A novel paddle-wheel shaped spirocyclic cyclotetraphosphazene from the thermolysis of a P(III) azide

The spirocyclic cyclotetraphosphazene [CH2(6-t-Bu-4-Me-C6H2O)2PN]4 (2) is obtained as one of the products from the thermolysis of the azide CH2(6-t-Bu-4-Me-C6H2O)2PN3 (1). An X-ray structure determination reveals that the compound has a paddle-wheel shaped structure with the phosphorus bearing only eight-membered rings [phosphazene/phosphocin]. The eight-membered phosphocin ring in 2 has a tub conformation, in contrast to the boat–chair conformation present in 1, possibly due to weak C–H…N interactions. Compound 2 could not be prepared from the traditional route of starting from octachlorocyclotetraphosphazene [N4P4Cl8] and hence the azide route is the only accessible pathway for 2.