Catalyst/cocatalyst nuclearity effects in single-site polymerization. Enhanced polyethylene branching and α-olefin comonomer enchainment in polymerizations mediated by binuclear catalysts and cocatalysts via a new enchainment pathway

Liting Li, Matthew V. Metz, Hongbo Li, Ming Chou Chen, Tobin J. Marks, Louise Liable-Sands, Arnold L. Rheingold

Research output: Contribution to journalArticle

177 Citations (Scopus)


The binuclear "constrained geometry catalyst" (CGC) (μ-CH2CH2-3,3′) {(η5-indenyl)[1-Me2Si- (tBuN)](ZrMe2}2 [EBICGC(ZrMe2)2; Zr2] and the trityl bisborate dianion (Ph3C+)2 [1,4-(C6F5) 3BC6F4B (C6F5)3]2- (B2) have been synthesized to serve as new types of multicenter homogeneous olefin polymerization catalysts and cocatalysts, respectively. Additionally, the complex [1-Me2Si(3-ethylindenyl)(tBuN)]ZrMe2 (Zr1) was synthesized as a mononuclear control. For the bimetallic catalyst or bisborate cocatalyst, high effective local active site concentrations and catalyst center-catalyst center cooperative effects are evidenced by bringing the catalytic centers together via either covalent or electrostatic bonding. For ethylene homopolymerization at constant conversion, the branch content of the polyolefin products (primarily ethyl branches) is dramatically increased as catalyst or cocatalyst nuclearity is increased. Moreover, catalyst and cocatalyst nuclearity effects are approximately additive. Compared to the catalyst derived from monometallic Zrl and monofunctional Ph3C+B (C6F5)4- (B1), the active catalyst derived from bimetallic Zr2 and bifunctional B2 produces ∼11 times more ethyl branches in ethylene homopolymerization via a process which is predominantly intradimer in character. Moreover, ∼3 times more 1-hexene incorporation in ethylene + 1-hexene copolymerization and ∼4 times more 1-pentene incorporation in ethylene + 1-pentene copolymerization are observed for Zr2 + B2 versus Zr1 + B1.

Original languageEnglish
Pages (from-to)12725-12741
Number of pages17
JournalJournal of the American Chemical Society
Issue number43
Publication statusPublished - Oct 30 2002


ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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