- Iron pentacarbonyl
Chembox new
Name = Iron pentacarbonyl
ImageFileL1 = Fe(CO)5.png
ImageSizeL1 = 150px
ImageNameL1 = Iron carbonyl
ImageFileR1 = Iron-pentacarbonyl-3D-vdW.png
ImageSizeR1 = 120px
ImageNameR1 = Iron carbonyl
IUPACName = pentacarbonyliron(0)
OtherNames = Pentacarbonyl ironIron carbonyl
Section1 = Chembox Identifiers
CASNo = 13463-40-6
PubChem = 26040
SMILES =
Section2 = Chembox Properties
Formula = Fe(CO)5
MolarMass = 195.90 g/mol
Appearance = straw-yellow liquid
Density = 1.45 g/cm3
Solvent = other solvents
SolubleOther = organic solvents
MeltingPt = -20 °C
BoilingPt = 103 °C
Section3 = Chembox Structure
MolShape = trigonal bipyramidal
Coordination = trigonal bipyramidal
Dipole = 0 D
Section7 = Chembox Hazards
ExternalMSDS =
NFPA-H = 2
NFPA-R = 1 | NFPA-O =W
NFPA-F = 3Iron pentacarbonyl, also known as iron carbonyl, is the compound with formula iron(carbonoxygen)5. Under
standard conditions Fe(CO)5 is a free-flowing, straw-colored liquid with a pungent odour. This compound is a common precursor to diverse iron compounds, including many that are useful inorganic synthesis . [Samson, S. ; Stephenson, G. R. "Pentacarbonyliron" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. DOI: 10.1002/047084289.] Fe(CO)5 is prepared by the reaction of fineiron particles withcarbon monoxide . Fe(CO)5 is inexpensively purchased.Iron pentacarbonyl is one of the
homoleptic metal carbonyl s; i.e. metal complexes bonded only to CO ligands. Other examples include octahedral Cr(CO)6 andtetrahedral Ni(CO)4. Most metal carbonyls have 18 valence electrons, and Fe(CO)5 fits this pattern with 8 valence electrons on Fe and five pairs of electrons provided by the CO ligands. Reflecting its symmetrical structure and charge neutrality, Fe(CO)5 is volatile; it is one of the most frequently encountered liquid metal complexes. Fe(CO)5 adopts a trigonal bipyramidal structure with the Fe atom surrounded by five COligand s: three inequatorial positions and two axially bound. The Fe-C-O linkages are each linear.Fe(CO)5 is the archetypal
fluxional molecule due to the rapid interchange of the axial and equatorial CO groups via theBerry mechanism on the NMR timescale. Consequently, the13CNMR spectrum exhibits only one signal due to the rapid interchange between nonequivalent CO sites.Iron carbonyl is sometimes confused with
carbonyl iron , a high-purity metal prepared by decomposition of iron pentacarbonyl.ynthesis and other iron carbonyls
The compound was described in a journal by Mond and Langer in 1891 as "a somewhat viscous liquid of a pale-yellow colour.". [cite journal | author = Mond, L.; Langer, C. | title = On iron carbonyls | journal = J. Chem. Soc., Trans. | year = 1891 | volume = 59 | pages = 1090–1093 | doi = 10.1039/CT8915901090] Samples were prepared by treatment of finely divided, oxide-free iron powder with carbon monoxide at room temperature.
Photolysis of Fe(CO)5 produces Fe2(CO)9, a yellow-orange solid, also described by Mond. When heated, Fe(CO)5 converts to small amounts of the
metal cluster Fe3(CO)12, a green solid, although simple thermolysis is not a useful synthesis (see below). Each iron carbonyl exhibits distinct reactivity.Key reactions
CO substitution reactions
Thousands of compounds are derived from Fe(CO)5. Substitution of CO by
Lewis base s, L, to give derivatives Fe(CO)5-xLx. Common Lewis bases includeisocyanide s, tertiaryphosphine s andarsine s, andalkene s. Usually these ligands displace only one or two CO ligands, but certain acceptor ligands such as PF3 and isocyanides can proceed to tetra- and pentasubstitution. These reactions are often induced with a catalyst or light. [Therien, M. J. and Trogler, W. C., "Bis(phosphine) derivatives of iron pentacarbonyl and tetracarbonyl(tri-tert-butylphosphine)iron(0)", Inorganic Syntheses, 1990, 28, 173-9 (photochemical reactions).] Illustrative is the synthesis of the bis(triphenylphosphine) complex Fe(CO)3(P(C6H5)3)2. [Keiter, R. L.; Keiter, E. A.; Boecker, C. A.; Miller, D. R. and Hecker, K. H., "Tricarbonylbis(phosphine)iron(0) complexes", Inorganic Syntheses, 1997, 31, 210-214.] This transformation can be accomplished photochemically, but it is also induced by the addition of NaOH or NaBH4. The catalyst attacks a CO ligand, which labilizes another CO ligand toward substitution. The electrophilicity of Fe(CO)4L is less than that of Fe(CO)5, so the nucleophilic catalyst, disengages and attacks another molecule of Fe(CO)5.Oxidation and reduction
Most metal carbonyls can be halogenated. Thus, treatment of Fe(CO)5 with
halogen s gives the ferrous halides Fe(CO)4X2 for X = I, Br, Cl. These species, upon heating lose CO to give the ferrous halides, such asiron(II) chloride .Reduction of Fe(CO)5 with Na gives Na2Fe(CO)4, "tetracarbonylferrate" also called Collman's reagent. The dianion is isoelectronic with Ni(CO)4 but highly nucleophilic. [OrgSynth | author = Finke, R. G.; Sorrell, T. N. | title = Nucleophilic Acylation with Disodium Tetracarbonylferrate: Methyl 7-Oxoheptanoate and Methyl 7-oxooctonoate | collvol = 6 | collvolpages = 807 | prep = cv6p0807]
Acid-base reactions
Fe(CO)5 is not readily protonated, but it is attacked by
hydroxide . Treatment of Fe(CO)5 with aqueous base produces [HFe(CO)4] -, the oxidation of which gives Fe3(CO)12. Acidification of solutions of [HFe(CO)4] - gives H2Fe(CO)4, the first metal hydride ever reported.Diene adducts
Dienes react with Fe(CO)5 to give (diene)Fe(CO)3, wherein two CO ligands have been replaced by two olefins. Many dienes undergo this reaction, notably
norbornadiene and1,3-butadiene . One of the more historically significant derivatives iscyclobutadieneiron tricarbonyl (C4H4)Fe(CO)3, where C4H4 is the otherwise unstablecyclobutadiene . [OrgSynth | author = Pettit, R.; Henery, J. | title = Cyclobutadieneiron Tricarbonyl | collvol = 6 | collvolpages = 310 | prep = cv6p0310] Receiving the greatest attention are complexes of the cyclohexadienes, the parent organic 1,4-dienes being available through theBirch reduction s. 1,4-Dienes isomerize to the 1,3-dienes upon complexation. [OrgSynth | author = Birch, A. J.; Chamberlain, K. B. | title =Tricarbonyl [(2,3,4,5-eta)-2,4-Cyclohexadien-1-one] ison and Tricarbonyl [(1,2,3,4,5-eta)-2-Methoxy-2,4-Cyclohexadien-1-yl] Iron(1+) Hexafluorophosphate(1-) from Anisole | collvol = 6 | collvolpages = 996 | prep = cv6p0996]Fe(CO)5 reacts in
dicyclopentadiene to form [Fe(C5H5)(CO)2] 2,cyclopentadienyliron dicarbonyl dimer . This compound, called "Fp dimer" can be considered a hybrid offerrocene and Fe(CO)5, although in terms of its reactivity, it resembles neither.Other uses
In
Europe , iron pentacarbonyl was once used as ananti-knock agent inpetrol in place oftetraethyllead . Two more modern alternative fuel additives areferrocene and methylcyclopentadienyl manganese tricarbonyl. Fe(CO)5 is used in the production of "carbonyl iron ", a finely divided form of Fe, a material used inmagnetic core s of high-frequencycoil s forradio s andtelevision s and for manufacture of the active ingredients of someradar absorbent material s (e.g.iron ball paint ). It is famous as a chemical precursor for the synthesis of various iron-basednanoparticle s.Iron pentacarbonyl has been found to be a strong flame speed inhibitor in oxygen based flames. [Citation
last = Lask
first = G.
last2 = Wagner
first2 = H. Gg.
title = Influence of additives on the velocity of laminar flames
journal = Eighth International Symposium on Combustion
volume =
issue =
pages = 432–438
date =
year = 1962
url =
doi =
id = ] Few hundred ppm of iron pentacarbonyl are known to reduce the flame speed ofstoichiometric methane -air flame by al most 50%. However due to its toxic nature it has not been used widely as flame retardant.Toxicity and hazards
Fe(CO)5 is toxic, which is of concern because of its volatility (vapour pressure: 21 mmHg at 20 °C). If
inhale d, iron pentacarbonyl may cause lung irritation,toxic pneumonitis , orpulmonary edema . Like other metal carbonyls, Fe(CO)5 isflammable . It is, however, considerably less toxic thannickel tetracarbonyl .References
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