Sodium cyclopentadienide
Chemical compound
From Wikipedia, the free encyclopedia
Sodium cyclopentadienide is an organosodium compound with the formula C5H5Na. The compound is often abbreviated as NaCp, where Cp− is the cyclopentadienyl anion.[1] Sodium cyclopentadienide is a colorless solid, although samples often are pink owing to traces of oxidized impurities.[2]
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 NaCp synthesized in an inert atmosphere | |||
| Names | |||
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| Preferred IUPAC name
Sodium cyclopentadienide | |||
| Other names
Sodium cyclopentadienylide, Cyclopentadienylsodium | |||
| Identifiers | |||
3D model (JSmol) |
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| ChemSpider | |||
| ECHA InfoCard | 100.023.306 | ||
| EC Number |
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PubChem CID |
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CompTox Dashboard (EPA) |
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| Properties | |||
| C5H5Na | |||
| Molar mass | 88.085 g·mol−1 | ||
| Appearance | colorless solid | ||
| Density | 1.113 g/cm3 | ||
| 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).
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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 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 pKa 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]
Electron-deficient cyclopentadienes are more likely to form naked anions. [C5(CF3)5]− (perfluoro-Cp*) has pKb ≥ 16 and typically behaves as a weakly coordinating anion.[15][16]
See also
- Lithium cyclopentadienide
- Potassium cyclopentadienyl