1,2-Bis(diphenylphosphino)ethane

[1663-45-2]  · C26H24P2  · 1,2-Bis(diphenylphosphino)ethane  · (MW 398.42)

(ligand for metal-catalyzed allylic alkylation;1 decarboxylation of allylic esters;2 1,3-diene synthesis;3 cycloaddition reactions;4 carbonylation reactions5)

Alternate Name: DIPHOS; dppe.

Physical Data: mp 140-142 °C.

Solubility: sol THF, CHCl3, CH2Cl2, Et2O, and other organic solvents.

Form Supplied in: white solid; widely available.

Handling, Storage, and Precautions: solutions are readily oxidized to the phosphine oxide and should be handled under N2 or Ar. Solid samples can be handled in air. DIPHOS exhibits cytotoxic activity.

Allylation.

DIPHOS has been extensively used for palladium-catalyzed addition of nucleophiles to allylic substrates. Addition of enolates to allylic acetates provides a convenient method for the allylation of ketones (eq 1).1 A variety of nitrogen6 and sulfur7 nucleophiles can also be utilized. Addition of diethyl sodiomalonate to vinylcyclopropyl tosylates produces methylenecyclopropanes (eq 2).8 Regioselective alkylation of allylic dicarbonates occurs at the primary carbonate followed by conversion to vinylcyclopropanes (eq 3).9 Addition of nucleophiles to propargyl carbonates is also catalyzed by palladium complexes of DIPHOS.10 b-Keto esters with only one active hydrogen give double alkylation products (eq 4). The reaction of propargylic carbonates with b-dicarbonyl compounds which contain two active hydrogens results in monosubstitution followed by intramolecular O-alkylation to form 4-methylene-4,5-dihydrofurans (eq 5).

Decarboxylation of Allylic Esters.

Palladium-DIPHOS catalyzes the decarboxylation of allyl esters (eq 6).2 O-Allyl dithiocarbonates undergo loss of COS with palladium(0)-DIPHOS to give thioethers.11 Allyl carbonates and S-allyl dithiocarbonates fail to react under similar conditions.

1,3-Diene Synthesis.

Palladium-DIPHOS complexes catalyze the formation of 1,3-dienes from the reaction of allenes, vinyl halides, and nucleophiles (eq 7).3 Use of benzylic halides leads to substituted vinylarenes.

Cycloaddition Reactions.

The [3 + 2] cycloaddition of Pd-trimethylenemethane intermediates with alkenes provides access to methylenecyclopentanes (eq 8). Electron-deficient alkenes with ester, nitrile, and sulfone substituents readily undergo reaction. The homo-Diels-Alder cycloaddition of norbornadiene with alkynes is catalyzed by a cobalt-DIPHOS complex (eq 9).12 Use of optically active phosphines produces deltacyclenes in high enantiomeric excesses (see (+)-trans-(2S,3S)-Bis(diphenylphosphino)bicyclo[2.2.1]hept-5-ene (NORPHOS)).

Carbonylation Reactions.

Palladium-DIPHOS catalyzes the alkoxycarbonylation of 3-chlorobutene in ethanol at 1 atm to give ethyl 3-pentenoate.5 Carbonylation of propargyl carbonates at 15 atm produces dienoic esters (eq 10).13


1. Fiaud, J.-C.; Malleron, J.-L. CC 1981, 1159.
2. Tsuji, J.; Ohashi, Y.; Minami, I. TL 1987, 28, 2397.
3. Ahmar, M.; Cazes, B.; Gore, J. TL 1984, 25, 4505.
4. Trost, B. M.; Chan, D. M. T. JACS 1979, 101, 6429.
5. Kiji, J.; Okano, T.; Konishi, H.; Nishiumi, W. CL 1989, 1873.
6. Tamura, R.; Hayashi, K.; Kai, Y.; Oda, D. TL 1984, 25, 4437.
7. Tamura, R.; Hayashi, K.; Kakihana, M.; Tsuji, M.; Oda, D. CL 1985, 229.
8. Stolle, A.; Salaun, J.; De Meijere, A. SL 1991, 327.
9. Trost, B. M.; Tometzki, G. B.; Hung, M.-H. JACS 1987, 109, 2176.
10. Tsuji, J.; Watanabe, H.; Minami, I.; Shimizu, I. JACS 1985, 107, 2196.
11. Lu, X.; Ni, Z. S 1987, 66.
12. Lautens, M.; Crudden, C. M. OM 1989, 8, 2733.
13. Tsuji, J.; Sugiura, T.; Minami, I. TL 1986, 27, 731.

Gregory T. Whiteker

Union Carbide Corporation, South Charleston, WV, USA



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