Geminal substitution

In geminal substitution, two incoming groups replace substituents on the same central atom. In cyclotriphosphazenes, $\mathrm{PC}{\mathrm{l}}_2\to \mathrm{P}{\mathrm{R}}_2$ gives a geminal pair. Primary amino groups can enable a base-catalyzed proton-abstraction/chloride-elimination route that is unavailable after substitution by a secondary amine.