5.svg) | |
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| Names | |
|---|---|
| IUPAC name Pentacarbonyliron(0) | |
| Other names Pentacarbonyl iron Iron carbonyl | |
| Identifiers | |
3D model (JSmol) | |
| ChEBI | |
| ChemSpider |
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| ECHA InfoCard | 100.033.323 |
| RTECS number |
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| UNII | |
| UN number | 1994 |
| |
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| Properties | |
| Fe(CO)5 | |
| Molar mass | 195.90 g/mol |
| Appearance | straw-yellow to brilliant orange liquid |
| Odor | musty |
| Density | 1.453 g/cm3 |
| Melting point | −21.0 °C (−5.8 °F; 252.2 K) |
| Boiling point | 103 °C (217 °F; 376 K) |
| Insoluble | |
| Solubility | Soluble in organic solvents slightly soluble inalcohol insoluble inammonia |
| Vapor pressure | 40 mmHg (30.6 °C)[1] |
Refractive index (nD) | 1.5196 (20 °C) |
| Structure | |
| D3h | |
| trigonal bipyramidal | |
| trigonal bipyramidal | |
| 0D | |
| Hazards | |
| Occupational safety and health (OHS/OSH): | |
Main hazards | Very toxic, highly flammable |
| GHS labelling: | |
   | |
| NFPA 704 (fire diamond) | |
| Flash point | −15 °C (5 °F; 258 K) |
| 49 °C (120 °F; 322 K) | |
| Explosive limits | 3.7–12.5% |
| Lethal dose or concentration (LD, LC): | |
LD50 (median dose) | 25 mg/kg (rat, oral) |
| NIOSH (US health exposure limits): | |
PEL (Permissible) | none[1] |
REL (Recommended) | TWA 0.1 ppm (0.23 mg/m3) ST 0.2 ppm (0.45 mg/m3)[1] |
IDLH (Immediate danger) | 0.4 ppm[1] |
| Safety data sheet (SDS) | ICSC 0168 |
| Related compounds | |
Related compounds |
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Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Iron pentacarbonyl, also known asiron carbonyl, is thecompound withformulaFe(CO)5. Understandard conditions Fe(CO)5 is a free-flowing, straw-colored liquid with a pungent odour. Older samples appear darker. This compound is a common precursor to diverse iron compounds, including many that are useful in small scaleorganic synthesis.[2]
Iron pentacarbonyl is ahomolepticmetal carbonyl, wherecarbon monoxide is the only ligandcomplexed with a metal. Other examples include octahedralchromium hexacarbonyl (Cr(CO)6) andtetrahedralnickel carbonyl (Ni(CO)4). Most metal carbonyls have18 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 isvolatile; 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 COligands: three inequatorial positions and two axially bound. The Fe–C–O linkages are each linear.
Fe(CO)5 exhibits a relatively low rate of interchange between the axial and equatorial CO groups via theBerry mechanism.[3] It is characterized by two intense νCO bands in the IR spectrum at 2034 and 2014 cm−1 (gas phase).[4]
Fe(CO)5 is produced by the reaction of fineiron particles withcarbon monoxide. The compound was described in a journal byMond and Langer in 1891 as "a somewhat viscous liquid of a pale-yellow colour."[5] Samples were prepared by treatment of finely divided, oxide-free iron powder with carbon monoxide at room temperature.
Industrial synthesis of the compound requires relatively high temperatures and pressures (e.g. 175atm at 150 °C)[6] as well as specialized, chemically resistant equipment (e.g. composed of copper-silveralloys). Preparation of the compound at the laboratory scale avoids these complications by using aniodideintermediate:[6]
The industrial production of this compound is somewhat similar to theMond process in that the metal is treated with carbon monoxide to give a volatile gas. In the case of iron pentacarbonyl, the reaction is more sluggish. It is necessary to use iron sponge as the starting material, and harsher reaction conditions of 5–30 MPa of carbon monoxide and 150–200 °C. Similar to the Mond process, sulfur acts as a catalyst. The crude iron pentacarbonyl is purified by distillation.Ullmann's Encyclopedia of Industrial Chemistry reports that there are only three plants manufacturing pentacarbonyliron;BASF in Germany andAmerican Carbonyl in Alabama have capacities of 9000 and 1500–2000 tonnes/year respectively.[7]
Most iron pentacarbonyl produced is decomposed on site to give purecarbonyl iron in analogy tocarbonyl nickel. Some iron pentacarbonyl is burned to give pureiron oxide. Other uses of pentacarbonyliron are small in comparison.[7]
Many compounds are derived from Fe(CO)5 by substitution of CO byLewis bases, L, to give derivatives Fe(CO)5−xLx. Illustrative is the synthesis of thebis(triphenylphosphine)iron tricarbonyl complex (Fe(CO)3(P(C6H5)3)2).[8] Common Lewis bases includeisocyanides, tertiaryphosphines andarsines, andalkenes. 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.[9] In addition to the photochemical route, substitution can also induced by NaOH orNaBH4. 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.
Irradiation of Fe(CO)5 with UV produces Fe(CO)4, which captures a variety of ligands to give adducts.[10] Specifically, excitation of the metal-to-COcharge-transfer band induces COphotolysis, generating singlet and triplet coordinatively-unsaturated Fe(CO)4 with high quantum yield. Prolonged irradiation in gas phase may proceed to further CO detach until atomic Fe formation.[11] In the absence of trapping substrates,Fe2(CO)9 is produced.[10]
Most metal carbonyls can be halogenated. Thus, treatment of Fe(CO)5 withiodine givesiron tetracarbonyl diiodide:
Reduction of Fe(CO)5 with Na givesNa2Fe(CO)4, "tetracarbonylferrate" also called Collman's reagent. The dianion is isoelectronic with Ni(CO)4 but highlynucleophilic.[12]
Fe(CO)5 is not readilyprotonated, but it is attacked byhydroxide. Treatment of Fe(CO)5 with aqueous base produces[HFe(CO)4]−, via themetallacarboxylate intermediate. Theoxidation of this monoanion givestriiron dodecacarbonyl, Fe3(CO)12. Acidification of solutions of [HFe(CO)4]− givesiron tetracarbonyl dihydride, H2Fe(CO)4.
Likewise, Fe(CO)5 reacts withHgSO4 to give the polymer [HgFe(CO)4]n.[13]
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, e.g.norbornadiene and1,3-butadiene. One of the more historically significant derivatives iscyclobutadieneiron tricarbonyl (C4H4)Fe(CO)3, where C4H4 is the otherwise unstablecyclobutadiene.[14]
Fe(CO)5 reacts indicyclopentadiene 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.
InEurope, iron pentacarbonyl was once used as ananti-knock agent inpetrol in place oftetraethyllead; it was produced byIG Farben and commercially marketed under the trade names, “Motolin” and “Monopolin”.[15] Two more modern alternative fuel additives areferrocene andmethylcyclopentadienyl manganese tricarbonyl. Fe(CO)5 is used in the production of "carbonyl iron", a finely divided form of Fe, a material used inmagnetic cores of high-frequency coils forradios andtelevisions and for manufacture of the active ingredients of someradar absorbent materials (e.g.iron ball paint). It is famous as a chemical precursor for the synthesis of various iron-basednanoparticles.
Iron pentacarbonyl has been found to be a strongflame speed inhibitor in oxygen based flames.[16] A few hundred ppm of iron pentacarbonyl are known to reduce theflame speed ofstoichiometricmethane–air flame by almost 50%. However due to its toxic nature it has not been used widely as aflame retardant.
Fe(CO)5 is toxic, which is of concern because of its volatility (vapour pressure: 21 millimetres of mercury (2.8 kPa) at 20 °C). Ifinhaled, 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.
TheNational Institute for Occupational Safety and Health has set arecommended exposure limit for iron pentacarbonyl at 0.1 ppm (0.23 mg/m3) over an eight-hour time-weighted average, and ashort-term exposure limit at 0.2 ppm (0.45 mg/m3).[17]
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