Phosphazenes

This chapter summarizes the chemistry of phosphazenes in the calendar year 2019. The topics covered are acyclic phosphazenes, cyclophosphazenes, polyphosphazenes and hybrid polymers. The synthesis, structure and reactivity of these systems are covered. The applications of these compounds are also reviewed. Acyclic phosphazenes also known as iminophosphoranes have been of interest from various points of view including their ability to function as strong bases, as organocatalysts and as ligands towards transition-, lanthanide- and main-group metal ions. Cyclophosphazenes have been of interest from the point of view of their ability to generate star-like structures containing a central core and functional arms. Cyclophsophazenes have also been useful as ligands in coordination chemistry. Phosphazene-based polymers including polyphosphazenes and hybrid polymers that contain a cyclophoszane core have also been discussed.