Iminophosphorane

Iminophosphorane (or, more correctly, phosphanimine) is a kind of organophosphorus compound with the formula R₃PNR'. Like the corresponding phosphine oxides and Wittig reagents, phosphanimines are ylides. Their bonding is described by two resonance structures.^[1]

Resonance structures for iminophosphoranes.

Tetraphenylphosphanimine, an example of a phosphanimine.

Preparation

Mechanism of iminophosphorane formation

Aza-ylides can be obtained via the reaction of a tertiary phosphine and an organic azide with the loss of dinitrogen. Triphenylphosphine is a commonly used phosphine.

Examples

The parent phosphanimine has the formula H₃P=NH (registry number 25682-80-8) remains only of theoretical interest. Of practical value are derivatives of triorganophosphines and organic amines. A prototype is the phenyl imide derivative of triphenylphosphine, a white, lipophilic solid.

Bis(triphenylphosphine)iminium chloride, a common iminophosphorane, is prepared in two steps from triphenylphosphine Ph₃P:^[2]

Ph₃P + Cl₂ → Ph₃PCl₂

2 Ph₃PCl₂ + NH₂OH·HCl + Ph₃P → [(Ph₃P)₂N]Cl + 4HCl + Ph₃PO

A phosphanimine is obtainable from trimethylsilyl azide and triphenylphosphine. Desilylation gives the anion Ph₃P=N⁻.^[3]

Reactions

Phosphanimines are one of the components in the aza-Wittig reaction. The other component is an aldehyde or a ketone. They also are components of the Staudinger ligation.^[4]

See also

• Phosphazenes are analogues of iminophosphoranes with the formula (R₂N)₃P=NR'