Highly Active Ethene Polymerization Catalysts with Unusual Imine Ligands - Late Transition Metal Polymerization Catalysis - page 61

ethene and acrylic ester was achieved [15] and even ethene polymerization in
water was observed [16].
The relatively simple reactions that lead to the chelate ligands also changed the
way single site catalysts are developed. In the synthesis of ligands, application of
parallel synthesis or even combinatorial methods created the opportunity to pre-
pare ligand structures in a large variety [17]. In the same process, the complexa-
tion to metals has been optimized for performing synthesis with a high selectivity
through the use of appropriate metal precursors. Furthermore, screening methods
for determining catalytic activity in a high throughput fashion of the catalyst (pre-
cursors) were established.
It may now be clear that this field of olefin polymerization research is develop-
ing at an impressive and never seen pace in this area. Today, some activity-struc-
ture relationships [11-13] were experimentally established and verified in a num-
ber of theoretical studies [18, 34]. The key structural feature of the ligand frame-
work of these catalysts is apparently sufficient steric shielding of the active cation-
ic center to suppress undesired chain termination pathways, mostly -hydrogen

elimination and associative olefin displacements, which are intimate features of
SHOP catalysts, leading to linear 1-olefins [19]. Steric shielding may, for example,
be effected by the use of bulky ortho-substituted aryl groups (e.g. 2,6-diisopropyl-
phenyl) attached to the peripheral imine nitrogen donor sites of the [N,N],

[N,N,N] and [N,O] ligands (Scheme 3.1).

Scheme 3.1 Axial steric shielding in N-aryl diimine (left), bis(imino)pyridine (right)
and salicyl imine (bottom) late transition metal polymerization catalysts.

Late transition metal compounds of the Group 10 with coordinated imine donor
ligands were often found to yield active catalysts. In this chapter we wish to re-
port on research carried out at or in cooperation with BASF polymer research on
catalysts that carry imine donor ligands. Our objective is to introduce a number of
“unusual” ligand frames for active catalysts. Unusual refers to being different to
the usual condensates of alkyl-substituted anilines with aldehydes and ketones.
The ligand frames that are described in the following include neutral (i) [N,N] di-
imine, (ii) [N,N,N] bis(imino)pyridine, monoanionic (iii) [N,O] salicyl imine, and