1,2-Bis(diphenylphosphino)ethane

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1,2-Bis(diphenylphosphino)ethane
dppe
IUPAC name 1,2-Bis(diphenylphosphino)ethane
CAS number 1663-45-2
Properties
Molecular formula (C6H5)2PCH2CH2P(C6H5)2
Molar mass 397.95 g/mol
Melting point

140-142 °C
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)
Infobox references

1,2-Bis(diphenylphosphino)ethane (dppe) is a commonly used bidentate ligand in coordination chemistry. Dppe is almost invariably chelated, although there are examples of unidentate (e.g., W(CO)5(dppe)) and of bridging behavior.1

Contents

Preparation

The preparation of dppe is conducted via the alkylation of NaPPh2 which is typically prepared from triphenylphosphine (P(C6H5)3) as follows:23

1. P(C6H5)3 + 2 Na → NaP(C6H5)2 + NaC6H5

NaP(C6H5)2, which is readily air-oxidized, is treated with 1,2-dichloroethane (ClCH2CH2Cl) to give dppe:

2. NaP(C6H5)2 + ClCH2CH2Cl → (C6H5)2PCH2CH2P(C6H5)2 + 2 NaCl

Reactions of dppe

Reduction

The reduction of dppe by lithium to give PhHP(CH2)2PHPh has been reported.4

1. Ph2P(CH2)2PPh2 + 4 Li → PhLiP(CH2)2PLiPh + 2 PhLi

Hydrolysis by water gives:

2. PhLiP(CH2)2PLiPh + 2 PhLi + 4H2O → PhHP(CH2)2PHPh + 4 LiOH + 2C6H6

Oxidation

Treatment of dppe with conventional oxidants such as hydrogen peroxide (H2O2), aqueous bromine (Br2), etc., always produces dppeO in low yield (e.g., 13%) as a result of non-selective oxidation leading to mixtures of the starting material, the monoxide, and dioxide.5 Selective mono-oxidation of dppe can be achieved by reaction with PhCH2Br to give dppeO.

3. Ph2P(CH2)2PPh2 + PhCH2Br → Ph2P(CH2)2PPh2(CH2Ph)+Br-

This is followed by purification and alkaline catalyzed hydrolysis of the mono-phosphonium salt.

4. Ph2P(CH2)2PPh2(CH2Ph)+Br- + NaOH + H2O → Ph2P(CH2)2P(O)Ph2

Coordination complexes of dppe

Ball-and-stick model of [PdCl2(dppe)]

Coordination complexes of dppe, and diphosphine ligands in general, are almost entirely used as homogeneous catalysts for a wide range of reactions. Chiral diphosphines are especially important to the pharmaceutical industry6 for their ability to catalyze asymmetric reactions7 Two simple coordination complexes of dppe include Pd(dppe)2 and Ir(dppe)2. Pd(dppe)2 can be prepared by reduction of Pd(II) with NaBH4. It is most conveniently prepared, however, in situ from Pd(OAc)2.5

References

  1. ^ Cotton, F.A.; Wilkinson, G. Advanced Inorganic Chemistry: A Comprehensive Text, 4th ed.; Wiley-Interscience Publications: New York, NY, 1980; p.246. ISBN 0-471-02775-8
  2. ^ W. Hewertson and H. R. Watson (1962). "283. The preparation of di- and tri-tertiary phosphines". J. Chem. Soc.: 1490–1494. doi:10.1039/JR9620001490. 
  3. ^ Girolami, G.; Rauchfuss, T.; Angelici, R. Synthesis and Technique in Inorganic Chemistry, 3rd ed.; University Science Books: Sausalito, CA, 1999; pp. 85-92. ISBN 0-935702-48-2
  4. ^ Dogan, J.; Schulte, J.B.; Swiegers, G.F.; Wild, S.B. (2000). "Mechanism of Phosphorus-Carbon Bond Cleavage by Lithium in Tertiary Phosphines. An Optimized Synthesis of 1, 2-Bis (phenylphosphino) ethane". J. Org. Chem. 65 (4): 951-957. doi:10.1021/jo9907336'). 
  5. ^ a b Encyclopedia of Reagents for Organic Synthesis 2001 John Wiley & Sons, Ltd
  6. ^ Stibbs, W. Technology & Services Business Briefing: Future Drug Discovery 2003.
  7. ^ Imamoto, Tsuneo (2001). "New P-chirogenic diphosphines and their use in catalytic asymmetric reactions". Pure and Applied Chemistry 73: 373. doi:10.1351/pac200173020373. 

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  • This page was last modified on 13 November 2008, at 23:37.

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