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

Interactions between silyl groups in various substituted silanes and molecu les that include groups that are potential electron pair donors have been i nvestigated by ab initio molecular orbital calculations. These calculations indicate that all the systems investigated should form weak adducts, depen ding upon the substituents on the silicon atom and the nature of the donor, and on the quality of the calculations. The interactions demonstrate disti nct directional preferences. In general, the most stable adducts were those in which the donor was oriented opposite to the electron-withdrawing subst ituent at the silicon. Preparation of single crystals of these adducts prov ed to be impossible, but new clathrates of tri-ortho-thymotide (TOT) with p henylsilane and 1,3-disilylbenzene have been prepared and their crystal str uctures determined. In both clathrates the silylbenzene molecules are locat ed in three different types of channels in the crystal structure of TOT. Cl ose intermolecular contacts between silicon atoms of silanes and oxygen ato ms of carbonyl groups of TOT were observed in two of the three channels. Th e geometry of the interactions was found to be consistent with computed str uctures of weak methylsilane-formaldehyde adducts. (C) 2000 Elsevier Scienc e B.V. All rights reserved.