[31277-98-2]  · C52H48P4Pd  · Bis[1,2-bis(diphenylphosphino)ethane]palladium(0)  · (MW 903.26)

(homogeneous catalyst most widely used in allylic substitution reactions;5 good catalyst for bulky substrates;1 slowly dissociating ligand that gives good stereoselectivity5)

Alternate Names: 1,2-ethylenebis(diphenylphosphine)palladium; bis(diphenylphosphinoethane)palladium(0); ethanediylbisdiphenylphosphinepalladium(0).

Physical Data: mp 234 °C.2

Solubility: sol nonprotic solvents.

Form Supplied in: yellow solid.

Analysis of Reagent Purity: 31P and 1H NMR in CDCl3 and 31P NMR in benzene.3

Preparative Methods: by reduction of palladium(II) with NaBH4,2 DIBAL-H, hydrazine, KOH/phosphine,4 or F-.3 Most conveniently prepared in situ from Pd(dba)2 or Pd(OAc)2.5,6

Purification: recrystallized from benzene-ethanol2 or ethanol.5

Handling, Storage, and Precautions: air and light sensitive. If stored under nitrogen or argon it is stable for about one month. Avoid inhalation. Use in a fume hood.

General Considerations.

Pd(dppe)2 is a homogeneous catalyst, commercially available but usually prepared in situ because of its sensitivity to oxygen.5,6 It is often used as a catalyst in allylic substitution reactions. This reaction proceeds via formation of a (p-allyl)palladium(II) complex by oxidative addition of palladium(0) to an allylic substrate. Subsequent nucleophilic attack on the p-allyl gives the product and liberates a palladium(0) complex. The latter complex can then activate a new substrate and this makes the reaction catalytic. The reaction is stereoselective and net retention is generally observed as a result of a double inversion (eq 1).

With the exception of Pd(dppe)21b there are few zerovalent palladium complexes that offer any advantage over the widely used Tetrakis(triphenylphosphine)palladium(0). Dppe is a bidentate ligand and therefore sterically less demanding than PPh3. It is used for bulky substrates and in reactions where it is important to have a stable initial alkene-metal complex.1a,7

In allylic substitution reactions, dppe forms a stable (p-allyl)palladium complex and the stability of the complex makes geometrical isomerization possible prior to nucleophilic attack (eq 2).8,9 If the starting material is cis, the trans product can be obtained if appropriate reaction conditions are used.8

Dppe is used in stereoselective allylic substitution reactions.10 Because of its slow dissociation from palladium in Pd(dppe)2, only a little Pd(dppe) is present in the solution. This is important because PdL2 is more nucleophilic than PdL411a and can displace Pd in (p-allyl)palladium complexes and cause a loss of stereoselectivity (eq 3).10,11

Different ligands afford different products in Pd0-mediated allylic substitutions.12 For example, dialkylpalladium complexes with chelating bidentate or monodentate phosphine ligands, respectively, react via different pathways. If a bidentate ligand with a carbon chain of 2-4 carbons between the phosphorus atoms is used, a cis complex is obtained.13 If instead a monodentate ligand or a bidentate ligand with a longer carbon chain is used, a trans complex is formed.14 These different complexes give rise to different products.15 Dppe favors reductive elimination whereas monodentate ligands favor b-elimination (eq 4). Variations in the carbon backbone can also affect the chelating power of the bidentate ligand and give rise to different product distributions.12i

In general, reactions catalyzed by Pd(dppe)2 are sensitive to the reaction conditions.16 By varying the temperature,12j solvent,7,16d,17 phosphine to palladium ratio,5,6,15 the source of Pd(dppe)2,5,6 or added bases,18 different products may be obtained.

Reactions with Pd(dppe)2 as the Catalyst.

There are some reactions where it is essential to use Pd(dppe)2 as the catalyst to obtain good results. For example, allylic substitution reactions where primary or secondary amines,8 Schiff bases,6,9a or carbanions9-19 act as nucleophiles give highest yields using the title reagent. One example is the cyclopropane forming reaction shown in eq 5.5,12f,20 Another example can be found in an annulation reaction used in a synthesis of alloyohimbone.21

Pd(dppe)2 is the best reagent for oxidation of cyclohexene,22 for CO insertion reactions,23 in some reactions employing CO2,12h,24 for the rearrangement of tetrahydrofurans to cyclopentanones,7 in the synthesis of 1,3-dienes by elimination of HOAc in an allylic acetate,5 and for the formation of a,b-unsaturated ketones from allyl enol carbonates.25 There are other reactions where Pd(dppe)2 can be used but is not always the best catalyst. The title reagent has been used for coupling reactions,16f,26 in homogenous hydrogenation,4b in oxidative homologation,27 and as a promotor for isomerizations of a-iodocarbonyls involving radical rather than organometallic intermediates.28

1. (a) Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G. Principles and Applications of Organotransition Metal Chemistry; University Science Books: Mill Valley, CA, 1987. (b) Heck, R. F. Palladium Reagents in Organic Syntheses; Academic: Orlando, FL, 1985.
2. Chatt, J.; Hart, F. A.; Watson, H. R. JCS 1962, 2537.
3. Lindsay, C. H.; Benner, L. S.; Balch, A. L. IC 1980, 19, 3503.
4. (a) Trost, B. M.; Schmuff, N. R.; Miller, M. J. JACS 1980, 102, 5979. (b) Stern, E. W.; Maples, P. K. J. Catal. 1972, 27, 120. (c) Mason, M. R.; Verkade, J. G. OM 1990, 9, 864.
5. Bäckvall, J. E.; Vågberg, J. O.; Zercher, C.; Genêt, J. P.; Denis, A. JOC 1987, 52, 5430.
6. Genêt, J. P.; Uziel, J.; Juge, S. TL 1988, 29, 4559.
7. Trost, B. M.; Runge, T. A. JACS 1981, 103, 7550.
8. Genêt, J. P.; Balabane, M.; Bäckvall, J. E.; Nyström, J. E. TL 1983, 24, 2745.
9. (a) Genêt, J. P.; Juge, S.; Achi, S.; Mallart, S.; Ruiz Montes, J.; Levif, G. T 1988, 44, 5263. (b) Visentin, G.; Piccolo, O.; Consiglio, G. J. Mol. Catal. 1990, 61, L1.
10. Granberg, K. L.; Bäckvall, J. E. JACS 1992, 114, 6858.
11. (a) Murahashi, S.-I.; Taniguchi, Y.; Imada, Y.; Tanigawa, Y. JOC 1989, 54, 3292. (b) Takahashi, T.; Jinbo, Y.; Kitamura, K.; Tsuji, J. TL 1984, 25, 5921.
12. (a) &AAring;kermark, B.; Vitagliano, A. OM 1985, 4, 1275. (b) &AAring;kermark, B.; Zetterberg, K.; Hansson, S.; Krakenberger, B.; Vitagliano, A. JOM 1987, 335, 133. (c) Tolman, C. A. CRV 1977, 77, 313. (d) Dekker, G. P. C. M.; Elsevier, C. J.; Vrieze, K.; van Leeuwen, P. W. N. M.; Roobeck, C. F. JOM 1992, 430, 537. (e) Alper, H.; Mahatantila, C. P. OM 1982, 1, 70. (f) Hansawa, Y.; Ishizawa, S.; Kobayashi, Y. CPB 1988, 36, 4209. (g) Cuvigny, T.; Julia, M.; Rolando, C. JOM 1985, 285, 395. (h) Inoue, Y.; Hibi, T.; Satake, M.; Hashimoto, H. CC 1979, 982. (i) Consiglio, G.; Morandini, F. CRV 1987, 87, 761. (j) An unexpected temperature dependency has been observed; Nilsson, Y. I. M.; Andersson, P. G.; Bäckvall, J. E. JACS 1993, 115, 6609.
13. Rosevear, D. T.; Stone, F. G. A. JCS(A) 1968, 164.
14. (a) Takahashi, K.; Miyake, A.; Hata, G. BCJ 1972, 45, 1183. (b) Iwamoto M.; Yuguchi, S. JOC 1966, 31, 4290. (c) Hata, G.; Miyake, A. BCJ 1968, 41, 2762.
15. (a) Yamamoto, T.; Saito, O.; Yamamoto, A. JACS 1981, 103, 5600. (b) Tatsumi, K.; Hoffman, R.; Yamamoto, A.; Stille, J. K. BCJ 1981, 54, 1857. (c) Ozawa, F.; Kurihara, K.; Yamamoto, T.; Yamamoto, A. BCJ 1985, 58, 399. (d) Yamamoto, A.; Yamamoto, T.; Komiya, S.; Ozawa, F. PAC 1984, 56, 1621. (e) Alper, H.; Hashem, K.; Heveling, J. OM 1982, 1, 775.
16. (a) Trost, B. M. ACR 1980, 13, 385. (b) Cuvigny, T.; Julia, M.; Rolando, C. JOM 1985, 285, 395. (c) Trost, B. M.; Molander, G. A. JACS 1981, 103, 5969. (d) Trost, B. M.; Runge, T. A. JACS 1981, 103, 7559. (e) Shimizu, I.; Minami, I.; Tsuji, J. TL 1983, 24, 1797. (f) Perry, R. J.; Turner, S. R. JOC 1991, 56, 6573. (g) Genêt, J. P.; Grisoni, S. TL 1986, 27, 4165. (h) Nicholas, P. P. JOC 1987, 52, 5266.
17. Shimizu, I.; Tsuji, J. JACS 1982, 104, 5844.
18. Genêt, J. P.; Grisoni, S. TL 1986, 27, 4165.
19. Genêt, J. P.; Balabane, M.; Legras, Y. TL 1982, 23, 331.
20. Genêt, J. P.; Balabane, M.; Charbonnier, F. TL 1982, 23, 5027.
21. Godleski, S. A.; Villhauer, E. B. JOC 1986, 51, 486.
22. Fusi, A.; Ugo, R.; Fox, F.; Pasini, A.; Cenini, S. JOM 1971, 26, 417.
23. Ciattini, P. G.; Morera, E.; Ortar, G. TL 1991, 32, 6449.
24. Inoue, Y.; Sasaki, Y.; Hashimoto, H. CC 1975, 718.
25. Shimizu, I.; Minami, I.; Tsuji, J. TL 1983, 24, 1797.
26. Madin, A.; Overman, L. E. TL 1992, 33, 4859.
27. (a) Li, P.; Alper, H. JOC 1986, 51, 4354. (b) Galamb, V.; Gopal, M.; Alper, H. OM 1983, 2, 801.
28. Curran, D. P.; Chang, C.-T. TL 1990, 31, 933.

Ylva I. M. Nilsson & Jan-E. Bäckvall

Uppsala University, Sweden

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