The complexing ability and structure of Si-substituted silatranes

The proton NMR spectra of Si-substituted silatranes, a new class of biologically active compounds, measured in the presence of Co²⁺, Ni²⁺ and Eu³⁺ ions are examined. These silatranes coordinate with Co²⁺ and Ni²⁺ through a nitrogen atom and with Eu³⁺ through an oxygen atom mainly without transition to the exo-form. The electronic structure of nitrogen in silatranes is the same as that of pyrrol nitrogen. This suggests that in silatranes a nitrogen lone pair and oxygen lone pairs form common electron system analogous, for example, to the π-system of unsaturated cycles.