Disodium Tetracarbonylferrate(-II)1

Na2Fe(CO)4
(Na2Fe(CO)4)

[14878-31-0]  · C4FeNa2O4  · Disodium Tetracarbonylferrate(-II)  · (MW 213.87) (Na2Fe(CO)4.1.5(1,4-dioxane))

[59733-73-2] (K2Fe(CO)4)

[16182-63-1]  · C4FeK2O4  · Dipotassium Tetracarbonylferrate(-II)  · (MW 246.09) ([Fe(CO)4]2-)

[22321-35-3]  · C4FeO4  · Disodium Tetracarbonylferrate(-II)  · (MW 167.89)

(carbonylating agent for halides, producing aldehydes and ketones;1 hydroacylates Michael acceptors;2 forms cyclic ketones from b- and g-haloalkenes;3 selectively reduces unsaturations a to a carbonyl;4 catalyst for dismutation of aromatic aldehydes to esters;5 produces [(h4-diene)Fe(CO)3] complexes via nucleophilic displacement6)

Physical Data: mp (K+2 salt) 270-273 °C (dec).

Solubility: sol THF, DMF, N-methylpyrrolidone (NMP), EtOH.

Form Supplied in: colorless to red solid; commercially available as 1:1.5 complex with 1,4-dioxane.

Preparative Methods: preparations of the sodium salt-dioxane complex7 and of the free sodium8 and potassium9 salts of tetracarbonylferrate have been published.

Handling, Storage, and Precautions: Na2Fe(CO)4 is very air sensitive and is pyrophoric. The solid is stable over moderately long periods of time under inert atmosphere at rt, if kept in the dark. The potassium salt is also air sensitive but is not pyrophoric. These materials are best stored and handled in a nitrogen or argon filled dry box. Tetracarbonylferrate is considered to be a neural, renal, and hepatic toxin and is a cancer suspect agent.

Carbonylation Reactions.

The tetracarbonylferrate dianion is a potent nucleophile. Its principal use is in the functionalization of halide compounds. Although Na2Fe(CO)4 does not enjoy the widespread popularity of its main group rival, the Grignard reagent, it does have the advantage of usually adding a carbonyl group to the substrate. Tetracarbonylferrate typically reacts readily with alkyl halides or tosylates (RX) at rt to generate RFe(CO)4-, a useful synthetic intermediate. The reaction proceeds with stereochemical inversion and is typically carried out in THF. However, more polar solvents, such as NMP, DMF, or N,N-dimethylacetamide (DMA) are often used to help decrease Na2Fe(CO)4 ion-pairing and hence accelerate the rate of reaction with less reactive substrates, such as alkyl chlorides. The formation of the alkyltetracarbonylferrate has been shown to fail on occasion, however. For example, when a b-lactam functionality is present, reductive ring opening occurs.10 Acylferrates, RCOFe(CO)3L- (L = CO, PPh3), may be prepared either by reaction of Fe(CO)42- with an acid halide or, more commonly, by migratory insertion through reaction of Fe(CO)42- with RX in the presence of CO or PPh3. The chemistry of RCOFe(CO)3L- in many cases is similar to that of RFe(CO)4- (eq 1), since the latter is subject to carbonyl insertion. Both produce unsymmetrical ketones upon addition of a second alkyl halide reagent.11-13

The utility of this chemistry has been enhanced (eq 2) through the use of catalytic Pd0. Aryl iodides oxidatively add to palladium and transmetalation occurs, opening a single-step route to aryl ketones.14 Alkyl- or acylferrates, when treated with oxygen (eq 1) followed by acidic workup, are converted to acids, allowing the overall transformation of RX to RCO2H.15

Similarly, the use of halogen gives acid halides, which are converted in situ to amides, esters, or acids. The acylferrates will react in situ with acid to produce aldehydes12 and are subject to CuI coupling, giving symmetrical a-diketones, RCOCOR.16 Tetracarbonylferrate may be used to produce cyclopentanones from d-dibromides (eq 3).17 However the formation of six- and seven-membered rings suffers from low yields.

Alkyl- and acyltetracarbonylferrates are susceptible to alkene insertion reactions. This phenomenon was initially recognized through the single-step preparation of alkyl ethyl ketones from RX, ethylene, and Fe(CO)42-.18 Later, reactions between these ferrates and various Michael acceptor alkenes were uncovered.2 Precursors to jasmone and g-jasmolactone have been produced (eq 4). Allenes insert into RFe(CO)4- to give [(h4-hydroxytrimethylenemethane)Fe(CO)3] complexes, which thermally rearrange to [(h4-enone)Fe(CO)3] complexes.19 Ethylene Oxide also inserts into the iron-acyl bond in RCOFe(CO)4-, giving an unisolated b-hydroxy ketone, which dehydrates to an a,b-unsaturated ketone.20 Yields of 60-80% are found. Cyclizations may be accomplished via alkene insertion. Cyclopentanones and cyclohexanones are produced by the tetracarbonylferrate treatment of monosubstituted alkenes bearing a b- or g-halide.1,3,21,22 The less hindered product prevails. 5-Bromo-1,2-pentadiene cyclizes to 2-methylcyclopenten-3-one. These cyclization reactions, which are carried out in THF with an acid workup, generally give moderate yields (30-75%); nevertheless some of the higher yields are found for the synthesis of the spirocyclic ketones which are otherwise accessible only with difficulty.

Reduction Reactions.

Tetracarbonylferrate more commonly functions as a nucleophile than as a reducing agent. Nevertheless, several valuable transformations involving selective reduction have been demonstrated. The most desirable of these allows reduction of an unsaturated group a to a carbonyl. The key step in the synthesis of 9,10-dihydroretinal (the reduction of the conjugated 9,10-alkene) was accomplished (eq 5) with the use of Fe(CO)42-.4 However, as illustrated, there is some tendency toward simultaneous reduction of the carbonyl group. The ability to reduce carbonyls mildly is exploited in the synthesis of cis-caronaldehyde (eq 6).23

More typically acid anhydrides are reduced to aldehydes (or occasionally to acids) by Na2Fe(CO)4 in THF.24 Intramolecular anhydrides produce aldehydic acids. Tetracarbonylferrate functions as a catalyst in the high yield dismutation of aromatic aldehydes.5 A plausible mechanism is presented (eq 7). The complex resulting from nucleophilic attack of Fe(CO)42- on RCHO is apparently sufficiently nucleophilic itself to attack another molecule of aldehyde. The aldehyde complex can also be partially alkylated in a competitive stoichiometric process. However, this reaction does not appear to be efficient enough to be of synthetic value. Alkyl- or acyltetracarbonylferrates give reductive coupling products with nitroaromatics.25 Upon reaction with nitrobenzene, they produce N-phenylamides.

Other Nucleophilic Substitutions.

The Fe(CO)42- anion forms S-bound complexes with nonenolizable thioketones.26 These can be acylated at the sulfur to produce thioesters. However, thioketones bearing enolizable protons are deprotonated by Fe(CO)42-. 1,1-Cyclopropanedicarboxylates are ring opened by tetracarbonylferrate to produce stabilized carbanions (eq 8).27 Alkylation may then be carried out at both ends of the dianion. Tetracarbonylferrate will also displace chloride from [(h6-C6H5Cl)Cr(CO)3].28 A variety of [(h4-1,3-diene)Fe(CO)3] complexes are accessible through the reaction of 1-methylallylic halides or phosphates with K2Fe(CO)4.6 Nevertheless, the direct synthesis of these complexes from the diene and Pentacarbonyliron or Nonacarbonyldiiron remains the preferred route.


1. (a) Collman, J. P. ACR 1975, 8, 342. (b) Collman, J. P.; Finke, R. G.; Cawse, J. N.; Brauman, J. I. JACS 1977, 99, 2515. (c) Collman, J. P.; Finke, R. G.; Cawse, J. N.; Brauman, J. I. JACS 1978, 100, 4766.
2. (a) Cooke, M. P., Jr.; Parlman, R. M. JACS 1977, 99, 5222. (b) Yamashita, M.; Tashika, H.; Suemitsu, R. CL 1989, 691. (c) Yamashita, M.; Tashika, H.; Uchida, M. BCJ 1992, 65, 1257.
3. McMurray, J. E.; Andrus, A. TL 1980, 21, 4687.
4. Arnaboldi, M.; Motto, M. G.; Tsujimoto, K.; Balogh-Nair, V.; Nakanishi, K. JACS 1979, 101, 7082.
5. Yamashita, M.; Watanabe, Y.; Mitsudo, T.; Takegami, T. BCJ 1976, 49, 3597.
6. (a) Butsugan, Y.; Yamashita, A.; Araki, S. JOM 1985, 287, 103. (b) Kerber, R. C.; Ribakove, E. C. OM 1991, 10, 2848.
7. Finke, R. G.; Sorrell, T. N. OS 1980, 59, 102.
8. (a) Strong, H.; Krusic, P. J., San Filippo, J., Jr. Inorg. Synth. 1986, 24, 157. (b) Strong, H.; Krusic, P. J., San Filippo, J., Jr., Inorg. Synth. 1990, 28, 203. (c) Devasagayaraj, A.; Periasamy, M. Transition Met. Chem. 1991, 16, 503.
9. Gladysz, J. A.; Tam, W. JOC 1978, 43, 2279.
10. Durst, T.; Georg, G. JOC 1983, 48, 2092.
11. Collman, J. P.; Winter, S. R.; Clark, D. R. JACS 1972, 94, 1788.
12. Cooke, M. P., Jr. JACS 1970, 92, 6080.
13. Sabo-Etienne, S.; Larsonneur, A.-M.; des Abbayes, H. CC 1989, 1671.
14. Koga, T.; Makinouchi, S.; Okukado, N. CL 1988, 1141.
15. Collman, J. P.; Winter, S. R.; Komoto, R. G. JACS 1973, 95, 249.
16. Devasagayaraj, A.; Periasamy, M., TL 1992, 33, 1227.
17. Yamashita, M.; Uchida, M.; Tashika, H.; Suemitsu, R. BCJ 1989, 62, 2728.
18. Cooke, M. P., Jr.; Parlman, R. M. JACS 1975, 97, 6863.
19. Roustan, J. L.; Guinot, A.; Cadiot, P. JOM 1980, 194, 367.
20. Yamashita, M.; Yamamura, S.; Kurimoto, M.; Suemitsu, R. CL 1979, 1067.
21. McMurry, J. E.; Andrus, A.; Ksander, G. M.; Musser, J. H.; Johnson, M. A. JACS 1979, 101, 1330.
22. Mérour, J. Y.; Roustan, J. L.; Charrier, C.; Collin, J. JOM 1973, 51, C24.
23. Liu, B. SC 1991, 21, 1577.
24. (a) Watanabe, Y.; Yamashita, M.; Mitsudo, T.; Tanaka, M.; Takegami, Y. TL 1973, 3535. (b) Watanabe, Y.; Yamashita, M.; Mitsudo, T.; Igami, M.; Takegami, Y. BCJ 1975, 48, 2490.
25. (a) Yamashita, M.; Watanabe, Y.; Mitsudo, T.; Takegami, Y. TL 1976, 1585. (b) Watanabe, Y.; Taniguchi, K.; Suga, M.; Mitsudo, T.; Takegami, Y. BCJ 1979, 52, 1869.
26. Alper, H.; Marchand, B.; Tanaka, M. CJC 1979, 57, 598.
27. Tamblyn, W. H.; Waltermire, R. E. TL 1983, 24, 2803.
28. (a) Heppert, J. A.; Thomas-Miller, M. E.; Swepston, P. N.; Extine, M. W. CC 1988, 280. (b) Heppert, J. A.; Thomas-Miller, M. E.; Scherubel, D. M.; Takusagawa, F.; Morgenstern, M. A.; Shaker, M. R. OM 1989, 8, 1199.

Robert D. Pike

The College of William and Mary, Williamsburg, VA, USA



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