(Aroyloxymethyl)trifluorosilanes: a new class of pentacoordinate silicon compounds

Abstract

A new class of organosilicon compounds containing a pentacoordinate silicon atom, (aroyloxymethyl)trifluorosilanes (AFS), has been prepared. The presence of an intramolecular coordinate F 3Si ← OC bond is supported by X-ray diffraction, IR spectroscopy and dipole moment data. Si ← O coordination in AFS has been shown to remain intact in the gaseous and liquid states below 420 K as well as in solution in most organic solvents. The dielectric constant of the medium significantly affects the nature of the coordinate Si ← O bond and that of the SiF, CO, COC bonds. In pyridine the intramolecular coordinate Si ← O interaction is disturbed or greatly weakened. At 420–500 K a reversible reaction takes place: ArC OOCH 2Si F 3 α ArCOOCH 2SiF 3 The changes in enthalpy and entropy are equal in this case: −△ H  8.1 ± 0.7 kcal/mol; −° S  15.3 ± 0.8 e.u. T  450 K An assignment of bands in the IR spectra of AFS resulting from vibrations of atoms in the SiF 3, >CO and COC groups is given. The electron impact-induced primary disintegration of the molecular ion 4-XC 6H 4COOCH 2Si ▪ mainly involves abstraction of a fluorine atom.