Hafnium and Zirconium Complexes Bearing SNN-Ligands Enhancing Catalytic Performances toward Ethylene/1-Octene Copolymerization

Abstract

The development of efficient catalysts is an ongoing pursuit in the field of olefin polymerization in order to synthesize desired polyolefins and to advance the present polymerization processes. In this contribution, the synthesis and characterization of a class of Hf and Zr complexes bearing SNN-tridentate ligands were described. The Hf (Hf1 and Hf2) and Zr (Zr1 and Zr2) trimethyl complexes were synthesized by one-pot reactions of thio-imino-quinoline ligands with in situ formed MMe4 (M = Hf, Zr). Both NMR analysis and X-ray diffraction study suggest the formation of thio-amido-quinoline metal complexes via methyl migration from Hf (or Zr) to the carbon of imine. These Hf and Zr complexes exhibited high activity and excellent thermal stability toward ethylene/1-octene copolymerization and an activity as high as 2.57 × 106 g(PE)·mol–1(cat)·h–1 was obtained by Hf1 even at 150 °C. The resultant polymers had moderate to high molecular weights (6.1–41.3 × 104 g·mol–1) with very broad distributions (D̵ = 6.8–34.7). NMR study revealed that multiple active species were formed when Hf1 was activated by 1 equiv. of [Ph3C][B(C6F5)4].

Synthesis of Amido-quinoline Hafnium and Zirconium Complexes with Improved Performances toward Ethylene/1-Octene Copolymerization

“…The C13− N1 distance is 1.460(6) Å, suggesting a typical C−N single bond. 29,31,33 These further confirm the amido-coordination in Hf1, which is fully consistent with the result by NMR analysis. Complex Hf4 in Figure 2 displays similar structural features, suggesting that other metal complexes should have similar coordination geometries.…”

“…These results suggest the migration of methyl, the addition of imino group, and the formation of amino group, similar as previous reports involving imine-type ligands. 33,36 To investigate the thermal stability of the newly developed complexes, Hf1 was refluxed in C 7 D 8 at 110 °C for 6 h, and the NMR analysis confirmed no decomposition, as shown in Figure S51. In order to firmly determine the structure of the metal complexes, single crystals of complexes Hf1 and Hf4 were obtained by recrystallization of their toluene solutions at room temperature and characterized by X-ray diffraction.…”

“…Such a metal-effect is also observed in previous reports for nitrogenbased Hf and Zr complexes. 28,31,34,41,55 For comparison, Hf5 (Scheme 1, C) was also prepared and tested for the copolymerization of ethylene with 1-octene. Under otherwise identical conditions (Table 1, run 11), Hf5 shows a relatively lower activity (58500 kg(POE)•mol −1 (M)•h −1 ) and incorporation capability (32.5 mol % 1-octene) than Hf1 (Figure 4).…”

“…In this study, a new family of imino-quinoline ligands is designed and synthesized by the p -TsOH catalyzed condensation reactions between 2-aldehyde-quinoline and various anilines (Scheme , D ). − Next, amido-quinoline complexes can be prepared by one-pot reactions of imino-quinoline ligands with in situ formed MMe 4 (M = Hf, Zr) with high yields. Thus, a cost-effective route to prepare highly thermally and chemically stable amido-quinoline complexes is discovered, which is remarkable for large-scale operations and greatly promising for practical utility.…”

Hafnium and Zirconium Complexes Bearing ONN-Tridentate Ligands and Their Catalytic Properties toward Olefin Polymerization

“…49 For the synthesis of metal complexes, HfMe 4 (or ZrMe 4 ) was in situ prepared by the reaction of HfCl 4 (or ZrCl 4 ) with 4 equiv of MeMgBr (3.0 M, Et 2 O solution) at −40 °C in toluene and then was used to react with compound 1 or 2 directly in this work (Scheme 1). 33,50 All of the metal complexes were isolated as red solids in high yields (76−82%).…”