Syntheses of chiral cyclotriphosphazenes and their use in cyclolinear polymers

The reaction of hexachlorocyclotriphosphazene with two equivalents of the c helating diols 2,2'-dioxybiphenyl and 2',2 "-dioxy-1',1 "-bi-2-naphthyl was investigated. Although a mixture of different stereoisomers may be expecte d, only the formation of the meso-compounds [(R,S)-(O, O)(2)Cl2P3N3] is fou nd (O,O stands for the diolate). Interestingly, when the remaining PCl2 gro up undergoes reaction with hard nucleophiles like 4-methoxy phenolate, a ch ange of configuration at one phosphorus center is observed and racemic mixt ures of chiral [(R,R)-(O,O)(2)(RO)(2)P3N3] and [(S,S)-(O,O)(2)(RO)(2)P3N3] phosphazenes are observed. Enantiomerically pure cyclotriphosphazenes were obtaines from either the (R)- or (S)-form of 2',2 "-dioxy-1',1 "-bi-2-napht hyl. Soft nucleophiles Like amines, however, do not affect the configuratio n at the phosphorus centers and allow the synthesis of meso-[(R,S)-(O,O)(2) ((RRN)-R-1)(2)P3N3] compounds. the bifunctional cyclotriphosphazenes [(O,O) (2)(4-OH-C4H4O)(2)P3N3] and [(R,S)-(O,O)(2)(H2N)(2)P3N3] were used in polya ddition reactions with hexymethylene di(isocyanate) to give cyclolinea poly mers of different stereochemical compositions corresponding to the stereoch emistry of the phosphazene precursor (i.e. either a racemic mixture of homo chiral polymer strands, enantiomerically pure polymers, or the meso-form of polymers was obtained). The properties of these polymers are discussed and a mechanism for the change of stereochemistry is proposed.