Thallium(I) Cyclopentadienide1

[34822-90-9]  · C5H5Tl  · Thallium(I) Cyclopentadienide  · (MW 269.48)

(cyclopentadienyl ligand)

Physical Data: mp >300 °C.

Solubility: sol organic solvents.

Form Supplied in: light yellow solid readily prepared from thallium hydroxide and dicyclopentadiene;2 commercially available. Drying: purified by sublimation.

Handling, Storage, and Precautions: stable for several months if stored under nitrogen in a Schlenk flask kept in the dark. All thallium compounds are extremely toxic to inhalation, skin contact, and ingestion. Toxicity is cumulative. Extreme caution should be used when handling these materials. Use in a fume hood.

General Discussion.

Thallium(I) cyclopentadienide is a versatile reagent for the introduction of the cyclopentadienyl ligand into metal complexes.3 For example, a novel iridium sandwich complex was prepared in 37% yield starting from TlCp (eq 1).4

Monosubstituted cyclopentadienes can be readily prepared from the reaction of TlCp and alkylating agents. This reagent is superior compared to lithium or sodium cyclopentadienide, since isomerization of the resultant monosubstituted cyclopentadiene is minimal. Additionally, product isolation is very simple since the thallium halide byproduct is very insoluble in organic solvents. In a synthesis of prostaglandins, monosubstituted cyclopentadienes were prepared using thallium cyclopentadienide (eq 2).5 The same strategy has been used by others to prepare several 5-substituted 1,3-cyclopentadienes cleanly.6

TlCp is also a convenient precursor for the preparation of 5-halo-1,3-cyclopentadiene (eq 3)7 and 5-heteroatom-substituted 1,3-cyclopentadiene (eq 4).8

TlCp reacts with acyl iodides to provide 1-acyl-1,3-cyclopentadienes in good yields (eq 5).9 The product dienes were used in an ensuing Diels-Alder reaction without isolation. The corresponding reaction with acid chlorides was too slow to be of practical utility.

TlCp reacts with electron-deficient alkenes such as Tetracyanoethylene by an addition-elimination pathway to produce an ionic thallium(I) salt (eq 6).10

1. (a) McKillop, A. PAC 1975, 43, 463. (b) McKillop, A.; Taylor, E. C. In Comprehensive Organometallic Chemistry; Wilkinson, G., Ed.; Pergamon: Oxford, 1982; Vol. 7, p 465.
2. Nielson, A. J.; Rickard, C. E. F.; Smith, J. M. Inorg. Synth. 1986, 24, 97.
3. Szajeck, L. P.; Shapley, J. R. OM 1991, 10, 2512.
4. The actual bonding situation in TlCp is a matter of debate. The h1 structure is drawn here for convenience.
5. Corey, E. J.; Koelliker, U.; Neuffer, J. JACS 1971, 93, 1489.
6. (a) Battiste, M. A.; Timberlake, J. F. JOC 1977, 42, 176. (b) Madhavan, G. V. B.; Martin, J. C. JOC 1986, 51, 1287. (c) Ranganathan, S.; Ranganathan, D.; Iyengar, R. T 1976, 32, 961.
7. Saunders, M.; Berger, R.; Jaffe, A.; McBride, J. M.; O'Neill, J.; Breslow, R.; Hoffmann, Jr., J. M.; Perchonock, C.; Wasserman, E.; Hutton, R. S.; Kuck, V. J. JACS 1973, 95, 3017.
8. Ishida, M.; Aoyama, T.; Kato, S. CL 1989, 663.
9. Grundke, G.; Hoffmann, H. M. R. JOC 1981, 46, 5428.
10. Freeman, M. B.; Sneddon, L. G. IC 1980, 19, 1125.

Mukund P. Sibi

North Dakota State University, Fargo, ND, USA

Nancy E. Carpenter

University of Minnesota, Morris, MN, USA

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