Nickel Polymerization Catalysts with Ylide Steering Ligands - Late Transition Metal Polymerization Catalysis - page 10

1.3
Ethylene Polymerization

1.3.1
Catalyst Activity [10, 12, 13]

Different ligand properties affect the homogeneously catalyzed oligo-/polymeriza-
tion of ethylene. The nickel catalysts with structurally intact ylide ligands have
considerably higher activities than comparable nickel phosphane systems. The
Me 3 P-nickel complex is even catalytically inactive. Frontier orbitals, as well as ac-
tivity of the catalysts are influenced by variations of the intact ylide ligand. Inter-
estingly, when the chelating acetylmethylene-triphenylphosphorane is kept un-
changed, the turnover increases with decreasing first ionization potential of the
structurally intact coordinating ylides [Eq. (10), bottom].

10

P reori/coord) of the
chelate-phosphorus reflects the properties of the intact steering ligand which are
transmitted by the nickel into the metallocycle. The “intact ylide”-dependent chem-
ical shift behavior is mirrored in the activity profile of the catalyst system [12].
When, on the other hand, the intact ylide ligand Me 3 PCH 2 is retained [Eq. (10),
top], the turnover increases in the sequence formyl-, acetyl-, benzoyl-methylene-tri-
phenylphosphorane, at 10 bar and approximately 100 C, to around 0.5 10 5 mole
reacted ethene per mole nickel per hour. This corresponds to a catalyst activity of
1.4 10 6 gPEor 1.4 tons PE produced per mole of catalyst without using any co-
catalyst or noncoordinating anions.

Likewise, the phosphorus-31 coordination chemical shift (