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Phosphazene



A phosphazene is any of a class of chemical compounds in which a phosphorus atom is covalently linked to a nitrogen atom by a double bond and to three other atoms or radicals by single bonds. Two examples are hexachlorophosphazene and bis(triphenylphosphine)iminium chloride.

Additional recommended knowledge

The corresponding polymers are polyphosphazenes.

Phosphazene bases

Phosphazene bases are strong non-metallic non-ionic and non-nucleophilic bases. They are stronger bases than regular amine bases such as DBU or Hünig's base. Protonation takes place at a nitrogen atom.

Two commercially available phosphazene bases are BEMP with a pKa of the conjugate acid of 27.6 and the phosphorimic triaminde t-Bu-4P (pKBH+ = 41.9) also known as Schwesinger base after one of its inventors[1].

In one application t-Bu-4P is employed in a nucleophilic addition converting the tert-butyl aldehyde to the alcohol[2] :

The active nucleophile is believed to be a highly reactive phosphazenium species with full negative charge on the arene sp2 carbon.

The related proazaphosphatrane superbases have a saturated P(NR)3 structure and protonation takes place at phosphorus.


References

  1. ^ Peralkylated Polyaminophosphazenes - Extremely Strong, Neutral Nitrogen Bases Angewandte Chemie International Edition in English Volume 26, Issue 11, Date: November 1987, Pages: 1167-1169 Reinhard Schwesinger, Helmut Schlemper doi:10.1002/anie.198711671
  2. ^ Phosphazene base-promoted functionalization of aryltrimethylsilanes Koichi Suzawa, Masahiro Ueno, Andrew E. H. Wheatley and Yoshinori Kondo Chem. Commun., 2006, 4850 - 4852, doi:10.1039/b611090h 10.1039/b611090h
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Phosphazene". A list of authors is available in Wikipedia.
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