title: 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 Ti(3+) centers that are investigated by multi-frequency continuous wave and pulse EPR methods. Two families of isolated, molecule-like Ti(3+) species have been identified. A comparison of the experimentally derived g tensors and (35,37)Cl hyperfine and nuclear-quadrupole tensors with DFT-computed values suggests that the dominant EPR-active Ti(3+)  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.
authors.affiliation: Dipartimento di Chimica and NIS, Università degli Studi di Torino, Via Giuria 7, 10125 Torino (Italy); Dutch Polymer Institute(DPI), P.O. Box 902, 5600 AX Eindhoven (The Netherlands); Department of Physics, University of Antwerp, Universiteitsplein 1, B-2610 Antwerp-Wilrijk (Belgium).
authors.forename: Elena
authors.initials: E
authors.lastname: Morra
authors.forename: Elio
authors.initials: E
authors.lastname: Giamello
authors.forename: Sabine
authors.initials: S
authors.lastname: Van Doorslaer
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Antinucci
authors.forename: Maddalena
authors.initials: M
authors.lastname: D'Amore
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Busico
authors.forename: Mario
authors.initials: M
authors.lastname: Chiesa
keywords: EPR spectroscopy; Ziegler-Natta catalysts; heterogeneous catalysis; polymerization; titanium