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Sodium cyclopentadienide is an organosodium compound with the formula C5H5Na. The compound is often abbreviated as NaCp, where Cp is the cyclopentadienide anion.[1] Sodium cyclopentadienide is a colorless solid, although samples often are pink owing to traces of oxidized impurities.[2]

Sodium cyclopentadienide
Sodium cyclopentadienide-B.gif
The cyclopentadienide anion
Other names
sodium cyclopentadienylide, cyclopentadienylsodium
3D model (JSmol)
ECHA InfoCard 100.023.306
EC Number 225-636-8
Molar mass 88.085 g·mol−1
Appearance colorless solid
Density 1.113 g/cm3
Solubility THF
Main hazards flammable
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



Sodium cyclopentadienide is commercially available as a solution in THF. It is prepared by treating cyclopentadiene with sodium:[3]

2 Na + 2 C5H6 → 2 NaC5H5 + H2

Commonly, the conversion is conducted by heating a suspension of molten sodium in dicyclopentadiene.[2] In former times, the sodium was commonly provided in the form of "sodium wire" or "sodium sand", a fine dispersion of sodium prepared by melting sodium in refluxing xylene and rapidly stirring.[4][5] Sodium hydride is a convenient base:[6]

NaH + C5H6 → NaC5H5 + H2

In early work, Grignard reagents were used as bases. With a pKa of 15, cyclopentadiene can be deprotonated by many reagents.


Sodium cyclopentadienide is a common reagent for the preparation of substituted cyclopentadienyl salts such as the ester and formyl compounds NaC5H4X (CO2Me, CHO):[7]

NaC5H5 + HCO2R → NaC5H4CHO + ROH

Sodium cyclopentadienide is a common reagent for the preparation of metallocenes. For example, the preparation of ferrocene[4] and zirconocene dichloride:[8]

2 NaC5H5 + FeCl2 → Fe(C5H5)2 + 2 NaCl
ZrCl4(thf)2 + 2 NaCp → Cp2ZrCl2 + 2 NaCl + 2 THF


The nature of NaCp depends strongly on its medium and for the purposes of planning syntheses, the reagent is often represented as a salt Na+
. Crystalline solvent-free NaCp, which is rarely encountered, is a "polydecker" sandwich complex, consisting of an infinite chain of alternating Na+ centers sandwiched between μ-η5:η5-C5H5 ligands.[9] As a solution in donor solvents, NaCp is highly solvated, especially at the alkali metal as suggested by the isolability of the adduct Na(tmeda)Cp.[10]

In contrast to alkali metal cyclopentadienides, tetrabutylammonium cyclopentadienide (Bu4N+C5H5) was found to be supported entirely by ionic bonding and its structure is representative of the structure of the cyclopentadienide anion (C5H5, Cp) in the solid state. However, the anion deviates somewhat from a planar, regular pentagon, with C–C bond lengths ranging from 138.0 -140.1 pm and C–C–C bond angles ranging from 107.5-108.8°.[11]

See alsoEdit


  1. ^ International Union of Pure and Applied Chemistry (2005). Nomenclature of Inorganic Chemistry (IUPAC Recommendations 2005). Cambridge (UK): RSCIUPAC. ISBN 0-85404-438-8. p. 262. Electronic version.
  2. ^ a b Tarun K. Panda, Michael T. Gamer, Peter W. Roesky "An Improved Synthesis of Sodium and Potassium Cyclopentadienide" Organometallics, 2003, 22, 877–878.doi:10.1021/om0207865
  3. ^ Cotton, F. Albert; Wilkinson, Geoffrey (1988), Advanced Inorganic Chemistry (5th ed.), New York: Wiley-Interscience, p. 139, ISBN 0-471-84997-9
  4. ^ a b Wilkinson, Geoffrey (1963). "Ferrocene". Organic Syntheses.; Collective Volume, 4, p. 473
  5. ^ Partridge, John J.; Chadha, Naresh K.; Uskokovic, Milan R. (1990). "An asymmetric hydroboration of 5-substituted cyclopentadienes: synthesis of methyl (1R,5R)-5-hydroxy-2-cyclopentene-1-acetate". Organic Syntheses.CS1 maint: Multiple names: authors list (link); Collective Volume, 7, p. 339
  6. ^ Girolami, G. S.; Rauchfuss, T. B. & Angelici, R. J. (1999). Synthesis and Technique in Inorganic Chemistry. CA: University Science Books: Mill Valley. ISBN 0935702482.
  7. ^ Macomber, D. W.; Hart, W. P.; Rausch, M. D. (1982). "Functionally Substituted Cyclopentadienyl Metal Compounds". Adv. Organomet. Chem. 21: 1–55. doi:10.1016/S0065-3055(08)60377-9.
  8. ^ Wilkinson, G.; Birmingham, J. G. (1954). "Bis-cyclopentadienyl Compounds of Ti, Zr, V, Nb and Ta". J. Am. Chem. Soc. 76 (17): 4281–84. doi:10.1021/ja01646a008.
  9. ^ Robert E. Dinnebier; Ulrich Behrens & Falk Olbrich (1997). "Solid State Structures of Cyclopentadienyllithium, -sodium, and -potassium. Determination by High-Resolution Powder Diffraction". Organometallics. 16: 3855–3858. doi:10.1021/om9700122.
  10. ^ Elschenbroich, C. (2006). Organometallics. Wiley-VCH: Weinheim. ISBN 978-3-527-29390-2.
  11. ^ Reetz, Manfred T.; Hütte, Stephan; Goddard, Richard (1995-03-01). "Tetrabutylammonium Salts of 2-Nitropropane, Cyclopentadiene and 9-Ethylfluorene: Crystal Structures and Use in Anionic Polymerization". Zeitschrift für Naturforschung B. 50 (3): 415–422. doi:10.1515/znb-1995-0316. ISSN 1865-7117.