Diphosphines

Diphosphines are a class of compounds used as ligands in inorganic and organometallic chemistry. They are identified by the presence of two phosphine ligands joined by a backbone, and are usually chelating.

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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 ^[1]. 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 Bu₂^tP(CH₂)₁₀PBu₂^t can give complexes that have as many as 72 atoms in a ring ^[2].

Common ligands

While there can be very many diphosphine ligands possible, there are some which are commonly used, and which are commercially available. These include:

• 1,1-Bis(diphenylphosphino)methane ("dppm")
• 1,2-Bis(diphenylphosphino)ethane ("dppe")
• 1,3-Bis(diphenylphosphino)propane ("dppp")
• 1,1'-Bis(diphenylphosphino)ferrocene ("dppf")

References

1. ^ 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
2. ^ 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