Highly Active Ethene Polymerization Catalysts with Unusual Imine Ligands - Late Transition Metal Polymerization Catalysis - page 72

Chart 3.4 [N,N,N] ligands 41 - 52 .

The complexes 53a - 62a (Chart 3.5) were synthesized in good yield from the li-
gands 41 - 52 by reaction with the appropriate metal halides (FeCl 2 , CoCl 2 , FeCl 3 ).
Almost all of the pyrrole-, indole-, and carbazole-containing systems afforded
stable Fe(II) and Co(II) complexes. The only exceptions are ligands 44 and 47
which contain only aryl substituents. This indicates that two pairs of o -phenyl
groups on the N-pyrrolyl substituents impose too much of a steric hindrance and/
or are too electron-withdrawing for the corresponding [N,N,N] metal complex to
form. The two Fe(III) precatalysts 54 c , 55 c were synthesized to evaluate the de-
pendence of the polymerization performance on the oxidation state of the metal
center. In total, twenty-one different N-azolyl complexes were prepared aiming at
a thorough structure-activity evaluation ( vide infra ).
All complexes 53a - 62a are paramagnetic, deeply colored, mostly dark green for
Fe(II) and dark brown for Co(II). They are thermally very stable, no melting or de-
composition is observed up to 300 C. These properties are parallel to those of

Gibson's and Brookhart's N-aryl bis(imino)pyridyl complexes [13].
For one representative of this family of precatalysts ( 61a ) suitable single crystals
for an X-ray structure analysis were obtained. Fig. 3.6 shows the molecular struc-
ture of Fe(II) complex 61a .