Dioxygen activation in photooxidation of diphenylmethane by a dioxomolybdenum(VI) complex anchored covalently onto mesoporous titania

A dioxomolybdenum(VI) complex has been covalently anchored onto mesoporous titania by a silicon-assisted transesterification route. The grafting of the complex to the mesoporous structure was confirmed by diffuse reflectance infrared Fourier transform, Raman and UV-Vis spectroscopy and by nitrogen sorption experiments. The ability of the grafted complex to activate molecular oxygen (O-2) has been evaluated in the photooxidation of diphenylmethane to produce benzophenone. The photooxidation of diphenylmethane was monitored continuously by in situ dispersive Raman spectroscopy. A scheme for the activation of molecular oxygen under very mild conditions is proposed. A comparison with the same complex anchored onto commercial titanium P-25 and silica gel revealed both the beneficial effect of the mesoporous structure and the existence of a synergistic effect between MoO/TiO2/O-2/light entities, which promotes the photooxidation process under green chemistry conditions. Finally, the heterogeneous catalyst is sustainable; it can be recycled and reused without significant loss in activity or selectivity.