Synthesis of a New Class of Fused Cyclotetraphosphazene Ring Systems

Octachlorocyclo­tetraphosphazene
(1) was reacted with butylamines [n-butyl, i-butyl, sec-butyl, and t-butyl] in a 1:0.8 mol ratio in THF to obtain cyclotetraphosphazenes
bearing a P-NH group, N4P4Cl7(NHR)
[R = n-butyl (2a), i-butyl (2b), sec-butyl (2c), t-butyl (2d)]­(2a–d). The cyclotetraphosphazene derivatives 2a, 2b, and 2c were treated with sodium hydride giving
rise to a new type of cyclophosphazene compounds (P8N8 ring) consisting of three fused tetramer rings (3a–c). Whereas reaction of sodium hydride with
the t-butylamino­cyclophosphazene derivative
(2d) gave a P–O–P bridged compound (4) presumably as a result of hydrolysis reaction associated
with moisture in the solvent. It is likely that the 16-membered cyclooctaphosphazene
derivatives (3a–c) are formed by
a proton abstraction/chloride ion elimination, intramolecular nucleophilic
attack, ring opening and intermolecular condensation processes, respectively.