Spermine-bridged gem-disubstituted cyclotriphosphazatrienes have been synthesised by two routes. In one route a spermine-bridged cyclophosphazene 2 reacted with monofunctional nucleophiles known to favour gem disubstitution in cyclophosphazene rings (e.g.tert-butylamine) to give 3b, or to favour formation of spiro-derivatives with difunctional nucleophiles (e.g. 1,3-propanediol) to give 3c. In the other route a gem-disubstituted cyclophosphazene (i.e. diphenyl, N3P3Ph2Cl4, compound 4) reacted with spermine to give 3a. The >P(N-spiro) group in each cyclophosphazene ring of 3a–c is stereogenic and
homotopic, and so it is expected, and confirmed, that the spermine-bridged gem-disubstituted cyclotriphosphazatrienes (3a–c) should be chiral and exist in meso and racemic forms. The proton-decoupled 31P NMR spectroscopy of 3a–c gave rise to two sets of signals in a 1 ∶ 1 ratio consistent with formation of meso and racemic forms. The meso and racemic forms of 3a (gem-diphenyl derivative) were separated by column chromatography and characterised by X-ray crystallography; this enabled the unequivocal assignment of the two sets of 31P NMR signals to the meso and racemic forms of 3a. This is the first time that the existence of chiral configurational isomers has been elucidated in the field of spermine-bridged
cyclophosphazene compounds, and only the second time in cyclophosphazene chemistry.
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