Covalent binding of a Fischer-type metal carbene in ordered mesoporous MCM-41-functionalized silica

The synthesis of ordered mesoporous silicas has received extensive attention due to their ordered arrangement, large surface area, and chemical stability. The pore size and pore volume of these materials make them suitable potential matrices for hosting. Here, we show that the covalent grafting of the Fischer carbene complex of tungsten [(CO)5WC(ph)OCH2CH3] onto the silanol groups in inner walls of ordered mesoporous MCM-41 silica has been successfully accomplished. The introduction of the carbene complex is made by following two distinct anchoring procedures. The first one goes through the reaction of a mesoporous silica functionalized with 3-aminopropyltriethoxy silane (APTES) and a tungsten carbene, while in the second approach a precursor previously synthesized by reacting APTES with the tungsten carbene is then anchored via a direct bond with the silanol groups of the interior mesoporous pore channels of silica. XRD, N2 adsorption/desorption, and TEM analysis provide strong evidence that the mesoporous support structure retains its long range ordering after the grafting process, despite a significant reduction of its specific surface area, pore volume and pore size. The chemical bonding of the tungsten carbene complex on the pore channels is also clearly confirmed by means of FTIR and solid-state NMR spectroscopy.

Model for a tungsten Fischer carbene covalently bound to mesoporous MCM-41. Figure optionsDownload as PowerPoint slide