Polymerization of Cyclopentene Using Metallocene Catalysts: Competitive Cis- and Trans-1,3 Insertion Mechanisms

Abstract

Hydrooligomerization or polymerization of cyclopentene using racemic 1,2-ethylenebis(η5-indenyl)zirconium dichloride (1) and methylaluminoxane leads to the production of poly(cis-1,3-cyclopentane). Analogous reactions using racemic 1,2-ethylenebis(η5-tetrahydroindenyl)zirconium dichloride (2) leads to the production of oligomers in which cyclopentene is incorporated in a cis- or trans-1,3 manner. Two plausible mechanisms for trans-1,3 insertion are presented which involve reversible β-hydrogen elimination reactions of unsaturated oligomers or direct interconversion of olefin hydride complexes via the intermediacy of a σ-CH complex. Copolymerization of cyclopentene and 3-cyclopentylcyclopentene-2-d (9) reveals that the former process can occur but is not competitive with simple copolymerization; this, in combination with other observations, suggests that reversible chain transfer is unlikely to account for trans-1,3 insertion. Polymerization of cyclopentene-d8 led to significantly different, instantaneous ...