Organometallic Phosphazenes: Synthesis and Rearrangement of Propynyl- and Propadienylcyclotriphosphazenes

A new series of 1,1-dialkyltetrachlorocyclotriphosphazenes with prop-2-ynyl (VI), prop-l,2-dienyl (V), and prop-l-ynyl (XII) substituents have been prepared. These syntheses involve the reactions of cuprio- or lithiophosphazene anions (II or IX) with prop-2-ynyl bromide which lead initially to the formation of the prop-2-ynyl complexes (VI). The prop-2-ynyl side group was found to undergo an alumina-initiated rearrangement to the prop-l,2-dienyl group (V), and both compounds VI and V underwent a methyllithium-initiated rearrangement to the prop-l-ynyl derivatives (XII). These organometallic-initiated rearrangements were monitored by 31P NMR spectroscopy. The structural characterization of all the new compounds is described, and the NMR results, together with the various rearrangements, are discussed in terms of electronic interactions between the C3H3 group and the phosphazene ring. The formation of the lithiophosphazene anion (IX, R = CH3) was studied by low-temperature 31P NMR spectroscopy, and the results are discussed in terms of the electron distribution within the phosphazene ring.