Iminophosphorane

Tetraphenylphosphanimine, an example of a phosphanimine.

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.

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'

References

  1. ^ Zhu, Lizhao; Kinjo, Rei (2023). "Reactions of main group compounds with azides forming organic nitrogen-containing species". Chemical Society Reviews. 52 (16): 5563–5606. doi:10.1039/D3CS00290J. hdl:10356/174235. PMID 37519098.
  2. ^ Ruff, J.K.; Schlientz, W.J. (1974). "μ-Nitridobis(triphenylphosphorus)(l+) ("PPN") Salts with Metal Carbonyl Anions". Inorganic Syntheses. Inorganic Synthesis. Vol. 15. pp. 84–90. doi:10.1002/9780470132463.ch19. ISBN 9780470132463.
  3. ^ Dehnicke, Kurt; Strähle, Joachim (1989). "Phosphorane iminato complexes of transition metals". Polyhedron. 8 (6): 707–726. doi:10.1016/s0277-5387(00)83838-3.
  4. ^ Bednarek, Christin; Wehl, Ilona; Jung, Nicole; Schepers, Ute; Bräse, Stefan (2020). "The Staudinger Ligation". Chemical Reviews. 120 (10): 4301–4354. doi:10.1021/acs.chemrev.9b00665. PMID 32356973.