Niobocene dichloride
Niobocene dichloride is the organometallic compound with the formula (CH)NbCl, abbreviated CpNbCl. This paramagnetic brown solid is a starting reagent for the synthesis of other organoniobium compounds. The compound adopts a pseudotetrahedral structure with two cyclopentadienyl and two chloride substituents attached to the metal. A variety of similar compounds are known, including CpTiCl. Preparation and structure. It was originally reported by Geoffrey Wilkinson. It is prepared via a multistep reaction beginning with treatment of niobium pentachloride with cyclopentadienylsodium: The compound adopts a "clamshell" structure characteristic of a bent metallocene where the Cp rings are not parallel, the average  Cp(centroid)-M-Cp angle being about 130.3°. The Cl-Nb-Cl angle of 85.6° is narrower than in zirconacene dichloride (97.1°) but wider than in molybdocene dichloride (82°). This trend is consistent with the orientation of the HOMO in this class of complex. Applications and further work. Unlike the related zirconacene and titanocene dichlorides, no applications have been found for this compound, although it has been studied widely. It was investigated as a potential anti-cancer agent.