A Spirocyclic System Comprising Both Phosphazane and Phosphazene Rings

The reaction of hexakis(cyclohexylamino) cyclotriphosphazene [NP(CyNH)2]3, 1, with phosphorus trichloride yields
[NP(CyN)2PCl]3, 2, which contains three four-membered phosphazane rings fused in spirocyclic fashion to a central
six-membered phosphazene ring and constitutes the first structurally characterized compound that comprises both
phosphazene and phosphazane rings. The peripheral P atoms feature stereoactive lone pairs, and, thus, 2 exists
in isomeric C3h and Cs forms. The spirocyclic phosphazene−phosphazane derivative 2 carries three reactive PCl
functions in peripheral positions, promising an interesting precursor molecule for the synthesis of extended phosphorus
nitrogen structures of high rigidity. Extension of the PN moiety can be achieved by reaction of 2 with a primary
amine yielding [NP(CyN)2PN(H)tBu]3, 3, which features a central scaffold of 6 phosphorus and 12 nitrogen centers
and aggregates via N−H···P hydrogen bonds in the solid state. On the contrary, the reaction of 1 with SbCl3
undergoes incomplete proton abstraction, resulting in the formation of the tricyclic compound N3P3(CyNH)4(CyNSbCl2)2,
4, which contains two four-coordinate Sb centers chelated by N(exo)−N(ring) sites of the phosphazene.