Bis(carbene)pyridine complexes of the early to middle transition metals: Survey of ethylene oligomerization and polymerization capability

Bis(carbene)pyridines of the type 2,6-bis(1-(alkyl/aryl)imidazol-2-ylidene)pyridine have been complexed to Ti, V, Cr, Fe, and Co and single-crystal X-ray structures obtained for two of the complexes (M = Cr, Fe). The structures confirm the tight chelate bite angles (ca. 76-79degrees) enforced by this ligand. All complexes have been evaluated as catalysts for ethylene oligomerization and polymerization in combination with a variety of cocatalysts. While Ti and V complexes of this ligand give rise to highly active ethylene polymerization catalysts, Cr complexes produce exceptionally active Schulz-Flory oligomerization catalysts in combination with MAO. In contrast, complexes of Fe and Co: are inactive, and possible reasons for this are suggested.