PMR spectra of Si-substituted silatrane derivatives

Silatranes and Their Tricyclic Analogs

“…1 H NMR studies of 3-methylsilatranes 238 , 4-organylsilatranes 61 and diastereomeric 3,7-dimethyl-and 3,7,10-trimethylsilatranes 238,239 revealed conformational rigidity of their substituted five-membered rings and the equatorial position of the C-substituent. It was shown that for most 3,7-dimethyl-and 3,7,10-trimethylsilatranes the diastereomer distributions are nearly statistical, indicating a kinetic control of the reactions leading to the formation of the silatrane cage 238 .…”

“…There are two viewpoints concerning the mechanism of epimerization of these conformers. The first suggests a synchronous conversion of all the three rings of the silatrane cage 238 , whereas the second proposes their non-correlated successive flips 239 .…”

“…It was shown that for most 3,7-dimethyl-and 3,7,10-trimethylsilatranes the diastereomer distributions are nearly statistical, indicating a kinetic control of the reactions leading to the formation of the silatrane cage 238 .…”

“…The X Si N bonding and the corresponding transfer of electron density in silatranes are well reflected in the values of their 1 H NMR chemical shifts 13,20,235,236 . Thus, the shielding of the substituent X protons in 1-organylsilatranes is higher than in the model tetracoordinate compounds, organyltriethoxysilanes XSi(OEt) 3 , whereas the NCH 2 protons in silatranes are less shielded than in triethanolamine and its tris-TMS ether.…”

“…Within a wider set of silatranes including 1-aryl-, 1-organoxy-and 1-halo derivatives, the υ values are correlated by a dual-substituent parameter equation, using the polar and resonance ( 1 and R 0 or F and R) constants of the substituent X 235 . Due to strong intermolecular dipole dipole interactions, the 1 H NMR chemical shifts of silatranes vary with concentration and solvent 235,240 . For example, the NCH 2 protons are more shielded (by 0.8 1.2 ppm) in benzene than in CDCl 3 solution.…”