text: All 5 carbon atoms of a Cp ligand are bound to the metal in the vast majority of M–Cp complexes. This bonding mode is called η-coordination. The M–Cp bonding arises from overlap of the five π molecular orbitals of the Cp ligand with the s, p, and d orbitals on the metal. These complexes are referred to as π-complexes. Almost all of the transition metals employ this coordination mode.
  In relatively rare cases, Cp binds to metals via only one carbon center. These types of interactions are described as σ-complexes because they only have a σ bond between the metal and the cyclopentadienyl group. Typical examples of this type of complex are group 14 metal complexes such as CpSiMe. An example of both is (CpFe(CO)).  It is probable that η-Cp complexes are intermediates in the formation of η-Cp complexes.
  Still rarer, the Cp unit can bond to the metal via three carbons. In these η-Cp complexes, the bonding resembles that in allyl ligands. Such complexes, sometimes called "slipped Cp complexes", are invoked as intermediates in ring slipping reactions.
  Moreover, inverse sandwich compounds with the "metal–Cp–metal" structures are known.