Sodium cyclopentadienide is an
organosodium compound
Organosodium chemistry is the chemistry of organometallic compounds containing a carbon to sodium chemical bond. The application of organosodium compounds in chemistry is limited in part due to competition from organolithium compounds, which are co ...
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 betwee ...
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
Tetrahydrofuran (THF), or oxolane, is an organic compound with the formula (CH2)4O. The compound is classified as heterocyclic compound, specifically a cyclic ether. It is a colorless, water-miscible organic liquid with low viscosity. It is ma ...
. It is prepared by treating cyclopentadiene
Cyclopentadiene is an organic compound with the chemical formula, 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 ab ...
with sodium:
:
The conversion can be conducted by heating a suspension of molten sodium in dicyclopentadiene.[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 and rapidly stirring.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 metallocenes. 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, a ...
and zirconacene dichloride:[ and zirconocene dichloride:
:
:
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
1,1'-Ferrocenedicarboxylic acid is the organoiron compound with the formula . It is the simplest dicarboxylic acid derivative of ferrocene. It is a yellow solid that is soluble in aqueous base. The 1,1' part of its name refers to the location of ...
.
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
In organometallic chemistry, a sandwich compound is a chemical compound featuring a metal bound by haptic, covalent bonds to two arene (ring) ligands. The arenes have the formula , substituted derivatives (for example ) and heterocyclic derivat ...
, 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 Na(tmeda
Tetramethylethylenediamine (TMEDA or TEMED) is a chemical compound with the formula (CH3)2NCH2CH2N(CH3)2. This species is derived from ethylenediamine by replacement of the four amine hydrogens with four methyl groups. It is a colorless liquid, ...
)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
Lithium cyclopentadienide is an organolithium compound with the formula C5H5Li. The compound is often abbreviated as LiCp, where Cp− is the cyclopentadienide anion. Lithium cyclopentadienide is a colorless solid, although samples often are p ...
References
{{Cyclopentadiene complexes
Organosodium compounds
Cyclopentadienyl complexes
Non-benzenoid aromatic carbocycles