Pentadienyl

In organic chemistry, pentadienyl refers to the unsaturated five-carbon chain with the formula C₅H₇. Three versions are discussed, all formally derived from 1,4-or 1,3-pentadiene C₅H₈:

pentadienyl radical with the formula H₂CCHCHCHCH₂
pentadienyl anion with the formula H₂CCHCHCHCH−2, an approximate description of pentadienyl lithium and related species.
pentadienyl cation with the formula H₂CCHCHCHCH+2, which is rarely invoked carbocation.

The situation is closely related to the allyl (C₃H₅) 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, Fe(C₅H₇)₂, the "open" analog of ferrocene. Only few pentadienyl complexes feature simple C₅H₇ ligands. More common is the dimethyl derivative 2,4-Me₂C₅H₅. 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:

Fe(C₅H₇OH)(CO)₃ + H⁺ → [Fe(C₅H₇)(CO)₃]⁺ + H₂O

Treatment of this cation with sodium borohydride gives the pentadiene complex:

[Fe(C₅H₇)(CO)₃]⁺ + H⁻ → Fe(C₅H₈)(CO)₃

References

↑ Seyferth, Dietmar; Pornet, Jacques (1980). "(2,4-Pentadienyl)trimethylsilane: A useful pentadienylation reagent". The Journal of Organic Chemistry. 45 (9): 1721–1722. doi:10.1021/jo01297a053.
↑ Smith, Michael B.; March, Jerry (2007), Advanced Organic Chemistry: Reactions, Mechanisms, and Structure (6th ed.), New York: Wiley-Interscience, ISBN 978-0-471-72091-1
↑ Lothar Stahl; Richard D. Ernst (2007). "Pentadienyl Complexes of the Group 4 Transition Metals". Advances in Organometallic Chemistry. 55: 137–199. doi:10.1016/S0065-3055(07)55003-3. ISBN 978-0-12-373978-0.{{cite journal}}: CS1 maint: periodical has ISBN (link)
↑ Richard D. Ernst (1988). "Structural and reactivity patterns in transition-metal-pentadienyl chemistry". Chem. Rev. 88 (7): 1255–1291. doi:10.1021/cr00089a013.
↑ Mahler, J. E.; Pettit, R. (1962). "Pentadienyl and Hexadienyl Carbonium Ions as Ligands in Stable Complex Cations". J. Am. Chem. Soc. 84 (8): 1511–1512. doi:10.1021/ja00867a051.

This article about a hydrocarbon is a stub. You can help Wikipedia by adding missing information.

[1] Seyferth, Dietmar; Pornet, Jacques (1980). "(2,4-Pentadienyl)trimethylsilane: A useful pentadienylation reagent". The Journal of Organic Chemistry. 45 (9): 1721–1722. doi:10.1021/jo01297a053.

[2] Smith, Michael B.; March, Jerry (2007), Advanced Organic Chemistry: Reactions, Mechanisms, and Structure (6th ed.), New York: Wiley-Interscience, ISBN 978-0-471-72091-1

[3] Lothar Stahl; Richard D. Ernst (2007). "Pentadienyl Complexes of the Group 4 Transition Metals". Advances in Organometallic Chemistry. 55: 137–199. doi:10.1016/S0065-3055(07)55003-3. ISBN 978-0-12-373978-0.{{cite journal}}: CS1 maint: periodical has ISBN (link)

[4] Richard D. Ernst (1988). "Structural and reactivity patterns in transition-metal-pentadienyl chemistry". Chem. Rev. 88 (7): 1255–1291. doi:10.1021/cr00089a013.

[5] Mahler, J. E.; Pettit, R. (1962). "Pentadienyl and Hexadienyl Carbonium Ions as Ligands in Stable Complex Cations". J. Am. Chem. Soc. 84 (8): 1511–1512. doi:10.1021/ja00867a051.