Infrared studies of SiH bonds and the structures of methylsilylamines and ethers

Abstract

Gas phase IR spectra have been investigated in a series of methylsilyl compounds, including MeSiHDX (X = F, Cl), MeSiHX2 (X = F, Cl), Me2SiHCl, (Me2SiH)2NH, (MeSiH2)3N, (MeSiHD)3N, (MeSiH2)2NMe,* (Me2SiH)2NMe,* MeSiH2NMe2,* Me2SiHNMe2, (MeSiHD)2O and (Me2SiH)2O. In the asterisked molecules, pairs of νSiH bands are seen which confirm the existence of fixed conformations. Amongst the other compounds, the single band seen is attributed on the basis of the α-Me substitutent effect to a fixed conformation in the cases of Me2SiHNMe2 and (Me2SiH)2O. In (Me2SiH)2NH and (MeSiH2)2O, free internal rotation about the SiN and SiO bonds seems likely. Apart from the possible case of (MeSiH2)3N, the spectra appear to be compatible with the electron diffraction evidence, and for the most part in broad agreement with the structures found. 2νSiH bands are in general harder to see in these amines and ethers than in Me2SiHCl. A likely transition to a (1, 1) local mode state is observed in (MeSiH2)3N. Determination of barriers to internal rotation in these molecules should be a high priority.