Synthesis and Structure of Carborane-Substituted Cyclic and Polymeric Phosphazenes

The synthesis of the first carborane-substituted cyclophosphazenes together with the preparation, by two different approaches, of the first carborane-substituted phosphazene linear polymers is reported. The cyclic derivatives IV are both precursors and model compounds for the analogous polymeric derivatives VI. The crystal and molecular structure of IV (R = phenyl) has been investigated by single-crystal X-ray diffraction techniques. The molecule contains a planar phosphazene trimer ring bound directly to the phenyl carboranyl group through a P-C bond. The absence of steric and electronic influences by the phosphazene and carboranyl units on each other is discussed. The crystals of IV (R = phenyl) are monoclinic with the space group P2₁/n and with a = 9.476 (3) Å, b = 12.984 (2) Å, c = 18.726 (3) Å, and β = 100.11 (3)° with V= 2268.2 (3) Å3 and Z = 4. The P-N bond distances are all similar and average 1.574 A. The P-C bond length is 1.820 A. and the Cl-P-C angle was found to be 102.4°. The reaction between high molecular weight poly(dichlorophosphazene), (NPCl₂)_n, and methyl- or phenyl-1-lithio-o-carborane was also studied. Chlorine substitution is a slow process, and is accompanied by chain cleavage. The nucleophilic replacement of the halogen atoms yielded high polymers of structure IX that contain up to 15% of the side groups as carboranyl units. The remaining chlorine atoms were replaced by treatment with sodium trifluoroethoxide. The properties and structure of the macromolecules are discussed.