ISSN:
1434-1948
Keywords:
Phosphazenes
;
Polymers
;
Chirality
;
Urethanes
;
TGA
;
Thermochemistry
;
Asymmetric synthesis
;
Chemistry
;
General Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The reaction of hexachlorocyclotriphosphazene with two equivalents of the chelating diols 2,2′-dioxybiphenyl and 2′,2′′-dioxy-1′,1′′-bi-2-naphthyl was investigated. Although a mixture of different stereoisomers may be expected, only the formation of the meso-compounds [(R,S)-(O,O)2Cl2P3N3] is found (O,O stands for the diolate). Interestingly, when the remaining PCl2 group undergoes reaction with hard nucleophiles like 4-methoxy phenolate, a change of configuration at one phosphorus center is observed and racemic mixtures of chiral [(R,R)-(O,O)2(RO)2P3N3] and [(S,S)-(O,O)2(RO)2P3N3] phosphazenes are observed. Enantiomerically pure cyclotriphosphazenes were obtaines from either the (R)- or (S)-form of 2′,2′′-dioxy-1′,1′′-bi-2-naphthyl. Soft nucleophiles like amines, however, do not affect the configuration at the phosphorus centers and allow the synthesis of meso-[(R,S)-(O,O)2(R1RN)2P3N3] compounds. the bifunctional cyclotriphosphazenes [(O,O)2(4-OH-C4H4O)2P3N3] and [(R,S)-(O,O)2(H2N)2P3N3] were used in polyaddition reactions with hexymethylene di(isocyanate) to give cyclolinea polymers of different stereochemical compositions corresponding to the stereochemistry of the phosphazene precursor (i.e. either a racemic mixture of homochiral 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.
Additional Material:
6 Ill.
Type of Medium:
Electronic Resource
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