Phosphazene bond dimerization

The addition of a molecule X—Z (often with Z = H) to a P=0, P=N, P=C or P=S double bond can always be a possibility. The reaction may occur with a distinct molecule, or it may even be intramolecular when XH is a constitutive part of the phosphorusbearing molecule. Structures such as A, A, A", C and C in Scheme 28 are representative of a large proportion of phosphorus compounds of (mono)phosphazenes, and of their cyclophosphazane dimers (over 1000 literature references ). 

Si—N bond cleavage can also be effected by germanium chlorides and bromides to give monomeric phosphazenes, e.g. MesP=NGeMeCl2, covalent dimers (19), and formally ionic dimers (20). Adducts formulated as... 

Phosphorus Compounds.—Treatment of the dioxaphospholen (635) with sulphur yields a mixture of the oxathiole (636) and fran -dibenzoylstilbene, PhCOCPh=CPhCOPh." 2-Phenyl-l,3,2-dioxaphospholan (637 R = Ph) dimerizes in solution to a ten-membered-ring compound, which was isolated as (638) by sulphurization." The cyclic thiophosphorous acid (639) exists in equilibrium with the betaine (640) in aqueous ethanol/ The spiro-compound (641), which contains a phosphorus-hydrogen bond, is formed by the action of (637 R = Cl) on diethyl tartrate. The phosphazene (642) spontaneously cyclizes to the spiro-compound (643). " Stable derivatives (645) and (646 R = Br) of five-co-ordinate phosphorus have been obtained by the action of bromine on the o-phenylene phosphite (644)/ The chlorine analogue (646 R Cl) reacts with 3,5-dimethylpyrazole to give the corresponding pyrazole derivative (646 R = 3,5-dimethylpyrazol-l-yl), which reversibly dimerizes to the zwitterion (647). ... 

The S (and Se) analogues of (7.239) fonn dimers in the solid state with P/N/P < 180° (7.240). On the other hand, the oxy analogue is monomeric and forms an internal H bond with P/N/P = 180°. In addition, the shorter P-N bond lengths in the oxy derivative indicate a considerable contribution from a phosphazene structure (7.418) below. 

Another chemical pathway observed for cyclotriphosphazenes N-methyl-1,3-propanediamine or 3-amino-1-propanol substitution is their dimerization, Scheme IS. Initially, the chlorinated trimer is substituted with one bidenate ligand, yielding (18). Treatment with sodium hydride extracts a proton from the secondary amine and facilitates a P-N bond forming reaction (19). This also has been demonstrated in a reaction between (18) and HCCP to give monodentate dimerization between phosphazene rings (20), Scheme 16. 

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