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. 76-79°) 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.