Sodium_cyclopentadienide

Sodium cyclopentadienide

Sodium cyclopentadienide

Chemical compound


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]

Quick Facts Names, Identifiers ...

Preparation

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

The conversion can be conducted by heating a suspension of molten sodium in dicyclopentadiene.[2] In former times, the sodium was 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 + 2 C5H6 → NaC5H5 + H2

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

Applications

Sodium cyclopentadienide is a common reagent for the preparation of metallocenes. For example, the preparation of ferrocene[4] and zirconocene dichloride:[7]

2 NaC5H5 + FeCl2 → Fe(C5H5)2 + 2 NaCl
ZrCl4(thf)2 + 2 NaCp → (C5H5)2ZrCl2 + 2 NaCl + 2 THF

Sodium cyclopentadienide is also used for the preparation of substituted cyclopentadienyl derivatives such as the ester and formyl derivatives:[8]

NaC5H5 + O=C(OEt)2 → NaC5H4CO2Et + NaOEt

These compounds are used to prepare substituted metallocenes such as 1,1'-ferrocenedicarboxylic acid.[9]

Structure

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+
C
5
H
5
. 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.[10] 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.[11]

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°.[12]

See also


References

  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. 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. Wilkinson, Geoffrey (1963). "Ferrocene". Organic Syntheses; Collected Volumes, vol. 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{{cite journal}}: CS1 maint: multiple names: authors list (link); Collected Volumes, vol. 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. 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.
  8. Macomber, D. W.; Hart, W. P.; Rausch, M. D. (1982). "Functionally Substituted Cyclopentadienyl Metal Compounds". Adv. Organomet. Chem. Advances in Organometallic Chemistry. 21: 1–55. doi:10.1016/S0065-3055(08)60377-9. ISBN 9780120311217.
  9. Petrov, Alex R.; Jess, Kristof; Freytag, Matthias; Jones, Peter G.; Tamm, Matthias (2013). "Large-Scale Preparation of 1,1′-Ferrocenedicarboxylic Acid, a Key Compound for the Synthesis of 1,1′-Disubstituted Ferrocene Derivatives". Organometallics. 32 (20): 5946–5954. doi:10.1021/om4004972.
  10. Robert E. Dinnebier; Ulrich Behrens & Falk Olbrich (1997). "Solid State Structures of Cyclopentadienyllithium, -sodium, and -potassium. Determination by High-Resolution Powder Diffraction". Organometallics. 16 (17): 3855–3858. doi:10.1021/om9700122.
  11. Elschenbroich, C. (2006). Organometallics. Wiley-VCH: Weinheim. ISBN 978-3-527-29390-2.
  12. 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. S2CID 45791403.

Share this article:

This article uses material from the Wikipedia article Sodium_cyclopentadienide, and is written by contributors. Text is available under a CC BY-SA 4.0 International License; additional terms may apply. Images, videos and audio are available under their respective licenses.