Synthesis and crystal structure of the bromide salt of the inside protonated form of the cage amine [(2.3)3]adamanzane, 1,4,8,12-tetraazatricyclo[6.6.3.24,12]nonadecane and synthesis of the bowl amine [(2.3)2.21]adamanzane, 1,5,9,12-tetraazabicyclo[7.5.2]hexadecane

Abstract

The reaction of 1,4,7-triazacyclononane with tris(3-chloropropyl)amine affords the inside monoprotonated form of the tricyclic amine 1,4,8,12-tetraazatricyclo[6.6.3.2^4,12]nonadecane (3), which was isolated as the bromide salt, [H[(2.3)³]adz]Br (yield 38%). The crystal structure of [H[(2.3)³]adz]Br·4H₂O has been solved by X-ray diffraction at T = 120 K. In the i⁺,i,i,i-H[(2.3)³]adz⁺ cation (3a) the acidic hydrogen atom and the lone pairs of the nitrogen atoms are oriented towards the inside of the cavity. The acidic hydrogen atom is attached to the apical nitrogen atom and both are positioned on a three-fold axis. The distances between the nitrogen atoms are in the range of 2.73(2)–2.99(1) Å. The inside coordinated proton in H[(2.3)³]adz⁺ (3a) is unusually inert to reaction with base (k_diss < 4 × 10^–9 s^–1 at 25 °C in 0.01 M NaOD). From ¹H and ¹³C NMR it is concluded that in slightly acidic (pH > 2) and in basic aqueous solutions the dominant form of the cage has all four lone pairs pointing into the cavity. In concentrated strong acid protonation occurs and is believed to involve inversion at one or several of the bridgehead nitrogen atoms. In concentrated boiling hydrochloric acid the cage undergoes a slow cleavage of one trimethylene bridge to give the bowl amine [(2.3)².2¹]adz (7), 1,5,9,12-tetraazabicyclo[7.5.2]hexadecane, which was isolated as the triprotonated bromide dichloride salt, [H₃[(2.3)².2¹]adz]BrCl₂·H₂O (yield 40%).