Phenylthallium Bis(trifluoroacetate)1


[23586-54-1]  · C10H5F6O4Tl  · Phenylthallium Bis(trifluoroacetate)  · (MW 507.53)

(reagent for preparation of substituted benzenes)

Physical Data: mp 184-189 °C

Solubility: sol MeOH, EtOH, MeCN, THF, DMSO.

Form Supplied in: colorless crystalline solid. Drying: in vacuo over sodium hydroxide.

Preparative Method: readily prepared from benzene.

Handling, Storage, and Precautions: all thallium compounds are extremely toxic (cumulative toxicity) to inhalation, skin contact, and ingestion; extreme caution should be used when handling these materials; use in a fume hood.

General Discussion.

Phenylthallium bis(trifluoroacetate) is a readily accessed and versatile reagent for conversion into a wide variety of other aromatic compounds. Uses for this reagent flourished once the straightforward route to aryl bistrifluoroacetates (treatment of the aromatic compound with a solution of Thallium(III) Trifluoroacetate (TTFA) in TFA) was published in 1969.2 The preparation of phenylthallium bis(trichloroacetate) has also been described. This reagent undergoes iodination, chlorination, nitrile formation, selenation, nitration, coupling, and palladium-catalyzed alkenation in good yield.3 A more recent modification4 allows the replacement of a trimethylsilyl group with thallium bis(trifluoroacetate) (eq 1).

Phenylthallium bis(trifluoroacetate) can be subsequently converted into numerous aromatic compounds, often without isolation of the bis(trifluoroacetate) salt. Transformation into aryl iodides is readily accomplished (eq 2)5 with rapid replacement of the thallium by iodine in high yield.

A method for the preparation of m-iodonitrobenzene from phenylthallium bis(trifluoroacetate) has been developed (eq 3).6 This simple method, noteworthy for its regiospecificity, avoids the often circuitous route of dinitration, mono-reduction to the amine, diazotization, and iodination.

Preparation of aryl nitroso and nitrile compounds from arylthallium salts has also been reported. In the case of nitrosation, a one-pot reaction of the arylthallium bis(trifluoroacetate) with n-propyl nitrite and HCl at rt in chloroform leads directly to the para-substituted nitroso compound.7 For the preparation of aryl nitriles, a variety of nitrile-delivery reagents have been examined (Potassium Cyanide,8 Cu(CN)2,9a Copper(I) Cyanide9) under varying conditions (photolysis in aqueous solution,8 pyridine,9a or acetonitrile9 reflux). The reaction of the aryl bis(trifluoroacetate) with copper(I) cyanide in acetonitrile gives the most reliable results in moderate to good yields, and is quite general (eq 4).9b

Phenols are also readily accessed by this methodology. In an interesting illustration of both boron and thallium chemistry, it was found that treatment of phenylthallium bis(trifluoroacetate) with Diborane yields Dihydroxy(phenyl)borane, which can be oxidized under standard conditions to give phenol (eq 5).10

Conversions of phenylthallium bis(trifluoroacetate) into thiocyanates, selenium compounds, and unsymmetric sulfones have also been described.11 All these transformations are carried out by heating the arylthallium salt with the appropriate reagent in dioxane. Copper(II) is critical to the success of these transformations, which proceed in moderate yield.

Carbonylation of phenylthallium bis(trifluoroacetate) has also been successfully demonstrated, providing methyl benzoate.12

In yet another demonstration of the synthetic utility of arylthallium bis(trifluoroacetates), the preparation of unsymmetrical biphenyl compounds has been developed (eq 6).13 Capture of the aryl radical by the solvent (benzene) leads to the product. Attempts to extend this methodology by the use of pyridine as solvent were unsuccessful. Use has been made of arylthallium reagents in a Palladium(II) Chloride-catalyzed preparation of symmetrical biaryls in yields ranging from 12 to 75% (eq 7).14

Related Reagents.

Thallium(I) Bromide; Thallium(III) Trifluoroacetate; Thallium(III) Trifluoroacetate--Palladium(II) Acetate.

1. (a) McKillop, A. PAC 1975, 43, 463. (b) McKillop, A.; Taylor, E. C. In Comprehensive Organometallic Chemistry; Wilkinson, G.; Stone, G. A.; Abel, E. W., Eds.; Pergamon: Oxford, 1982; Vol. 7, p 465.
2. (a) McKillop, A.; Fowler, J. L.; Zelesko, M. J.; Hunt, J. D.; Taylor, E. C.; McGillivray, G. TL 1969, 2423. See also: (b) McKillop, A.; Hunt, J. D.; Zelesko, M. J.; Fowler, J. S.; Taylor, E. C.; McGillivray, G.; Kienzle, F. JACS 1971, 93, 4841. (c) Taylor, E. C.; Kienzle, F.; Robey, R. L.; McKillop, A.; Hunt, J. D. JACS 1971, 93, 4845.
3. Uemura, S.; Miyoshi, H.; Wakasugi, M.; Okano, M.; Itoh, O.; Izumi, T.; Ichikawa, K. BCJ 1980, 53, 553.
4. Bell, H. C.; Kalman, J. R.; Pinhey, J. T.; Sternhell, S. TL 1974, 3391.
5. McKillop, A.; Hunt, J. D.; Zelesko, M. J.; Fowler, J. S.; Taylor, E. C.; McGillivray, G.; Kienzle, F. JACS 1971, 93, 4841.
6. Taylor, E. C.; Altland, H. W.; McKillop, A. JOC 1975, 40, 3441.
7. Taylor, E. C.; Danforth, R. H.; McKillop, A. JOC 1973, 38, 2088.
8. Taylor, E. C.; Altland, H. W.; Danforth, R. H.; McGillivray, G.; McKillop, A. JACS 1970, 92, 3520.
9. (a) Uemura, S.; Ikeda, Y.; Ichikawa, K. T 1972, 28, 3025. (b) Taylor, E. C.; Katz, A. H.; McKillop, A. TL 1984, 25, 5473.
10. Breuer, S. W.; Pickles, G. M.; Podesta, J. C.; Thorpe, F. G. CC 1975, 36.
11. (a) Thiocyanation: Uemura, S.; Uchida, S.; Okano, M.; Ichikawa, I. BCJ 1973, 46, 3254. (b) Selenation: Uemura, S.; Toshimitsu, A.; Okano, M.; Ichikawa, K. BCJ 1975, 48, 1925. (c) Sulfone formation: Hancock, R. A.; Orszulik, S. T. TL 1979, 3789.
12. Larock, R. C.; Fellows, C. A. JOC 1980, 45, 363.
13. Taylor, E. C.; Kienzle, F.; McKillop, A. JACS 1970, 92, 6088.
14. Uemura, S.; Ikeda, Y.; Ichikawa, K. CC 1971, 390.

Mukund P. Sibi

North Dakota State University, Fargo, ND, USA

Nancy E. Carpenter

University of Minnesota, Morris, MN, USA

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