Structural studies and catalytic activity of MCM-41 and MCM-48 modified with the titanocenophane [SiMe₂(η⁵-C₅H₄)₂]TiCl₂

Titanium(IV)-grafted mesoporous silicas have been prepared by diffusion of an excess of the ansa-bridged titanocene [SiMe₂(η⁵-C₅H₄)₂]TiCl₂ into the channels of hexagonal MCM-41 and cubic MCM-48 in dichloromethane or tetrahydrofuran at room temperature. The choice of solvent determines the course of the reaction and hence the activity of the resulting materials as catalysts in the catalytic epoxidation of cyclooctene with tert- butylhydroperoxide. Magic-angle spinning (MAS) NMR (¹³C, ²⁹Si) spectroscopy was used to characterise the local environment of the surface- bound titanium active sites. When dichloromethane is used, the dominant species anchored to the surface are isolated ansa-bridged titanocene fragments. When THF is used, the [SiMe₂(η⁵-C₅H₄)₂] unit is lost with the concomitant formation of surface-bound Ti(IV) species coordinated by THF molecules. These materials showed the best catalytic performance per Ti atom for the conversion of cyclooctene. All materials were further characterised by means of elemental analysis, powder X-ray diffraction (XRD), N₂ adsorption and FTIR spectroscopy.