Abstract
Hafnium complexes have drawn attention for their application as post-metallocene catalysts with unique performance in olefin polymerization. In this work, a series of half-metallocene HfMe2 complexes, bearing a tetrahydroquinoline framework, as well as a series of [Namido,N,Caryl]HfMe2-type post-metallocene complexes, bearing a tetrahydrophenanthroline framework, were prepared; the structures of the prepared Hf complexes were unambiguously confirmed by X-ray crystallography. When the prepared complexes were reacted with anhydrous [(C18H37)2N(H)Me]+[B(C6F5)4]−, desired ion-pair complexes, in which (C18H37)2NMe coordinated to the Hf center, were cleanly afforded. The activated complexes generated from the half-metallocene complexes were inactive for the copolymerization of ethylene/propylene, while those generated from post-metallocene complexes were active. Complex bearing bulky isopropyl substituents (12) exhibited the highest activity. However, the activity was approximately half that of the prototype pyridylamido-Hf Dow catalyst. The comonomer incorporation capability was also inferior to that of the pyridylamido-Hf Dow catalyst. However, 12 performed well in the coordinative chain transfer polymerization performed in the presence of (octyl)2Zn, converting all the fed (octyl)2Zn to (polyolefinyl)2Zn with controlled lengths of the polyolefinyl chain.
Highlights
Polyolefins (POs) are the most abundant polymers, which are mostly produced using the Ziegler-Natta catalyst
12 performed well in the coordinative chain transfer polymerization performed in the presence of2 Zn, converting all the fed2 Zn to2 Zn with controlled lengths of the polyolefinyl chain
The Ti-based half-metallocenes characteristically exhibit, similar to the Zr-based metallocene catalysts, higher α-olefin incorporation in ethylene/α-olefin copolymerizations, which enables the commercial production of polyolefin elastomers (POE)
Summary
Polyolefins (POs) are the most abundant polymers, which are mostly produced using the Ziegler-Natta catalyst. The conventional heterogeneous multi-site Ziegler-Natta catalyst has been replaced with homogeneous single-site catalysts, the former is still a main player in the production of POs. The use of homogeneous single-site catalysts originated with the serendipitous discovery of methylaluminoxane (MAO) by Kaminsky [1]. The initial Zr-based metallocene catalysts, Ti-based half-metallocenes, and post-metallocenes with non-cyclopentadienyl ligands, were developed successively (Scheme 1) [2,3]. A typical example of half-metallocenes is [Me2 Si(η5 -Me4 C5 )(Nt Bu)]TiCl2 , which was discovered in the early 1990s at Dow (II Scheme 1) [4]. A typical example of post-metallocenes is the pyridylamido-Hf complex
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