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).