<Li> Bis (cyclooctatetraenyl) complexes: M (C H), such as U (C H) and Th (C H) (both actinocenes). </Li> <Li> Bis (cyclobutadienyl) complexes: M (C H), such as Fe (C H). </Li> <P> Sandwich complexes are even known containing purely inorganic ligands, such as Fe (C Me) (P) and ((P) Ti). </P> <P> Metallocenes including just one facially - bound planar organic ligand instead of two gives rise to a still larger family of half - sandwich compounds . The most famous example is probably methylcyclopentadienyl manganese tricarbonyl . Such species are occasionally referred to as piano - stool compounds, at least when there are three diatomic ligands in addition to the hydrocarbon "seat" of the piano stool . The name derives from the similarity of the structure to such a "stool" with the seat being a facial planar organic compound, e.g. benzene or cyclopentadiene, and the legs being ligands such as CO or allyl . </P>

Write one method of preparation of sandwich compounds