Iron(II) Phthalocyanine

[132-16-1]  · C32H16FeN8  · Iron(II) Phthalocyanine  · (MW 568.41)

(oxidation of terminal alkenes to methyl ketones; 1,4-oxidation of 1,3-dienes; allylic oxidation of cyclic alkenes; siloxane elimination from silylamides to form nitriles)

Physical Data: mp >300 °C.

Form Supplied in: black powder.

Handling, Storage, and Precautions: store tightly sealed in a cool, dry place.

Preparation of Methyl Ketones from Alkenes (Wacker Oxidation).

Methyl ketones are conveniently prepared from terminal alkenes by Wacker oxygenation using a catalytic amount of Palladium(II) Chloride and Copper(II) Chloride.1 The reaction can be slow and chlorinated byproducts are usually observed. Iron phthalocyanine (Fe(Pc)) serves as the oxygen-activating complex in a multicatalyst system used to perform Wacker-type2 oxidation reactions (eq 1).2b This catalyst system offers a chloride-free environment in which alkenes are smoothly converted to methyl ketones with molecular oxygen, under mild conditions, in moderate to high yield. Unlike typical Wacker oxidations using CuCl2, no chlorinated byproducts are formed.1a,3 In addition, the removal of chloride from the system increases the rate of reaction.4 In the catalyst system, Fe(Pc) reoxidizes hydroquinone to benzoquinone, which serves to reoxidize Pd0 to PdII after PdII catalyzes the oxidation of the alkene to the ketone (eq 1). In the present catalyst system, acid (HClO4) is added to prevent the rapid precipitation of Pd from the aqueous DMF reaction mixture. The reoxidation of hydroquinone by other means,5 including electrochemical reoxidation,6 has been reported.

1,4-Oxidation of Conjugated Dienes.7

Conjugated dienes can be oxidized to cis-1,4-diols and 1,4-diacetates when treated with the above catalyst system in acetic acid or alcohol (eqs 2 and 3).

Aerobic Allylic Oxidation of Alkenes.6c

Exposure of cyclohexene to the above described catalyst system in acetic acid gives the desired allylic oxidation product (eq 4). Again, Fe(Pc) and molecular oxygen take the place of less convenient oxygen sources such as MnO2.8

Epoxidation of Alkenes.

In a comparison of transition metal phthalocyanines, iron(II) phthalocyanine most effectively catalyzes the epoxidation of alkenes when Iodosylbenzene is the oxygen donor.9 It is less effective than other metal-phthalocyanine catalysts when NaOCl is used as the oxygen donor. A mixture of cis- and trans-epoxides are produced from cis-alkenes. In the presence of 2,6-di-t-butyl-p-cresol, highly stereoselective epoxidation of the cis-alkene is observed.

Preparation of Nitriles from Amides.10

Iron phthalocyanine readily catalyzes the decomposition of bis(trimethylsilyl)amides to give nitriles under relatively mild conditions (75 °C, 6 h, 100%, eq 5). This serves as a useful alternative to the less general thermal decomposition of bis(silylamides)11 or the thermal decomposition of monosilylamides in the presence of stoichiometric amounts of an acidic reagent.12 Catalytic amounts of fluoride ion or simple Lewis acids such as FeCl3, ZnCl2, or AlCl3, are also effective reagents for this transformation.

1. (a) Tsuji, J.; Nagashima, H.; Nemoto, H. OS 1984, 62, 9. (b) Bäckvall, J.-E. In Heterogeneous Catalysis and Fine Chemicals; Guisnet, M., et al., Eds.; Elsevier: Amsterdam, 1988; p 105.
2. (a) Henry, P. M. Palladium-Catalyzed Oxidation of Hydrocarbons; Reidel: Dordrecht, 1980. (b) Bäckvall, J. E.; Hopkins, R. B. TL 1988, 29, 2885. (c) Srinivasan, S.; Ford, W. T. J. Mol. Catal. 1991, 64, 291.
3. Stangl, H.; Jira, R. TL 1970, 3589.
4. Henry, P. M. JACS 1964, 86, 3246. ibid 1966, 88, 1595.
5. Heumann, A.; Akermark, B. AG(E) 1984, 23, 453.
6. (a) Bäckvall, J. E.; Gogoll, A. J. TL 1988, 29, 2243. (b) Tsuji, J.; Minato, M. TL 1987, 28, 3683.
7. (a) Bäckvall, J. E.; Awasthi, A. K.; Renko, Z. D. JACS 1987, 109, 4750. (b) Bäckvall, J. E.; Gogoll, A. CC 1987, 1236. (c) Bäckvall, J. E.; Hopkins, R. B.; et al. JACS 1990, 112, 5160.
8. Heumann, A.; Akermark, B. AG(E) 1984, 23, 453.
9. Larsen, E.; Jorgensen, K. A. ACS 1989, 43, 259.
10. Rigo, B.; Lespagnol, C.; Pauly, M. TL 1986, 27, 347.
11. (a) Birkofer, L.; Ritter, A. AG(E) 1965, 4, 417. (b) Klebe, J. F. In Advances in Organic Chemistry; Taylor, E. C., Ed.; Wiley: New York, 1972; p 97.
12. (a) Hallensleben, M. L. TL 1972, 2057. (b) Schwarz, G.; Alberts, H.; Kricheldorf, H. R. LA 1981, 1257.

Mark W. Zettler

The Dow Chemical Company, Midland, MI, USA

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