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Org. Synth. 1970, 50, 21
DOI: 10.15227/orgsyn.050.0021
CYCLOBUTADIENEIRON TRICARBONYL
[Iron, tricarbonyl 4-1,3-cyclobutadiene)-]
Submitted by R. Pettit1 and J. Henery.
Checked by J. Napierski and R. Breslow.
1. Procedure
Caution! Benzene has been identified as a carcinogen; OSHA has issued emergency standards on its use. All procedures involving benzene should be carried out in a well-ventilated hood, and glove protection is required.
In a well-ventilated hood a 500-ml., three-necked flask is immersed in an oil bath and fitted with a condenser and a mechanical stirrer; a T-piece is inserted through a rubber stopper placed in the top of the condenser. One lead of the T-piece is connected to a nitrogen supply and the other to a gas bubbler. cis-3,4-Dichlorocyclobutene [Org. Synth., Coll. Vol. 6, 422 (1988)], 20 g. (0.16 mole), and 125 ml. of anhydrous benzene are added to the flask, and the apparatus is flushed with nitrogen. Diiron nonacarbonyl, 25 g. (Note 1) is then added, the flow of N2 is stopped, and the mixture is heated to 50–55°, with stirring. After about 15 minutes the initial rapid evolution of carbon monoxide becomes greatly diminished and an additional 8 g. of the nonacarbonyl is added; additional 8-g. quantities are added at intervals (approximately 15 minutes), governed by the rate of carbon monoxide evolution. The addition is continued until no more carbon monoxide is liberated (Note 2), and the reaction mixture is stirred at 50° for an additional hour. Approximately 140 g. of diiron nonacarbonyl is required for the complete conversion of the dichlorocyclobutene, the total reaction time being about 6 hours.
The contents of the flask are then filtered with suction through Filtercel and the residue, while kept in the Buchner funnel, is thoroughly washed with pentane until the washings are colorless (Note 3). The pentane and much of the benzene are evaporated from the combined filtrates with a water aspirator.
The residual liquid is transferred to a flask equipped with an efficient fractionating column and distilled under reduced pressure. Benzene is removed first, followed by considerable quantities of iron pentacarbonyl (b.p. 20°, 30 mm.); when the diiron nonacarbonyl has been removed, the pressure is reduced further and cyclobutadieneiron tricarbonyl2 is collected as a pale yellow oil, b.p. 47° (3 mm.), yielding 13.8–14.4 g. (45–46% based on dichlorocyclobutene), (Note 4).
2. Notes
1. Diiron nonacarbonyl is readily available through photolysis of iron pentacarbonyl.3
2. The conversion of the dichlorocyclobutene to cyclobutadieneiron tricarbonyl can be conveniently monitored by GC. On a 5 ft. × 1/8 in. column of 20% Carbowax on Chromosorb W, under conditions where the retention time of dichlorocyclobutene is 2.6 minutes, the retention time of cyclobutadieneiron tricarbonyl is 2.4 minutes.
3. The brown insoluble residue is frequently pyrophoric if it is allowed to dry; it should be immediately wetted with water before it is disposed of.
4. In some preparations the last portion of the distillate of the complex may be dark green in color. This color is due to trace amounts of Fe3(CO)12. If desired, this can be readily removed by chromatography over alumina. The submitters report a similar yield on three times the scale.
3. Discussion
Cyclobutadieneiron tricarbonyl may also be produced by the reaction of 3,4-dichlorocyclobutene with disodium irontetracarbonyl4 and by irradiation of α-pyrone followed by treatment with diiron nonacarbonyl.4 The method outlined here is the most convenient, especially when considerable quantities (10 g. or more) of cyclobutadieneiron tricarbonyl are required. The analogous reaction of derivatives of 3,4-dihalocyclobutenes with diiron nonacarbonyl affords the corresponding cyclobutadieneiron tricarbonyl complexes. Cyclobutadieneiron tricarbonyl can be oxidized to generate cyclobutadiene in situ.5
This preparation is referenced from:
6
References and Notes
  1. Deceased, December 10, 1981; work done at the Department of Chemistry, The University of Texas at Austin, Austin, Texas 78712.
  2. G. F. Emerson, L. Watts, and R. Pettit, J. Am. Chem. Soc., 87, 131 (1965).
  3. E. H. Braye and W. Huebel, Inorg. Syn., 8, 178 (1966).
  4. M. Rosenblum and C. Gatsonis, J. Am. Chem. Soc., 89, 5074 (1967).
  5. L. Watts and R. Pettit, Advan. Chem. Series, "Werner Centennial," 62, 549 (1966).
  6. R. G. Amiet, P. C. Reeves, and R. Pettit, Chem. Commun., 1208 (1967).

Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)

Cyclobutadieneiron tricarbonyl

4-1,3-cyclobutadiene)-

Diiron nonacarbonyl

disodium irontetracarbonyl

Benzene (71-43-2)

carbon monoxide (630-08-0)

nitrogen (7727-37-9)

Pentane (109-66-0)

iron pentacarbonyl

α-Pyrone (504-31-4)

Iron, tricarbonyl

nonacarbonyl

dichlorocyclobutene

3,4-dichlorocyclobutene

cis-3,4-Dichlorocyclobutene (2957-95-1)