Phosphazene
Phosphazenes are 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. While other substitutions produce relatively persistent compounds, in organic synthesis the term largely refers to species with three amino substituents bound to phosphorus. The compounds are unusually stable examples of the phosphorane class of molecules and have a remarkable proton affinity. As such, they are one of the eminent examples of neutral, organic superbases. Two examples are hexachlorocyclotriphosphazene and bis(triphenylphosphine)iminium chloride. Phosphazenes are also known as iminophosphoranes and phosphine imides.
The corresponding polymers are polyphosphazenes. Phosphinimide ligands can be used in catalysis.
Phosphazene bases are strong non-metallic non-ionic and low-nucleophilic bases. They are stronger bases than regular amine or amidine bases such as Hünig's base or DBU. Protonation takes place at a doubly bonded nitrogen atom. Related to phosphazene bases are the proazaphosphatrane bases, which have a saturated P(NR)3 structure and protonate at phosphorus.
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