Theoretical studies of the mechanism for the synthesis of silsesquioxanes. 1. Hydrolysis and initial condensation

The mechanisms for the hydrolysis of SiHCl3 to form HSi(OH)(3) and the condensations of SiH3OH and HSi(OH)3 are studied by using ab initio electronic structure methods including electron correlation via second and fourth order perturbation theory and coupled cluster calculations. In the gas phase, the barrier heights for the hydrolysis and silanol condensation reactions are quite high, ranging from 20 to 30 kcal/mol. The barrier for the condensation of HSi(OH)(3) is much smaller as a result of hydrogen bond stabilization of the transition state. Addition of just one extra water molecule is sufficient to reduce the calculated barriers to very small values or zero.