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Preparation

The first salt of cyclopentadienide to be reported was potassium cyclopentadienide, prepared by Johannes Thiele. In 1901 there was not much interest in the topic.³

Sodium cyclopentadienyl is prepared by treating cyclopentadiene with sodium:⁴

The conversion can be conducted by heating a suspension of molten sodium in dicyclopentadiene.⁵ 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.⁶⁷ Sodium hydride is a convenient base:⁸

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

Sodium cyclopentadienide is commercially available as a solution in THF.

Applications

Sodium cyclopentadienide is a common reagent for the preparation of metallocenes. For example, the preparation of ferrocene⁹ and zirconocene dichloride:¹⁰

Sodium cyclopentadienide is also used for the preparation of substituted cyclopentadienyl derivatives such as the ester and formyl derivatives:¹¹

These compounds are used to prepare substituted metallocenes such as 1,1'-ferrocenedicarboxylic acid.¹²

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+C5H−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.¹³ 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.¹⁴

In contrast to alkali metal cyclopentadienides, tetrabutylammonium cyclopentadienide (Bu4N+C5H−5) was found to be supported entirely by ionic bonding and its structure is representative of the structure of the cyclopentadienide anion (C5H−5, 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°.¹⁵

See also

• Lithium cyclopentadienide
• Potassium cyclopentadienyl

References

1. International Union of Pure and Applied Chemistry (2005). Nomenclature of Inorganic Chemistry (IUPAC Recommendations 2005). Cambridge (UK): RSC–IUPAC. ISBN 0-85404-438-8. p. 262. Electronic version. /wiki/International_Union_of_Pure_and_Applied_Chemistry ↩

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 /wiki/Doi_(identifier) ↩

3. Johannes Thiele (January 1901). "Ueber Abkömmlinge des Cyclopentadiëns". Berichte der Deutschen Chemischen Gesellschaft (in German). 34 (1): 68–71. doi:10.1002/CBER.19010340114. ISSN 0365-9496. Wikidata Q126217369. /wiki/Johannes_Thiele_(chemist) ↩

4. Cotton, F. Albert; Wilkinson, Geoffrey (1988), Advanced Inorganic Chemistry (5th ed.), New York: Wiley-Interscience, p. 139, ISBN 0-471-84997-9 0-471-84997-9 ↩

5. 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 /wiki/Doi_(identifier) ↩

6. Wilkinson, Geoffrey (1963). "Ferrocene". Organic Syntheses; Collected Volumes, vol. 4, p. 473. /wiki/Geoffrey_Wilkinson ↩

7. 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. http://www.orgsyn.org/demo.aspx?prep=cv7p0339 ↩

8. Girolami, G. S.; Rauchfuss, T. B. & Angelici, R. J. (1999). Synthesis and Technique in Inorganic Chemistry. CA: University Science Books: Mill Valley. ISBN 0935702482.{{cite book}}: CS1 maint: publisher location (link) 0935702482 ↩

9. Wilkinson, Geoffrey (1963). "Ferrocene". Organic Syntheses; Collected Volumes, vol. 4, p. 473. /wiki/Geoffrey_Wilkinson ↩

10. Wilkinson, G.; Birmingham, J. G. (1954). "Bis-cyclopentadienyl Compounds of Ti, Zr, V, Nb and Ta". J. Am. Chem. Soc. 76 (17): 4281–84. Bibcode:1954JAChS..76.4281W. doi:10.1021/ja01646a008. /wiki/Geoffrey_Wilkinson ↩

11. 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. 9780120311217 ↩

12. 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. /wiki/Doi_(identifier) ↩

13. 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. /wiki/Organometallics ↩

14. Elschenbroich, C. (2006). Organometallics. Wiley-VCH: Weinheim. ISBN 978-3-527-29390-2. 978-3-527-29390-2 ↩

15. 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. https://doi.org/10.1515%2Fznb-1995-0316 ↩