Isolation and Characterization of Nongeminal Cyclic Methylphenylphosphazene Tetramers

Heating pure samples of the cyclic phosphazenes, cis- or trans-[Me(Ph)PN]3, yielded mixtures
of the cis and trans isomers of the cyclic phosphazene trimers, [Me(Ph)PN]3, and all four geometric isomers
of the tetramers, [Me(Ph)PN]4. Varying the temperature and heating times changes the ratio of these
components. Following the thermolysis by NMR spectroscopy indicated that only a mixture of the two
isomeric trimers occurred initially. Longer heating times produced mixtures of the isomers of the tetramer.
Column chromatography and solubility differences were used to separate each of the isomers of the tetramer.
Spectroscopic and X-ray crystallographic studies suggest that the four different geometrical isomers of the
tetramer can be described as cone, partial cone, 1,2-alternate, and 1,3-alternate by analogy to calix[4]arene.