CRYSTAL-STRUCTURES OF SALTS OF MONOPROTONATED AND TRIPROTONATED [3(6)]ADAMANZANE, 1,5,9,13-TETRAAZATRICYCLO[7.7.3.3(5,13)]DOCOSANE, AND EQUILIBRIUM STUDIES OF THE REACTIONS BETWEEN MONOPROTONATED, DIPROTONATEDAND TRIPROTONATED SPECIES, RESPECTIVELY, HAVING NONE, ONE AND 2 LONE PAIRS POINTING OUTWARDS

The structures of bromide salt of the inside monoprotonated tricyclic amine 1,5,9,13-tetraazatricyclo[7.7.3.3(5,13)]docosane, i(+),i,i,i-[H[ 3(6)]adz]Br and of the tetrabromozincate bromide salt of its triproton ated form, i(+),i,o(+),o(+)-[H-3[3(6)]adz][ZnBr(4)lBr-H2O have been de termined by X-ray diffraction techniques. In acidic solution i(+),i,i, i-H[3(6)]adz(+) reacts with one hydrogen ion and at the same time unde rgoes inversion at one nitrogen group to give the diprotonated species i(+),i,i,o(+)-H-2[3(6)]adz(2+) as shown by H-1 and C-13 NMR spectrosc opy and glass-electrode measurements. The thermodynamic data for the c oncentration equilibrium constant for the protonation/inversion reacti on are -log K-ial= 3.122(5) M, Delta H degrees(K-ial)=12.0(8) kJ mol(- 1), Delta S degrees(K-ial)= -20(3) J mol(-1) K-1 (25 degrees C, I=1 M (Na,H)Cl. The equilibration reaction between the mono-and dipotonated species is slow on the NMR timescale (25 degrees C). The lifetime of t he diprotonated species has been studied by the temperature dependence of its H-1 NMR spectrum, which at room temperature corresponds to C-3 v symmetry but at higher temperature exhibits coalescence correspondin g to an approach toward a time-averaged T-d symmetry. The latter is in terpreted as a fast exchange of the outside coordinated proton between the four sites in i(+),i,i,o(+)-H-2[3(6)]adz(2+). The exchange reacti on is acid catalyzed, and a pathway involving the triprotonated specie s i(+),i,o(+),o(+) -H-3[3(6)]adz(3+) is assumed to be the rate-determi ning step. In acidic solution i(+),i,i,o(+)-H-2[36]adz(2+) is very ine rt with respect to exchange of the inside coordinated proton (k(ex)<3 x10(-9) s(-1)). The H[3(6)]adz(+) species is much more stable than its smaller analouge with respect to C-N cleavage. In 1-3 M HCl H[2(4).3( 2)]adz(+) is shown to undergo an acid catalyzed cleavage of one of the trimethylene bridges to give quantitatively the parent bowl adamanzan e [2(4).3(1)]adz without further cleavage of N-C bonds. In contrast, t he H[3(6)]adz(+) species withstands boiling for days in concentrated h ydrochloric acid.