Effect of Cocatalysts on the Catalytic Activities of Tantalum‐ and Niobium‐Based Catalysts for Ring‐Opening Metathesis Polymerization of Norbornene

A series of pentavalent tantalum and niobium complexes with aryloxy ligands was prepared, and their catalytic behavior for the ROMP of norbornene was studied in the presence of an alkylaluminum cocatalyst. Tantalum complexes 1–4 showed very high activity for the ROMP of NBE in combination with iBu3Al to give high‐molecular‐weight polymers. In contrast, the niobium complexes 5 and 6, as well as NbCl5, exhibited very high activity upon activation with Me3Al to give high‐molecular‐weight polymers. magnified image