Phosphazene


Phosphazenes refer to classes of organophosphorus compounds featuring phosphorus with a double bond between P and N. One class of phosphazenes have the formula RN=P3. These phosphazenes are also known as iminophosphoranes and phosphine imides. They are superbases. Another class of compounds called phosphazenes are represented with the formula n, where X = halide, alkoxide, amide. One example is hexachlorocyclotriphosphazene. Bisiminium chloride is also referred to as a phosphazene. This article focuses on those phosphazenes with the formula RN=P3.

Phosphazene bases

Phosphazene bases are strong non-metallic non-ionic and low-nucleophilic bases. They are stronger bases than regular amine or amidine bases. Protonation takes place at a doubly bonded nitrogen atom. Related to phosphazene bases are the Verkade bases, which feature P with three amido substituents and a transannular amine. The pKa's of + also known as Schwesinger base after one of its inventors.
In one application t-Bu-P4 is employed in a nucleophilic addition converting the pivaldehyde to the alcohol:
The active nucleophile is believed to be a highly reactive phosphazenium species with full negative charge on the arene sp2 carbon.
Besides organic synthesis, phosphazene bases are used as basic titrants in non-aqueous acid-base titration. Their advantages for this are: they are very strong bases in many solvents and their conjugate acids are inert and non-HBD cations.