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 [188.8.131.52 sup 4,12]nonadecane (3), which was isolated as the bromide salt, [H[(2.3)sup 3]adz]Br (yield 38%). The crystal structure of [H[(2.3)sup 3]adz]Br x 4H sub 2 O has been solved by X-ray diffraction at T = 120 K. In the i sup +,i,i,i-H[(2.3) sup 3] adz sup + 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)sup 3]adz sup + cation (3a) is unusually inert to reaction with base (k sub diss < 4 x 10 sup -9 s sup-1 at 25 degrees C in 0.01 M NaOD). From sup 1 H and sup 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) sup 2. 2 sup 1]adz (7), 1,5,9,12-tetraazabicyclo[7.5.2]hexadecane, which was isolated as the triprotonated bromide dichloride salt, [H sub 3[(2.3) sup 2. 2 sup 1]adz]BrCl sub 2 x H sub 2 O (yield 40%).
|Journal||J. Chem. Soc., Perkin Trans.|
|Publication status||Published - 1999|