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

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 1 H and 13 C NMR spectroscopy. However, only the presence of several conformers has been detected by means of 1 H NMR spectroscopy at 113 K; determination of the Δν (Hz) and Δ G # (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.