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Primary amines can favor geminal disubstitution through a proton-abstraction route. The first substitution leaves an exocyclic $\mathrm{PCl}(\mathrm{NHR})$ group. Its remaining N–H proton provides a pathway unavailable to a fully substituted amino group: base removes H, chloride elimination gives a reactive low-coordinate phosphorus intermediate with increased exocyclic P–N bonding, and a second amine attacks that same phosphorus. proton transfer then gives $\mathrm{P}(\mathrm{NHR}{)}_2$. Thus the directing effect is not simply the inductive effect of an amino group.

This needs a qualification: “primary amine” alone does not specify a universal product distribution. Substituent, solvent and base concentration affect whether the proton-abstraction route outcompetes direct nucleophilic substitution. Kinetic and trapping experiments with aromatic primary amines support the base-catalyzed route to geminal products, while also finding direct substitution pathways under other conditions.^[ref]

Setharampattu S. Krishnamurthy coauthored kinetic studies of aromatic-amine reactions with hexachlorocyclotriphosphazene. Rate measurements and methanol trapping support a base-promoted elimination-addition pathway under the studied conditions.

The mechanistic conclusion concerns a specified reaction regime. Direct substitution can remain important under other conditions, illustrating how chemical kinetics tests pathways rather than assigning one universal mechanism to a compound.^[ref]

Sivapackia Ganapathiappan coauthored research on phosphazene.^[ref]

A phosphazene contains phosphorus–nitrogen bonding often represented with formal P=N units. Ionic bonding and negative hyperconjugation provide a modern account; formal double-bond drawings do not require phosphorus $3d$ pi bonding.