Sodium cyclopentadienide

"NaCp" redirects here. For other uses, see NACP (disambiguation).

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

NaCp synthesized in an inert atmosphere
Names
Preferred IUPAC name Sodium cyclopentadienide
Other names Sodium cyclopentadienylide, Cyclopentadienylsodium
Identifiers
CAS Number	4984-82-1 Y
3D model (JSmol)	Interactive image
ChemSpider	71032 Y
ECHA InfoCard	100.023.306
EC Number	225-636-8
PubChem CID	78681
CompTox Dashboard (EPA)	DTXSID9063665
InChI InChI=1S/C5H5.Na/c1-2-4-5-3-1;/h1-5H;/q-1;+1 Y Key: OHUVHDUNQKJDKW-UHFFFAOYSA-N Y 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	88.085 g·mol−1
Appearance	colorless solid
Density	1.113 g/cm3
Solubility in water	decomposition
Solubility	THF
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	flammable
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

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 from cyclopentadiene and molten sodium metal:^[4][2] Sodium can also be provided as "sodium wire" or "sodium sand", the fine suspension produced when molten sodium is mixed with refluxing xylene, then cooled.^[5][6] The highly exothermic metallation can undergo catastrophic thermal runaway without proper cooling, as occurred in the T2 Laboratories explosion and fire.^[7]

Alternatively, many reagents deprotonate cyclopentadiene; it has pK_a 15. Early work used Grignard reagents as bases, but sodium hydride is more convenient nowadays:^[8]

NaH + C₅H₆ → NaC₅H₅ + H₂

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 ferrocene^[5] and zirconocene dichloride:^[9]

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:^[10]

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

These compounds are used to prepare substituted metallocenes such as 1,1'-ferrocenedicarboxylic acid.^[11]

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
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.^[12] 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.^[13]

In contrast to alkali metal cyclopentadienides, tetrabutylammonium cyclopentadienide (Bu
₄N⁺
C
₅H⁻
₅) was found to be supported entirely by ionic bonding and its structure is representative of the structure of the cyclopentadienide anion (C
₅H⁻
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°.^[14]

See also

• Lithium cyclopentadienide
• Potassium cyclopentadienyl