Formation of elastomeric polypropylene promoted by the dynamic complexes [TiCl2{N(PPh2)2}2] and [Zr(NPhPPh2)4]

Olaf Kühl*, Thomas Koch, Fernando B. Somoza, Peter C. Junk, Evamarie Hey-Hawkins, Dorit Plat, Moris S. Eisen

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

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Abstract

The homoleptic phosphinoamide complex [Zr(NPhPPh2)4] (1) and the bisamido complex [TiCl2{N(PPh2)2}2] (2) were prepared from ZrCl4 and four equivalents of LiNPhPPh2 and from TiCl4 and one equivalent of [Li(THF)N(PPh2)2]2. In the solid state, the four NPhPPh2 ligands in 1 exhibit η2 coordination. The ZrN4P4 fragment is highly symmetrical and almost of D2 symmetry. Hence, the complex is chiral, and the two enantiomers cocrystallize in the asymmetric unit. In solution, 1 exhibits signals for the six-coordinate complex [Zr(η2-NPhPPh2)21-NPhPPh2)2]. In the presence of methylalumoxane (MAO), 1 and 2 are active catalysts for the formation of high-molecular-weight elastomeric polypropylene. The formation of elastomeric polypropylene is a consequence of an epimerization mechanism of the last-inserted monomer, indicating no detachment of the growing polymer chain from the metal center during this process. Fractionation studies of all the elastomeric polymers show no atactic fractions. As corroboration for this mechanism, we have shown that these complexes are active catalysts for the isomerization and oligomerization of 1-octene, as well as for the rapid isomerization of allylbenzene to trans-methylstyrene.

Original languageEnglish
Pages (from-to)116-125
Number of pages10
JournalJournal of Organometallic Chemistry
Volume604
Issue number1
DOIs
StatePublished - 5 Jun 2000
Externally publishedYes

Keywords

  • Homoleptic zirconium phosphinoamide complex
  • Molecular structure
  • Polymerisation of propylene
  • Titanium bisamido dichloride complex

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