Kinetic studies of aminolysis reactions of chlorocyclophosphazenes

Aminolysis reactions of halogenocyclophosphazenes constitute an important class of nucleophilic substitution reactions at a four-coordinate phosphorus(V) centre (I, 2). Several conclusions have been drawn from preparative experi- ments on the probable importance of steric and electronic factors relating to the nucleophile (3,4), However, the pre- cise role of solvents in influencing the stereochemistry of products formed in the aminolysis reactions of halogeno- cyclophosphazenes has not been fully unravelled, although it is clearly of major importance (3,5). Detailed kinetic studies and the interpretation of activation parameters in mechanistic terms are essential for a better understanding of these complex reactions. Earlier studies in this direction are limited to the reactions of hexachlorocyclotriphosphaza-triene, N3P3C1 6, with methylamine and dlmethylamlne in tetrahydrofuran (6). Kinetic studies of the reactions of N3P3C16 with piperidine and diethylamine in benzene have also been reported but activation parameters have not been deter-mined (7). We have initiated detailed kinetic studies of the reactions of halogenocyclophosphazenes with different amines in different solvents in order to obtain a better understanding of the stereoselectivlty observed in many preparative studies and in particular, to place the previous mechanistic hypo-thesis (2, 3) on a sounder basis. We report here our preliminary results