Syntheses and experimental studies on the relative stabilities of spiro, ansa, and bridged derivatives of cyclic tetrameric fluorophosphazene.

Reactions of (CF2CH2OSiMe3)2 and CF2(CF2CH2OSiMe3)2 with N4P4F8 (1) in a 1:2.5 molar ratio resulted in the formation of monospiro compounds [(CF2CH2O)2PN](F2PN)3 (2) and [CF2(CF2)CH2O)2PN](F2PN)3 (4) as well as the intermolecular bridged compounds F7N4P4OCH2CF2CF2CH2OP4N4)F7 (3) and F7N4P4OCH2CF2CF2CF2CH2OP4N4F7 (5). An equimolar reaction of dilithiated 1,3-propanediol with 1 resulted in the 1,3-ansa-substituted compound CH2(CH2O)2[P(F)N]2(F2PN)2 (6) as the major product in good yield. However, an analogous reaction of the dilithiated 1,3-propanedithiol with 1 gave only the spirocyclic compound CH2(CH2S)2(PN)(F2PN)3 (8). The molecular structures of 2 and 6 were determined by single-crystal X-ray diffraction. In the presence of catalytic amounts of CsF in THF, the bridged compound 3 was converted to the spirocyclic compound 2 while the 1,3-ansa compound 6 under similar conditions transformed into the monospiro-substituted compound CH2(CH2O)2 (PN)(F2PN)3 (7). These transformations were monitored by time-dependent 19F and 31P NMR studies.