title: Facing unexpected reactivity paths with Zr(IV)-pyridylamido polymerization catalysts.
abstract: This work provides original insights to the better understanding of the complex structure-activity relationship of Zr(IV)-pyridylamido-based olefin polymerization catalysts and highlights the importance of the metal-precursor choice (Zr(NMe(2))(4) vs. Zr(Bn)(4)) to prepare precatalysts of unambiguous identity. A temperature-controlled and reversible σ-bond metathesis/protonolysis reaction is found to take place on the Zr(IV)-amido complexes in the 298-383 K temperature range, changing the metal coordination sphere dramatically (from a five-coordinated tris-amido species stabilized by bidentate monoanionic {N,N(-)} ligands to a six-coordinated bis-amido-mono-amino complexes featured by tridentate dianionic {N(-),N,C(-)} ligands). Well-defined neutral Zr(IV)-pyridylamido complexes have been prepared from Zr(Bn)(4) as metal source. Their cationic derivatives [Zr(IV) N(-),N,C(-)}Bn](+)[B(C(6)F(5))(4)](-) have been successfully applied to the room-temperature polymerization of 1-hexene with productivities up to one order of magnitude higher than those reported for the related Hf(IV) state-of-the-art systems. Most importantly, a linear increase of the poly(1-hexene) M(n) values (30-250 kg mol(-1)) has been observed upon catalyst aging. According to that, the major active species (responsible for the increased M(n) polymer values) in the aged catalyst solution, has been identified.
authors.affiliation: Institute of Chemistry of OrganoMetallic Compounds, ICCOM-CNR, Via Madonna del Piano, 10-50019 Sesto F.no, Florence, Italy.
authors.forename: Lapo
authors.initials: L
authors.lastname: Luconi
authors.forename: Andrea
authors.initials: A
authors.lastname: Rossin
authors.forename: Giulia
authors.initials: G
authors.lastname: Tuci
authors.forename: Incoronata
authors.initials: I
authors.lastname: Tritto
authors.forename: Laura
authors.initials: L
authors.lastname: Boggioni
authors.forename: Jerzy J
authors.initials: JJ
authors.lastname: Klosin
authors.forename: Curt N
authors.initials: CN
authors.lastname: Theriault
authors.forename: Giuliano
authors.initials: G
authors.lastname: Giambastiani