Syntheses of Chiral Cyclotriphosphazenes and Their Use in Cyclolinear Polymers

Chiral configurations in cyclophosphazene chemistry

“…37.76 kcal/mol) so both R-and S-forms are stable at room temperature and the two enantiomers are commercially available as well as the racemate. Chiral spirophosphazenes containing BN groups can be obtained by the reaction of trimer, N 3 P 3 Cl 6 , with the appropriate number of equivalents of BN (R/S, R or S) to give mono- (148), di- (149) or tri-spiro (150) derivatives as reported by several research groups [178][179][180][181][182][183] and summarized in Fig. 29.…”

“…29. (R/S) [178] (R/S) [178] (R) [181,183] (RR) [179] (RRR) [180] (S) [181] (SS) [179] (SSS) [180] a n u s c r i p t spiro-BN moiety (151 [181], 152 [184]) but that 153 [183] has three centers of chirality, one from BN and two from the spiro-(2-methylamino)ethanolato groups, which may exist as meso or racemic forms; the cis (meso) form is found for 153. The BN group may also form ansa-derivatives, in which there may be two (154 [182]) or even three (155 [182]) centers of chirality.…”

“…RRR/SSS and RRS/SSR, SRS/RSR, SRR/RSS). In the solid state it has been observed by X-ray crystallography that mono-BP (161) exists as the racemate [190], bis-BP (162) is observed as the meso form [179] and the tris-BP (163) is observed as the racemate containing mixed R and S forms (RRS/SSR etc.) [186].…”

“…In this case the stereochemistry was recorded for both racemic (170 [179] and 171 [196]) and meso (172 [196], 173 [197], 174 [198]) diastereoisomers, although for a number of structures the stereogenic properties were not recorded for either racemic (175 [199], 176 [200], 177 [201] ) or meso (178 [202], 179 [200]) compounds. The bis-BP motif is very common in metallocyclophosphazenes but the stereogenic properties were only stated in one study where the racemic form of bis-BP was observed (180 [203]).…”

“…Although bis-spiro-BP cyclophosphazenes (162) are expected to exist in solution as equal proportions of meso and a racemic diastereoisomers, Dez et al [179] reported that only the meso form was observed by X-ray crystallography and also in solution as the 31 P NMR only showed one set of signals in the crude reaction mixture. They also reported that the reaction of 162 (meso form) with a hard nucleophile such as 4-methoxyphenolate resulted in a racemic mixture (170) necessitating a change of configuration at one phosphorus center, whereas reaction of 162 with soft nucleophiles like amines, meso isomers were observed and there is no change of configuration at a phosphorus center [179].…”