Phosphorus–nitrogen compounds. Part XXVII. The reaction of phenylmagnesium bromide with hexachlorocyclotriphosphazatriene
Hexachlorocyclotriphosphazatriene, N3P3Cl6, reacts with phenylmagnesium bromide in a range of solvents, and under a variety of conditions, to yield only fully phenylated species. These belong to two types, cyclic and acyclic. The former is represented by hexaphenylcyclotriphosphazatriene, N3P3Ph6, the latter by a rather complex mixture of phosphazenylmagnesium complexes. These, on treatment with Brønsted acids, yield phosphazenium salts; heptaphenyltriphosphazatrienium chloride and bromide, N3P3Ph7H2X (X = Cl or Br), were isolated pure. The isolation of triphenylphosphine oxide and diphenylphosphinic acid in approximately 1 : 1 ratio from the hydrolytic degradation of the crude mixture of phosphazenium salts suggests that the above two pure species may not be major reaction products.
2,2,4,4-Tetrachloro-6,6-diphenyl-, N3P3Ph2Cl4, and 2,2-dichloro-4,4,6,6-tetraphenyl-cyclotriphosphazatriene, N3P3Ph4Cl2, react in the same manner as, but much more slowly than, the hexachloride, N3P3Cl6. The reaction is discussed in terms of the biphilic character of the Grignard reagent. A mechanism is suggested involving ring cleavage to a phosphazenylmagnesium complex, and recyclisation of this to hexaphenylcyclotriphosphazatriene.