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Gong S, Ma H, Huang J: Zirconium and hafnium complexes supported by linked bis (beta-diketiminate) ligands: synthesis, characterization and catalytic application in ethylene polymerization. Dalton Trans. 2009 Oct 21;(39):8237-47. Epub 2009 Aug 10.
Zirconium and hafnium complexes bearing new 1,2-ethanediyl- or 1,3-propanediyl-linked bis (beta-diketiminate) ligands, [{C (n) H (2n)-(BDI (Ar))(2)}MCl (2)] (Ar = 2,6-Me (2)-C (6) H (3), 2,6-Cl (2)-C (6) H (3), 2,6-(i) Pr (2)-C (6) H (3); M = Zr, n = 2 (4a-c), n = 3 (5a-c); M = Hf, n = 2 (6b)), were synthesized via the reaction of MCl (4).2THF and one equivalent of dilithium salt of the corresponding ligand. Distorted trigonal prismatic and octahedral coordination geometries as well as C (1)-symmetric structures are found for zirconium complexes and in the solid state. Variable temperature (1) H NMR spectra indicated the fluxional nature of and in solution. Upon activation with methylaluminoxane (MAO), all these complexes except hafnium complex displayed moderate catalytic activities for ethylene polymerization. 1,2-Ethanediyl-linked complexes and are generally more active than their 1,3-propanediyl-linked analogues. The substituents at the ortho-positions of the phenyl rings have different effect on the catalytic activities of 1,2-ethanediyl-linked series or 1,3-propanediyl-linked series. It is noteworthy that even at a low Al/Zr molar ratio of 500, the catalytic activities of these zirconium complexes could be retained. Polyethylenes with broad molecular weight distributions (MWD = 15.3-20.3) were produced, which might result from the fluxional character of the zirconium complexes. The linear structure of obtained polyethylenes was further determined by (13) C NMR spectroscopy and DSC analysis. |
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