New zwitterionic spirocyclic lambda Si-5-silicates with two ethane-1,2-diolato(2-), oxalato(2-), or benzene-1,2-diolato(2-) ligands - Synthesis, structure, and dynamic behavior

The syntheses of the zwitterionic spirocyclic lambda(5)Si-silicates 6-9 are described. These chiral zwitterions contain a pentacoordinate (formally ne gatively charged) silicon atom and a tetracoordinate (formally positively c harged) nitrogen atom. Compounds 6 . 1/2HO(CH2)(2)OH, 7, 8 . CH3CN, and 9 w ere studied by solution-state (H-1, C-13, Si-29) and solid-state (Si-29 CP/ MAS) NMR experiments. In addition, all compounds were structurally characte rized by single-crystal X-ray diffraction. The dynamic behavior (Berry-type enantiomerization) of 7-9 in solution was studied by VT 1H NMR experiments . These experimental studies were completed by ab initio investigations of the related anionic model species 10-12.