Org. Synth. 1970, 50, 21
DOI: 10.15227/orgsyn.050.0021
CYCLOBUTADIENEIRON TRICARBONYL
[Iron, tricarbonyl (η4-1,3-cyclobutadiene)-]
Submitted by R. Pettit
1 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 N
2 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.
32.
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 Fe
3(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:
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
Cyclobutadieneiron tricarbonyl
(η4-1,3-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)
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