ISOLATION, NMR SPECTRA AND X-RAY CRYSTAL STRUCTURES OF TWO ISOMERIC N₃P₃CL₂[O(CH₂)₃O]₂DERIVATIVES. THE FIRST EXAMPLE OF DISPIRO / SPIRO-ANSA ISOMERISM IN PHOSPHAZENE CHEMISTRY. COMPARISONS OF TRANS-ANNULAR BRIDGED CYCLOPHOSPHAZENES

Conformational polymorphism in a chiral spiro-cis-ansa-bridged cyclotriphosphazene derivative

“…The smaller deviations in the form with respect to that of the form indicate that less strain on the system is induced by this arrangement. This is not accompanied by a decrease of the PÁ Á ÁP non-bonded distance, as has been observed in similar, but shorter, ansa-bridged N 3 P 3 systems (Contractor et al, 1986), because the PÁ Á ÁP cross-ring separations are comparable to those observed in unstrained N 3 P 3 -containing structures (Contractor et al, 1986).…”

The structural and stereogenic properties of pentaerythritoxy-bridged cyclotriphosphazene derivatives: spiro–spiro, spiro–ansa and ansa–ansa isomers

“…2.64 A ˚) between the ansa-carrying atoms compared the average of 2.78 A ˚in unstrained cyclophosphazenes. 22,23 It is also found that the cyclophosphazene ring in cis-ansa bridged spirane compounds is similarly non-planar, that there is significant shortening of the non-bonded P • • • P distance between the ansa-carrying atoms (ca. 2.66 A ˚) and the nitrogen atom between the phosphorus atoms carrying the ansa moiety is furthest out-of-plane by about 0.26 A on average (Table 5).…”

Retention of Configuration in the Nucleophilic Substitution Reactions of Some Nine‐Membered Ansa Derivatives of Cyclotriphosphazatriene

“…A closer look shows that these nitrogen atoms are forced a great deal out of the plane of the other ring atoms. The resultant strain, observed earlier, [11] facilitated easier ring opening-polymerisations. However, the subject of inversion versus retention of configuration was not addressed, the ansa grouping being usually the last to be introduced.…”

“…A similar saddle shape is adopted by compound 4 through P(2)···N(2). Compared with a compound containing the eight-membered ansa ring of the P-O-CH 2 -CH 2 -CH 2 -O-P moiety, where the nitrogen atom deviates by 0.523 from the mean N 3 P 3 plane, [11] the deviation from the mean plane of the N 3 P 3 ring is significantly smaller for compounds 2-4 which have nine-membered ansa rings containing the P-O-CH 2 -CF 2 -CF 2 -CH 2 -O moiety, namely 0.184 for N(1) of 2, 0.158 for P(1) of compound 4 and only 0.133 for N(1) of the asymmetrically substituted compound 3. Notably compound 3 has two different centres of chirality, > P(OR)Cl and > P(OR)(pyr), and the XScheme 1.…”