Niobocene dichloride

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.

Niobocene dichloride
Names
IUPAC name
Dichloridobis (η5-cyclopentadienyl)niobium
Other names
Niobocene dichloride
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.159.630
EC Number
  • 631-385-9
RTECS number
  • QU0400000
Properties
C10H10Cl2Nb
Molar mass 294 g/mol
Appearance brown solid
Melting point dec.
Boiling point dec.
soluble (hydrolysis)
Solubility in other solvents sparingly in chlorocarbons
Hazards
R-phrases (outdated) 36/37/38
S-phrases (outdated) 26-36
Related compounds
Related compounds
 Cp2TiCl2
Cp2MoCl2

Cp2VCl2

Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

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]

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

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.[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]

References
  1. Wilkinson, G.; Birmingham, J. G. (1954). "Bis-cyclopentadienyl Compounds of Ti, Zr, V, Nb and Ta". J. Am. Chem. Soc. 76 (17): 4281–4284. doi:10.1021/ja01646a008.
  2. C. R. Lucas (1990). "Dichlorobis(η5 -Cyclopentadienyl) Niobium(IV)". Dichlorobis(η5-Cyclopentadienyl)Niobium(IV). Inorg. Synth. Inorganic Syntheses. 28. pp. 267–270. doi:10.1002/9780470132593.ch68. ISBN 0-471-52619-3.
  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. doi:10.1107/S0567740874007011
  4. Mokdsi, G.; Harding, M. M. (2001). "A1H NMR study of the Interaction of Antitumor Metallocenes with Glutathione". J. Inorg. Biochem. 86 (2–3): 611–616. doi:10.1016/S0162-0134(01)00221-5. PMID 11566334.
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