Bis(chloromethylsilyl)amine and bis(chloromethylsilyl)methylamine; preparation, reactivity and spectroscopic studies of their stereoisomers and conformers‡

Abstract

The compounds NH(SiHMeCl)₂ 1 and NMe(SiHMeCl)₂ 2 have been prepared by treating SiHMeCl₂ with CaCl₂·8NH₃ and NH₂Me respectively. Each was characterised by elemental analysis, mass spectrometry, NMR and IR spectroscopy. Dipole moments were also measured. The NMR spectra indicate that both compounds form 1∶1 mixtures of the rac and meso diastereomers, their abundances corresponding to a statistically controlled synthetic pathway. The NMR and mass spectra also show that 1,5-dichloro-1,2,3,4,5-pentamethyltrisilazane, SiHMe[NMe(SiHMeCl)]₂ 3, which is formed as a side product in the synthesis of 2, also consists of two diastereomers. Variable-temperature ¹H NMR spectra of NH(SiHMeCl)₂ indicate participation of H(N) in hydrogen bonding. The compound is decomposed by heat and reacts with pyridine to form NH₄Cl, SiHMeCl₂ and polysilazanes, whereas NMe(SiHMeCl)₂ shows only slight decomposition up to 80 °C and does not react with pyridine. Infrared spectra in the ν(SiH) region are interpreted in terms of the results of ab initio calculations of frequency, intensity and conformer abundance. The two bands near 2200 cm^–1 in the spectrum of 2 have their origin in two effects: different orientations of the Si–H bonds relative to the Si–N–Si plane in several conformers and an unprecedented strong dipole–dipole coupling between the two Si–H bond stretching motions in situations where the bonds are roughly parallel. The absence of such an observed splitting for 1 is likely to be due in part to signal averaging during a free internal rotation. Significant couplings are also calculated to occur between Si–Cl bond-stretching motions, whose source must be different from that for the Si–H bond stretches.