Heterogeneous Polymerization Catalysts Derived from Transition Metal Alkyl Compounds

Heterogeneous Polymerization Catalysts Derived from Transition Metal Alkyl Compounds 

The surfaces of some types of silica and alumina freed from adsorbed water contain acidic -OH groups. Ballard et al. (15) showed that these -OH groups react readily with transition metal alkyls giving stable compounds that are highly active polymerization catalysts for olefins. These systems are best described with reference to silica. 

In this way the number of -OH groups per gram of support that are available for reaction with the transition metal alkyl, can be measured. If this information is combined with surface-area measurements, the number of 

Transition metal alkyl compounds react with the -OH groups on the surface of silica in a manner similar to that described for the silanol [reaction (13)] and as with the latter more than one type of bonding is possible. Silica dried at 200°C reacts with Zr(allyl)4 to give two molecules of propene per metal atom and utilizing in the course of this process two -OH groups per metal atom. The chemistry of the process is accurately described by the equation 

The structure of (XIV) is confirmed by reacting with n-butanol and measuring the amount of propene produced as shown by reaction (16). 

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