Electronic effects in (ethylthioalkyl)trialkoxysilanes and corresponding silatranes

The ionization energies of compounds of the general formula EtS(CH2)(n)SiX3 (SiX3 = trimethoxysilyl or silatranyl, R = H, Me; n = 1-3) were measured b y He(I) photoelectron spectroscopy. The positions of charge-transfer bands in the electronic absorption spectra of tetracyanoethylene complexes of the se compounds were determined. The linear dependences of the ionization ener gies of the sulfur lone pair, of the charge-transfer frequencies of the tet racyanoethylene complexes, as well as of the basicities relating to the str ength of H-complex formation of the compounds with phenol on the inductive constants of the (CH2)(n)SiX3 groups suggest that the latter groups are ele ctron donors with respect to the sulfur atom at any n. The deviation from t he linear dependences of the spectral characteristics of (ethylthiomethyl)t rialkoxysilanes is explained in terms of n,sigma* coupling in the S-CH2-Si fragment, which takes place both in the gas phase and in solution.