Conformational Analysis of (1,1′-Phenyl-1,1′-silacyclohex-1-yl)disiloxane. DFT and Low-Temperature 13C NMR Spectroscopy Study

Resumo

The DFT and MP2 theoretical conformational analysis of the recently synthesized (1,1′-phenyl-1,1′-silacyclohex-1-yl)disiloxane has revealed the energetic preference of the Ph_ax,Ph_ax conformer. The Ph_ax,Ph_ax: Ph_ax,Ph_eq: Ph_eq,Ph_eq conformers ratio has been estimated as of 46.6: 33.1: 20.3 from the M062X/6-311G(d,p) free energy simulation, suggesting the possibility of detecting individual conformers experimentally, e.g., by low-temperature ¹H and ¹³C NMR spectroscopy. However, only the presence of several conformers has been detected by means of ¹H NMR spectroscopy at 113 K; determination of the Δν (Hz) and ΔG^# (kcal/mol) parameters for the 6-membered ring interconversion has been impossible due to the signals broadening at low temperature, signal temperature shifts, and extremely low barrier of ring inversion at T_c < 113 K.