Metal and Counteranion Nuclearity Effects in Organoscandium-Catalyzed Isoprene Polymerization and Copolymerization

Jiazhen Chen, Yanshan Gao, Shuoyan Xiong, Massimiliano Delferro, Tracy L. Lohr, Tobin J. Marks

Research output: Contribution to journalArticle

11 Citations (Scopus)

Abstract

The binuclear organoscandium half-sandwich complexes (Me3SiCH2)2(THF)Sc[C5Me4-Si(CH3)2-(CH2)n-Si(CH3)2-C5Me4]Sc(CH2SiMe3)2(THF) (n = 0, Sc-C0-Sc; n = 2, Sc-C2-Sc) and monometallic C5Me4SiMe3Sc(CH2SiMe3)2(THF) (Sc1) were prepared and fully characterized by conventional spectroscopic, analytical, and diffraction techniques. These complexes are active catalysts for isoprene polymerization and ethylene/isoprene copolymerization upon activation by the co-catalysts trityl perfluoroarylborate (Ph3C+)B(C6F5)4- (B1) and trityl bisperfluoroarylborate (Ph3C+)2[1,4-(C6F5)3BC6F4B(C6F5)3]2- (B2). Marked catalyst and co-catalyst nuclearity effects on product polymer microstructure are achieved in isoprene polymerization. Thus, the percentage of cis-1,4- units in the polyisoprene products increases from 24% (Sc1) to 32% (Sc-C2-Sc) to 48% (Sc-C0-Sc) as the catalyst nuclearity increases and the Sc···Sc distance contracts. The binuclear catalysts regulate the isometric unit distributions and favor 3,4-3,4-3,4 blocks. Furthermore, the percentage of polyisoprene trans-1,4- units increases ∼5 times when binuclear co-catalyst (B2) is used, in comparison to B1. In ethylene/isoprene copolymerizations, the binuclear catalysts produce polymers with higher molecular weights (Mn = (3.4-6.9) × 104 polydispersity of = 1.4-2.0) and with comparable isoprene enchainment selectivity versus Sc1 under identical reaction conditions. However, isoprene incorporation is curiously reduced by ∼50% when B2 is used versus B1. These results highlight the importance of both ion pairing and imposed nuclearity in these polymerizations, and these results indicate that both catalyst and co-catalyst nuclearities can be used to access specific polyisoprene polymer/copolymer microstructures.

Original languageEnglish
Pages (from-to)5214-5219
Number of pages6
JournalACS Catalysis
Volume7
Issue number8
DOIs
Publication statusPublished - Aug 4 2017

Keywords

  • bimetallic catalysis
  • ion pairing
  • isoprene polymerization
  • nuclearity effects
  • scandium

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)

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