Nature and Scope of the Catalyst

A sizeable number of well-defined, single component Group Vlll transition metal catalysts were synthesized in our laboratory at B. F. Goodrich. Two of these are illustrated in Fig. 4.4. The most active catalysts of this class are invariably the nickel systems. 

These systems were extensively studied with the goal of finding even better, more efficient catalysts. Based on these studies it appears that the key attributes for high activity appear to be three-fold (1) the transition metal center is complexed only by metal olefin Tt-bonds and a metal-carbon rr-bond (which can be part of an allylic system), (2) the metal center is cationic, and (3) the counter-ion is a weakly coordinating anion. 

for a highly active, single-component catalyst for the addition polymerization of norbornenes it seems that a necessary requirement is accessibility to the metal by the norbornene substrate. We refer to this family of catalysts as being naked since all of their ligands (olefins) are readily displaced by the norbornene monomer to afford a highly active cationic metal nucleus nickel catalysts being preferred. The envisaged active site is illustrated in Fig. 4.5. 

Catalysts of this type have been studied extensively for the polymerization of butadiene [32], the oligomerization of styrene [33], and the dimerization of acrylates [34]. Indeed it was my becoming aware of this work that led to all of our subsequent discoveries. 

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