Formation of Lewis acidic support materials via chemisorption of trimethylaluminum on mesoporous silicate MCM-41

The chemisorption of trimethylaluminum on dehydrated mesoporous MCM-41 is described. The sorption capacity of the silicate material was examined by addition of various amounts of the organoaluminum reagent and monitored by elemental analysis, FTIR spectroscopy, and nitrogen physisorption measurements. Multinuclear (H-1, C-13, Al-27) solid-state NMR studies reveal a methyl surface population with a SiCH3/AlCH3 ratio of approximately 0.45 and suggest a highly distorted geometry and polarized charge density, respectively, at the aluminum centers. Air-exposed samples indicate the formation of four-and six-coordinate aluminum. The AlMe3-modified MCM-41 materials exhibit a strong Lewis acidic behavior, as derived from a novel "test reaction", involving an intermetallic Lewis acid-base competition reaction between the support system and the spectroscopically versatile, n-hexane-soluble complex Y[N(SiHMe2)(2)](3)(THF)(2). Additionally, the rare earth dimethylsilylamide reagent seems to be a promising probe molecule for examining the alkylation capability of such organoaluminum-modified support materials.