O-Alkylated Derivatives of 1,3,5-Triamino-1,3,5-trideoxy-cis-inositol: Triamine Ligands with Unexpectedly High Affinity toward Divalent Transition- and d(10)-Metal Ions.

The ligands all-cis-2,4,6-trimethoxycyclohexane-1,3,5-triamine (tmca) and all-cis-2,4,6-tribenzoxycyclohexane-1,3,5-triamine (tbca) were prepared almost quantitatively by using [Ni(taci)2]2+ (taci = 1,3,5-triamino-1,3,5-trideoxy-cis-inositol) as precursor, where Ni2+ acted as a very efficient protecting group for the nitrogen donors. The structure of tmca in solution was investigated by NMR spectroscopy. A strongly solvent-dependent conformational equilibrium was observed. In CD3CN, a chair conformation with three axial amino groups formed exclusively, whereas in D2O, the conformation with three equatorial amino groups predominated. This effect, as well as conformational changes in the course of stepwise protonation, is discussed in terms of hydrogen bonding effects. The crystal structure of H3tmca3+ exhibits a chair conformation with three equatorial ammonium groups and three axial methoxy groups. The trihydrochloride hydrate crystallizes in the monoclinic space group P21/n, a = 11.057(5) A, b = 9.960(6)...