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Org. Synth. 1961, 41, 96
DOI: 10.15227/orgsyn.041.0096
RUTHENOCENE
[Ruthenium, dicyclopentadienyl-]
Submitted by D. E. Bublitz, William E. McEwen, and Jacob Kleinberg1.
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 RuIII and Ru0) 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.

References and Notes
  1. Department of Chemistry, University of Kansas, Lawrence, Kans.
  2. G. Brauer, "Handbuch der präparativen anorganischen Chemie," Ferdinand Enke Verlag, Stuttgart, Germany, 1952, p. 1194.
  3. G. Wilkinson, J. Am. Chem. Soc., 74, 6146 (1952).
  4. E. O. Fischer and H. Grubert, Ber., 92, 2302 (1959).

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)