Structure and basicity. Part V. Amino-derivatives of 2,2,4,4-tetrachloro-6,6-diphenyl- and 2,2-dichloro-4,4,6,6-tetraphenyl-cyclotriphosphazatrienes: the evaluation of substituent constants for phenyl and alkylamino-groups

Abstract

The basicities of a number of the aminolysis and ammonolysis products, N₃P₃Ph₂Cl_{4 –n}R_n and N₃P₃Ph₄Cl_{2 –n}R_n(R = NH₂, NHMe, NHEt, NHC₆H₁₁, NHBu^t, NMe₂, NEt₂, or NC₅H₁₀) of 2,2,4,4-tetrachloro-6,6-diphenyl-, N₃P₃Ph₂Cl₄, and 2,2-dichloro-4,4,6,6-tetraphenyl-cyclotriphosphazatrienes, N₃P₃Ph₄Cl₂, have been measured in nitrobenzene. Two isomers of the compounds N₃P₃Ph₂Cl₂R₂ are known in two of the series (R = NHMe or NC₅H₁₀) but the structures of these had not hitherto been determined. An analysis of the basicity data proves that they are geminal and non-geminal isomers and that the stronger base has the geminal structure. Assignments of structure can also be made with some confidence for those compounds in the N₃P₃Ph₂Cl₂R₂ series for which only one isomer has been obtained.

Sufficient information is now available to carry out approximate calculations of the effects on the pK′_a values of replacing chlorine atoms by amino- or phenyl groups, and phenyl groups by amino-groups. There are important differences from the mono-substituted pyridines. For example, in the phosphazenes the replacement of phenyl by amino-groups increases the electron-density more at the ring nitrogen atom α than at that γ to the ring atom at which the replacement has occurred.