Palladium(II) Acetylacetonate

[14024-61-4]  · C10H14O4Pd  · Palladium(II) Acetylacetonate  · (MW 304.66)

(occasionally used as a homogeneous PdII catalyst; used mainly as source of Pd0 catalysts after reduction in the presence or absence of ligands)

Physical Data: mp 205 °C (dec).

Solubility: insol H2O; slightly sol benzene, ether, ethanol; sol chloroform.

Form Supplied in: orange needle-like crystals; widely available.

Purification: recrystallization from benzene.

Generation of Carbenes from Diazo Compounds.

Pd(acac)2 is used as a catalyst for carbene generation from diazo compounds. For example, treatment of the a-diazo-b-keto ester shown in eq 1 with Pd(acac)2 (9 mol %) at 80 °C in benzene gave the cyclopropane derivative in 78% yield as the only isolated product.1 This product is different from the furan derivative obtained by the catalysis of Rh2(OAc)4.

Generation of Pd0 Species.

Many reactions are catalyzed by Pd0 catalysts.2 The Pd0 complexes Tetrakis(triphenylphosphine)palladium(0) and Bis(dibenzylideneacetone)palladium(0) are commercially available. More conveniently, PdII salts are reduced in situ to Pd0. For this purpose, Palladium(II) Acetate is most widely used, but Pd(acac)2 is sometimes preferable because it can be easily obtained in better quality by recrystallization. Pd(acac)2 is reduced in situ in the presence or absence of a ligand (L) to form Pd0Ln complexes, which can be used as catalysts. Various reducing agents such as metal hydrides (NaBH4, LiAlH4, i-Bu2AlH), RLi, RMgX, CO, alkenes, and phosphines are used. In the most convenient method of reduction, Pd(acac)2 is treated with Tri-n-butylphosphine in THF (eq 2). The solution turns quickly to pale yellow, and a very active Pd0 catalyst is generated.3 Reactions catalyzed by Pd0 in the presence, or absence, of a phosphine ligand are shown below.

Hydrogenolysis of Allylic Formates and Carbonates.

The catalyst shown in eq 2 has been used for the regioselective and stereoselective generation of either C-20 epimer in steroid side chains by the Pd0-catalyzed hydrogenolysis of C-20 allylic carbonates.4 The unnatural stereochemistry at C-20 was generated from the trans-allylic carbonate (eq 3), and the natural stereochemistry was generated by the hydrogenolysis of the cis-allylic carbonate (eq 4). Commonly used Pd(Ph3P)4 or Pd2(dba)3 were inactive. This method of the palladium-catalyzed hydrogenolysis has been applied to the regioselective and stereoselective generation of cis- and trans-fused decalins and hydrindanes.5

Displacement Reactions of Vinyl Sulfones.

Pd0 species generated from Pd(acac)2 and a Grignard reagent catalyze the reaction of vinyl sulfones with Grignard reagents. Displacement takes place with Methylmagnesium Bromide and hydrogenolysis takes place with Ethylmagnesium Bromide (eq 5).6,7

1. Hoye, T. R.; Dinsmore, C. J.; Johnson, D. S.; Korkowski, P. F. JOC 1990, 55, 4518.
2. (a) Tsuji, J. Organic Synthesis with Palladium Compounds; Springer: Berlin, 1980. (b) Heck, R. F. Palladium Reagents in Organic Syntheses; Academic: New York, 1985. (c) Trost, B. M. COS 1991, 3, 435, 481, 521, 551; 1991, 4, 585. (d) Tsuji, J. Palladium Reagents and Catalysts; Wiley: New York, 1995.
3. Mandai, T.; Matsumoto, T.; Tsuji, J.; Saito, S. TL 1993, 34, 2513.
4. Mandai, T.; Matsumoto, T.; Kawada, M.; Tsuji, J. JOC 1992, 57, 6090; T 1994, 50, 475.
5. Mandai, T.; Matsumoto, T.; Kawada, M.; Tsuji, J. JOC 1992, 57, 1326; Mandai, T.; Matsumoto, T.; Kawada, M.; Tsuji, J. T 1993, 49, 5483.
6. Fabre, J. L.; Julia, M. TL 1983, 24, 4311.
7. Belloch, J.; Virgili, M. TL 1991, 32, 4583.

Jiro Tsuji

Okayama University of Science, Japan

Copyright 1995-2000 by John Wiley & Sons, Ltd. All rights reserved.