In organic chemistry, pentadienyl refers to the unsaturated five-carbon chain with the formula . Three versions are discussed, all formally derived from 1,4-or 1,3-pentadiene : pentadienyl radical with the formula pentadienyl anion with the formula , an approximate description of pentadienyl lithium and related species. pentadienyl cation with the formula , which is rarely invoked carbocation. The situation is closely related to the allyl () derivatives, which also are discussed in three states, being derived from propylene.
Production and structure Pentadienyl "anion" 1,4-or 1,3-Pentadiene can be deprotonated with butyl lithium, providing lithium pentadienyl.
Pentadienyl radical Pentadienyl radicals are intermediates in the degradation of 1,4-dienes, as found in some fats. Like the pentadienyl anions, the radicals are planar.
Organometallic chemistry In organometallic chemistry, the pentadienyl anion is a ligand, the acyclic analogue of the more-common cyclopentadienyl anion. The pentadienyl anion is generated by deprotonation of pentadiene. A number of complexes are known, including bis(pentadienyl) iron, , the "open" analog of ferrocene. Only few pentadienyl complexes feature simple ligands. More common is the dimethyl derivative 2,4-. Additionally, many pentadienyl ligands are cyclic, being derived from the addition of hydride to η6-arene complexes or hydride abstraction from cyclohexadiene complexes.
The first pentadienyl complex to be reported was derived from protonolysis of a complex of pentadienol:
Treatment of this cation with sodium borohydride gives the pentadiene complex:
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