Cyclopentadiene thallium sulfate

In contrast to other organothallium(I) compounds, cyclopentadienyl-thallium(I) is a remarkably stable compound. Samples can be stored in sealed bottles for months without appreciable decomposition occurring it is unaffected by water and dilute alkali and it is only slowly oxidized by air at room temperature. Cyclopentadienyltballium(I) was first prepared by Meister in 1956 by addition of freshly distilled cyclopentadiene to a suspension of thallium(I) sulfate in dilute potassium hydroxide solution 101, 102). A number of variations of this procedure have been described (5, 25, 34, 56), and the compound has been made in other ways 35, 56,110, 164), but Meister s preparation, in which the yield of crude product is greater than 90%, remains the method of choice. Purification of crude cyclopenta-dienylthallium(I) is best accomplished by vacuum sublimation, and purity of samples can readily be assessed by gas-liquid chromatography on silicone oil at 170° C using hydrogen as carrier gas (7). 

Thallium(I) sulfate (25 g, 0.0495 mole) and sodium hydroxide (8 g, 0.2 mole) are dissolved in 250 mL of water in a 500-mL round-bottomed flask. Freshly cracked cyclopentadiene (8.2 mL) is added, the flask is stoppered, and the solution is stirred magnetically for 12 hr. The brown precipitate is removed by filtering, washed with 50 mL of water followed by 50 mL of methanol, and dried under vacuum for 2 hr. The solid is transferred to a water-cooled sublimation apparatus. A plug of glass wool is placed on top, and the TlCp is sublimed at 90-100° at 10" torr. The sublimation should be continued until no further product sublimes onto the cold finger after the bulk of the TlCp has been scraped away. A brown powdery residue remains after the sublimation is completed. Yield 24.4 g, (91% ). 

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