Side Reactions in Homogeneous Catalysts

Concomitant with continued olefin insertion into the metal-carbon bond of the titanium-aluminum complex, alkyl exchange and hydrogen-transfer reactions are observed. Whereas the normal reduction mechanism for transition-metal-organic complexes is initiated by release of olefins with formation of hydride followed by hydride transfer (184, 185) to an alkyl group, in the case of some titanium and zirconium compounds a reverse reaction takes place. By the release of ethane, a dimetalloalkane is formed. In a second step, ethylene from the dimetalloalkane is evolved, and two reduced metal atoms remain (119). 

Some of the aging process which occurs with homogeneous and hetero- 

Most titanium(IV) alkyls tend to be reduced by aluminum alkyls in a complicated sequence of reactions accompanied by evolution of alkane and alkene. The catalytic activity of the bis(cyclopentadienyl)titanium-aluminum complexes is associated with the titanium alkyl. Hence, it is very interesting to investigate the mechanism of any reductive reaction. In order to study side reactions in the absence of polymerization, highly alkylated systems completely free of halogen are preferred. Moreover, reduction takes place much faster, the higher the alkyl-group content of the added aluminum alkyl. 

Dimetalloalkanes are formed in those systems in which separation of alkanes occurs without polymerization of olefins. 

Numerous intermediate steps have been elucidated for the soluble zirconium system (187). Because of the much greater resistance of zir- 

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