Zirconium and hafnium complexes based on 2-aryl-8-arylaminoquinoline ligands: synthesis, molecular structure, and catalytic performance in ethylene copolymerization

Abstract

A general and efficient approach toward new zirconium and hafnium complexes based on 2-aryl-8-arylaminoquinoline ligands was developed. These precursors, when activated with MAO/borate cocatalyst and supported on silica, result in active olefin polymerization catalysts. The ethylene copolymers produced under industrially relevant conditions show very high molecular weights and unique microstructures defined by the multisite nature of the catalyst. A site-diversification mechanism is proposed to explain the presence of at least five individual sites, as deduced from 3D-TREF analysis of ethylene-butene copolymers.

Reaction of 2,8-Bis(o-hydroxyaryl)quinolines with Group 4 Metal Alkyls Resulting in Three Distinct Coordination Modes of the Tridentate Ligand. X-ray Structure of Complexes and Performance as Precursors in Ethylene Polymerization Catalysis

“…Under our testing conditions the Zr complexes seem to be more active than their Ti and Hf analogues (complex 21 vs complexes 20 and 22, respectively). The catalysts of this study show very steep deactivation, as illustrated by the ethylene consumption curves vs time (Figure 3), similarly to what was observed for quinoline-based [CNN] complexes, 15 in remarkable contrast with the very good shelf life of catalyst samples stored before the test. In the case of complex 21 the catalyst demonstrated retention of the initial performance in a supported MAO/borate preactivated recipe for over 1 month.…”

“…A series of ethylene copolymerization reactions were carried out with complexes 20 – 24 , 30 , and 31 , as well as the earlier reported bis(phenoxy)pyridine complex 32 (Scheme ), , under industrially relevant slurry polymerization conditions using silica-supported recipes, preactivated with a mixed MAO/borate cocatalyst, a system that was earlier reported by us to result in active catalysts on combination with postmetallocenes (Table ).…”

“…Our synthetic approach was based on 2,8-dibromoquinoline, a strategic starting material which is easily accessible in three steps from 2-bromoaniline . The two bromine atoms of the precursor have substantially different reactivities, allowing very selective sequential introduction of substituents, an approach used earlier during the synthesis of 2-phenyl-8-phenylaminoquinoline and related quinoline-based [CNN]-type ligand precursors used in the synthesis of group 4 complexes . The latter study demonstrated the effectiveness of Pd-catalyzed Suzuki and Negishi couplings for introduction of an aryl fragment into the 2-position of the quinoline.…”

“…Interestingly, while the quinoline-based [CNN] complexes demonstrate a very good M w control with H 2 , as indicated by the continuous drop of M w of polymer samples with an increase of H 2 level in the reactor, 15 the catalysts based on the new complexes 21 and 23 show very little effect (compare run 10 vs 4, Tables 3 and 4; see Figure 5).…”

Preparation of Pyridylamido Hafnium Complexes for Coordinative Chain Transfer Polymerization

“…In other catalysis [performed with Pd complexes constructed via N-heterocyclic carbene (NHC) ligands], the influence of substituents at the 2,6-position in aryl-N moieties is substantial, and derivatization of the NHC ligand has been carried out by replacing common 2,6-diisopropylphenyl-N parts with 2,6-di(3-pentyl)phenyl-N and 2,6-di(3-heptyl)phenyl-N moieties [30,31]. Much research has also been performed on I [32][33][34][35][36][37][38], and the synthesis of its analogs with the aim to improve the catalytic performance deserves attention [7,29,[39][40][41][42]. Subtle change in the ligand framework sometimes results in dramatic improvement in the polymerization performance and, hence, modification of the substituents has been a main research theme in the development of postmetallocecenes [43][44][45][46][47][48][49].…”