Vanadyl Bis(acetylacetonate)1

[3153-26-2]  · C10H14O5V  · Vanadyl Bis(acetylacetonate)  · (MW 265.18)

(precatalyst for oxidation of several functional groups in combination with alkyl hydroperoxides or oxygen;1 especially useful for the regio- and diastereoselective epoxidation of allylic alcohols,2 the oxidation of tertiary amines to N-oxides,3 and the oxidation of sulfides to sulfoxides4 using an alkyl hydroperoxide as the oxidant)

Alternate Name: bis(acetylacetonato)oxovanadium(IV).

Physical Data: mp 256-259 °C; d 1.50 g cm-3.

Solubility: insol H2O; sol EtOH, CH2Cl2, CHCl3, C6H6.

Form Supplied in: blue-green crystals; widely available.

Handling, Storage, and Precautions: generally used without further purification. Can be handled safely in the open. Should be stored in a cool, dry place in the absence of light. Contact with skin, eyes, and mucous membranes should be avoided. Toxic if swallowed. Generally performs best as an oxidation catalyst when used under anhydrous conditions. Oxidants contaminated with H2O such as 70% t-butyl hydroperoxide (TBHP) are therefore usually dried prior to use with VO(acac)2.

Precursor for Soluble Vanadium(V) Catalysts.

VO(acac)2 is a precatalyst for the oxidation of several functional groups, usually using an alkyl hydroperoxide as the oxidant.1b Reaction of VO(acac)2 with an alkyl hydroperoxide quickly oxidizes the vanadium from the +4 to the +5 oxidation state. The resulting organic soluble Vv complexes, whose structure can be represented as VO(OR)3, are usually the actual catalysts in these reactions.1 VO(acac)2 is a commercially available, stable, crystalline, organic soluble solid and therefore a convenient source of vanadium for oxidation reactions. In contrast, organic soluble VV compounds, suitable for these reactions, are not as widely available nor as easily handled and therefore not as convenient a source of vanadium as VO(acac)2.5

Epoxidation of Allylic Alcohols.

Soluble Vv compounds are the preferred catalysts for nonenantioselective epoxidation of allylic alcohols to epoxy alcohols using alkyl hydroperoxides, especially t-Butyl Hydroperoxide, as oxidants.2,6 VV compounds with alkyl hydroperoxides are also capable of epoxidation of nonfunctionalized alkenes7 to epoxides but at rates ca. 100 times less than for the corresponding allylic alcohols.6a This rate differential allows the regioselective monoepoxidation of substrates like geraniol (eq 1).

MoVI/TBHP and peracids efficiently epoxidize allylic alcohols as well but, because they also rapidly epoxidize nonfunctionalized alkenes, they tend not to be as regioselective as VV/TBHP.1 Other d0 transition metal catalysts, such as WVI and TiIV, epoxidize allylic alcohols slower and less efficiently than VV and therefore are not as useful for this type of epoxidation reaction.7 Diastereoselective epoxidation is often observed in VV-catalyzed epoxidations of chiral allylic alcohols, especially cyclic allylic alcohols.6a,8,9 Diastereoselective epoxidation of homoallylic and bishomoallylic alcohols have also been reported.6a,10 VV/TBHP often complements the diastereoselectivity of peracids and MoVI/TBHP observed for the epoxidation of secondary allylic alcohols.6a,8 For example, epoxidation of 2-cyclooctenol gives either the corresponding cis- or trans-epoxy alcohol with high diastereoselectivity, depending on whether VO(acac)2/TBHP or m-Chloroperbenzoic Acid is used (eq 2).11

Hydroxyepoxidation of Alkenes.

VO(acac)2 catalyzes the transformation of allylic hydroperoxides to epoxy alcohols.12 This process presumably involves intermolecular transfer of oxygen from the hydroperoxide portion of an allylic hydroperoxide to the alkene portion of either a second allylic hydroperoxide or an allylic alcohol derived from hydroperoxide reduction (eq 3).13

VO(acac)214 and other forms of vanadium15 also catalyze the transformation of alkenes to epoxy alcohols using molecular oxygen as the oxidant. This process involves initial oxidation of the alkene to an allylic hydroperoxide either by radical or photolytic processes followed by intermolecular epoxidation to give primarily the epoxy alcohol and usually several byproducts. A convenient photolytic process producing singlet oxygen in the presence of the alkene and a catalytic amount of VO(acac)2 has been developed to promote this transformation in good yield and high diastereoselectivity (eq 4).14 An obvious requirement of this reaction is that the starting alkene must readily undergo photooxygenation to give the intermediate allylic hydroperoxide. Titanium Tetraisopropoxide and molybdenyl bis(acetylacetonate) also act as catalysts in this reaction, sometimes with better yields and/or selectivity.14

Oxidation of Amines.

VV/TBHP efficiently oxidizes tertiary amines to N-oxides (eq 5).16 The reaction is carried out under anhydrous conditions and therefore allows the preparation of anhydrous amine oxides. VV/TBHP oxidizes aniline to nitrobenzene (eq 6).17

Oxidation of Sulfides to Sulfoxides.

Similar to the oxidation of tertiary amines to N-oxides, VV/TBHP oxidizes sulfides to sulfoxides in high yield (eq 7).4,18 The reaction is usually carried out at room temperature in an alcoholic solvent.

Other Oxidation Reactions.

VO(acac)2 rapidly oxidizes 3,5-di-t-butylpyrocatechol at room temperature to the corresponding muconic acid anhydride, 2-pyrone, and o-quinone using oxygen as the oxidant (eq 8).19 This method is more selective for the anhydride than oxygenation with Dichlorotris(triphenylphosphine)ruthenium(II). Vv/TBHP has also been used in the catalytic oxidation of hydrocarbons.20 These reactions probably occur by radical mechanisms and are usually not highly selective.

Related Reagents.

Vanadyl Bis(acetylacetonate)-Azobisisobutyronitrile.

1. (a) Vilas Boas, L. F.; Costa Pessoa, J. In Comprehensive Coordination Chemistry; Wilkinson, G., Ed.; Pergamon: Oxford, 1987; Vol. 3, Chapter 33. (b) Mimoun, H. In Comprehensive Coordination Chemistry; Wilkinson, G., Ed.; Pergamon: Oxford, 1987; Vol. 6, Chapter 61.3.
2. Sharpless, K. B.; Michaelson, R. C. JACS 1973, 95, 6136.
3. Sheng, M. N.; Zajacek, J. G. OSC 1988, 6, 501.
4. Cenci, S.; Di Furia, F.; Modena, G.; Curci, R.; Edwards, J. O. JCS(P2) 1978, 979.
5. (a) Chisholm, M. H.; Rothwell, I. P. In Comprehensive Coordination Chemistry; Wilkinson, G., Ed.; Pergamon: Oxford, 1987; Vol. 2, Chapter 15.3. (b) Bradley, D. C.; Mehrotra, R. C.; Gaur, D. P. Metal Alkoxides; Academic: New York, 1978. (c) Clark, R. J. H. The Chemistry of Titanium and Vanadium; Elsevier: Amsterdam, 1968.
6. (a) Sharpless, K. B.; Verhoeven, T. R. Aldrichim. Acta 1979, 12, 63. (b) Rao, A. S. COS 1991, 7, Chapter 3.1. (c) Jorgensen, K. A. CRV 1989, 89, 431.
7. (a) Sheldon, R. A.; Kochi, J. K. Metal-Catalyzed Oxidations of Organic Compounds; Academic: New York, 1981. (b) Gould, E. S.; Hiatt, R. R.; Irwin, K. C. JACS 1968, 90, 4573.
8. (a) Mihelich, E. D. TL 1979, 49, 4729. (b) Rossiter, B. E.; Verhoeven, T. R.; Sharpless, K. B. TL 1979, 49, 4733.
9. (a) Ziegler, F. E.; Jaynes, B. H.; Saindane, M. T. TL 1985, 26, 3307. (b) Marino, J. P.; de la Pradilla, R. F.; Laborde, E. JOC 1987, 52, 4898. (c) Stevens, R. V.; Chang, J. H.; Lapalme, R.; Schow, S.; Schlageter, M. G.; Shapiro, R.; Weller, H. N. JACS 1983, 105, 7719. (d) Rowley, M.; Kishi, Y. TL 1988, 29, 4909.
10. (a) Luteijn, J. M.; de Groot, A. JOC 1981, 46, 3448. (b) Pirrung, M. C.; Thomson, S. A. JOC 1988, 53, 227. (c) Corey, E. J.; De, B. JACS 1984, 106, 2735. (d) Nakayama, K.; Yamada, S.; Takayama, H.; Nawata, Y.; Iitaka, Y. JOC 1984, 49, 1537.
11. Itoh, T.; Jitsukawa, K.; Kaneda, K.; Teranishi, S. JACS 1979, 101, 159.
12. Allison, K.; Johnson, P.; Foster, G.; Sparke, M. B. Ind. Eng. Chem., Prod. Res. Dev. 1966, 5, 166.
13. Lyons, J. E. Adv. Chem. Ser. 1974, 132, 64.
14. Adam, W.; Braun, M.; Griesbeck, A.; Lucchini, V.; Staab, E.; Will, B. JACS 1989, 111, 203.
15. (a) Gould, E. S.; Rado, M. J. Catal. 1969, 13, 238. (b) Lyons, J. E. TL 1974, 32, 2737. (c) Kaneda, K.; Jitsukawa, K.; Itoh, T.; Teranishi, S. JOC 1980, 45, 3004. (d) Arzoumanian, H.; Blanc, A.; Hartig, U.; Metzger, J. TL 1974, 12, 1011.
16. (a) Sheng, M. N.; Zajacek, J. G. JOC 1968, 33, 588. (b) Takano, S.; Sugihara, Y.; Ogasawara, K. H 1992, 34, 1519. (c) Kuhnen, L. CB 1966, 99, 3384.
17. Howe, G. R.; Hiatt, R. R. JOC 1970, 35, 4007.
18. (a) Curci, R.; Di Furia, F.; Testi, R.; Modena, G. JCS(P2) 1974, 752. (b) Curci, R.; Di Furia, F.; Modena, G. In Fundamental Research in Homogeneous Catalysis; Ishii, Y.; Tsutsui, M., Eds.; Plenum: New York, 1978; Vol. 2, p 255.
19. Tatsuno, Y.; Tatsuda, M.; Otsuka, S. CC 1982, 1100.
20. (a) Mimoun, H.; Chaumette, P.; Mignard, M.; Saussine, L.; Fischer, J.; Weiss, R. NJC 1983, 7, 467. (b) Spirina, I. V.; Alyasov, V. N.; Glushakova, V. N.; Sharodumora, N. A.; Sergeeva, V. P.; Balakshina, N. N.; Malennikov, V. P.; Aleksandrove, Y. A.; Razuvaev, G. A. JOC 1982, 18, 1570.

Bryant E. Rossiter&dead;

Brigham Young University, Provo, UT, USA

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