Sodium Tetracarbonylhydridoferrate

NaHFe(CO)4

[53558-55-7]  · C4HFeNaO4  · Sodium Tetracarbonylhydridoferrate  · (MW 191.89)

(alkylation of carbonyl compounds and amines with aldehydes; reduction of a,b-unsaturated carbonyl compounds, enamines, and nitro compounds; carbonylation of alkenes)

Physical Data: X-ray structure of the HFe(CO)4- ion as the PPN+ salt has been reported.1

Solubility: sol THF, ethanol, methanol.

Form Supplied in: prepared as a solution in THF or in methanol.

Analysis of Reagent Purity: IR (THF) 1997 (m), 1903 (sh), 1878 (s), 1851 (sh) cm-1; 1H NMR (THF, C6D6) d -8.74 (32 °C).

Preparative Methods: Method A. To a stirred suspension of Sodium Amalgam (100 g of mercury and 0.76 g of sodium) in dry THF (50 mL), Pentacarbonyliron (1.5 mL, 11 mmol) is added dropwise under argon. The mixture is stirred for 2 h at room temperature, and the excess of amalgam is removed through a sidearm. The suspension is treated with water (0.2 mL, 11 mmol) and the resulting NaHFe(CO)4 is used immediately. Method B. To a stirred solution of Sodium Hydroxide (33 mmol) in methanol (50 mL), pentacarbonyliron (1.5 mL, 11 mmol) is added under nitrogen or argon. The mixture is stirred for 2 h under reflux and the resulting solution of NaHFe(CO)4 is used immediately. The corresponding potassium salt of HFe(CO)4- is prepared similarly from Potassium Hydroxide.

Handling, Storage, and Precautions: must be prepared and transferred under inert gas (Ar or N2).

Dimerization.

When the light yellow aqueous solution of NaHFe(CO)4 is allowed to stand for a few days, it becomes dark red due to the formation of a dimeric anion (eq 1). The dimer slowly gives off hydrogen and forms a dinuclear iron carbonyl anion.2

Reaction with Acetylene.

Reaction of an alkaline aqueous solution of HFe(CO)4- with acetylene followed by acidic workup provides H2[HC=CHFe2(CO)8].3 The structure of the complex has been determined on the basis of chemical and spectroscopic evidence.3,4 Analogous complexes are obtained from propyne and 2-butyne by essentially similar methods.4 In an aprotic solvent such as methylene chloride, the HFe(CO)4- ion (prepared as [N(PPh3)2][FeH(CO)4] from KHFe(CO)4 and bis(triphenylphosphine)iminium chloride in methanol) reacts with methyl propiolate, dimethyl acetylenedicarboxylate, ethynyl methyl ketone, and propiolaldehyde to give (h3-acryloyl)tricarbonylferrates by trans addition of the hydride to the acetylenic bond (eq 2).5

Alkylation of Carbonyl Compounds and Amines with Aldehydes.

Treatment of an aldehyde or a ketone with formaldehyde in the presence of HFe(CO)4- in ethanol or water results in reductive methylation of the carbonyl compounds in high yield (eq 3).6 The reaction also occurs with carbonyl compounds and alkyl, aryl, and heterocyclic aldehydes in the presence of HFe(CO)4- to provide a variety of substituted carbonyl compounds.7

Indole can also be reductively alkylated or arylated in the 3-position by aliphatic or aromatic aldehydes using the same procedure (eq 4).8 The facile alkylation and arylation of primary and secondary amines and of ammonia by aldehydes in the presence of HFe(CO)4- has also been reported (eq 5).9 A practical advantage of this method is the possibility of obtaining a predominantly mono- or dialkyl derivative by using a 1:1:1 or 1:2:2 molar ratio of amine, aldehyde, and HFe(CO)4-, respectively.

Reduction of a,b-Unsaturated Carbonyl Compounds.

Treatment of unsaturated carbonyl derivatives (ketones, aldehydes, esters, lactones, nitriles) with HFe(CO)4-, generated in situ from iron pentacarbonyl and NaOH in methanol, gives the corresponding saturated derivatives in high yield.10 The method is very mild and possesses the following characteristics: (1) overreduction of the ketonic groups is negligible; (2) ester functions are not reduced; (3) reductive coupling of ketones to pinacols, frequently encountered with Birch conditions, is not observed; (4) no skeletal rearrangement, often observed during Clemmensen reduction, takes place; (5) phenyl and furyl groups are not affected; and (6) the rate of reduction is influenced by steric environments around double bonds; reduction is slower for a sterically hindered double bond. As to the stereochemistry of the reduction, cholest-4-en-3-one is converted selectively into the corresponding 5b-cholestanone having cis stereochemistry (eq 6), whereas D1,9-2-octalone is reduced to afford a stereoisomeric mixture of 2-decalones (eq 7).

In an aprotic solvent under ambient conditions, a,b-unsaturated esters selectively insert into the hydrogen-iron bond of HFe(CO)4- (prepared by protonation of Na2[Fe(CO)4] in THF with 1 equiv of acetic acid) to give alkyl-iron complexes (eq 8). On treatment with alkyl iodide, the alkyl complexes give the corresponding hydroacylated products (eq 8).11

The HFe(CO)4- derivatives prepared from triethylenediamine (33 mol), deionized water (33 mmol), and pentacarbonyliron (11 mmol) are effective in reducing a,b-unsaturated carbonyl compounds to the saturated alcohols.12 With prochiral compounds the reaction proceeds stereospecifically. For example, HFe(CO)4-, generated in situ in THF, reacts with (+)-carvone at 60 °C for 9 days under an argon atmosphere to give (-)-neodihydrocarveol in almost quantitative yield (eq 9). Similarly, (+)-neodihydrocarveol is obtained exclusively from (-)-carvone.

Reduction of Enamines and Nitro Compounds.

Enamines are converted to the corresponding saturated tertiary amines.13 For example, enamines such as N-(1-cyclohexenyl)morpholine, N-(1-phenylvinyl)morpholine, and N-(2-methyl-1-propenyl)piperidine readily react with an alcoholic solution of HFe(CO)4- with the absorption of CO at room temperature to give the corresponding amines in high yield (eqs 10-12).

An application of HFe(CO)4- as a reducing reagent in the preparation of primary amines from nitro compounds, mainly substituted nitrobenzenes, has also been reported (eq 13).14 The reduction is exothermic and gives the corresponding amines in excellent yields. The ferrate has also high reactivity for nitrosobenzene and moderate reactivity for azobenzene.14 Nitrocyclohexane reacts slowly to provide cyclohexylamine in good yield.14

Carbonylation of Alkenes.15

HFe(CO)4- reacts with ethyl acrylate at 40-70 °C under an atmosphere of carbon monoxide to give methylmalonate in high yield after treatment of the reaction mixture with alcoholic iodine and hydrogen chloride solutions (eq 14). Both crotonate and 3-butenoate give ethylmalonate as a major product and methylsuccinate and glutarate as minor ones (eq 15). Styrene, on treatment with iron ferrate under CO, yields two isomeric aldehydes, a- and b-phenylpropionaldehyde (eq 16). Ethyl caproate and enanthate are obtained from 1-pentene and 1-hexene, respectively, in poor yield.

Other Reactions.

The reaction of HFe(CO)4- with [M(CO)3(a-diimine)Br] yields novel heterodinuclear hydride species (eq 17).16 The structure of these bimetallic compounds has been determined by X-ray crystallography. The HFe(CO)4- anion is also an effective catalyst for the steam gasification of Miike coal.17 It is also used for hydrodimerization of acrylonitrile to provide adiponitrile.18 With Na2S.9H2O, it provides iron carbonyl sulfide clusters.19

Related Reagents.

Potassium tetracarbonylhydridoferrate is prepared and used in a similar fashion to the sodium salt.6,9,20,21 Tetramethylammonium tetracarbonylhydridoferrate is readily prepared by reaction of pentacarbonyliron with KOH and Me4NBr in aqueous solution. Similar transformations may be performed with this reagent, including high yielding reduction of acid chlorides to aldehydes.22


1. Smith, M. B.; Bau, R. JACS 1973, 95, 2388.
2. Sternberg, H. W.; Markby, R.; Wender, I. JACS 1956, 78, 5704; 1957, 79, 6116.
3. Wender, I.; Friedel, R. A.; Markby, R.; Sternberg, H. W. JACS 1955, 77, 4946; 1956, 78, 3621.
4. Clarkson, R.; Jones, E. R. H.; Wailes, R. C.; Whiting, M. C. JACS 1956, 78, 6206.
5. Mitsudo, T-A; Watanabe, Y.; Nakanishi, H.; Morishima, I.; Inubushi, T.; Takegami, Y. JCS(D) 1978, 1298.
6. Cainelli, G. F.; Panunzio, M.; Umani-Ronchi, A. TL 1973, 2491.
7. Cainelli, G. F.; Panunzio, M.; Umani-Ronchi, A. JCS(P1) 1975, 1273.
8. Boldrini, G. P.; Panunzio, M.; Umani-Ronchi, A. CC 1974, 359.
9. Boldrini, G. P.; Panunzio, M.; Umani-Ronchi, A. S 1974, 733.
10. Noyori, R.; Umeda, I.; Ishigami, T. JOC 1972, 37, 1542.
11. Mitsudo, T-A.; Watanabe, Y.; Yamashita, M.; Takegami, Y. CL 1974, 1385.
12. Yamashita, M.; Miyoshi, K.; Okada, Y.; Suemitsu, R. BCJ 1982, 55, 1329.
13. Mitsudo, T-A.; Watanabe, Y.; Tanaka, M.; Atsuta, S.; Yamamoto, K.; Takegami, Y. BCJ 1975, 48, 1506.
14. Watanabe, Y.; Mitsudo, T-A.; Yamashita, M.; Takegami, Y. BCJ 1975, 48, 1478.
15. Masada, H.; Mizuno, M.; Suga, S. BCJ 1970, 43, 3824.
16. (a) Keijsper, J.; Grimberg, P.; van Koten, G.; Vrieze, K.; Kojic-Prodic, B.; Spek, A. L. OM 1985, 4, 438. (b) Keijsper, J.; Grimberg, P.; van Koten, G.; Vrieze, K.; Cristophersen, M.; Stam, C. H. ICA 1985, 102, 29.
17. Suzuki, T.; Mishima, M.; Kitaguchi, J.; Watanabe, Y. CL 1982, 985.
18. Misono, A.; Uchida, Y.; Tamai, K.; Hidai, M. BCJ 1967, 40, 931.
19. Markó, L.; Takács, J.; Papp, J.; Markó-Monostory, B. ICA 1980, 45, L189.
20. Alper, H.; Paik, H.-N. JOC 1977, 42, 3522.
21. Yamashita, M.; Watanabe, Y.; Mitsudo, T.; Takegami, Y. BCJ 1978, 51, 835.
22. Cole, T. E.; Pettit, R. TL 1977, 781.

M. Mahmun Hossain & Anjan K. Saha

University of Wisconsin-Milwaukee, WI, USA



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