Phosphorus–nitrogen compounds. Part XXVII. The reaction of phenylmagnesium bromide with hexachlorocyclotriphosphazatriene

Abstract

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.