In 1980, the pentamethylcyclopentadienyl ligand, C 5 Me, was introduced to prepare the lanthanide complexes with all metals in the series . and ( C 5 Me 5 ) 2 Sm, making a breakthrough in f-block metallocenes, since both of these two organosamarium ( II ) complexes were unexpectedly found to participate in the coordination, activation and transformation of a variety of unsaturated compounds, including olefins, internal alkynens, phosphaalkynes, carbon monoxide, carbon dioxide, isonitriles, diazine derivatives, imines and polycyclic aromatic hydrocarbons ( PAHs ).
