Potassium Tris(1,1,1,2,2,3,3,4,4,5,5,6,6,7,7,11,11,12,12,13,13,14,14,15,15,16,16,17,17,17-triacontafluoro-8,10-heptadecanedionato) Ruthenate

[195870-97-4]  · C51H3F90O6RuK  · (2558.57)

(reagent used for epoxidation of alkenes)

Physical Data: mp 162-163°C.

Solubility: soluble in perfluorooctyl bromide and other perfluorinated solvents, MeOH and THF; slightly soluble in diethyl ether.

Form Supplied in: violet crystals, not commercially available; major impurity: perfluorohexane.

Preparative Methods: the complex is prepared from the corresponding diketone 1 and RuCl3 in the presence of base (eq 1).1

A ruthenium(III) chloride solution in water/EtOH is refluxed for 4 h, thereafter an ethereal solution of the perfluorinated diketone 1 is added, followed by potassium bicarbonate. The mixture is then left to reflux for 1 h. Extraction with perfluorohexane and further recrystallization from acetone/chloroform gives the product in a 62% yield. The above diketone 1 is obtained by condensation2,3 of the corresponding perfluorinated methyl ester and perfluorinated methylketone in the presence of NaOMe in diethyl ether.

Handling, Storage, and Precautions: the compound can be stored at room temperature and in the presence of moisture for several months. It decomposes at temperatures >60°C. Data on toxicity are not known yet; it is suggested that use the same precautions as for the other salts of Ru(II) be used.

Epoxidation

The potassium tris(1,1,1,2,2,3,3,4,4,5,5,6,6,7,7,11,11,12,12,13,13,14,14,15,15,16,16,17,17,17 triacontafluoro-8,10-heptadecanedionato) ruthenate complex has been used in fluorous biphasic system catalysis (FBS) for the epoxidation of disubstituted alkenes (eq 2).1

The FBS4,5 is based on the property of perfluorinated solvents to be immiscible with most organic solvents at room temperature, and completely miscible with them at temperatures >50-60°C. In this way, a catalyst containing perfluorinated ‘ponytails’ is selectively soluble in a perfluorinated phase, but it reacts with the substrate in a homogeneous catalytic system when the temperature is increased. After cooling down, the reaction system separates into two phases again: the catalyst is recovered only in the perfluorinated one and can be easily recycled, while the products are in the organic solvent. Another advantage of the FBS is the high solubility of several gases6 in the perfluorinated medium; consequently, it is suitable for ‘green’ oxidations7-9 with molecular oxygen.

This ruthenium compound produces a violet solution in perfluorooctyl bromide, but in the presence of aldehydes and O2 it quickly becomes brown; probably due to the formation of Ru(III) or oligomeric species with mixed valences. However, the brown solution shows the same activity as the violet one and can be recycled several times. It is important to carry out the reaction at the lowest temperature possible (not more than 60°C) in order to avoid the decomposition of the complex.

The compound is suitable for selective epoxidations of disubstituted alkenes in the presence of molecular oxygen and isopropylaldehyde,1,10,11 with yields around 71-85% and reaction times between 8 and 16 h; functional groups such as esters or carboxylic acids are very well tolerated, and terminal double bonds are not reactive at all under these conditions. After the reaction, the perfluorinated phase containing the ruthenium complex can be recycled up to ten times with negligible loss of activity1 (from 100% conversion in the first run to 85% at the 10th run). Because of the recyclability of the catalyst, the work-up of the organic phase containing the product is quite simple and clean.

Related Reagents.

‘fluorous tin hydride’.


1. Klement, I.; Lütjens, H.; Knochel, P., Angew. Chem., Int. Ed. Engl. 1997, 36, 1454.
2. Massyn, C.; Pastor, R.; Cambon, A., Bull. Soc. Chim. Fr. 1974, 5, 975 (CAN 82, 30716).
3. Pedler, A. E.; Smith, R. C.; Tatlow, J. C., J. Fluorine Chem. 1972, 1, 433 (CAN 76, 153168).
4. Horváth, I. T.; Rabai, J., Science 1994, 266, 72.
5. de Wolf, E.; van Koten, G.; Deelman, B.-J., Chem. Soc. Rev. 1999, 28, 37.
6. Sharts, C. M.; Reese, H. R.; Ginsberg, K. A.; Multer, F. K.; Nielson, M. D.; Greenburg, A. G.; Peskin, G. W.; Long, D. M., J. Fluorine Chem. 1978, 11, 637 (CAN 89, 118226).
7. Pozzi, G.; Cinato, F., Chem. Commun. 1998, 887.
8. Betzemeier, B.; Lhermitte, F.; Knochel, P., Synlett 1999, 489.
9. Klement, I.; Knochel, P., Synlett 1996, 1004.
10. Yamada, T.; Takai, T.; Rhode, O.; Mukaiyama, T., Chem. Lett. 1991, 1.
11. Yamada, T.; Takai, T.; Rhode, O.; Mukaiyama, T., Bull. Chem. Soc. Jpn 1991, 64 , 2109.

Gianna Ragagnin & Paul Knochel

Ludwig Maximilian Universität, München, Germany



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