Rearrangements by Metal Ions and Complexes

The view of the mechanism by which transition metals catalyze such reactions that has gained widest acceptance pictures those reactions as being initiated by electrophilic (oxidative) attack on one of the strained cr-bonds. Such oxidative attack is then followed by carbonium-ion-like migrations and bond cleavages, which eventually are concluded by the expulsion of the metal ion. Some evidence for carbonium-ion intermediates has been obtained from results of reactions in nucleophilic solvents in which the intermediate carbonium ion can be trapped. 

Many details concerning these reactions have been established, but there are also unanswered questions regarding relationships between the catalytic metal ion and the product composition. For example, the course of isomerization of tricyclo[4.1.0.0 ]heptane, 2, with more than a dozen transition-metal derivatives 

The strain energy associated with the small-ring systems in the substrates provides the driving force for these rearrangement reactions. Unstrained hydrocarbons do not react with the various transition-metal species that cause bond-switching in strained hydrocarbons. 

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