Abstract
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 triprotonated form, i(+),i,o(+),o(+)-[H-3[3(6)]adz][ZnBr(4)lBr-H2O have been determined 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 undergoes 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 spectroscopy and glass-electrode measurements. The thermodynamic data for the concentration equilibrium constant for the protonation/inversion reaction 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 the diprotonated species has been studied by the temperature dependence of its H-1 NMR spectrum, which at room temperature corresponds to C-3v symmetry but at higher temperature exhibits coalescence corresponding to an approach toward a time-averaged T-d symmetry. The latter is interpreted 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 reaction is acid catalyzed, and a pathway involving the triprotonated species i(+),i,o(+),o(+) -H-3[3(6)]adz(3+) is assumed to be the rate-determining step.
In acidic solution i(+),i,i,o(+)-H-2[36]adz(2+) is very inert 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 adamanzane [2(4).3(1)]adz without further cleavage of N-C bonds. In contrast, the H[3(6)]adz(+) species withstands boiling for days in concentrated hydrochloric acid.
In acidic solution i(+),i,i,i-H[3(6)]adz(+) reacts with one hydrogen ion and at the same time undergoes 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 spectroscopy and glass-electrode measurements. The thermodynamic data for the concentration equilibrium constant for the protonation/inversion reaction 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 the diprotonated species has been studied by the temperature dependence of its H-1 NMR spectrum, which at room temperature corresponds to C-3v symmetry but at higher temperature exhibits coalescence corresponding to an approach toward a time-averaged T-d symmetry. The latter is interpreted 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 reaction is acid catalyzed, and a pathway involving the triprotonated species i(+),i,o(+),o(+) -H-3[3(6)]adz(3+) is assumed to be the rate-determining step.
In acidic solution i(+),i,i,o(+)-H-2[36]adz(2+) is very inert 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 adamanzane [2(4).3(1)]adz without further cleavage of N-C bonds. In contrast, the H[3(6)]adz(+) species withstands boiling for days in concentrated hydrochloric acid.
Original language | English |
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Journal | Acta Chemica Scandinavica |
Volume | 52 |
Pages (from-to) | 289-295 |
Publication status | Published - 1998 |