Org. Synth. 1961, 41, 96
DOI: 10.15227/orgsyn.041.0096
RUTHENOCENE
[Ruthenium, dicyclopentadienyl-]
Submitted by D. E. Bublitz, William E. McEwen, and Jacob Kleinberg
1.
Checked by Hans G. Essler and John H. Richards.
1. Procedure
A 500-ml. three-necked flask is equipped with a Trubore stirrer, reflux condenser, and a pressure-equalizing dropping funnel that carries an inlet for admission of nitrogen. The system is purged with nitrogen (Note 1), and 300 ml. of 1,2-dimethoxyethane (Note 2) is added, followed by 7.2 g. (0.312 g. atom) of sodium either as wire or freshly cut small pieces. The solution is stirred, and 31.0 ml. (0.376 mole) of cyclopentadiene (Note 3) is added dropwise. When the evolution of hydrogen has almost ceased, the mixture is maintained at slightly below the reflux temperature for 1–2 hours. In the event that all the sodium does not dissolve, the solution is cooled to room temperature, a few milliliters more of cyclopentadiene added, and the mixture heated again until dissolution of the sodium is complete.
A mixture of 14.6 g. (0.07 mole) of ruthenium trichloride and 2.4 g. (0.024 g. atom) of ruthenium metal (Note 4) is added, and the reaction mixture is heated and stirred under nitrogen for 80 hours (Note 5) at slightly below the reflux temperature. With the use of stirring, the solvent is removed at aspirator pressure, and the flask then refilled with nitrogen. The solid is transferred to a sublimator in a dry-box containing a nitrogen atmosphere (Note 6) and sublimed at 0.1 mm. pressure with a heating bath at 130° (Note 7). The sublimate is dissolved in benzene and passed through a 1 × 12-in. column of activated alumina. Evaporation of the benzene gives 12.2–15.1 g. (56–69%) of ruthenocene, m.p. 199–200° (Note 8).
2. Notes
1.
The submitters used prepurified
nitrogen, obtained from Matheson Company, Inc., East Rutherford, New Jersey, without further purification. The checkers passed Linde (H. P. Dry)
nitrogen successively through
chromous chloride solution, solid
potassium hydroxide,
Ascarite, and solid
phosphorus pentoxide.
2.
1,2-Dimethoxyethane is dried over
sodium wire and then distilled under
nitrogen from
lithium aluminum hydride just before use.
3.
For preparation of
cyclopentadiene from the dimer, see G. Wilkinson,
Org. Syntheses, Coll. Vol. 4, 475 (1963). The
dicyclopentadiene used as starting material was dried by passage through a 1 × 12-in. column of activated alumina prior to cracking.
4.
Ruthenium trichloride was prepared by chlorination of powdered
ruthenium at 650–700°
2 with the use of metal obtained from Goldsmith Bros. Smelting and Refining Co., 111. N. Wabash Ave., Chicago 2, Illinois. Complete chlorination could not be effected under these conditions, and on the average about 85% of the metal was converted to trichloride. Consequently, in all the preparations of
ruthenocene, mixtures of trichloride and metal, as obtained from the chlorination reaction, were employed. The equations given for the preparation are idealized; the submitters believe that during the course of reaction the trichloride is gradually reduced to dichloride by
ruthenium metal, and that it is the dichloride which reacts with
sodium cyclopentadienide.
5.
Somewhat lower yields than those reported are obtained when the reaction is carried out for a shorter period of time.
6.
From this point on, the solid materials are pyrophoric, especially the residual solids from the sublimation process. However, the
ruthenocene obtained by sublimation is not pyrophoric. The checkers found that careful addition of the sublimation residues to water under
nitrogen destroys their pyrophoric character.
7.
The checkers found the use of a Dry Ice-cooled sublimation finger advantageous.
8.
The yield reported here is based on the total amount of
ruthenium (both Ru
III and Ru
0) available for formation of
ruthenocene. An additional quantity of
ruthenocene may be obtained by extraction of the pyrophoric residue from the sublimation step with
benzene in a Soxhlet extractor under a
nitrogen atmosphere. The
benzene solution is filtered through activated alumina, the solvent evaporated, and the residue sublimed.
3. Discussion
Ruthenocene has been prepared in 20% yields by reaction of
cyclopentadienylmagnesium bromide with
ruthenium(III) acetylacetonate.
3 More recently,
4 the compound has been made in 43–52% yield by treatment of
sodium cyclopentadienide with
ruthenium trichloride in
tetrahydrofuran or
1,2-dimethoxyethane.
4. Merits of the Preparation
Ruthenocene is an example of a stable π-bonded organometallic compound which undergoes substitution reactions similar to those displayed by ferrocene. Because ruthenocene has heretofore been relatively unavailable, its chemistry has not been extensively studied.
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
Ruthenocene
Ascarite
ruthenium(III) acetylacetonate
Benzene (71-43-2)
hydrogen (1333-74-0)
nitrogen (7727-37-9)
potassium hydroxide (1310-58-3)
sodium (13966-32-0)
Tetrahydrofuran (109-99-9)
lithium aluminum hydride (16853-85-3)
chromous chloride (10049-05-5)
CYCLOPENTADIENE (542-92-7)
dicyclopentadiene (77-73-6)
Ruthenium, dicyclopentadienyl-
ruthenium trichloride (14898-67-0)
sodium cyclopentadienide (4984-82-1)
1,2-dimethoxyethane (110-71-4)
cyclopentadienylmagnesium bromide
ruthenium (7440-18-8)
phosphorus pentoxide (1314-56-3)
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