New Upswing of Organolanthanoid Research: A Very Promising Revival of Organocerium( IV ) Chemistry and the First Stable Lanthanoid( II/III )–Carbene Complexes

Less conventional oxidation states of the lanthanoids become important in complexes in which ligands such as trimethylsilyl-substituted cyclooctatetraene anions or imidazol-2-ylidenes coordinate to the metal ion. These types of Lnn+ complexes (n ≠ 3), which were still ignored ten years ago, may have sandwich or even oligodecker structures (see, for example, picture on the right) or contain carbene-like η1-bound ligands.