A general strategy for the rational design of size-selective mesoporous catalysts.

A series of functionalized mesoporous silicas with cagelike pore topology has been synthesized and screened for size-selective catalytic transformations. The aluminum-catalyzed Meerwein-Ponndorf-Verley (MPV) reduction of differently sized aromatic aldehydes (benzaldehyde and 1-pyrenecarbox-aldehyde) has been investigated as a test reaction. The catalysts were synthesized in a two-step grafting sequence comprising pore-size engineering of mesoporous silicas (SBA-1, SBA-2, SBA-16) with long-chain alkyl dimethylaminosilanes and surface organoaluminum chemistry with triethylaluminum [{Al(CH(2)CH(3))3}2].

Advanced surface functionalization of periodic mesoporous silica: Kinetic control by trisilazane reagents.

The surface reactions of mesoporous silica MCM-41 with a series of new trisilylamines (trisilazanes) (SiHMe2)2NSiMe2R and (SiMe2Vin)2NSiMe2R (R = indenyl, norpinanyl, chloropropyl, 3-(N-morpholin)propyl; Vin = vinyl), disilylalkylamine (SiHMe2)iPrNSiMe2(CH2)3Cl, and monosilyldialkylamines Me2NSiMe2R (R = indenyl, chloropropyl, 3-(N-morpholin)propyl) were investigated. 1H, 13C, and 29Si MAS NMR spectroscopy, nitrogen adsorption/desorption, infrared spectroscopy, and model reactions with calix[4]arene as a mimic for an oxo surface were used to clarify the chemical nature of surface-bonded silyl groups. The trisilylamines exhibited a comparatively slow surface reaction, which allowed for the adjustment of the amount of silylated and nonreacted SiOH groups and led to a stoichiometric distribution of surface functionalities.