cyclopentadienyl
Noun
Meaning
cyclopentadienyl (plural cyclopentadienyls)
(organic chemistry) The univalent anion derived from cyclopentadiene; contains a ring of delocalized electrons; forms metallocene compounds with transition metals.
Examples
According to the IUPAC definition, a metallocene contains a transition metal and two cyclopentadienyl ligands coordinated in a sandwich structure, i.e., the two cyclopentadienyl anions are on parallel planes with equal bond lengths and strengths.
Ansa-metallocenes are derivatives of metallocenes with an intramolecular bridge between the two cyclopentadienyl rings.
In the structure shown at right, the two pentagons are the cyclopentadienyl anions with circles inside them indicating they are aromatically stabilized.
Like indium, thallium cyclopentadienyl compounds contain thallium(I), in contrast to gallium(III).
Organoberkelium compounds Berkelium forms a trigonal (η 5 –C 5 H 5 ) 3 Bk metallocene complex with three cyclopentadienyl rings, which can be synthesized by reacting berkelium(III) chloride with the molten beryllocene ( Be (C 5 H 5 ) 2 ) at about 70 °C.
In metallocenes of the type (C 5 R 5 ) 2 M, the cyclopentadienyl rings rotate with very low barriers.