Lower oxidation states cyclopentadienyls

Cu ( j -C5H5)2] is not. Likewise, Fe and Ni carborane derivatives are extremely stable. Conversely, metallocarboranes tend to stabilize lower oxidation states of early transition elements and complexes are well established for Ti", Zr , Hf , V , Cr and Mn" these do not react with H2, N2, CO or PPh3 as do cyclopentadienyl derivatives of these elements. 

Tris(i/5-cyclopentadienyl)lanthanides were the first authentic organolanth-anides to be prepared1 and bis(t/5-cyclopentadienyl)lanthanide(II) compounds have played a germinal part in the development of lower oxidation state organolanthanide chemistry.2 These cyclopentadienyls are sources of coordination compounds of structural interest and are reagents for the synthesis of other organolanthanides, for example, bis- and mono(t)5-cyclopentadienyl)lanthanide(III) derivatives.2... 

The majority of titanium organometallic chemistry involves complexes in which the titanium is in its highest oxidation state (+4) and cyclopentadienyl see Cyclopenta-dienyl) derivatives serve as ancillary ligands. However, considerable chemistry has also been developed in which the titanium is in the +3 and +2 oxidation state, with lesser amounts of chemistry known for titanium in lower oxidation states (+1, 0). Since the early 1980s, chemists have placed considerable emphasis on the fine-tuning of the stracture and reactivity of titanium organometallic... 

The number of niobium and tantalum coordination compounds in oxidation states lower than II is limited, and they often are organometallic derivatives involving carbonyl, cyclopentadienyl, or alkenic ligands. 

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