-5,6,7-trihydro-quinolylnickel halides: polymerizing ethylene to highly branched and lower molecular weight polyethylenes

Cycloalkyl-modified 8-arylimino-5,6,7-trihydroquinolylnickel pre-catalysts, activated with either MAO or Et2AlCl, are highly active for the polymerization of ethylene into branched polyethylene waxes with narrow polydispersity.

Targeting polyethylene waxes: 9-(2-cycloalkylphenylimino)-5,6,7,8-tetrahydrocycloheptapyridylnickel halides and their use as catalysts for ethylene polymerization

A series of 9-(2-cycloalkylphenylimino)-5,6,7,8-tetrahydrocycloheptapyridine derivatives (L1–L3) was synthesized, and reacted with nickel halides to form their corresponding nickel complexes (bromide: Ni1–Ni3; chloride: Ni4–Ni6). All organic compounds and nickel complexes were well characterized. The structure of a representative complex Ni1 was determined by a single crystal X-ray study, revealing a distorted trigonal bipyramidal geometry at the nickel centre. Upon activation with either modified methylaluminoxane (MMAO) or diethylaluminium chloride (Et2AlCl), all nickel complexes showed high activities toward ethylene polymerization. The obtained polymers were confirmed to be polyethylene waxes with low molecular weights (in the range of 1.83 to 6.78 kg mol−1) and narrow polydispersity (PDI: 1.38–1.78); moreover, the obtained polyethylenes were highly branched ones. These polyethylene waxes have potential application as functional adducts of lubricants or pour-point depressants.

Constrained formation of 2-(1-(arylimino)ethyl)-7-arylimino-6,6-dimethylcyclopentapyridines and their cobalt(II) chloride complexes: synthesis, characterization and ethylene polymerization

A series of 2-(1-(arylimino)ethyl)-7-arylimino-6,6-dimethylcyclopentapyridine derivatives (L1-L5) was synthesized, and individually reacted with cobalt(II) chloride to form the corresponding cobalt chloride complexes (C1-C4). These compounds were characterized, and the single crystal X-ray diffraction for two representative cobalt complexes was carried out. The molecular structures indicate that 2,7-bis(arylimino)cyclopentapyridines act as tridentate ligands; however, one of the Co-N coordinative bonds is weak due to the spatial separation of nitrogen atoms. Upon activation with either MAO or MMAO, all cobalt complexes exhibit catalytic activities toward ethylene. Polymerization takes place in the presence of MAO with activities of approximately 10(4) g of PE per (mol of Co) per h, but oligomerization occurs in the presence of MMAO with the activities higher by one order of magnitude. The resultant products, either polyethylenes or oligomers, display high linearity. Relatively low activities observed for cobalt complexes discussed reflect the importance of the appropriate spatial arrangement of the three donor nitrogen atoms.

Enhancing thermo-stability to ethylene polymerization: synthesis, characterization and the catalytic behavior of 1-(2,4-dibenzhydryl-6-chlorophenylimino)-2-aryliminoacenaphthylnickel halides

A series of 1-(2,4-dibenzhydryl-6-chlorophenylimino)-2-aryliminoacenaphthylene derivatives (L1-L5) was synthesized and reacted with nickel halides to form the corresponding nickel complexes LNiX2 (X = Br, Ni1-Ni5; X = Cl, Ni6-Ni10). The molecular structures of representative complexes Ni2 and Ni5 were determined by single crystal X-ray diffraction, indicating the distorted square planar geometry around the nickel atom of complex Ni2 and the distorted tetrahedral geometry around the nickel atom of complex Ni5, respectively. Upon activation with low amounts of ethylaluminium sesquichloride (Et3Al2Cl3, EASC), all nickel complexes exhibited high activities up to 1.09 x 10(7) g of PE per mol of Ni per h toward ethylene polymerization, producing branched polyethylenes. Most importantly, these systems showed good thermo-stability, even at 80 degrees C maintaining the activity with 3.76 x 10(6) g of PE per mol of Ni per h.

Controlling the molecular weights of polyethylene waxes using the highly active precatalysts of 2-(1-aryliminoethyl)-9-arylimino-5,6,7,8-tetrahydrocycloheptapyridylcobalt chlorides: synthesis, characterization, and catalytic behavior

A series of 2-(1-aryliminoethyl)-9-arylimino-5,6,7,8-tetrahydrocycloheptapyridylcobalt chlorides were synthesized and characterized using FT-IR and elemental analysis, and the molecular structures of complexes , and were confirmed to present a pseudo-square-pyramidal or trigonal-bipyramidal geometry around the cobalt center using single-crystal X-ray diffraction. Upon activation with either methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), all cobalt precatalysts gave high activities up to the level of 10(7) gPE mol(-1) (Co) h(-1) toward ethylene polymerization, being one of most active cobalt-based precatalysts. In comparison with cobalt analogues, the title precatalysts generally possessed longer lifetime along with good thermo-stability; moreover, the resultant polyethylenes were highly linear and unimodal in most cases.

Synthesis, characterization, and ethylene polymerization of 1-[2,4-bis(bis(4-fluorophenyl)methyl)naphthylimino]-2-aryliminoacenaphthylnickel bromides: influences of polymerization parameters on polyethylenes

A series of 1-[2,4-bis(bis(4-fluorophenyl)methyl)naphthylimino]-2-aryliminoacenaphthylene derivatives (L1–L5) was prepared and used to react with (DME)NiBr2 to form the title complexes (C1–C5). The organic compounds were characterized by 1H/13C NMR measurements, FT-IR spectra and elemental analysis. Meanwhile, the nickel complexes were analyzed by FT-IR spectra, elemental analysis, and single-crystal X-ray diffraction of the representative complex C1, which indicated a distorted tetrahedral geometry around the nickel center. Upon activation with diethylaluminum chloride (Et2AlCl), all the title nickel complexes were highly active for ethylene polymerization, resulting in polyethylenes with high molecular weights ranging from 0.86–5.58 × 105 g mol−1 and narrow polydispersity (1.22–1.99). Moreover, significant influences of polymerization parameters on the resultant polyethylenes were examined and are discussed.

Ultra-high molecular weight elastomeric polyethylene using an electronically and sterically enhanced nickel catalyst

A collection of ten related 1,2-bis(imino)acenaphthene-nickel(II) halide complexes, [1-[2,6-{(C6H5)2CH}2-4-{C(CH3)3}-C6H2N]-2-(ArN)C2C10H6]NiX2 (X = Br: Ar = 2,6-Me2C6H3Ni1, 2,6-Et2C6H3Ni2, 2,6-iPr2C6H3Ni3, 2,4,6-Me3C6H2Ni4, 2,6-Et2-4-MeC6H2Ni5) and (X = Cl: Ar = 2,6-Me2C6H3Ni6, 2,6-Et2C6H3Ni7, 2,6-iPr2C6H3Ni8, 2,4,6-Me3C6H2Ni9, 2,6-Et2-4-MeC6H2Ni10), each bearing one sterically and electronically enhanced N-2,6-dibenzhydryl-4-t-butylphenyl group, have been prepared and fully characterized. The unsymmetrical nature of the chelating bis(imino)acenaphthene is confirmed in the paramagnetic 1H NMR spectra for Ni1–Ni10, while the molecular structures of Ni1, Ni2 and Ni6 highlight the unequal steric protection of the nickel center imposed by their respective N,N-ligands. On activation with either Et2AlCl or MMAO, all the nickel complexes were highly active catalysts in ethylene polymerization [as high as 1.26 × 107 g of PE per mol of Ni per h] affording exceptionally high molecular weight (up to 3.1 × 106 g mol−1) hyper-branched polyethylene. Analysis of the mechanical properties reveals the ultra-high molecular weight polymers possess high tensile strength, excellent shape fixity and elastic recovery (up to 69%) as well as high elongation at break (eb = 843.9%); such materials offer a promising alternative to current thermoplastic elastomers (TPEs).

Bisimino-functionalized dibenzo[a,c]acridines as highly conjugated pincer frameworks for palladium(II): synthesis, characterization and catalytic performance in Heck coupling

A new pair of highly conjugated ligands, 10-[1-(arylimino)ethyl]-14-[(arylimino)methyl]dibenzo[a,c]acridine (aryl = 2,6-Me2Ph L1, 2,6-Et2Ph L2) incorporating both aldimine and ketimine units, have been prepared by a straightforward sequence of organic transformations from phenanthrene-9,10-dione. Cyclopalladation occurs readily at ambient temperature on treating L1 or L2 with PdCl2(NCCH3)2 in aprotic solvents to afford exclusively (NketimineNC)Pd(II) chloride pincer complexes Pd1 or Pd2, respectively. By contrast in methanol, Pd1 or Pd2 are isolated as the minor product with aldehyde-containing Pd3 or Pd4 as the major one, the result of hydrolysis of the pendant aldimine units in Pd1 and Pd2, respectively. All the ligands and palladium complexes have been characterized by FT-IR, 1H and 13C NMR spectroscopy, mass spectrometry and elemental analysis; the molecular structures for L1, Pd1, Pd2, Pd3 and Pd4 are also reported. Using low catalyst loadings (0.0005–0.002 mol%) and elevated temperatures (140–200 °C), Pd1–Pd4 are able to efficiently mediate the coupling of haloarenes with vinyl-containing substrates with turnover numbers as high as 174000; the effects of steric/electronic variation within the substrate and NNC-pincer complex on catalyst performance are examined.

Efficient acceptorless dehydrogenation of secondary alcohols to ketones mediated by a PNN-Ru(II) catalyst

Four types of ruthenium(II) complexes, [fac-PNN]RuH(PPh3)(CO) (A), [fac-PNHN]RuH(η1-BH4)(CO) (B), [fac-PNHN]RuCl2(PPh3) (C) and [fac-PNHN]RuH(η1-BH4)(PPh3) (D) (where PNHN and PNN are N-(2-(diphenylphosphino)ethyl)-5,6,7,8-tetrahydroquinoline-8-amine and its deprotonated derivative), have been synthesized and assessed as catalysts for the acceptorless dehydrogenation of secondary alcohols to afford ketones. It was found that C, in combination with t-BuOK, proved the most effective and versatile catalyst allowing aromatic-, aliphatic- and cycloalkyl-containing alcohols to be efficiently converted to their corresponding ketones with particularly high values of TON achievable. Furthermore, the mechanism for this PNN-Ru mediated process been proposed on the basis of a number of intermediates that have been characterized by EI-MS and NMR spectroscopy. These catalysts show great potential for applications in atom-economic synthesis as well as in the development of organic hydride-based hydrogen storage systems.

Highly linear polyethylenes using the 2-(1-(2,4-dibenzhydrylnaphthylimino)ethyl)-6-(1-(arylimino)ethyl)-pyridylcobalt chlorides: synthesis, characterization and ethylene polymerization

The series of 2-(1-(2,4-dibenzhydrylnaphthylimino)ethyl)-6-(1-(arylimino)ethyl)pyridine derivatives and their cobalt chlorides (Co1−Co5) were synthesized and fully characterized. The representative complexes Co2 and Co3 were confirmed by single crystal X-ray diffraction analyses, indicating pseudo-square-pyramidal geometry around the cobalt centre. All cobalt complexes, activated with either methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), exhibited high activities towards ethylene polymerization, and produced polyethylenes with high molecular weight and highly linear feature as well as unimodal distribution.