Preparation of crystal-like periodic mesoporous phenylene-silica derivatized with ferrocene and its use as a catalyst for the oxidation of styrene

Abstract

The surface silanol groups in crystal-like mesoporous phenylene-silica have been derivatized with trimethylsilyl, benzyldimethylsilyl and dimethylsilyl(ferrocene) groups by performing a post-synthetic grafting reaction with the corresponding chlorosilane precursors. The success of the grafting procedure was demonstrated by transmission FT-IR spectroscopy and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and ¹³C and ²⁹Si magic-angle spinning (MAS) NMR spectroscopy. Powder X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and N₂ adsorption data for the modified materials indicated preservation of the mesostructure as well as the molecular-scale periodicity in the pore walls. Ferrocene and the ferrocenyl-modified periodic mesoporous organosilica (PMO) were employed in the catalytic oxidation of styrene at 55 °C using either hydrogen peroxide or tert-butylhydroperoxide as an oxidant. The main reaction product was always benzaldehyde (BzCHO), and other products included styrene oxide, benzoic acid and 2-hydroxyacetophenone. Using a styrene : H₂O₂ molar ratio of 1 : 5, the highest BzCHO yields at 24 h were 65% (85% selectivity) for ferrocene (semibatch conditions involving stepwise addition of H₂O₂, 1 mol% Fe) and 34% (83% selectivity) for the modified PMO (batch conditions, 0.06 mol% Fe). The modified PMO could be recovered and reused, albeit with a drop in catalytic activity due to partial metal leaching during the first catalytic run.