Geometry of intramolecular silicon complexes: an ab initio estimation of the sensitivity to the effect of medium. (Aroyloxymethyl)trifluorosilanes

Abstract

The effect of medium on the geometry of the (benzoyloxymethyl)trifluorosilane (1) molecule was studied by the HF and MP2 methods with the 6-31G(d), 6-311G(d), and 6-311+G(d,p) basis sets, as well as using the Onsager SCRF model, the PCM approach, and the data of X-ray diffraction study. Molecule 1 has a low complexation energy (5.4 kcal mol–1 according to MP2(Full)/6-31G(d)+ZPE calculations and ∼6.8 kcal mol–1 according to IR spectroscopy data), while its geometric parameters are the least sensitive to the effects of medium among all hypervalent silicon compounds studied to date. Nevertheless, the results obtained revealed a pronounced deformation of the Si←O coordination bond in 1 on going from the gas phase to the polar solution and crystal. This serves as a theoretical substantiation of the hypothesis that substantial changes in the IR and NMR spectral characteristics of the (O—Si)-chelate (aroyloxymethyl)trifluorosilanes upon variation of external factors are due to geometric reasons. Analysis of the electron density distribution according to Bader indicates that the Si←O bond in molecule 1 can be treated as a covalent bond of high polarity.