Metallocene

Name:
Metallocene
Detailed information:
An organometallic coordination compound obtained as a cyclopentadienyl derivative of a transition metal or metal halide. The metal is bonded to the cyclopentadienyl ring by electrons moving in orbitals extending above and below the plane of the ring (pi bond). There are three types of metallocenes: (1) dicyclopentadienyl-metals with the general formula (C₅H₅)₂M, (2) dicyclopentadienyl-metal halides with the general formula (C₅H₅)₂MX_1-3, (3) monocyclopentadienyl-metal compounds with the general formula C₅H₅MR_1-3, where R is CO, NO, halide group, alkyl group, etc. Types (1) and (2) are known as molecular sandwiches since the two cyclopentadiene rings lie above and below the plane on which the metal atom is situated.Most metallocenes are crystalline and those belonging to the first transition series of the periodic table, from vanadium to nickel, have the same melting point, 173C. The metal complexes are soluble in many organic solvents while the halides are soluble primarily in polar solvents. When the central metal atom is in a stable oxidation state the metallocene is not decomposed by high temperature, air, water, dilute acids, or bases.Some metallocenes, such as ferrocene, undergo a wide variety of aromatic ring substitution reactions, including Friedel-Crafts acylation, arylation, and sulfonation; a few such as nickelocene and cobaltocene are too unstable to be directly substituted.

Derivation:

The most important industrial method is the reaction of a cyclopentadienide (for example the sodium salt) with a transition metal halide in an organic solvent.

Use:

Catalysts, polymers, UV absorbers, reducing agents, free radical scavengers, antiknock agents.

See Ferrocene; Cobaltocene; Nickelocene; Titanocene Dichloride; Zirconocene Dichloride; Uranocene.