Sodium cyclopentadienide
Encyclopedia
Sodium cyclopentadienide is an organosodium compound with the formula
C5H5Na. The compound is often abbreviated as NaCp or CpNa, where Cp− is the cyclopentadienide anion
. Cp is also used as an abbreviation for the cyclopentadienyl
ligand
in coordination chemistry.
. It is prepared by treating cyclopentadiene
with sodium
:
Commonly, the conversion is conducted by heating a suspension of molten sodium in dicyclopentadiene
. 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, was common. Sodium hydride
is a convenient base:
In early work, Grignard reagents were used as bases. With a pKa
of 15, cyclopentadiene can be deprotonated by many reagents.
The nature of NaCp depends strongly its medium and for the purposes of planning syntheses, the reagent is often represented as a salt Na+C5H5−. 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. 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.
s. For example, the preparation of ferrocene
and zirconocene dichloride
:
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....
C5H5Na. The compound is often abbreviated as NaCp or CpNa, where Cp− is the cyclopentadienide anion
Cyclopentadiene
Cyclopentadiene is an organic compound with the formula C5H6. This colorless liquid has a strong and unpleasant odor. At room temperature, this cyclic diene dimerizes over the course of hours to give dicyclopentadiene via a Diels–Alder reaction...
. Cp is also used as an abbreviation for the cyclopentadienyl
Cyclopentadienyl complex
A cyclopentadienyl complex is a metal complex with one or more cyclopentadienyl groups . Based on the type of bonding between the metals and the cyclopentadienyl]] moieties, cyclopentadienyl complexes are classified into the following three categories: a) π-complexes, b) σ-complexes, and c) ionic...
ligand
Ligand
In coordination chemistry, a ligand is an ion or molecule that binds to a central metal atom to form a coordination complex. The bonding between metal and ligand generally involves formal donation of one or more of the ligand's electron pairs. The nature of metal-ligand bonding can range from...
in coordination chemistry.
Preparation
Sodium cyclopentadienide is commercially available as a solution in THFTetrahydrofuran
Tetrahydrofuran is a colorless, water-miscible organic liquid with low viscosity at standard temperature and pressure. This heterocyclic compound has the chemical formula 4O. As one of the most polar ethers with a wide liquid range, it is a useful solvent. Its main use, however, is as a precursor...
. It is prepared by treating cyclopentadiene
Cyclopentadiene
Cyclopentadiene is an organic compound with the formula C5H6. This colorless liquid has a strong and unpleasant odor. At room temperature, this cyclic diene dimerizes over the course of hours to give dicyclopentadiene via a Diels–Alder reaction...
with sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
:
- 2 Na + 2 C5H6 → 2 NaC5H5 + H2HydrogenHydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
Commonly, the conversion is conducted by heating a suspension of molten sodium in dicyclopentadiene
Dicyclopentadiene
Dicyclopentadiene, abbreviated DCPD, is a chemical compound with formula C10H12. At room temperature, it is a white crystalline solid with a camphor-like odor. Its energy density is 10,975 Wh/l....
. 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
Xylene
Xylene encompasses three isomers of dimethylbenzene. The isomers are distinguished by the designations ortho- , meta- , and para- , which specify to which carbon atoms the two methyl groups are attached...
and rapidly stirring, was common. Sodium hydride
Sodium hydride
Sodium hydride is the chemical compound with the empirical formula NaH. It is primarily used as a strong base in organic synthesis. NaH is representative of the saline hydrides, meaning it is a salt-like hydride, composed of Na+ and H− ions, in contrast to the more molecular hydrides such as...
is a convenient base:
- NaH + C5H6 → NaC5H5 + H2
In early work, Grignard reagents were used as bases. With a pKa
Acid dissociation constant
An acid dissociation constant, Ka, is a quantitative measure of the strength of an acid in solution. It is the equilibrium constant for a chemical reaction known as dissociation in the context of acid-base reactions...
of 15, cyclopentadiene can be deprotonated by many reagents.
The nature of NaCp depends strongly its medium and for the purposes of planning syntheses, the reagent is often represented as a salt Na+C5H5−. 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
Bridging ligand
A bridging ligand is a ligand that connects two or more atoms, usually metal ions. The ligand may be atomic or polyatomic. Virtually all complex organic compounds can serve as bridging ligands, so the term is usually restricted to small ligands such as pseudohalides or to ligands that are...
-η5
Hapticity
The term hapticity is used to describe how a group of contiguous atoms of a ligand are coordinated to a central atom. Hapticity of a ligand is indicated by the Greek character 'eta', η. A superscripted number following the η denotes the number of contiguous atoms of the ligand that are bound to...
:η5-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
Adduct
An adduct is a product of a direct addition of two or more distinct molecules, resulting in a single reaction product containing all atoms of all components. The resultant is considered a distinct molecular species...
Na(tmeda)Cp.
Applications
Sodium cyclopentadienide is a common reagent for the preparation of metalloceneMetallocene
A metallocene is a compound typically consisting of two cyclopentadienyl anions bound to a metal center in the oxidation state II, with the resulting general formula 2M. Closely related to the metallocenes are the metallocene derivatives, e.g. titanocene dichloride, vanadocene dichloride...
s. For example, the preparation of ferrocene
Ferrocene
Ferrocene is an organometallic compound with the formula Fe2. It is the prototypical metallocene, a type of organometallic chemical compound consisting of two cyclopentadienyl rings bound on opposite sides of a central metal atom. Such organometallic compounds are also known as sandwich compounds...
and zirconocene dichloride
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:...
:
- 2 NaC5H5 + FeCl2 → Fe(C5H5)2 + 2 NaCl
- ZrCl4(thf)2 + 2 NaCp → Cp2ZrCl2 + 2 NaCl + 2 THF