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
[edit]Pentadienyl "anion"
[edit]1,4-or 1,3-Pentadiene can be deprotonated with butyl lithium, providing lithium pentadienyl.[1]
Pentadienyl radical
[edit]Pentadienyl radicals are intermediates in the degradation of 1,4-dienes, as found in some fats. Like the pentadienyl anions, the radicals are planar.[2]
Organometallic chemistry
[edit]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.[3][4]
The first pentadienyl complex to be reported was derived from protonolysis of a complex of pentadienol:[5]
- 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
[edit]- ↑ 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. |