Water-trimer clusters as nucleophilic reagents in hydrolyses of substrates for metal-alkoxides - a computational study

Density-functional-theory calculations were performed to simulate hydrolysis paths of eight metal-methoxides, M(OMe)(n) M = Al and Ga for n = 3, M = Si, Ge, Ti, and Zr for n = 4 and M = V and Nb for n = 5. Those paths are initial steps of the sol-gel process and were found to consist of substrates M(OMe), and water-trimer clusters, strain-free hydrogen-bond networks are constructed at transition states (TSs) and may cause ready bond interchanges, i.e., M-O bond cleavage and formation and switch of O-H covalent and O . . .H hydrogen bonds. TSs have zwitterionic characters and are stabilized substantially by the solvent effect, The calculated activation energies correlate well with energies of the lowest unoccupied molecular orbitals according to the frontier-orbital theory. (C) 2001 Elsevier Science B.V. All rights reserved.