Synthesis, structures, and olefin polymerization characteristics of group 4 catalysts [Zr{(OAr)2py}Cl2(D)] (D = O-donors, Cl[HPR 3]) supported by tridentate pyridine-2,6-bis(aryloxide) ligands

Abstract

The Zr(IV) complexes [Zr(L1)X2(D)] [H 2L1 = 2,6-di(3-tert-butyl-5-methylphen-2-ol)pyridine; X = Cl, D = thf (1), OEt2 (2), acetophenone (3), benzophenone (4), 2-acetonaphthone (5), Cl[fHPR3] {R = Me (6), Et (7); R3 = Me2Ph (8)}; X = CH2Ph (9)] have been synthesized, and the crystal structures of 3, 4, and 7 have been determined. These catalysts, assisted by the robustness and chelating strength of the pyridine-bis(phenolate) moiety, exhibit excellent activities for ethylene polymerization in conjunction with MAO. Studies to assess the impact of the donor group during the catalytic process suggest that the same active species is generated by 1-8/MAO and the donor group does not play an active role. Even higher activities are observed for the 1/iBu3Al/Ph3CB(C6F5) 4 system in ethylene polymerization and propylene copolymerization reactions (36 590 and 15 700 g of polymer (mmol of catalyst)-1 h -1, respectively), with the latter displaying good C3 incorporation (25.4 mol % C3). Insight into the catalytic behavior of the 1/MAO system has been derived from GPC and NMR characterization of the polymers prepared under different reaction conditions. 1H and 13C NMR end-group analyses reveal resonances for saturated methyl chain-end groups only and undetectable or negligible levels of unsaturated vinyl chain ends. This indicates that for the polymerization chain-transfer mechanism, the conventional β-H transfer reactions to the metal/monomer are insignificant and the unusual chain transfer to Al pathway is vastly dominant. © 2006 American Chemical Society.