Synthesis of 1-Halo- and 1 -Alkyl-1-phenyItetrachlorocyclotriphosphazene Polymerization “Monomers” from Bi(cyclophosphazenes)

A new synthetic route has been developed for the preparation of 1-halo- and 1-alkyl-1-phenyltetrachlorocyclotriphosphazenes of general formula N₃P₃C1₄X(C₆H₆) (5), where X = C1, Br, or I, and N₃P₃C1₄(C₆H₅)(R) (6), where R = CH₃, C₂H₅, nC₃H₇, n-C₄H₉, t-C₃H₇, or CH₂CH=CH₂, respectively. These compounds are prospective polymerization monomers, most of which cannot be prepared by other routes. The synthetic procedure involves the interaction of l,l′-diphenyl-3,3,3’,3’,5,5,5’,5′-octachlorobifcyclo-triphosphazene) (2) with LiBEt3H to give a triethylborane-substituted anion, 3. Anion 3 reacts with proton-releasing agents to give 1-hydrido-l-phenyltetrachlorocyclotriphosphazene (4) or with alkyl halides to give 6. The hydridophosphazene 4 reacts with halogen in CC1₄ to give 5. Alternatively, compounds 5 (X = Cl, Br) can be prepared via the reaction of 3 with CC1₄ or CHBr₃, respectively. Compound 5 (X = Br) was found to react with NaF in acetonitrile at reflux to give exclusively N₃P₃C1₄F(C₆H₅). The structural characterization of these compounds by spectroscopic and mass spectrometric techniques is discussed, together with the reaction mechanism. In addition, the crystal and molecular structure of 5 (X = Cl) has been investigated by single-crystal X-ray diffraction techniques. The crystals are monoclinic with the space group P2₁/c and with a = 8.579 (1) Å, b = 14.612 (3) Å, c = 11.771 (3) Å, and β = 99.26 (1)° with V = 1456.4 (9) A3 and Z = 4.