Wen-Hua Sun

Nickel complex pre-catalysts in ethylene polymerization: new approaches to elastomeric materials

Recent progress on nickel-based complex pre-catalysts has been reviewed. Variation of the complex models by employing different types of heteroatom-containing ligands and the new features associated with the resulting highly branched polyethylenes is discussed. The discussions focus on the influence that fine tuning of the substituents has on the catalytic properties of their nickel complexes. The resultant polyethylene exhibits high branching and can be classified as an elastomeric material. Thus, such nickel complex pre-catalysts have a bright future in both the academic and industrial arenas.

Conjugated Ligands Modulated Sandwich Structures and Luminescence Properties of Lanthanide Metal–Organic Frameworks

A conjugated ligand, 2-(carboxylic acid)-6-(2-benzimidazolyl) pyridine (Hcbmp), and a series of Lanthanide metal-organic frameworks (MOFs) [Ln(2)(cbmp)(ox)(3)(H(2)O)(2)](2)·2H(3)O(+)·7H(2)O (Ln = Sm (3), Eu (4), and Gd (5), H(2)ox = oxalic acid) have been designed and assembled. To elucidate how the conjugated ligands modulate the structures and luminescence properties, we carried out the structural characterizations and luminescence studies of complexes 3 and 4, and their corresponding oxalate complexes [Ln(ox)(1.5)(H(2)O)(3)]·2H(2)O (Ln = Sm (1) and Eu (2)) were also investigated for comparison. The changes of luminescence behaviors upon dehydration and D(2)O-rehydration processes are presented and discussed in detail. The results indicated that, the cbmp(-) ligands distribute on both sides of the ox(-)-Ln bilayer network to construct a sandwich structure. Moreover, the lowest triplet state of cbmp(-) ligands can match well the energy levels of the Sm(3+) and Eu(3+) cations which allow the preparation of new Ln-MOF materials with enhanced luminescence properties. Meanwhile, the crystallinity of solid states produces more substantial change in the luminescence behaviors than removal or replacement of effective nonradiative relaxers.

Late transition metal complexes bearing 2,9-bis(imino)-1,10-phenanthrolinyl ligands: synthesis, characterization and their ethylene activity

Abstract A series of iron, cobalt and nickel halide complexes, LMX2 (M=Fe, X=Cl; M=Co, X=Cl; M=Ni, X=Br) bearing 2,9-bis(imino)-1,10-phenanthrolinyl ligands [L=2,9-(ArNCH)2C12H6N2] were synthesized. The solid-state structures of 4 and 7 have been determined by single-crystal X-ray diffraction study. Treatment of the complexes LMX2 with methylaluminoxane (MAO) leaded to activate ethylene as oligomerization catalysts.

Synthesis, characterisation and ethylene oligomerization behaviour of N -(2-substituted-5,6,7-trihydroquinolin-8-ylidene)arylaminonickel dichlorides

A series of N-(2-substituted-5,6,7-trihydroquinolin-8-ylidene)-arylaminonickel(II) dichlorides were synthesized by the one-pot stoichiometric reaction of nickel dichloride, 2-chloro- or 2-phenyl-substituted 5,6,7-trihydroquinolin-8-one, and the corresponding anilines. All nickel complexes were characterized by elemental and spectroscopic analysis. The molecular structures of representative nickel complexes, determined by the single-crystal X-ray diffraction, indicate the different coordination numbers around nickel either four with more bulky ligands or five with less bulky ligands. All nickel complexes, activated with ethylaluminium sesquichloride (Et3Al2Cl3), showed high activities (up to 9.5 × 106 g mol−1 h−1) in ethylene oligomerization for dimer and trimers.

Bi- and tri-dentate imino-based iron and cobalt pre-catalysts for ethylene oligo-/polymerization

Recent progress on the use of iron and cobalt complex pre-catalysts for ethylene reactivity is reviewed. The review is organized in terms of the denticity of the chelate ligands employed, with particular reference to the influence of the ligand frameworks and their substituents on the catalytic performance for ethylene oligomerization/polymerization catalysis. The majority of the systems bear tri-dentate ligation at the iron/cobalt centre, though it is clear that bi-dentate iron/cobalt complex pre-catalysts have also attracted significant attention. Such systems produce in most cases highly linear products ranging from oligomeric α-olefins to high molecular weight polyethylene, and as such are promising candidates for both academic and industrial considerations.

Cobalt and nickel complexes bearing 2,6-bis (imino) phenoxy ligands: syntheses, structures and oligomerization studies

Abstract A series of new cobalt and nickel complexes LMX2 (M=Co, X=Cl; M=Ni, X=Br) bearing 2, 6-bis(imino)phenoxy ligands were synthesized. The solid-state structures of 1 and 4 have been determined by single-crystal X-ray diffraction study. Treatment of the complexes LMX2 with methylaluminoxane (MAO) leads to active catalysts for oligomerization of ethylene with catalytic activities in the range of 1.2×105–2.1×105 g mol−1 h−1 atm−1 for Ni complexes, and ∼103 g mol−1 h−1 atm−1 for Co complexes. The oligomers were olefins from C4 to C16.

Synthesis, characterization and ethylene polymerization behavior of nickel dihalide complexes bearing bulky unsymmetrical α-diimine ligands

A series of nickel(II) dihalide complexes (C1–C10) bearing unsymmetrical α-diimine ligands of the type 2,4-dibenzhydryl-N-(2-phenyliminoacenaphthylenylidene)-6-methylbenzenamine (L1–L5) were synthesized and fully characterized. Single-crystal X-ray diffraction revealed a distorted tetrahedral geometry around the nickel center in the complexes C3, C5 and C9. Upon activation with modified methylaluminoxane (MMAO), all nickel pro-catalysts performed with high activities in ethylene polymerization, producing highly branched polyethylene products.

Ethylene oligomerization promoted by group 8 metal complexes containing 2-(2-pyridyl)quinoxaline ligands

Abstract Ni II , Co II and Fe II complexes of 2-(2-pyridyl)quinoxaline were synthesized and used in the ethylene oligomerization with methyl-aluminoxane (MAO) as cocatalyst. The nickel complex system mainly produced α-olefins with good activity, while the cobalt and iron complexes showed only marginal activity.

Ethylene polymerization by 2-iminopyridylnickel halide complexes: synthesis, characterization and catalytic influence of the benzhydryl group

A series of 2-(2-benzhydrylbenzenamino)pyridine ligands (L1–L13) was synthesized and used as bidentate N^N ligands with nickel halides to afford the corresponding nickel dihalide complexes L(2)Ni(2)Cl(4) C1–C13 and L(2)NiBr(2) D1–D13. All ligands and complexes were characterized by IR and NMR spectroscopy, and by elemental analysis. The molecular structures of the representative complexes C1·2CH(3)OH, C5·2H(2)O, D4, D7 and D9 were confirmed by single-crystal X-ray diffraction studies. Upon activation with either methylaluminoxane (MAO) or ethylaluminium sesquichloride (Et(3)Al(2)Cl(3), EASC), these nickel pre-catalysts exhibited high activities (up to the range of 10(7) g mol(-1) (Ni) h(-1)) towards ethylene polymerization, producing branched polyethylenes with narrow polydispersity.

Methylaluminium 8-quinolinolates: synthesis, characterization and use in ring-opening polymerization (ROP) of ε-caprolactone

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.