Niobocene dichloride explained

Niobocene dichloride is the organometallic compound with the formula (C₅H₅)₂NbCl₂, abbreviated Cp₂NbCl₂. 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 Cp₂TiCl₂.

Preparation and structure

It was originally reported by Geoffrey Wilkinson.^[1] It is prepared via a multistep reaction beginning with treatment of niobium pentachloride with cyclopentadienylsodium:^[2]

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 zirconocene 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.^[3]

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.^[4]

Notes and References

1. G. . Wilkinson . Geoffrey Wilkinson . J. G. . Birmingham . Bis-cyclopentadienyl Compounds of Ti, Zr, V, Nb and Ta. . 76. 17. 1954. 4281–4284 . 10.1021/ja01646a008.
2. Book: C. R. Lucas . Dichlorobis(η ⁵ -Cyclopentadienyl) Niobium(IV) . Inorganic Syntheses . . 2007 . 28 . 267–270 . 978-0-471-52619-3 . 10.1002/9780470132593.ch68.
3. K. Prout, T. S. Cameron, R. A. Forder, and in parts S. R. Critchley, B. Denton and G. V. Rees "The crystal and molecular structures of bent bis-π-cyclopentadienyl-metal complexes: (a) bis-π-cyclopentadienyldibromorhenium(V) tetrafluoroborate, (b) bis-π-cyclopentadienyldichloromolybdenum(IV), (c) bis-π-cyclopentadienylhydroxomethylaminomolybdenum(IV) hexafluorophosphate, (d) bis-π-cyclopentadienylethylchloromolybdenum(IV), (e) bis-π-cyclopentadienyldichloroniobium(IV), (f) bis-π-cyclopentadienyldichloromolybdenum(V) tetrafluoroborate, (g) μ-oxo-bis[bis-π-cyclopentadienylchloroniobium(IV)] tetrafluoroborate, (h) bis-π-cyclopentadienyldichlorozirconium" Acta Crystallogr. 1974, volume B30, pp. 2290–2304.
4. Mokdsi, G. . Harding, M. M. . A¹H NMR study of the Interaction of Antitumor Metallocenes with Glutathione . J. Inorg. Biochem. . 2001 . 86 . 2–3 . 611–616 . 10.1016/S0162-0134(01)00221-5. 11566334 .