Lanthanide cyclooctatetraene dianion

Controversy exists in naming sandwich organometallic actinide and lanthanide compounds of cyclooctatetraene dianion [8]annulene dianion and [8]annulene-metal(X) complex are chosen here because these names properly describe the delocalization of charge in the ligand and also emphasize the formal oxidation state of the metal in the complex. 

Uranocene (15.19), a key discovery from 1%8, showed that the higher radius and charge of relative to the lanthanides allows stabilization of the planar, aromatic, lOrr-electron cyclooctatetraene dianion (cot ) in U(cot)2. This pyrophoric 22e compound also shows the failure of the 18e rule in the 5/ elements. 

The bis([8]annulene)lanthanate(III) anions which are complexed by an [8]annulenelanthanate(III) cation are the only other class of complexes which contain two [8]annulene dianions in a sandwich arrangement about a lanthanide(III) ion. This class was first reported for the cerium(III) ion, from the reduction of a cerium(IV) alkoxide with triethylaluminum in the presence of cyclooctatetraene.3 ... 

Cyclooctatetraene CgHg (COT) can be an 8-electron L4 ligand. With the alkaline metals, lanthanides and actinides however, COT is found as the aromatic COT dianion with 10 electrons (Hiickel s rule 4n -1- 2n electrons, n = 2). 

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