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Diphosphane
Stereo structural formula of diphosphane with explicit hydrogens	Ball-and-stick model of diphosphane
Names
	IUPAC name Diphosphane
	Systematic IUPAC name Diphosphane (substitutive); Tetrahydridodiphosphorus(P—P) (additive)
	Other names Diphosphine
Identifiers
CAS Number	13445-50-6 ;
3D model (JSmol)	Interactive image;
ChEBI	CHEBI:35880 ;
ChemSpider	122832 ;
PubChem CID	139283;
CompTox Dashboard (EPA)	DTXSID40924074 ;
	InChI InChI=1S/H4P2/c1-2/h1-2H2 Key: VURFVHCLMJOLKN-UHFFFAOYSA-N ;
	SMILES PP;
Properties
Chemical formula	H4P2
Molar mass	65.980 g·mol−1
Melting point	−99 °C (−146 °F; 174 K)
Boiling point	63.5 °C (146.3 °F; 336.6 K) (Extrapolated, decomposes)
Related compounds
Other anions	ammonia; hydrazine; triazane
Other cations	diphosphines
Related Binary Phosphorus halides	diphosphorus tetrafluoride; diphosphorus tetrachloride; diphosphorus tetrabromide; diphosphorus tetraiodide
Related compounds	phosphane; triphosphane; diphosphene; diphosphenes
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

Diphosphane, or diphosphine, is an inorganic compound with the chemical formula P₂H₄. This colourless liquid is one of several binary phosphorus hydrides. It is the impurity that typically causes samples of phosphine to ignite in air.

Properties, preparation, reactions

Diphosphane adopts the gauche conformation (like hydrazine, less symmetrical than shown in the image) with a P−P distance of 2.219 angstroms. It is nonbasic, unstable at room temperature, and spontaneously flammable in air. It is only poorly soluble in water but dissolves in organic solvents. Its ¹H NMR spectrum consists of 32 lines resulting from an A₂XX'A'₂ splitting system.^[1]

Diphosphane is produced by the hydrolysis of calcium monophosphide, which can be described as the Ca²⁺ derivative of P4−2. According to an optimized procedure, hydrolysis of 400 g of CaP at −30 °C gives about 20 g of product, slightly contaminated with phosphine.

Reaction of diphosphane with butyllithium affords a variety of condensed polyphosphine compounds.

Organic diphosphanes

A variety of organic derivatives of diphosphane are known, but asymmetric diphosphanes are only stable at cryogenic temperatures. Otherwise, the substituents facily redistribute on the phosphorus centers to give a mixture of products. On the other hand, there appears to be a substantial barrier to chiral inversion.^[2]

The central bond is weak, and easily adds substituents.^[3]

The simplest synthesis method heats a phosphorus halide and a phosphane:

Ph₂PCl + HPPh₂ → Ph₂P-PPh₂ + HCl↑

Alkali metals can replace the hydrogen in that reaction (i.e., a dialkylphosphide), and in some rare cases a dialkylamine can replace the halide. Symmetric diphosphanes are easily prepared by reductive coupling, e.g. tetraphenyldiphosphine from chlorodiphenylphosphine:

2 ClPPh₂ + 2 Na → Ph₂P−PPh₂ + 2 NaCl

Ultraviolet radiation decomposes mercury(II) dialkylphosphides to the metal and a dialkylphosphane.^[4]

The methyl compound P₂Me₄ is prepared by the reduction of Me₂P(S)−P(S)Me₂, which is produced by methylation of thiophosphoryl chloride with methylmagnesium bromide.^[5]

References

^ Marianne Baudler, Klaus Glinka (1993). "Monocyclic and polycyclic phosphines". Chem. Rev. 93 (4): 1623–1667. doi:10.1021/cr00020a010.
^ Phosphorus: Chemistry, Biochemistry and Technology, Sixth Edition, 2013, D.E.C. Corbridge, CRC Pres, Taylor Francis Group, ISBN 978-1-4398-4088-7. pp. 421-422.
^ Corbridge 2013, p. 422.
^ Corbridge 2013, pp. 421–422.
^ Butter, S. A.; Chatt, J. (1974). "Ethylenebis(dimethylphosphine)". Inorganic Syntheses. Vol. 15. p. 185. doi:10.1002/9780470132463.ch41. ISBN 9780470132463. {{cite book}}: |journal= ignored (help)