Inductive Effects in Neutral Pentacoordinated Silicon Compounds Containing a Si ← N Dative Bond. A Theoretical Study

Using ab initio MP2 and DFT calculations, we have studied the structure of a series of pentacoordinated silicon compounds containing a Si ← N dative bond and the influence of inductive effects on the Si ← N bond. The study includes two series of model systems, namely, Si(NH3)XnY4-n (X = OH, Y = H or CH3; n ranging from 0 to 4) and Si(NH3)(NH2)H2X (X = Cl or H), methyl(2,2‘,2‘ ‘-nitrilotriethoxy)silane, methyl(2,2‘,3-nitrilodiethoxypropyl)silane, 8-(trifluorosilylamino)quinoline, 8-(trimethylsilylamino)quinoline, a dimer of Me2NSiH2Cl, and a pentamer of Me2NSiH3. All these structures have dative Si ← N bonds. The nature of the bonds was analyzed using the Laplacian of the charge density distribution and the natural bond orbital (NBO) partitioning scheme. The calculations show that the dissociation energy of the Si ← N dative bond in the model systems is always lower than 9 kcal mol-1 and that the Si ← N bond length gets shorter as the number of electron-withdrawing groups linked to silicon increases. The different aggregation mode between the dimer of Me2NSiH2Cl and the pentamer of Me2NSiH3 is also analyzed.