Structural investigations of phosphorus-nitrogen compounds. 4. Steric and electronic effects in dibenzylamino derivatives of hexachlorocyclotriphosphazatriene and 4,4,6,6-tetrachloro-2,2-diphenylcyclotriphosphazatriene.

Abstract

A systematic study is presented on the products of aminolysis of N(3)P(3)Cl(6) (1) and N(3)P(3)Ph(2)Cl(4) (4) with dibenzylamine. Two series of mono- and disubstituted derivatives of compounds (1) and (4), namely N(3)P(3)Cl(5)[N(CH(2)Ph)(2)] (2) and N(3)P(3)Cl(4)[N(CH(2)Ph)(2)](2) (3) and N(3)P(3)Ph(2)Cl(3)[N(CH(2)Ph)(2)] (5) and N(3)P(3)Ph(2)Cl(2)[N(CH(2)Ph)(2)](2) (6) [where (2), (3), (5) and (6) are new structures], are investigated in order to determine whether steric or electronic effects prevail in the formation of dibenzylamino-substituted cyclophosphazenes. The influence of an electron-releasing group (i.e. phenyl) on the stereochemistry and degree of substitution of the product is analysed by comparison of the above two series. The difference in unsymmetrically substituted endocyclic P-N bond lengths, Delta, is used as a measure of the degree of the electronic contribution, in combination with basicity constants, to quantify the degree of the electron-releasing capacity of the R group. In order to compare geminal versus non-geminal substitution, a difunctional secondary amine was used to form the compound N(3)P(3)Cl(4)[NMe(CH(2))(3)NMe] (7) (a reinvestigation) for inclusion in this study. It is shown that electron-releasing groups have a greater effect on the lengthening of P-Cl bonds as opposed to endocyclic P-N bonds and that this effect is greater in the non-geminal PRCl case than for geminal PCl(2). However, steric effects are shown to be dominant in the reactions of dibenzylamine with N(3)P(3) derivatives, with a disposition to a trans stereochemistry in bisdibenzylamino derivatives.