Lithium Trichloropalladate

LiPdCl3

[22587-92-4]  · Cl3LiPd  · Lithium Trichloropalladate  · (MW 219.71)

(catalyst for alkylation and arylation of alkenes by organomercurials;1-12 catalyst for heteroannulation reactions;13-16 catalyst for coupling of organometallics with aryl and alkyl halides17-20)

Solubility: prepared and used in acetonitrile; THF, DMSO, HMPA, H2O have been used as solvent additives in reactions.

Preparative Methods: usually prepared as a solution in acetonitrile by stirring anhydrous Palladium(II) Chloride with a small excess of anhydrous Lithium Chloride overnight at rt,1 or by refluxing for 30-60 min.5-8 Obviously, this reagent exists as a complex with the solvent.

Handling, Storage, and Precautions: the solution of LiPdCl3 in acetonitrile is usually used immediately after preparation. No data are available for the toxicity of this compound.

Arylation and Alkylation of Alkenes with Organomercurials.

Organomercury compounds react with LiPdCl3 (see also Dilithium Tetrachloropalladate(II)) to give organopalladium compounds that undergo the alkene insertion-elimination process to give aryl(alkenyl)-substituted alkenes (eq 1).1 This reaction is sometimes called the Heck reaction.

Palladium is readily reoxidized under the reaction conditions by mercury(II) salts (or Copper(II) Chloride) and thus only catalytic amounts are required.1,3,4,9 Practically any arylmercury(II) salt will function as an arylating agent in this reaction. In general, strong electron-donating groups (p-methoxy, o-hydroxy, p-diethylamino) decrease the yields, while good coordinating groups, for example amino groups, retard or even completely stop the reaction because they form stable, unreactive complexes with palladium.1 The rates of reaction and the regioselectivity depend on both steric and electronic factors.1,2 The less sterically hindered the alkene, the greater the rate, and the new C-C bond is formed at the least sterically hindered or at the most electron-deficient carbon atom. The regioselectivity is highest when a strong electron-withdrawing group such as CN, CO2Me, or Ph is attached to the double bond and therefore styrene, acrylonitrile, acrolein, and methyl acrylate are the most useful alkenes in the Heck reaction.1-9 Quinones can be also used as substrates for arylation.11 Several interesting examples of heterocyclic mercury salts have been used as arylation agents, including porphyrins,5,12 substituted pyrroles,8 and sydnones.7 Utilization of vinyl mercurials gives conjugated dienes.3,4

Heteroannulation.

A variety of oxygen- and nitrogen-containing heterocycles can be prepared from p-allylpalladium compounds bearing carboxylic acid,14,15 phenol,14,16 alcohol,14 amide,14 and amino13 functionality. Addition of base liberates an oxygen or nitrogen nucleophile that displaces the palladium with the formation of the carbon-heteroatom bond. Usually these p-allylpalladium compounds are prepared in situ by reaction of alkenes or dienes, as well as vinylcyclopropanes, with organomercurials and LiPdCl3. Functional groups necessary for further cyclization can be attached either to the organomercurial (eq 2)14,16 or the alkene (eq 3).15 The shortcoming of this procedure is the need to use equal amounts of the palladium salt and organomercurial.

Arylation of Unsaturated Compounds.

Arylmercurials react with allylic halides in the presence of LiPdCl3 and CuCl2 (as reoxidant) at room temperature in acetonitrile to produce allyl aromatic derivatives (eq 4). A wide variety of allyl aromatic compounds can be obtained by this procedure, even ones containing nitro, ester, and aldehyde groups.17 Catalytic amounts of LiPdCl3 and 10-30 mol% of CuCl2 generally must be used to obtain optimum yields.

LiPdCl3 has also been used, among other palladium catalysts, for cross-coupling reactions of organometallic compounds with aryl halides.18-20


1. (a) Heck, R. F. JACS 1968, 90, 5518. (b) Heck, R. F. Organotransition Metal Chemistry; Academic: New York, 1974.
2. Yamamoto, A. Organotransition Metal Chemistry; Wiley: New York, 1986.
3. Kim, J. I.; Lee, J. T. Bull. Korean Chem. Soc. 1986, 7, 472.
4. Kim, J. I.; Lee, J. T. Bull. Korean Chem. Soc. 1986, 7, 142.
5. Smith, K. M.; Miura, M.; Morris, I. K. JOC 1986, 51, 4660.
6. Nizova, G. V.; Shul'pin, G. B. IZV 1987, 2070.
7. Kalinin, V. N.; Min, S. F. Metallorg. Khim. 1989, 2, 473.
8. Ganske, J. A.; Pandey, R. K.; Postich, M. J.; Snow, K. M.; Smith, K. M. JOC 1989, 54, 4801.
9. Bumagin, N. A.; Andryukhova, N. P.; Beletskaya, I. P. DOK 1990, 313, 107.
10. Gupta, R. B.; Kaloustian, M. K.; Eranck, R. W.; Blount, J. F. JACS 1991, 113, 359.
11. Singh, P. K.; Rohtagi, B. K.; Khanna, R. N. SC 1992, 22, 987.
12. Morris, I. K.; Snow, K. M.; Smith, N. W.; Smith, K. M. JOC 1990, 55, 1231.
13. Kasahara, A.; Murakami, S.; Shimizu, I. CI(L) 1982, 906.
14. Larock, R. C.; Harrison, L. W.; Hsu, M. H. JOC 1984, 49, 3664.
15. Larock, R. C.; Leuck, D. J.; Harrison, L. W. TL 1987, 28, 4977.
16. Larock, R. C.; Song, H. SC 1989, 19, 1463.
17. Heck, R. F. JACS 1968, 90, 5531.
18. Bumagin, N. A.; Kalinovskii, I. O.; Ponomarov, A. B.; Beletskaya, I. P. DOK 1982, 265, 1138.
19. Bumagin, N. A.; Bumagina, I. G.; Beletskaya, I. P. DOK 1984, 274, 818.
20. Bumagin, N. A.; Kalinovskii, I. O.; Beletskaya, I. P. IZV 1983, 1619.

Vladimir V. Popik

St. Petersburg State University, Russia



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