Palladium(II) Chloride-Copper(II) Chloride1


[7647-10-1]  · Cl2Pd  · Palladium(II) Chloride-Copper(II) Chloride  · (MW 177.32) (CuCl2)

[7447-39-4]  · Cl2Cu  · Palladium(II) Chloride-Copper(II) Chloride  · (MW 134.45)

(oxidation and carbonylation of alkenes; carbonylation of amines, alcohols)

Physical Data: PdCl2, mp 680 °C; CuCl2, mp 630 °C (dec).

Solubility: PdCl2 sol water, acetone, alcohol; CuCl2 sol water, acetone, alcohol.

Form Supplied in: PdCl2, red-brown crystals; CuCl2, yellow/brown powder; both widely available.

Handling, Storage, and Precautions: CuCl2 is deliquescent and forms the green-blue dihydrate on exposure to moist air.

Oxidation of Alkenes to Ketones, Aldehydes, and Acetals.2

Palladium(II) Chloride combined with Copper(II) Chloride is the catalyst for the Wacker reaction, which was originally used to oxidize ethylene to acetaldehyde.3 Subsequent work broadened the application to a variety of alkenes. Typically, terminal alkenes yield only methyl ketones.4 In the presence of alcohols, acetals are obtained.5 Cyclization reactions can occur with hydroxyalkenes.6 In general, these reactions can be accomplished more selectively with Palladium(II) Chloride-Copper(I) Chloride.

Hydrocarboxylation/Hydroesterification of Alkenes.

PdCl2/CuCl2 is a useful reagent for hydrocarboxylating alkenes to carboxylic acids (eq 1).7 The reaction proceeds in good yield and is highly regioselective, favoring the branched carboxylic acid over the linear isomer. Hydroesterification to give the analogous ester occurs equally well, again with the branched isomer predominating (eq 2).8 With a diol as the alcohol, only the monoester is obtained.9

Internal alkynes are hydroesterified to (E)-unsaturated monoesters resulting from cis addition (eq 3).10 However, terminal alkynes are oxidatively carbonylated to give predominantly the (Z)-unsaturated diesters (eq 4). Under similar conditions in the presence of base, terminal alkynes can also be non-oxidatively carbonylated to the acetylenecarboxylate ester.11

Hydroxyalkenes will cyclize under similar conditions to give the five- or six-membered ring saturated lactone (eq 5).12 Chiral additives, especially poly-L-leucine, afford the cyclized lactone with as high as 61% ee.13

Oxidative Carbonylation of Alkenes.

In contrast to hydroesterification, oxidative carbonylation (or alkoxycarbonylation) is an oxidation that converts alkenes to vinyl esters, a-alkoxy esters, or diesters depending on the reaction conditions.14 Typically, CuCl2 is used as a stoichiometric oxidant, because in the presence of oxygen and water (which would be coproduced in the presence of oxygen) the CO can be oxidized to CO2 and the alkene can be oxidized to the ketone or aldehyde. Linear, terminal alkenes are oxidized to either the alkoxy ester or to the diester, depending on whether base (NaOAc) is present or not (eq 6).15 The alkoxyester arises from trans addition whereas the diester arises from a cis addition. The choice of re-oxidant can also control the reaction pathway: CuCl2/O2 favors the branched alkoxy monoester, whereas CuCl/O2 favors the diester.16 Oxidative carbonylation can also occur using acetic anhydride solvent with NaCl.17 Cyclic alkenes give both the cis-1,2- and cis-1,3-diesters along with a variable amount of trans-2-methoxy ester.15 Allenes are oxidatively carbonylated to the a-alkoxy ester.18 Butadiene can be dicarbonylated to linear hexenedioate diesters in high yields.15e Terminal alkynes are dicarbonylated to maleic anhydride derivatives.19

Cyclization can occur with hydroxyalkenes to give pyran or furan carboxylates;20 allenes are similarly cyclized.21 The carbon-oxygen bond tends to form at the more substituted end of the double bond; the geometry of the alkene can also determine the ring size (eq 7).20 Aminoalkenes cyclize similarly, especially if protected as the carbamates, tosylamides, or ureas.22 The latter can use both nitrogen atoms to form bicyclic molecules (eq 8).

Bis-carbonylation occurs with homoallylic alcohols (eq 9).23 The use of CuCl appears to mitigate the need for additives such as epoxides or orthoesters in these reactions.18 Dihydroxy alkenes can form bicyclic ether-lactones (eq 10).24 A similar reaction occurs with a carboxylic acid group at the terminus.25

Oxidative Carbonylation of Heteroatoms.

Amines and alcohols can be oxidatively carbonylated to the carbamate and carbonate esters in alcohol solvents.26

Related Reagents.

Palladium(II) Acetate; Palladium(II) Chloride; Palladium(II) Chloride-Copper(I) Chloride.

1. (a) Maitlis, P. M. The Organic Chemistry of Palladium; Academic: New York, 1971; Vol. 2. (b) Tsuji, J. Organic Synthesis with Palladium Compounds; Springer: Berlin, 1980. (c) Henry, P. M. Palladium Catalyzed Oxidation of Hydrocarbons; Reidel: Dordrecht, 1980. (d) Heck, R. F. Palladium Reagents in Organic Syntheses; Academic: New York, 1985.
2. (a) Tsuji, J. S 1984, 369. (b) Tsuji, J. COS 1991, 7, 449.
3. Smidt, J.; Hafner, W.; Jira, R.; Sedlmeier, J.; Sieber, R.; Rüttinger, R.; Kojer, H. AG 1959, 71, 176.
4. (a) Tsuji, J.; Nagashima, H.; Nemoto, H. OS 1983, 62, 9. (b) Alper, H.; Januszkiewicz, K.; Smith, D. J. H. TL 1985, 26, 2263. (c) Januszkiewicz, K.; Alper, H. TL 1983, 24, 5159.
5. Lloyd, W. G.; Luberoff, B. J. JOC 1969, 34, 3949.
6. Reviews: (a) Heck, R. F. Palladium Reagents in Organic Syntheses; Academic: New York, 1985; p 66. (b) Hosokawa, T.; Murahashi, S.-I. H 1992, 33, 1079.
7. Alper, H.; Woell, J. B.; Despeyroux, B.; Smith, D. J. H. CC 1983, 1270.
8. Despeyroux, B.; Alper, H. ANY 1983, 415, 148.
9. Fergusson, S. B.; Alper, H. CC 1984, 1349.
10. Alper, H.; Despeyroux, B.; Woell, J. B. TL 1983, 5691.
11. Tsuji, J.; Takahashi, M.; Takahashi, T. TL 1980, 21, 849.
12. (a) Alper, H.; Leonard, D. TL 1985, 26, 5639. (b) Alper, H.; Leonard, D. CC 1985, 511.
13. Alper, H.; Hamel, N. CC 1990, 135.
14. Fenton, D. M.; Steinwood, P. J. JOC 1972, 37, 2034.
15. (a) Stille, J. K.; James, D. E.; Hines, L. F. JACS 1973, 95, 5062. (b) Stille, J. K.; Hines, L. F.; Fries, R. W.; Wong, P. K., James, D. E.; Lau, K. Adv. Chem. Ser. 1974, 132, 90. (c) James, D. E.; Hines, L. F.; Stille, J. K. JACS 1976, 98, 1806. (d) James, D. E.; Hines, L. F.; Stille, J. K. JACS 1976, 98, 1810. (e) Stille, J. K.; Divakaruni, R. JOC 1979, 44, 3474.
16. (a) Inomata, K.; Toda, S.; Kinoshita, H. CL 1990, 1567. (b) Toda, S.; Miyamoto, M.; Kinoshita, H.; Inomata, K. BCJ 1991, 64, 3600.
17. Urata, H.; Fujita, A.; Fuchikami, T. TL 1988, 29, 4435.
18. Alper, H.; Hartstock, F. W.; Despeyroux, B. CC 1984, 905.
19. Zargarian, D.; Alper, H. OM 1991, 10, 2914.
20. Semmelhack, M. F.; Bodurow, C. JACS 1984, 106, 1496.
21. (a) Lathbury, D.; Vernon, P.; Gallagher, T. TL 1986, 27, 6009. (b) Walkup, R. D.; Park, G. TL 1987, 28, 1023.
22. (a) Tamaru, Y.; Kobayashi, T.; Kawamura, S.; Ochiai, H.; Yoshida, Z. TL 1985, 26, 4479. (b) Tamaru, Y.; Hojo, M.; Higashimura, H.; Yoshida, Z. JACS 1988, 110, 3994. (c) Tamaru, Y.; Hojo, M.; Yoshida, Z. JOC 1988, 53, 5731. (d) Tamaru, Y.; Tanigawa, H.; Itoh, S.; Kimura, M.; Tanaka, S.; Fugami, K.; Sekiyama, T.; Yoshida, Z. TL 1992, 33, 631. (e) review: Tamaru, Y.; Yoshida, Z. JOM 1987, 334, 213.
23. (a) Tamaru, Y.; Hojo, M.; Yoshida, Z. TL 1987, 28, 325. (b) Tamaru, Y.; Hojo, M.; Yoshida, Z. JOC 1991, 56, 1099.
24. Tamaru, Y.; Kobayashi, T.; Kawamura, S.; Ochiai, H.; Hojo, M.; Yoshida, Z. TL 1985, 26, 3207.
25. Tamaru, Y.; Higashimura, H.; Naka, K.; Hojo, M.; Yoshida, Z. AG(E) 1985, 24, 1045.
26. (a) Alper, H.; Hartstock, F. W. CC 1985, 1141. (b) Alper, H.; Vasapollo, G.; Hartstock, F. W.; Mlekuz, M.; Smith, D. J. H.; Morris, G. E. OM 1987, 6, 2391. (c) Tam, W. JOC 1986, 51, 2977.

Timothy T. Wenzel

Union Carbide Corporation, South Charleston, WV, USA

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