Exohedral η5-π-complexes of fullerene C20

The problem of stabilization of polyhedral carbon clusters, which do not obey the isolated pentagon rule, is discussed taking a dodecahedral fullerene C20 as an example. Ab initio MO LCAO calculations in the HF/3-21G approximation showed that fullerene C20 as well as its C20H5 hydrides with C5v symmetry can form stable 2η5-π-complexes of the CpFeC20FeCp and H5C20FeC20H5 types. The energies of the η5-Fe--C20 π-bonds in these complexes were compared with those of the Fe--Cp bond in ferrocene and the Fe--C60 bond in the η5-π-C60H5FeCp complex.