A theoretical and experimental study of weak silane-electron donor interactions

Interactions between silyl groups in various substituted silanes and molecules that include groups that are potential electron pair donors have been investigated by ab initio molecular orbital calculations. These calculations indicate that all the systems investigated should form weak adducts, depending upon the substituents on the silicon atom and the nature of the donor, and on the quality of the calculations. The interactions demonstrate distinct directional preferences. In general, the most stable adducts were those in which the donor was oriented opposite to the electron-withdrawing substituent at the silicon. Preparation of single crystals of these adducts proved to be impossible, but new clathrates of tri-ortho-thymotide (TOT) with phenylsilane and 1,3-disilylbenzene have been prepared and their crystal structures determined. In both clathrates the silylbenzene molecules are located in three different types of channels in the crystal structure of TOT. Close intermolecular contacts between silicon atoms of silanes and oxygen atoms of carbonyl groups of TOT were observed in two of the three channels. The geometry of the interactions was found to be consistent with computed structures of weak methylsilane-formaldehyde adducts. (C) 2000 Elsevier Science B.V. All rights reserved.