Preparation of the First Examples of Ansa−Spiro Substituted Fluorophosphazenes and Their Structural Studies: Analysis of C−H···F−P Weak Interactions in Substituted Fluorophosphazenes

The reactions of fluorophosphazenes, endo ansa FcCH2P(S)(CH2O)2[P(F)N]2(F2PN) (1) (Fc = ferrocenyl) and spiro
[RCH2P(S)(CH2O)2PN](F2PN)2 (R = Fc (2), C6H5 (3)], with dilithiated diols have been explored. The study resulted
in the formation of the first examples of ansa−spiro substituted fluorinated cyclophosphazenes as well as a bisansa
substituted fluorophosphazene. The bisansa compound {1,3-[FcCH2P(S)(CH2O)2]}{1,5-[CH2(CH2O)2]}N3P3F2 (4)
was found to be nongeminaly substituted with both the ansa rings in cis configuration, which is in stark contrast
to the observations on cyclic chlorophosphazenes where geminal bisansa formation has been observed. The ansa−spiro compounds (5−7) underwent the ansa to spiro transformation leading to dispiro compounds in the presence
of catalytic amounts of CsF at room temperature. Two of the ansa−spiro compounds, endo-{3,5-[FcCH2P(S)(CH2O)2]}{1,1-[CH2(CH2O)2]}N3P3F2 (5) and endo-{3,5-[FcCH2P(S)(CH2O)2]}{1,1-[FcCH2P(S)(CH2O)2]}N3P3F2 (6),
were structurally characterized, and the crystal structures indicate boat−chair conformation as well as crown
conformation for the eight-membered ansa rings. Weak C−H···F−P interactions observed in the crystal structures
of the ansa−spiro substituted fluorophosphazene derivatives have been analyzed and compared with C−H···F−P
interactions of other fluorinated phosphazenes and thionyl phosphazenes.