Highly Active Ethene Polymerization Catalysts with Unusual Imine Ligands - Late Transition Metal Polymerization Catalysis - page 59

3
Highly Active Ethene Polymerization Catalysts
with Unusual Imine Ligands
Gerrit A. Luinstra *, Joachim Queisser, Benno Bildstein,
Hans-Helmut Görtz, Christoph Amort, Michael Malaun, Alexander Krajete,
Gerald Werne, Marc O. Kristen, Norbert Huber, and Christoph Gernert
3.1
Introduction
The commercial production of polyolefins from ethene and propene was greatly
progressed with the discovery of what came to be known as Ziegler-Natta cata-
lysts and Phillips & Union Carbide type catalysts [1]. They opened the possibility
of preparing polyolefins with new and interesting material properties under what
at that time would be considered mild conditions with respect to pressure and
temperature. A further impact in this area came from the observation that mix-
tures of alkylating agents with metallocene halides of Groups 3 and 4 catalyze 1-
olefin polymerization [2]. These “single site” catalysts differ from their heteroge-
neous counterparts in that they are (in theory) truly single sited, i.e. only one type
of a coordinatively unsaturated complex is involved in the migratory insertion of
the olefinic monomer. The resulting polyolefins are therefore usually uniform and
of one type of (statistic) microstructure. This is often advantageous for the
material in a specific application, and allows one to establish relationships be-
tween the molecular structure of the precatalysts and the material properties of
the polymers [3]. The latter aspect is important for producing macromolecular tai-
lor-made materials from properly designed catalysts. In fact, the state of the art in
metallocene polymerization catalysis has reached an extraordinary high level of so-
phistication [4] regarding the understanding of the polymerization process in
many of its aspects [5], and the design and improvement of ligands for high per-
formance catalysts, for example using models based upon molecular or quantum
mechanics [6]. At the same time, a number of shortcomings arose, including (i)
the often tedious multistep synthesis of precatalysts with complicated ligands, (ii)
the high reactivity/oxophilicity of the (activated) complexes toward functional
groups, and (iii) the unavoidable use of a large excess of costly activating reagents
[7]. The latter is of particular industrial relevance because polyolefins are generally
commodity products and new polyolefins with improved properties that are ob-
tainable with metallocene catalysts tend to become very quickly commodities and
thus have to compete with the established low(er) price standard polyolefins.
Therefore, the (re)discovery [8] in the last decade of the 20 th century of late tran-
sition metals as polyolefin catalysts with relatively simple ligands received an im-