Microstructure Control of Ethene Homopolymers Through Tailored Ni,Pd(II) Catalysts - Late Transition Metal Polymerization Catalysis - page 41

Fig. 2.11 Synthesis of mono condensation products.
ment of the corresponding aryl Grignard compounds with trimethylborate [25].
The huge steric demand of the symmetric diimine ligands requires a synthesis
similar to that of the symmetric analogues. The new asymmetric diimine ligands
are accessible by a two step procedure. In a first reaction the mono condensation
product is synthesized by combination of equimolar amounts of diketone and the
corresponding amino compound at ambient temperature. Subsequently, condensa-
tion of the resulting ketimine with a further amino component is performed.
Two routes are conceivable for the preparation of the mono condensation prod-
uct. Route A in Fig. 2.11 starts from the diisopropyl aniline ( 2e ) resulting in a liq-
uid ketimine ( 7a ) which can easily be purified by vacuum distillation of the reac-
tion mixture. Route B used the terphenylamino compounds ( 2b , c ) to give the sol-
id products ( 7b , c ). Following these approaches, the p - tert -butyl substituted ( 8c )
and the p -methoxy substituted ligand ( 8b ) can be easily synthesized in yields up
to 85%. The corresponding nickel dibromo complexes (Fig. 2.12, 9b , c ) resulted
from in situ reactions of the ligands with (DME)NiBr 2 in toluene solution [37].
2.3.2
Polymerization Reactions
The nickel dibromo complexes were activated for the polymerization of ethene by
addition of MAO at ambient temperature. Owing to the high catalyst activities
and the precipitating polymers, the polymerization experiments were performed