Ring-opening polymerization of norbornene initiated by tungsten alkylidene complexes. Activation by AlCl3

Addition of aluminium compounds to the stable metal‐carbene complex tetracarbonyl[4–5‐η‐1‐methoxy‐4‐pentenylidene]tungsten (1), showing an intramolecular coordination of double bond to the transition metal, leads to highly active catalytic systems in the polymerization of norbornene. It is shown that, in optimal conditions, AlCl3 is more efficient than AlEt3 for cyclo‐olefin polymerization. From spectroscopic studies (UV‐visible, 1H and 13C NMR) of the activated system 1‐AlCl3, a mechanism of activation by AlCl3 is proposed involving a modification of the nature of carbene 1 by the Lewis acid.