Investigation of Dynamic Intra‐ and Intermolecular Processes within a Tether‐Length Dependent Series of Group 4 Bimetallic Initiators for Stereomodulated Degenerative Transfer Living Ziegler–Natta Propene Polymerization

Abstract

, 4 (n = 6), and 5 (n = 4) were prepared in high yield through a simple, onepot synthesis involving 2 equiv. of in situ generated (h 5 -C 5 Me 5 )Zr(Me) 3 and the corresponding bis-carbodiimide,Compounds 3-5 were found to be highly isoselective for the living Ziegler-Natta polymerization of propene upon 100% activation using 2 equiv. of the borate co-initiator, [PhNHMe 2 ] [BA C H T U N G T R E N N U N G (C 6 F 5 ) 4 ] (2), with the degree of stereoselectivity decreasing slightly as the two metal centers are brought closer together [cf., 3 (s = 0.92) > 4 (s = 0.91) > 5 (s = 0.89)]. Under conditions of sub-stoichiometric activation by 2, all three bimetallic initiators, 3-5, were found to engage in degenerative transfer living Ziegler-Natta polymerization involving rapid and reversible methyl group transfer between active, (cationic) and dormant, (neutral) methyl, polymeryl zirconium centers. Under these conditions, the frequency of mr triad stereoerror incorporation into the polypropene (PP) microstructure decreases as the two metal centers are brought closer together as a result of increasing barriers for metal-centered epimerization within the neutral metal site due to correspondingly greater non-bonded steric interactions vis-à-vis mononuclear 1.

Ligands with Two Monoanionic N,N‐Binding Sites: Synthesis and Coordination Chemistry

“…Due to the limited stability of bis(carbodiimide)s, which are prone to polymerization reactions, the first route is restricted to only a few examples. However, it offers the advantage that the respective dinuclear aluminum, titanium, and zirconium complexes are directly obtained in yields >80 % without the isolation of the respective bis(amidine). Notably, for the reactions of bis(carbodiimide)s with trimethylaluminum, different products are obtained, depending on both the stoichiometry and the reaction conditions (Scheme ) .…”

“…In addition to the different types of mononuclear complexes, a variety of di‐ and also polynuclear bis(amidinate) complexes have been reported so far (Figure and Figure , respectively). Heteroleptic dinuclear complexes of type G belong to the first observed bis(amidinate)s, but remain limited to certain examples employing the elements aluminum, titanium, and zirconium . This is somewhat unfortunate keeping the promising catalytic ability of dinuclear aluminum (ring‐opening (co)polymerization of cyclic esters and synthesis of cyclic carbonates) and zirconium complexes (stereoselective, living, coordinative chain‐transfer polymerization of propene) in mind.…”

Alkene Polymerization Catalysts Bearing Tridentate Phenoxyamine Ligands with sp3 C Donors

“…This suggests that upon activation of the diastereoisomeric mixture of [rac-Lig 1 HfBn 2 -a/b], a similar active species is generated for each separate diastereoisomer. [8,11,12,18,19,[48][49][50][51][52] In both 1-hexene and propylene polymerizations, living behavior only occurred when using BA C H T U N G T R E N N U N G (C 6 F 5 ) 3 as a cocatalyst. 4 ] at 258C resulted in similar molecular weights and molecular weight distributions with activity trends reflecting those previously established.…”

Ex uno plures (“aus Einem Vieles”): Konzepte zur Erweiterung des Polyolefin‐Repertoires durch reversiblen Gruppentransfer

“…[16] Eine weitere Konsequenz dieser Gesamtbedingungen ist, dass der teure Borat-Cokatalysator entgegen den Erwartungen tatsächlich nur in einer kleinen substöchiometrischen Menge benötigt wird, um durch lebende ZN-Polymerisation zu Präzisions-olefinen zu gelangen (siehe unten).…”

“…Sita und Mitarbeiter [16] schlugen einen Mechanismus der lebenden degenerativen Gruppentransfer-Koordinationspolymerisation vor und konnten diesen dann experimentell nachweisen (Schema 1). Demnach erfolgt zwischen zwei Populationen von Übergangsmetallspezies, die bezüglich des Kettenwachstums aus "aktiven" Fortpflanzungszentren und "ruhenden" Zentren bestehen, ein reversibler Austausch über einen raschen (Nichtpolymeryl)-Gruppentransfer, insbesondere mit X = Me oder Cl.…”