The Basicity of Silylamines and Alkylamines: An Equilibrium Study of the Competitive Borane Adduct Formation

Abstract

Abstract In order to investigate the Lewis acid/base chemistry of silylamines in solution, the equilibrium reactions of Me3SiNMe2 / Me3SiNMe2(BH3) and different amines NR3 / amineboranes NR3(BH3) were monitored by 1H NMR spectroscopy in C6D6 and CDCI3 at 60 °C. For the equilibrium of the reference silylamine/-borane and Me3CNMe2 / Me3CNMe2(BH3) values K = 0.35 (AG = 3.1 kJ mol-1) in C6D6 and K = 0.50 (AG = 2.0 kJ mol-1) in CDCl3 have been estimated, showing that both the silylamine and the C/Si-analogous organic amine have very similar donor properties. Small amines like NMe3 proved to be much more powerful donors than the silylamine Me3SiNMe2, whereas bulky amines are less efficient donors, indicating that steric effects play an important role. The formation of BH3 adducts of Me2NSiH3 and (H3Si)3N which could not be followed experimentally owing to the low stability of the products, has been studied by quantum chemical calculations. A comparison with data for Me3N(BH3) shows that the silylamines are poorer donors, but the reason for this remains unclear