Org. Synth. 1956, 36, 31
DOI: 10.15227/orgsyn.036.0031
FERROCENE
[Iron, dicyclopentadienyl-]
[I. METALLIC SODIUM METHOD]
Submitted by G. Wilkinson
1
Checked by N. J. Leonard, Kenneth L. Rinehart, Jr., Donald J. Casey, and Sung Moon.
1. Procedure
In a 250-ml. three-necked flask, fitted with a mechanical stirrer, a reflux condenser, and an inlet for admission of nitrogen, is placed 100 ml. of tetrahydrofuran (Note 1). With stirring, 27.1 g. (0.166 mole) of anhydrous ferric chloride is added in portions, followed by 4.7 g. (0.084 g. atom) of iron powder (Note 2). The mixture is heated with stirring under nitrogen at the reflux temperature for 4.5 hours, giving a gray powder with a brown supernatant liquid.
During this time, a second system is assembled, consisting of a 500-ml. three-necked flask fitted with a mechanical stirrer, a reflux condenser topped with a calcium chloride-filled drying tube attached to a xylene-filled bubbler, and a pressure-equalizing dropping funnel through which a slow stream of nitrogen is passed into the flask. In the flask are placed 200 ml. of sodium-dried xylene and 11.5 g. (0.5 g. atom) of sodium. The mixture is heated to boiling, and the sodium is finely dispersed by rapid stirring (Note 3). Stirring is continued while the mixture is allowed to cool in a nitrogen atmosphere. The cooled mixture is allowed to settle, and the bulk of the xylene is siphoned. Tetrahydrofuran (200 ml.) (Note 1) is added through the separatory funnel, and to the stirred mixture, cooled in ice, is added 42 ml. (0.5 mole) of cyclopentadiene (Note 4) in portions during 1 hour (Note 5). Stirring is continued for 2–3 hours in the cold, after which only a small amount of sodium remains unreacted.
The cooled contents of the 250-ml. flask containing ferrous chloride (Note 6) are added to the cold sodium cyclopentadienide solution while passing a stream of nitrogen through both flasks. The combined mixture is stirred for 1.25 hours at a temperature just below reflux. Solvent is removed by distillation, and the ferrocene is extracted from the residue with several portions of refluxing petroleum ether (b.p. 40–60°). The product is obtained by evaporation of the petroleum ether solution. Ferrocene may be purified by recrystallization from pentane or cyclohexane (hexane, benzene, and methanol have also been used) or by sublimation. The yield is 31–34 g. (67–73%) (Note 7), m.p. 173–174°.
2. Notes
1.
Tetrahydrofuran may be purified by refluxing over solid
potassium hydroxide, followed by distillation from
lithium aluminum hydride.
Tetrahydrofuran may be replaced by
ethylene glycol dimethyl ether (dimethoxyethane). The submitter has indicated that either solvent may be freed conveniently from water, alcohols, and moderate amounts of peroxides by passing the commercial solvent through a
column (2 in. diameter × 2–3 ft. length) of Linde Air Products "Molecular Sieves" (type 13X 1/16-in. pellets), at a rate of approximately 100 ml. per minute.
2.
The quality of the
iron used in preparing the
ferrous chloride has a marked effect on the yield of
ferrocene. The checkers employed Rascher and Betzold (730 N. Franklin, Chicago, Ill.) 300-mesh
iron powder, reduced by
hydrogen. When 40-mesh
iron filings were used, the yield of
ferrocene was much lower (ca. 33%).
3.
The checkers employed a "Mixmaster"-type motor and a
Hershberg stirrer made from
tantalum wire.
4.
Cyclopentadiene, b.p.
40°, is obtained by heating commercial
85% dicyclopentadiene (e.g., from Matheson, Coleman and Bell Company, Norwood, Ohio) under a
short column (¾ in. diameter × 8–12 in. length) filled with glass helices. The distilled
cyclopentadiene is collected in a
receiver which is maintained at Dry Ice temperature until the
cyclopentadiene is used.
Methylcyclopentadiene and other substituted cyclopentadienes such as
indene may also be employed for the synthesis of the correspondingly substituted ferrocenes. In these cases, the reaction of the hydrocarbon with
sodium is much slower than with
cyclopentadiene, and refluxing for several hours is required to complete the reaction.
5.
Under the best conditions,
sodium cyclopentadienide gives pale yellow or orange solutions. Traces of air lead to red or purple solutions, as does insufficiently purified solvent, without, however, lowering the reaction yield appreciably. If
1,2-dimethoxyethane is used, in which
sodium cyclopentadienide is less soluble than in
tetrahydrofuran, white crystals may be obtained at this point.
6.
Ferrous chloride may be substituted by
ferric chloride directly, with a corresponding reduction in yield, since the
sodium cyclopentadienide solution will reduce
ferric chloride.
7.
The submitter reported yields up to
90% by this method.
[II. DIETHYLAMINE METHOD]
Submitted by G. Wilkinson
1
Checked by N. J. Leonard, Kenneth L. Rinehart, Jr., and Peter Woo.
1. Procedure
The conditions given in the preceding preparation are used for obtaining a suspension of 0.25 mole of ferrous chloride in 100 ml. of tetrahydrofuran (Note 1), contained in a 250-ml. flask. The tetrahydrofuran is then removed under reduced pressure until the residue is almost dry. The flask is cooled in an ice bath, and to the residue is added a mixture of 42 ml. (0.5 mole) of cyclopentadiene and approximately 100 ml. (about 1 mole) of diethylamine. The mixture is stirred vigorously at room temperature for 6–8 hours or, conveniently, overnight. The excess amine is removed under reduced pressure, and the residue is extracted repeatedly with refluxing petroleum ether. The extract is filtered hot, and the solvent is evaporated to leave ferrocene. The product is purified by recrystallization from pentane or cyclohexane or by sublimation. The yield is 34–39 g. (73–84%), m.p. 173–174°.
2. Notes
1.
All precautions with regard to the purification of
tetrahydrofuran, the quality of the
iron powder, the rapid stirring, the maintenance of a
nitrogen atmosphere, and the handling of
cyclopentadiene, described in the preceding preparation, are followed.
3. Discussion
The methods of preparation of
ferrocene have been reviewed by Pauson
2 and by Fischer.
3 Ferrocene has been made by the reaction of
ferric chloride with
cyclopentadienylmagnesium bromide,
4 by the direct thermal reaction of
cyclopentadiene with
iron metal,
5 by the direct interaction of
cyclopentadiene with
iron carbonyl,
6 by the reaction of
ferrous oxide and
cyclopentadiene in the presence of
chromic oxide,
7 by the reaction of
ferrous chloride with
sodium cyclopentadienide in liquid
ammonia,
8 and from
cyclopentadiene and
ferrous acetylacetone-dipyridine complex.
9 Method I is based on that developed by Wilkinson and his co-workers for
ferrocene and many analogous compounds.
10Although not so generally applicable for the preparation of dicyclopentadienyl metal compounds as the
sodium cyclopentadienide procedure, Method II represents the simplest preparation of
ferrocene. The amine procedure also may be employed for
dicyclopentadienylnickel (about
80% yield), using
nickel bromide obtained by the action of
bromine on
nickel metal powder and
1,2-dimethoxyethane as the solvent. The method of preparation given here is a modified version
10d of that originally described,
11 and it has been studied by others.
12,13This preparation is referenced from:
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
petroleum ether
Ferrocene
sodium-dried xylene
ferrous acetylacetone-dipyridine complex
ammonia (7664-41-7)
Benzene (71-43-2)
methanol (67-56-1)
hydrogen (1333-74-0)
iron,
iron filings,
iron powder (7439-89-6)
bromine (7726-95-6)
nitrogen (7727-37-9)
cyclohexane (110-82-7)
nickel metal powder (7440-02-0)
potassium hydroxide (1310-58-3)
sodium (13966-32-0)
ferric chloride (7705-08-0)
xylene (106-42-3)
diethylamine (109-89-7)
Pentane (109-66-0)
tantalum wire (7440-25-7)
indene (95-13-6)
Tetrahydrofuran (109-99-9)
lithium aluminum hydride (16853-85-3)
hexane (110-54-3)
chromic oxide (1308-38-9)
ferrous chloride (7758-94-3)
CYCLOPENTADIENE (542-92-7)
dicyclopentadiene (77-73-6)
Iron, dicyclopentadienyl-
sodium cyclopentadienide (4984-82-1)
ethylene glycol dimethyl ether,
1,2-dimethoxyethane (110-71-4)
dimethoxyethane (534-15-6)
Methylcyclopentadiene
cyclopentadienylmagnesium bromide
iron carbonyl
ferrous oxide
dicyclopentadienylnickel
nickel bromide
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