Organometallic chemistry of fullerenes: ?2- and ?5-(?)complexes

The reactivity of the fullerenes is primarily a function of their strain, as measured by the pyramidalization angle or curvature of the conjugated carbon atoms. A consideration of the orientation of the π-orbitals shows that η2-complexation reactions lead to reaction products with the fullerenes that are very similar to those obtained from unstrained alkenes. Furthermore, a large amount of strain energy is released in this reaction, so it is clear just why this reaction is important in fullerene chemistry. On the other hand, it is shown that the π-orbitals of C60 are poorly oriented for overlap with an exohedral metal atom centered over the five- or six-membered rings, but well disposed for overlap with an endohedral metal atom centered under the five- or six-membered rings.