Sodium cyclopentadienide

Sodium cyclopentadienide
	; The cyclopentadienide anion
Names
	Other names sodium cyclopentadienylide, cyclopentadienylsodium
Identifiers
CAS Number	4984-82-1 ;
3D model (JSmol)	Interactive image;
ChemSpider	71032 ;
ECHA InfoCard	100.023.306
EC Number	225-636-8
PubChem CID	78681;
	InChI InChI=1S/C5H5.Na/c1-2-4-5-3-1;/h1-5H;/q-1;+1 Key: OHUVHDUNQKJDKW-UHFFFAOYSA-N ; InChI=1S/C5H5.Na/c1-2-4-5-3-1;/h1-5H;/q-1;+1; Key: OHUVHDUNQKJDKW-UHFFFAOYSA-N;
	SMILES [Na+].c1[cH-]ccc1;
Properties
Chemical formula	C5H5Na
Molar mass	88.08 g·mol−1
Appearance	colorless solid
Solubility in water	decomposition
Solubility	THF
Hazards
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 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]

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

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 pK_a of 15, cyclopentadiene can be deprotonated by many reagents.

Applications

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

Structure

The nature of NaCp depends strongly its medium and for the purposes of planning syntheses, the reagent is often represented as a salt Na⁺
C
₅H⁻
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.^[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]

References

↑ 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.
1 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
↑ Cotton, F. Albert; Wilkinson, Geoffrey (1988), Advanced Inorganic Chemistry (5th ed.), New York: Wiley-Interscience, p. 139, ISBN 0-471-84997-9
1 2 Wilkinson, Geoffrey (1963). "Ferrocene". Organic Syntheses. ; Collective Volume, 4, p. 473
↑ 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. ; Collective Volume, 7, p. 339
↑ Girolami, G. S.; Rauchfuss, T. B. & Angelici, R. J. (1999). Synthesis and Technique in Inorganic Chemistry. CA: University Science Books: Mill Valley. ISBN 0935702482.
↑ 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.
↑ 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.
↑ 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.
↑ Elschenbroich, C. (2006). Organometallics. Wiley-VCH: Weinheim. ISBN 978-3-527-29390-2.
↑ 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.

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[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.

[Roesky-2] 1 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

[ferrocene-4] 1 2 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. ; 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.