Phosphazene

Phosphazenes refer to various classes of organophosphorus compounds featuring phosphorus with a double bond between P and N. One class of phosphazenes have the formula. These phosphazenes are also known as iminophosphoranes and phosphine imides. They are superbases.

BEMP and ''t''-Bu-P₄

Well known phosphazene bases are BEMP with an acetonitrile pK_a of the conjugate acid of 27.6 and the phosphorimidic triamide t-Bu-P₄ also known as Schwesinger base. BEMP and P4-t-Bu|t-Bu-P₄ have attracted attention because they are low-nucleophilic, which precludes their participating in competing reactions. Being non-ionic, they are soluble in nonpolar solvents. Protonation takes place at a doubly bonded nitrogen atom. The pK_a's of, where R = Me and pyrrolidinyl, are 42.7 and 44, respectively. These are the highest pK_a recorded for the conjugate acid of charge-neutral molecular base.
In one implementation, t-Bu-P₄ catalyzes the conversion of pivaldehyde to the alcohol: Phosphazene bases have been used as basic titrants in non-aqueous acid–base titrations.

Other classes of phosphazenes

Also called phosphazenes are represented with the formula, where X = halogen, alkoxy group, amide and other organyl groups. One example is hexachlorocyclotriphosphazene. Bis(triphenylphosphine)iminium chloride is also referred to as a phosphazene, where Ph = phenyl group. The present article focuses on those phosphazenes with the formula.