Sodium cyclopentadienide is an
organosodium compound with the
formula
In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a '' chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betw ...
C
5H
5Na. The compound is often abbreviated as NaCp, where Cp
− is the cyclopentadienide anion. Sodium cyclopentadienide is a colorless solid, although samples often are pink owing to traces of oxidized impurities.
[
]
Preparation
Sodium cyclopentadienide is commercially available as a solution in THF. It is prepared by treating cyclopentadiene
Cyclopentadiene is an organic compound with the formula C5H6.LeRoy H. Scharpen and Victor W. Laurie (1965): "Structure of cyclopentadiene". ''The Journal of Chemical Physics'', volume 43, issue 8, pages 2765-2766. It is often abbreviated CpH bec ...
with sodium
Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable ...
:
:
The conversion can be conducted by heating a suspension of molten sodium in dicyclopentadiene
Dicyclopentadiene, abbreviated DCPD, is a chemical compound with formula C10H12. At room temperature, it is a white brittle wax, although lower purity samples can be straw coloured liquids. The pure material smells somewhat of soy wax or campho ...
.[Tarun K. Panda, Michael T. Gamer, Peter W. Roesky "An Improved Synthesis of Sodium and Potassium Cyclopentadienide" Organometallics, 2003, 22, 877–878.] 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
In organic chemistry, xylene or xylol (; IUPAC name: dimethylbenzene) are any of three organic compounds with the formula . They are derived from the substitution of two hydrogen atoms with methyl groups in a benzene ring; which hydrogens are ...
and rapidly stirring.Sodium hydride
Sodium hydride is the chemical compound with the empirical formula Na H. This alkali metal hydride is primarily used as a strong yet combustible base in organic synthesis. NaH is a saline (salt-like) hydride, composed of Na+ and H− ions, in c ...
is a convenient base:
:
In early work, Grignard reagent
A Grignard reagent or Grignard compound is a chemical compound with the general formula , where X is a halogen and R is an organic group, normally an alkyl or aryl. Two typical examples are methylmagnesium chloride and phenylmagnesium bromide ...
s were used as bases. With a p''K''a of 15, cyclopentadiene can be deprotonated by many reagents.
Applications
Sodium cyclopentadienide is a common reagent for the preparation of metallocene
A metallocene is a compound typically consisting of two cyclopentadienyl anions (, abbreviated Cp) bound to a metal center (M) in the oxidation state II, with the resulting general formula Closely related to the metallocenes are the metallocene d ...
s. For example, the preparation of ferrocene
Ferrocene is an organometallic compound with the formula . The molecule is a complex consisting of two cyclopentadienyl rings bound to a central iron atom. It is an orange solid with a camphor-like odor, that sublimes above room temperature, ...
and zirconacene dichloride:[ and ]zirconocene dichloride
Zirconocene dichloride is an organozirconium compound composed of a zirconium central atom, with two cyclopentadienyl and two chloro ligands. It is a colourless diamagnetic solid that is somewhat stable in air.
Preparation and structure
Zircon ...
:
:
:
Sodium cyclopentadienide is also used for the preparation of substituted cyclopentadienyl derivatives such as the ester and formyl derivatives:
:
These compounds are used to prepare substituted metallocenes such as 1,1'-ferrocenedicarboxylic acid.
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 . 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''- ''η''5:''η''5-C5H5 ligands. As a solution in donor solvents, NaCp is highly solvated, especially at the alkali metal as suggested by the isolability of the adduct
An adduct (from the Latin ''adductus'', "drawn toward" alternatively, a contraction of "addition product") is a product of a direct addition of two or more distinct molecules, resulting in a single reaction product containing all atoms of all co ...
Na( tmeda)Cp.
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°.
See also
* Lithium cyclopentadienide
References
{{Cyclopentadiene complexes
Organosodium compounds
Cyclopentadienyl complexes
Non-benzenoid aromatic carbocycles