Metallocene

Article By:

Slocum, Donald W. Argonne National Laboratory, Argonne, Illinois.

Last reviewed:January 2020

DOI:https://doi.org/10.1036/1097-8542.419000

A bis-cyclopentadienyl derivative of a transition metal whose bonding involves overlap of ns, (n − 1)d, and np orbitals of the metal with molecular orbitals of appropriate symmetry of each cyclopentadienyl ring. The resulting complexes often possess two parallel rings (sandwich structure), but in some cases, for example those involving the titanium subgroup of metals, the rings are canted (Fig. 1). Numerous monocyclopentadienyl complexes (half-sandwich complexes) also exist, as do systems containing three and even four η⁵-bonded cyclopentadienyl rings; these latter systems are not metallocene complexes. Moreover, compounds constituted of parallel ring systems that are not both η⁵-bonding cyclopentadienyls (mixed-sandwich complexes) are not metallocene complexes. Metals in the periodic table commonly known to form metallocene complexes are titanium, zirconium, hafnium, vanadium, chromium, molybdenum, tungsten, manganese, iron, ruthenium, osmium, cobalt, rhodium, and nickel. See also: Coordination complexes

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