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]
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]
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.