Cossee-Arhnan mechanism

Most metallocene catalysts are active only in the presence of an [MeAl( x-0)] cocatalyst. This alkylates the group 4 metal and also removes a chloro-ligand, thereby creating a coordi-natively unsaturated, cationic metal centre. The pathway for chain growth follows the Cossee-Arhnan mechanism (Figure 27.16 and equation 27.31). 

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