Characterization of phenyl-substituted pentacoordinated compounds of main group elements by 1H NMR

Abstract

Analysis of the aromatic region of the 1H NMR spectra of some phenyl substituted pentacoordinated compounds of main group elements (Si, Pb, P, As, Sb, S, Te, I) revealed a characteristic low-field multiplet, assignable to ortho protons, separated from a more intense high-field multiplet, assignable to the meta and para protons. The data imply that an increase in the magnitude of the multiplet separation may be correlated with a decrease in electronegativity of the central atom and an increase in electronegativity of attached ligands. These effects are consistent with a delocalization of the aromatic π electron density into vacant d orbitals of the central atom as well as a strengthening of the central atom sigma bond. The enhanced mutiplet separation for equatorially oriented phenyl groups in a trigonal bipyramid or axially oriented ones in a rectangular pyramid is diagnostic in indicating the presence of the pentacoordinated state for main group element compounds in solution.