Selective Reactivity of the Phosphorus−Chlorine and Carbon−Chlorine Bonds in Cyclic Chlorocarbaphosphazenes:  An Unusual Activation of a Carbon−Nitrogen Bond in Trialkylamines^†

Acyclic tertiary amines such as triethylamine and tri-n-propylamine used as HCl scavengers in nucleophilic substitution reactions of cyclic chlorocarbaphosphazenes [N₃PC₂Cl₄ (I) and N₃P₂CCl₅ (II)] with (CF₂)_n(CF₂CH₂OH)₂ [n = 0 (III) or 1 (IV)] are found to undergo a facile C−N bond cleavage with the regiospecific substitution of the dialkylamino groups on the ring carbon atoms of the carbaphosphazene. In the case of cyclic amines such as 1-methylpiperidine and 4-methylmorpholine, the cleavage was found to occur regiospecifically at the N−CH₃ bond, resulting in the ring substitution of the cyclic secondary amino group on the dicarbaphosphazene ring carbon atoms. The polyfluoro diol III forms a spirocyclic ring exclusively at the phosphorus site in compounds [CF₂CH₂O]₂PN₃C₂[N(C₂H₅)₂]₂ (1), [CF₂CH₂O]₂PN₃C₂[N(C₃H₇)₂]₂ (2), [CF₂CH₂O]₂PN₃C₂[NCH₂(CH₂)₃CH₂]₂ (3), and [CF₂CH₂O]₂PN₃C₂[N(CH₂)₂O(CH₂)₂]₂ (5) along with the formation of carbon-substituted carbaphosphazenes, Cl₂PN₃C₂[NCH₂(CH₂)₃CH₂]₂ (4) and Cl₂PN₃C₂[N(CH₂)₂O(CH₂)₂]₂ (6). Reaction of II with III in the presence of triethylamine affords the dispiro product [CF₂CH₂O)₂]₂P₂N₃C[N(C₂H₅)₂] (7), which crystallizes in a polar orthorhombic space group, Cmc2₁. Upon refluxing of I or II with R₃N (R = C₂H₅, n-C₃H₇) in toluene, the amino-substituted carbaphosphazenes, Cl₂PN₃C₂[N(C₂H₅)₂]₂ (8), Cl₄P₂N₃C[N(C₂H₅)₂] (9), and Cl₄P₂N₃C[N(n-C₃H₇)₂] (10) are obtained in good yields. Hydrolysis of 8 leads to the formation of Cl(O)PN(H)N₂C₂[N(C₂H₅)₂]₂ (11). When lithium salts of the fluoro diols III and IV are reacted with I or II in diethyl ether, the P−Cl bond is selectively substituted, yielding the spirocyclic [CF₂CH₂O]₂PN₃C₂Cl₂ (12), [CF₂(CF₂CH₂O)₂]PN₃C₂Cl₂ (13), [CF₂CH₂O]₂P₂N₃CCl₃ (14), and [(CF₂CH₂O)₂]₂P₂N₃CCl (15). The C−Cl bonds in 12 and 14 were easily substituted by their reaction with 4-FC₆H₄XNa (X = O or S) to form [CF₂CH₂O]₂PN₃C₂[4-FC₆H₄O]₂ (16) and [CF₂CH₂O]₂PN₃C₂[4-FC₆H₄S]₂ (17). Reactions of 12 and 13 with (CH₃)₃SiN(CH₃)₂ under mild conditions result in the elimination of (CH₃)₃SiCl along with the formation of [CF₂CH₂O]₂PN₃C₂[N(CH₃)₂]₂ (18). The X-ray analyses of 13 and 18 represent the first examples of eight-membered spirocyclic phosphazenes. The thermal behavior of II, 9, 10, 14, and 15 has also been investigated at 120 °C. Single-crystal X-ray diffraction studies were carried out for 1, 2, 7, 9−14, and 16−19, and these compounds are also characterized using IR, ¹H, ¹³C, ¹⁹F and ³¹P NMR spectroscopy, MS, and elemental analysis.