Intramolecular O → Si donor-acceptor interaction in R2P(=O)CH2CH2SiF3 molecules: Synthesis of dialkyl [2-(trifluorosilyl)ethyl]phosphonate and bis[(chloromethyl)dimethylsilyl] styrylphosphonate

Abstract

The reaction of diethyl [2-(triethoxysilyl)ethyl]phosphonate with boron trifluoride etherate was used to synthesize diethyl [2-(trifluorosilyl)ethyl]phosphonate. The reaction of bis(trimethylsilyl) styrylphosphonate with chloro(chloromethyl)dimethylsilane gave bis[(chloromethyl)dimethylsilyl] styrylphosphonate. Multinuclear 1H, 13C, 19F, 29Si, and 31P NMR spectroscopy established the absence of a P=O → Si coordination bond in these compounds and the four-coordinate state of the silicon atom. Evidence for this finding was obtained by B3LYP/6-31G(d) quantum-chemical calculations. However, the same calculations for R2P(=O)· CH2CH2SiF3 (R = Me, Me2N) showed the presence in such molecules of an O → Si coordination bond both in the gas phase and in CHCl3 solution. The distance between the O and Si atoms in this series molecules decreases with R in the order: MeO > Me > Me2N. The axial Si-F bond length increases in the same order and parallels the order of the Hammet σ 0 m constants of these substituents, relating to their interaction with π-electron systems.