Chemistry Of Zwitterionic Penta-Coordinate Silicon Compounds Of The (Ammoniomethyl)Bis[Glycolato(2-)-O-1,O-2]Silicate Type In Aqueous And Nonaqueous Solution

The zwitterionic spirocyclic lambda(5)Si-silicates bis[glycolato(2-)-O-1,O-2][(trimethylammonio)methyl]silicate ([OCH2C(O)O](2)SiCH2NMe3, 3) and bis[2-methyllactato(2-)-O-1,O-2][(trimethylammonio)methyl]silicate ([OCMe2C(O)O](2)SiCH2NMe3, 4) were synthesized by treatment of the zwitterionic lambda(5)Si-silicate F4SiCH2NMe3 with 2 mol. equiv. of Me3SiOCR2C(O)OSiMe3 (R = H, Me) (formation of 4 mol. equiv. of Me3SiF). Compounds 3 (isolated as 3o2/3MeCN after drying in vacuo) and 4 were studied by solution H-1, C-13, and Si-29 NMR spectroscopy and by solid-state VACP/MAS C-13, N-15, and Si-29 NMR experiments, and the solvates 3oMeCN and 4o2MeCN were structurally characterized by single-crystal X-ray diffraction. These experimental investigations were complemented by computational studies of the zwitterions 3 and 4 and the anionic model species bis[2-methyllactato(2-)-O-1,O-2]hydridosilicate(1-) ([OCMe2C(O)O](2)SiH-, 8). Compounds 3o2/3MeCN and 4 and their already known derivatives [OCH2C(O)O](2)SiCH2NMe2H (1) and [OCMe2C(O)O](2)SiCH2NMe2H (2) were studied for their dynamic behavior (Lambda/Delta-enantiomerization) in solution by VT H-1 NMR spectroscopy. In addition, compounds 1, 2, 3o2/3MeCN, and 4 were studied in CD3OD and D2O with H-1, C-13, and Si-29 NMR experiments.