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.G. L. Miessler and D. A. Tarr “Inorganic Chemistry” 3rd Ed, Pearson/Prentice Hall publisher, {{ISBN|0-13-035471-6}}.
Examples
The parent hydride compound is the hypothetical molecule PH5.
Pentaphenylphosphorane (Ph5P) is stable.{{Note|Quin}} A Guide to Organophosphorus Chemistry Louis D. Quin 2000 John Wiley & Sons {{ISBN|0-471-31824-8}}
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:{{cite journal |doi=10.1021/ja00449a044 |title=Some acyclic pentaalkoxyphosphoranes |year=1977 |last1=Chang |first1=Lydia L. |last2=Denney |first2=Donald B. |last3=Denney |first3=Dorothy Z. |last4=Kazior |first4=Richard J. |journal=Journal of the American Chemical Society |volume=99 |issue=7 |pages=2293–2297 }}
:{{chem2|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.