2,2′-Bis(methylene)biphenylidene-bridged bis(3-indenyl) dichloride complexes of Ti, Zr and Hf as catalyst precursors for ethylene polymerization

doi:10.1016/j.poly.2018.01.015

Polyhedron

Volume 144, 1 April 2018, Pages 176-186

https://doi.org/10.1016/j.poly.2018.01.015 Get rights and content

Abstract

ansa metallocene complexes of Ti, Zr and Hf were synthesized, characterized and tested as catalysts for homogeneous ethylene polymerization. The ligand system comprises two indenyl moieties tethered at the 1,1′-positions via a 2,2′-dimethyl biphenylene bridge. The ligand precursor was obtained by the reduction of diphenic acid using lithium aluminum hydride (LiAlH₄), followed by the reaction with phosphorus tribromide, and, finally, the reaction with indenyllithium. The corresponding group (IV) metal complexes were synthesized by deprotonation of the ligand precursors using n-BuLi followed by reactions of the corresponding metal tetrachloride. After activation with methylaluminoxane (MAO), the zirconium and hafnium complexes proved as highly active catalysts for ethylene polymerization. The zirconium complex 6 showed the best performance with 12,460 kg PE/mol cat. h. The titanium complex 5 showed no catalytic activity obviously because of decomposition reactions.

Graphical abstract

2,2′-Bis(methylene)biphenylidene-bridged bis(3-indenyl) dichloride complexes of Ti, Zr and Hf as catalyst precursors for ethylene polymerization.

Introduction

The activity and stereoselectivity of a metallocene-based catalyst in olefin polymerization can be significantly influenced by slight structural variations in the bridging unit (structure property relationship) [1], [2], [3], [4], [5], [6], [7], [8]. In this context ansa bis(indenyl) complexes of Ti, Zr and Hf with dimethylsilylene bridges and sterically demanding 4-aryl substituents proved as highly isoselective catalyst precursors for the polymerization of propylene [9], [10], [11] and ethylene [12], [13]. In this study, the synthesis of new ansa titanocene, zirconocene, and hafnocene dichloride complexes is reported. The title complexes comprise two indenyl or 3-methylindenyl ligands, tethered at the 1-positions, via a 2,2′-bis(methylene)-1,1′-biphenylidene bridge. Moreover, the catalytic behavior of the prepared ansa metallocene catalysts in the homopolymerization of ethylene was investigated after activation with methylaluminoxane (MAO).

Section snippets

Preparation of the ligand precursors 3 and 4

Diphenic acid was converted to the corresponding 2,2-bis(hydroxymethyl) biphenyl (1) according to a reported method [14]. Reduction of diphenic acid with lithium aluminum hydride in THF and purification by crystallization from a chilled methanol solution gave 1 in good yield. Treatment of the diol compound 1 with phosphorus tribromide in methyl-ene chloride afforded 2,2′-bis(bromomethyl) biphenyl 2 [15]. Compounds 3 and 4 were then obtained via reactions of 2,2′-bis(bromomethyl) biphenyl 2 with

General

All reactions were carried out under an inert gas atmosphere of pure oxygen-free argon using standard Schlenk techniques. n-Pentane, n-hexane, diethyl ether, toluene, and tetrahydrofuran were purified by distillation over Na/K alloy. Diethyl ether was additionally distilled over lithium aluminum hydride. Toluene was additionally distilled over phosphorus pentoxide. Methylene chloride and carbon tetrachloride were dried over phosphorus pentoxide. Deuterated organic solvents (CDCl₃, CD₂Cl₂, and C₆

Conclusions

This series of ansa metallocene complexes allows a perfect comparison of the role of the metal in identical complexes. The polymerization of ethylene after the activation of the catalyst precursor with MAO confirms that zirconium as a metal gives the best performance in terms of catalyst activity and molecular weight of the produced polymer. The titanium complex did not show any activity under identical reaction conditions. An explanation could be decomposition reactions of the catalyst at

Acknowledgements

The authors thank the Deutsche Akademischer Austauschdienst, DAAD, for financial support and Dr. W.P. Kretschmer for the GPC measurements.

References (22)

T. Ooi et al.
Tetrahedron
(2006)
M.R. Machat et al.
Organometallics
(2017)
G. Theurkauff et al.
Organometallics
(2016)
M.R. Machat et al.
Organometallics
(2017)
M.E.M. Abdelbagi et al.
Polyhedron
(2017)
B. Wang
Coord. Chem. Rev.
(2006)
C. Alonso-Moreno et al.
Inorg. Chem. commun.
(2009)
W. Kaminsky et al.
Polyolefins J.
(2015)
C. Redshaw et al.
Chem. Soc. Rev.
(2012)
M.C. Baier et al.
Angew. Chem. Int. Ed.
(2014)

W. Kaminsky (ed.), “Polyolefins: 50 years after Ziegler and Natta”, Springer, Adv. Polymer Science 2013/14,...

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2,2′-Bis(methylene)biphenylidene-bridged bis(3-indenyl) dichloride complexes of Ti, Zr and Hf as catalyst precursors for ethylene polymerization

Abstract

Graphical abstract

Introduction

Section snippets

Preparation of the ligand precursors 3 and 4

General

Conclusions

Acknowledgements

Tetrahedron

Organometallics

Organometallics

Organometallics

Polyhedron

Coord. Chem. Rev.

Inorg. Chem. commun.

Polyolefins J.

Chem. Soc. Rev.

Angew. Chem. Int. Ed.