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Probing the Coordinative Unsaturation and Local Environment of Ti3+ Sites in an Activated High‐Yield Ziegler–Natta Catalyst

Abstract

The typical activation of a fourth generation Ziegler–Natta catalyst TiCl4/MgCl2/phthalate with triethyl aluminum generates Ti3+ centers that are investigated by multi‐frequency continuous wave and pulse EPR methods. Two families of isolated, molecule‐like Ti3+ species have been identified. A comparison of the experimentally derived g tensors and 35,37Cl hyperfine and nuclear‐quadrupole tensors with DFT‐computed values suggests that the dominant EPR‐active Ti3+ species is located on MgCl2(110) surfaces (or equivalent MgCl2 terminations with tetra‐coordinated Mg). O2 reactivity tests show that a fraction of these Ti sites is chemically accessible, an important result in view of the search for the true catalyst active site in olefin polymerization.

Ausgeklügelte EPR‐Experimente wurden verwendet, um die Koordinationsumgebung der Ti3+‐Zentren in einem aktivierten MgCl2‐fixierten industriellen Ziegler‐Natta(ZN)‐Katalysator zu ermitteln. Die Ergebnisse liefern die erste detaillierte Charakterisierung potenzieller katalytisch aktiver Zentren in einem industriellen ZN‐Katalysator. Grün=Cl, gelb=Mg2+.

Authors:   Elena Morra, Elio Giamello, Sabine Van Doorslaer, Giuseppe Antinucci, Maddalena D'Amore, Vincenzo Busico, Mario Chiesa
Journal:   Angewandte Chemie
Volume:   127
edition:   16
Year:   2015
Pages:   4939
DOI:   10.1002/ange.201412052
Publication date:   23-Feb-2015
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