Zirconium and hafnium complexes supported by linked bis(β-diketiminate) ligands: synthesis, characterization and catalytic application in ethylene polymerization

Abstract

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.