ELECTRONIC-STRUCTURE OF ORGANOSILICON COMPOUNDS .3. ITERATIVE MAXIMUM OVERLAP CALCULATIONS ON SOME CYCLIC AND POLYCYCLIC SILANES

The electronic structures of a large number of cyclic and polycyclic silanes were investigated by the iterative maximum overlap approximation (IMOA) approach. The angular strain energy in small silacarbocycles is discussed in terms of the hybrid spn contents and the deviation angles from SiC and CC bond vectors. Several subtle changes following insertion of two spiro-annelated cyclopropyl rings to silacyclopropane are rationalized in terms of a considerable rehybridization of the silicon and spiro-junction carbon atoms. The calculated geometries are compared with available experimental data. Theoretical estimates of bond and dihedral angles are in good accordance with the measured values. The calculated interatomic distances are, however, less accurate. The calculated heats of formation of the examined compounds and the J(SiH) and J(SiC) spin-spin coupling constants for the directly bonded nuclei are briefly discussed. The calculated heats of formation are consistent with those derived by the MINDO/3 method. © 1979.