QUANTUM-CHEMICAL STUDY OF PENTACOORDINATED SILICON-COMPOUNDS - SI-SUBSTITUTED (O-SI)DIMETHYL(N-ACETYLACETAMIDOMETHYL)SILANES

The mechanisms and self-consistency of the changes in geometric parame ters, charge distribution, orbital structure and energy of the ''soft' ' coordination center XSiC3O in Si-substituted (O-Si)dimethyl(N-acetyl acetamidomethyl)silanes upon variation of the nature of the substituen t X (X = OCOCH3, OCOCF3, F, Cl, Br, I) have been established by the PM 3 method. They have been found to be in complete correspondence with t he experimental data and the hypervalent bonding model. In contrast to the prediction of the standard donor-acceptor complex model, a decrea se in the ionization potential of the donor upon the formation of the 3c-4e XS<--O bond has been demonstrated. Significant shortcomings of t he PM3 method in quantitative estimations of the complexation energy a nd the gas-phase geometry have been pointed out.