title: The amido-bridged zirconocene's reactivity and catalytic behavior for ethylene polymerization.
abstract: Reaction of the amido-bridged zirconium complex (CpSiMe(2)NSiMe(2)Cp)ZrCH(3) (1) (Cp = C(5)H(4)) with half an equivalent of B(C(6)F(5))(3) or Ph(3)CB(C(6)F(5))(4) afforded the binuclear zirconium complexes [(CpSiMe(2)NSiMe(2)Cp)Zr)(2)(mu-CH(3))][RB(C(6)F(5))(3)] (2a, R = CH(3), 2b, R = C(6)F(5)) with a methyl group as the bridge between the two zirconium atoms. In the presence of one equivalent of B(C(6)F(5))(3) or Ph(3)C(C(6)F(5))(4), 1 was transformed to the zwitterionic complexes [(CpSiMe(2)NSiMe(2)Cp)Zr][RB(C(6)F(5))(3)] (3a, R = CH(3), 3b, R = C(6)F(5)) which are free of a metal-bound sigma-alkyl ligand. 2b is stable with Me(3)Al while 3b combined with Me(3)Al to form a hetero-binuclear complex [(CpSiMe(2)NSiMe(2)Cp)Zr(mu-CH(3))]Al(CH(3))(2)][B(C(6)F(5))(4)] (4) as shown by NMR spectroscopy at room temperature. Treatment of 2a or 3a with an excess of Me(3)Al led to (CpSiMe(2)NSiMe(2)Cp)Zr(C(6)F(5)) (5) through a group exchange process. 2b, 3a and 5 have been characterized by X-ray diffraction studies. 2b, 2b, 3a and 3b were highly active catalysts for ethylene polymerization and copolymerization with 1-octene in the presence of trialkylaluminium, but the binuclear zirconium complexes (2a and 2b) showed higher activities than their mononuclear counterparts 3a and 3b. Polymerization activities varied with the trialkylaluminiums and increased with the trialkylaluminium concentration applied in the system. The product existed mainly in the form of Al(PE)(3) with polymeric chains, and its molecular weight and distribution were greatly influenced by the type and amount of trialkylaluminium applied in the catalytic system.
authors.affiliation: Institute of Chemical and Engineering Sciences, A*STAR (Agency for Science, Technology and Research), Singapore, 1 Pesek Road, Jurong Island, Singapore 627833. wang_cun@ices.a-star.edu.sg
authors.forename: Cun
authors.initials: C
authors.lastname: Wang
authors.forename: Martin
authors.initials: M
authors.lastname: van Meurs
authors.forename: Ludger P
authors.initials: LP
authors.lastname: Stubbs
authors.forename: Boon-Ying
authors.initials: BY
authors.lastname: Tay
authors.forename: Xiang-Jie
authors.initials: XJ
authors.lastname: Tan
authors.forename: Srinivasulu
authors.initials: S
authors.lastname: Aitipamula
authors.forename: Jacob
authors.initials: J
authors.lastname: Chacko
authors.forename: He-Kuan
authors.initials: HK
authors.lastname: Luo
authors.forename: Pui-Kwan
authors.initials: PK
authors.lastname: Wong
authors.forename: Suming
authors.initials: S
authors.lastname: Ye