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Nickelocene



Nickelocene
IUPAC name nickelocene
Other names Bis(cyclopentadienyl)nickel(II)
Identifiers
CAS number 1271-28-9]
RTECS number QR6500000
Properties
Molecular formula C10H10Ni
Molar mass 188.88 g/mol
Appearance Green crystals
Density  ? g/cm3, solid
Melting point

171-173 °C

Solubility in water insoluble
Structure
Coordination
geometry
D5h, D5d
Dipole moment 0 D
Hazards
Main hazards flammable
R-phrases 49-11-22-43
S-phrases 53-36/37/39-45
Related Compounds
Related compounds CoCp2, FeCp2
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)

Infobox disclaimer and references

Nickelocene is the chemical compound with the formula Ni(η5-C5H5)2. Also known as bis(cyclopentadienyl)nickel or NiCp2 this bright green paramagnetic solid is of enduring academic interest, although it has few real applications.

Additional recommended knowledge

Contents

Structure and bonding

Ni(C5H5)2 belongs to a group of organometallic compounds called metallocenes. Metallocenes usually adopt sandwich structures in which a metal ion is sandwiched between two parallel cyclopentadienyl rings, a structure which not only confers stability but also solubility in organic solvents and volatility (nickelocene readily sublimes under vacuum). In its crystalline form the molecule has D5h symmetry, in which the two rings adopt an eclipsed conformation.

The Ni center can be considered to have a 2+ charge, and the Cp rings are each considered to be a cyclopentadienyl anion (Cp-), related to cyclopentadiene by deprotonation (this structure is similar to ferrocene). In terms of its electronic structure, three pairs of d electrons on nickel are allocated to the three d orbitals involved in Ni - Cp bonding: dxy, dx2–y2, dz2. One of the two remaining d-electrons resides in each of the dyz and dxz orbitals, giving rise to the molecule's paramagnetism. Nickelocene, with 20 valence electrons, has the highest electron count of the transition metal metallocenes. Cobaltocene, Co(C5H5)2, is, however, a stronger reducing agent.

Preparation

Nickelocene was first prepared by E. O. Fischer in 1953, shortly after the discovery of ferrocene, the first metallocene compound. The modern synthesis entails treatment of anhydrous sources of NiCl2 with sodium cyclopentadienyl:

[Ni(NH3)6]Cl2 + 2 NaC5H5 → Ni(C5H5)2 + 2 NaCl + 6 NH3

Chemical properties

Like many organometallic compounds, Ni(C5H5)2 decomposes in air. Thus samples are typically stored cold and protected from air, although samples can tolerate exposure for several minutes without noticeable decomposition.

Most chemical reactions of nickelocene are characterized by its tendency to yield 18-electron products with loss or modification of one Cp ring.

Ni(C5H5)2 + 4 PF3 → Ni(PF3)4 + organic products

The reaction with secondary phosphines follows a similar pattern:

2 Ni(C5H5)2 + 2 PPh2H → [Ni2(PPh2)2(C5H5)2] + 2 C5H6

Nickelocene can be oxidized to the corresponding cation, which contains Ni(III).

Gaseous Ni(C5H5)2 decomposes to a Ni mirror upon contact with a hot surface, releasing the hydrocarbon ligands as gaseous coproducts. This process has been considered as a means of preparing Ni films.

References

     
    This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Nickelocene". A list of authors is available in Wikipedia.
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