Highly Active Ethene Polymerization Catalysts with Unusual Imine Ligands - Late Transition Metal Polymerization Catalysis - page 92

Fig. 3.13 Six chamber autoclave for parallel screening of polymerization catalysts.

The (N,O)-NiR(donor) complexes could effectively be activated by reaction with
the triphenylmethylium tetrakis(pentafluorophenyl)borate. With other reagents
such as (COD) 2 Ni, N,N-dimethylanilinium tetrakis(pentafluorophenyl)borate or
MAO only traces of polymer were obtained. With tris(pentafluorophenyl)borane
an activity below 50 g PE (g Ni ·h) -1 was observed (experiments in toluene at
20 C, 20 bar ethene 5 h).

In Tab. 3.10 data of the initial screening experiments with triphenylmethylium
tetrakis(pentafluorophenyl)borate as activator are collected. A more accurate study
was performed with the most promising derivatives for ethene polymerization
(Tab. 3.11).
The majority of these are (N,O)NiMe(CH 2 =PPh 3 ) compounds. For benchmark-
ing, a recently reported catalyst based on salicylimine (with 2,6-diisopropyl and o -
5-antracyl substituent) was included in the study ( 135 ) [14a]. It can be concluded
from Tab. 3.11 that the five-membered alkoxyimine nickel compounds are active
catalysts in the polymerization of ethene with activities that compare well with the
salicyl imine single site (N,O) nickel catalysts [14]. The activity depends on the
substitution pattern of the ligand; highest activities are obtained from complexes
that have isopropyl substituents in the ortho positions of the imine phenyl group
and two aryl or methyl groups on the alkoxy carbon. Most non-metallocene late
transition metal polymerization catalysts contain peripheral 2,6-diisopropylphenyl
imine moieties ( vide infra ), therefore it is interesting to see that in this system de-
rivatives with methyl groups at the phenyl group are also fairly active. It might be
inferred that, for polymer formation, a minimum steric bulk is a prerequisite, but
not necessarily arising from an imine moiety. Fig. 3.14 shows a graphical repre-