Niobocene dichloride

Niobocene dichloride, formally dichlorobis(η5-Cyclopentadienyl)niobium(IV), is the chemical compound with the formula (C5H5)2NbCl2 or Cp2NbCl2. This paramagnetic brown solid is a useful starting reagent. It is being investigated as an anti-cancer agent.

The compound is a pseudotetrahedral with two cyclopentadienyl and two chloro substituents attached to the metal. A variety of similar compounds are known, including Cp2TiCl2.

It is prepared via a multistep reaction beginning with reductive alkylation of niobium pentachloride with cyclopentadienylsodium:
 * NbCl5 + 6 NaC5H5  →   5 NaCl + (C5H5)4Nb + organic products
 * (C5H5)4Nb +  2 HCl  + 0.5 O2)    →     [{C5H5)2NbCl}2O]Cl2  +  2 C5H6
 * 2 HCl +  [{(C5H5)2NbCl}2O]Cl2  +  SnCl2   →   2 (C5H5)2NbCl2  +  SnCl4  +  H2O