1,2-Bis(diphenylphosphino)ethane

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1,2-Bis(diphenylphosphino)ethane
1,2-Bis(diphenylphosphino)ethane
dppe
Chemical name 1,2-Bis(diphenylphosphino)ethane
Chemical formula (C6H5)2PCH2CH2P(C6H5)2
Molecular mass 397.95 g/mol
Melting point 140-142 °C
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]

Preparation

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

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.[3]

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.[4] 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

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 [5] for their ability to catalyze asymmetric reactions [6] 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.[4]

dppe analogues

dppe is one compound of a larger class of ligands known as the diphosphines. The most widely used diphosphine ligands are the bis(diphenylphosphino)alkanes, Ph2P(CH2)nPPh2. These can be prepared from X(CH2)nX (X=halogen) and YPPh2 (Y=alkali metal) in THF [7]. Bidentate phosphines with only one bridging group such as dppm tend to promote metal-metal interaction or bond formation because the two donor P atoms are so close together. The use of chelate phosphines with many bridging groups giving long flexible chains has quite a different effect. For example, the chelate phosphine Bu2tP(CH2)10PBu2t can give complexes that have as many as 72 atoms in a ring [1].

dppv

Dppv is the acronym for 1,2-bis(diphenylphosphino)ethylene, (C6H5)2PCH=CHP(C6H5)2. Both cis (m.p. 125 °C) and trans (m.p. 126°C) isomers are known, being derived from the respective isomers of ClCH=CHCl. The substitution of chloride is stereospecific. The cis isomer, however, is almost exclusively used for applications of a ligand.

dmpe

dmpe
Chemical name 1,2-bis(dimethylphosphino) ethane
Chemical formula (CH3)2PCH2CH2P(CH3)2
Molecular mass 150.14 g/mol
CAS Number 23936-60-9
Boiling point 180 °C
Flash point 2 °F
Density 0.9 g/mL at 25 °C
Disclaimer and references

Dmpe is prepared in a similar way to that of dppe.

1. (CH3)2P-P(CH3)2 + 2Na → 2NaP(CH3)2
2. 2NaP(CH3)2 + ClCH2CH2Cl → (CH3)2PCH2CH2P(CH3)2 + 2NaCl

Dmpe should be handled with care. It is toxic and exposure to the air may result in ignition.

Dppf

1,1'-Bis(diphenylphosphino)ferrocene (dppf) is also used as a ligand. As its name implies, its backbone is made up of a ferrocene moiety, as opposed to the ethylene backbone of dppe.

References

  1. 1.0 1.1 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. 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
  3. Dogan, J.; Schulte, J.; Swiegers, G.; Wild, B.; J. Org. Chem. 2000, 65, 951-957.
  4. 4.0 4.1 Encyclopedia of Reagents for Organic Synthesis 2001 John Wiley & Sons, Ltd
  5. Stibbs, W. Technology & Services Business Briefing: Future Drug Discovery 2003.
  6. Imamoto, T. Pure Appl. Chem., 2001 Vol. 73, No. 2, 373-37
  7. Wilkinson, G.; Gillard, R.; McCleverty, J. Comprehensive Coordination Chemistry: The synthesis, reactions, properties & applications of coordination compounds, vol.2.; Pergamon Press: Oxford, UK, 1987; p. 993. ISBN 0-08-035945-0

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