Phosphoranes

A phosphorane (IUPAC name: λ5-phosphane) is a functional group in organophosphorus chemistry with pentavalent phosphorus. Phosphoranes have the general formula PR5.

Phosphoranes of the type PX5 adopt a trigonal bipyramidal molecular geometry with the two apical bonds longer than the three equatorial bonds. Hypervalent bonding is described by inclusion of non-bonding MOs, as also invoked for the closely related molecule phosphorus pentafluoride.[1]

Examples

The parent hydride compound is the hypothetical molecule PH5.

Pentaphenylphosphorane (Ph5P) is stable.[2]

Pentaalkoxyphosphoranes are more common with electronegative substituents. Examples of P(OR)5 (R = alkyl), have however been prepared by reaction of phosphites with benzene alkyl sulfenates:[3]

P(OR)3 + 2 ROSC6H5 → P(OR)5 + (SC6H5)2

Wittig reagents

Phosphoranes of the type R3P=CR2 are more common and more important. Phosphoranes are also considered to be one of the resonance structures of ylides, these compounds feature a tetrahedral phosphorus center including a phosphorus–carbon double bond. These compounds are used as reagents in the Wittig reaction, for instance methylenetriphenylphosphorane or Ph3P=CH2.

See also

References
  1. G. L. Miessler and D. A. Tarr “Inorganic Chemistry” 3rd Ed, Pearson/Prentice Hall publisher, ISBN 0-13-035471-6.
  2. ^ A Guide to Organophosphorus Chemistry Louis D. Quin 2000 John Wiley & Sons ISBN 0-471-31824-8
  3. Chang, Lydia L.; Denney, Donald B.; Denney, Dorothy Z.; Kazior, Richard J. (1977). "Some acyclic pentaalkoxyphosphoranes". Journal of the American Chemical Society. 99 (7): 2293–2297. doi:10.1021/ja00449a044.
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