Parametric calculations of Mo-allyl complexes anchored on silica

The SiO₂ anchored Mo(η³-C₃H₅)₄ catalyst was modeled by means of the CNDO-UHF parametrical method. Two models (two separated centers (TSC) and two adjacent centers (TAC)) were proposed for the silica pre-treated at relatively low temperature. An analysis of total energies, bond indexes, diatomic energies, and parametric diatomic binding energies for selected bonds suggests the existence of both models on the surface. However, TSC is favored with respect to TAC. Furthermore, it is observed an allyl group interaction with the support through a C-O bond that leads to a C-C bond activation. Also, C-H activation is found due to Mo-H interaction. These results support several features of the generally accepted mechanism for olefin metathesis in this type of catalyst. Finally, experimental results of NMR, obtained in previous work by some of the authors, are interpreted by inequivalency of different allyl ligands.