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 disclaimer and 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

[edit] Preparation

The preparation of dppe is conducted via the alkylation of NaPPh2 which is typically prepared from triphenylphosphine (P(C6H5)3) as follows:[2][3]

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

[edit] Reactions of dppe

[edit] 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

[edit] 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

[edit] Coordination complexes of 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 industry[6] for their ability to catalyze asymmetric reactions[7] 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]

[edit] 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.; Swiegers, G.; Wild, B.; J. Org. Chem. 2000, 65, 951-957.
  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, T. Pure Appl. Chem., 2001 Vol. 73, No. 2, 373-37
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